Chemistry for You [updated] 019837576X, 9780198375760

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This interactive book is supported by over 1000 resources designed to assist in teaching and learning in preparation for your exams, with resources [aunched directly from the book page Each chapter includes:

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Student Map and Summary Learning Objectives and a Plenary

Checklist and a Revision Quiz

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Editabte Help and Extension Worksheets*

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PowerPoints to hetp with common misconceptions and fu[[ colour images of all key diagrams

Animations and Simulations to i[[ustrate dynamic situations Drag-and-drop activities, with Quizzes

And also:

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Teacher Maps and Technician Cards Answers to Further Questions, with Model Answers to examination questions

Further support for 'How Science Works' Hetp with Key Skitts

Specification 'Mapping Grids' which show you details of coverage for your particutar exam. You can also find these at www.chemistryforyou.co.uk

You can personatise your Kerboodle Books by:

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Adding links to relevant websites Drawing, hightighting and adding your own notes

+These worksheets include Help Sheets, lnvestigation Sheets, Practice Sheets, Diagram Sheets and Research Sheets and atso cover some additionalCCSE and ICCSE topics.

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UPDATED

Lawtie RYan f{t

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for All fif;SE Examinations

Nelson Thornes

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Text O Lawrie Ryan 2006, 201 1 Original illustrations @ Nelson Thornes Ltd and Lawrie Ryan 2011

The right of Lawrie Ryan to be identified as author of this work has been asserted by him in accordance with the Copyright, Designs and Patents Act 1988. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording or any information storage ani retrieval system, without permission in writing from the publisher or under licence from the copyright Licensing Agency Limited, of saffron House, 6-10 Kirby Street, London ECI N 8TS. Any person who commits any unauthorised act in relation to this publication may be liable to criminal prosecution and civil claims for damages. Published in 201 1 by: Nelson Thornes Delta Place 27 Bath Road Cheltenham GL53 7TH United Kingdom

131415/10987654 A catalogue record of this book is available from the British Library.

lsBN 978 1 4085 0921 0 lllustrations by Barking Dog, Peters & Zabransky, Jane Cope, IFA Design Ltd, Jordan Publishing Design, Harry Venning and Tony Wilkins Page malie-up by Tech-Set Ltd, Tyne & Wear with revisions by Fakenham Photosetting Ltd Printed in China

Website: The website at www.chemistryforyou.co.uk gives you details of exactly which pages in this book you need to study for your particular GCSE examination course. Make sure you visit this website and save or print out the correct sections. They will show you: . which topics you need to learn for your particular examination, and o which page numbers to read in this book.

'Whot is the use of o book,' thought Alice, 'without pictures or conversotions?'

Lewis Coroll, Alice in Wonderland 'l think Mr C.S. Lewis is o very good writer. But he hos one foiling. There ore no funny bits in his books.' 'You ore right there,' Miss Honey soid. Roold Dohl, Matildo Chemistry ... is one of the broodest bronches of science, if for no other reoson thon, when we think obout it, everything is chemistry. Luciono Coglioti, The Two Faces of Chemistry Indulge your possion for science ... but let your science be humon, ond such os moy hove o direct reference to oction ond society. Dovid Hume, An Inquiry Concerning Human Understanding

Introduction Chemistry for You is designed to introduce you to the bosic ideos of Chemistry. It will show you how these ideqs help to exploin the moteriols in our world, ond how they con be chonged. From your troiners to the spoce shuttle, chemists work to develop new moteriols. Chemistry for You oims to be interesting ond help you poss your exoms, whether you ore using it to study Core Science, Additionol Science or Chemistry ot GCSE. This Revised Edition covers oll of the lotest specificotions from the Exominotion Boords. You con find more informotion of www.chemistrvforvou.co.uk The book is corefully loid out so thot eoch new ideo is introduced ond developed on o single poge or on two focing poges. Throughout the book there ore mony experiments for you to do. A hqzord sign meons your teocher should give you further odvice (for exomple to weor eye protection). Plenty of guidonce is given on the results of these experiments, in cose you don't ocfuolly do o porticulor procticol or ore studying ot home. You willfind the ideos introduced in Chopter 1 'How science works' useful throughout your GCSE. Refer bock to it whenever you tockle on investigotion.

Eoch new chemicolword is printed in bold ond importont points ore ploced in o box. There is o summory of importont ideos qt the end of eoch chopter. There ore questions ot the end of eoch chopter. They olwoys stort with on eosy fill-in-the-missingwords question useful for revision ond writing notes. At the end of eoch of the 7 moin sections you will find plenty of further questions. These ore token from recent GCSE popers or hove been written for the lotest specificotions by exominers. There is on Extro Section ot the end of the book. You willfind odvice on Key Skills, coursework, coreers, revision ond exominotion techniques in this section.

Throughout the book, cortoons ond rhymes ore used to help exploin ideos. The 'Chemistry At Work' poges willolso show you how Chemistry is useful to us in everydoy life. You ore encouroged to think obout ond discuss scientific issues thot offect us qll, both now ond in the future. However, obove oll I hope thot you will find Chemistry eqsier to understond qnd thot using the book willbe fun! I would like to thonk my fomily (Judy, Nino ond Alex) for their omozing support ond understonding throughout this lotest re-editioning of Chemistry for You.

Lowrie Ryon

Contents The Foundctions of

Chemietry

Chonging Moteriols 1O Acids ond qlkqlis 124 Chemistry at work: Sulfuric ocid, H2SOa 134 Chemistry at work: Neutralisation 136 139 11 Products from 150 Naphtha Chemistry at work: 153 12 Polymers Chemistry at work: Getting rid of plastic

oil

waste 162 13 Corbon chemistry 164 14

Products from Metol Ores ond Rocks 6 7

8

9

Extroction of metqls 70 Chemistry at work: Uses of steel 78 Chemistry at work: Preuenting rust 79 Elecholysis 82 Chemistry at work: Recycling metals 90 Chemistry at work: Cars for scrap 91 Chemistry at work: The costs of exploiting metal ores 98 Solt 102 Chemistry at work: Products t'rom salt 106 Limestone 709 Chemistry at work: New deuelopments in conuete and gloss 116 Chemistry at work: Quarrying limestone 717 Further questions on Products from Metal Ores and Rocks 779

Chemistry at work: Uses of ethanol 169 Chemistry at work: Uses of esters 772 Plont oils 774 Chemistry at work: Detergents 778 Chemistry at work: Cooking 184 Further questions on Changing Materials 787

Rqtes ond Energy 15 Energy chonges 192 Chemistry at work: Putting out t'ires 797 Chemistry ot work: Hydrogen as o fuel

200

16

Rotes of

reoction 203

Chemistry at work: Uses of enzymes 216

17

Reversible

reoctions 220

Chemistry at work: Deueloping ideas

about acids 228 18 Products from oir 230 Chemistry at work: The Haber process 232 Further questions on Rates and Energy 242

Structure ond Bonding

Extro sections

19 Ionic compounds 248 Chemistry of work: lonic compounds

halides 254 20 Covolent bonding 256 Chemistry at work: Carbon 260 21

-

Chemistry at work: Fullerenes 262 Metols qnd structures 268

Chem$ry at work: Super-conductors 269 Chemistry at tuork: Alloys 272 Further questions on Structure and

Bonding

276

Eorth Chemistry 22 Water 284 23

24

Chemistry at work: Uses of water 286 The otmosphere 300 Chemistry at work: Uses o/ nitrogen 301 Chemistry at work: Uses of oxygen 303 Chemistry at work: Uses of carbon dioxide 305 Chemistry at work: Ozone 306 The Eqrth 310 Chemistry at work: Predicting uolcanoes

Answers to Key

skills

moles 374 376

Doing your coursework 378 Suggestions for o revision

progromme 383 Revisiontechniques 384 Exominotion technique 386 Coreers using Chemistry 388 Doto poges (elements ond ions) Periodic

Index

Toble

390

392

394

Acknowledgements

400

Chemists moke new moteriols thqt chonge the world in mony woys...

319 Chemistry at work: Predicting earthquakes 320 Further questions on Earth Chemistry 322

Synthesis ond Anolysis From everyday materials, such as

25 Moking new moteriols 328

cosmelics

Chemistry at work: What is nanotechnology? 336 Chemistry at work: Applications of nanotechnology 337

26 Moles 340 27 Anolysis 360 Chemistry at work: lnstrumental onolysis 364 Further questions on Synthesis ond Anolysis 370

... to the materials used in the space shuttle

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Why we need to know obout how science works

Science hos helped to shope the world we

live in todoy. Scientists hove solved problems, using

evidence, ond hove mode modern technologies possible. This hos brought greot benefits for oll of us but hos olso creoted problems. Pollution of our environment is one mojor concern - qnd scientists ore qlso essentiol in deoling with this issue. We ollhove to moke decisions obout how we leod our lives. Knowing more obout'how

works'will help you form your own opinions obout importont issues. These will include decisions obout your diet, your tronsport, your work ond your free time. science

Some people have claimed that the MlrrlR jab can cause autism in some bables. However, the evidence used to identify a link was only taken from a small sample ol cases.

You will need to question evidence ond to weigh up conflicting ideos. For exomple: . Will you ollow your children to hove the MMR job ? . Will you buy o cor ? If so, which one will be leost hormful to our environment ? . Will the lotest food score in the news offect whot you eot ? o Will you vote for o porty who wont to expond nucleor power

?

To onswer such questions you should consider the evidence

ovoiloble. Then you need to judge if the evidence is bqsed on 'good science' (You willfind some people use evidence thot is not scientific ot oll to onswer scientific questions.)

Good euidence thot

provides

Reliqble evidence will be repeotoble. If someone else collected the dqto ogoin it would be the some (or similqr). So you con trusf relioble doto. It is then volid evidence only if it olso octuolly meosures whot you intended to find out obout. So scientists need relioble ond volid evidence to drow firm conclusions. .,1:i-ffi.i$;1r1

,,,

There ore some questions

thqt science reolly helps us to onswer. These ore usuolly questions thot stort 'How con we. . .?' But there ore other questions bosed on beliefs ond opinions thot it con't onswer. Society os o whole, which includes scientists, hos to try ond onswer the 'Should we . . .?' type questions.

Example obout pollution in o river from o thot were sensitive enough occurotely to get relioble downsheom from the if you olso hove doto from

)

Observing

Observing things is the link between the reolworld ond science. But observotion is not os simple os you might think. Surely two people looking of the some event will see the some thing, won't they ? Sports fons will know thot's not true ! But whot obout something like o freshly pointed iron gote One person sees o nice colour thot motches o house. Another sees on iron borrier protected ogoinst rusting. So whot you see depends on whot you know olreody.

?

No

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You cqn use existing theories to explain ideos.

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This forms o hypothesis. You con then use your hypothesis to moke o prediction. You con go on to test your prediction by collecting evidence. This moy or moy not support your prediction. If on existing theory is not bocked up by observotions from your tests, first of oll check the observotions. If they prove to be correct, then the theory itself might need to be chonged. This is one woy in which science develops over time.

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You need to observe things corefully to see if porticulor voribles ore importont, or not, in on investigotion. Example You ore investigoting how

reqct with dilute ocid

On observing the type of test tube you use gloss.

Observotions con olso be the storting point for new investigotions, experiments or surveys.

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Moking meosurements

Scientists must olso think obout the meosurements they moke when judging how strong their evidence is. Are they relioble (ore they repeotoble) ond volid (do they meosure whot you intended)? There will usuolly be slight differences in meosurements when you repeot them. This is becouse it is hord to meosure the volue of o vorioble under exactly the some conditions every time.

Example You meosure the volume of o gos given off in o reoction using o dilute gos syringe. hydrochloric the room might You repeot the experiment but the acid hove chonged. This will offect your volume reoding? o If the temperofure gets higher,

nge

marble chips

You should olso consider the occurocy of your meosuring instrument

Accurocy tells us how neor the true reading your meosurement is. Example probobly give reodings neorer the true volue reodings would olso depend on on using ond storing the pH the reodings won't be relioble don t , in different lobs by different If the coll the pH reproducible. pH meter is qlso likely to hove better resolution. It respond to chonges in pH. This moy not motter in some experiments. But it could be significont, for exomple, in enzyme investigotions.

thon o

The

precision of o meosuring instrument

is olso importont

A precise instrument will hove smoll scqle divisions. It will give the some reoding ogoin ond ogoin under exoctly the some conditions. But precision ond occurocy ore not the some thing: Example A student weighs exocfly 2.51gof iron on two different bolonces. He repeots this 4 times on eoch bolonce true value

B 2.55

set of repeot grouped closely

true value

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2.55

Bolonce B produces on occurote meon volue (the overoge of the 4 reodings is 2.51 g) but the set of reodings ore not precise (the reodings ore spreod out).

Errors Then we olso hove humon error in meosurements

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In the first cortoon the If he repeots his be spreod This is , his portner is more is not reoding the in the burette correctly.

error. reodings be too high or too low it motter in this cose ?

?

In some investigotions you should repeot your meosurements. This is especiolly importont when meosurements ore tricky to moke The number of repeots will depend on the occurocy you need. E

Anomqlous results You should olso look out for onomqlous results. These meosurements do not motch the generol pottern found, or lie well outside the ronge of other repeot meosurements. If you find on onomolous meosurement, try to work out why it hoppened. If it wos coused by poor meosurement in the first ploce, you con just discord it. (See first cortoon obove.)

o o

Cg

o o

x

E

x x

x x

f

x don't include this anomalous result

time(s)

Graph showing all repeat measurements

plotted and a line of best fit

9

F Designing

on investigotion

The best woy to onswer some scientific questions is to design o foir test. Example You ore looking qt the reoction between metol corbonotes ond dilute hydrochloric ocid. The reoctions ollproduce carbon dioxide gos. You might wont to investigote this question: 'Whot might offect how quickly the reoction tokes ploce ?' You con stort by moking o list of the voriobles that might offect the rote of the chemicol

reoction, e.g.

:

o temperoture, o conientrotion of ocid, o surfoce oreo of corbonote,

o

.

type of corbonote, type of ocid.

You con select ony one of these voriobles to investigote Imogine you choose to vory the concentration oJ

the acid you use. This will be your independent voriqble.

measuring

50cm3 of dilute hydrochloric acid

o

o o o

But how willyou judge how quickly the reoction

o

tokes ploce

o

o

?

There ore different woys to judge this. Imogine you decide to meosure the time

it

takes to giue off a certain uolume ol carbon dioxide gas. The time it tokes is cqlled the dependent voriable.

chips

foir test, we should only vory one thing ot o time (in this cose it will be the concentrotion of the ocid). So we should try to keep ollthe other voriobles thot might motter constont. These qre the control voriobles. They will include temperoture, surfoce oreo ond the type of ocid ond corbonote used.

To moke this o

Choosing volues of voriobles You would hove to corry out o few triol experiments to decide on how much corbon dioxide to collect eoch time. These might show thot for reosonoble omounts of qcid ond corbonote, 20 cm3 would give sensible times - not too long ond not too short. You could olso choose your ronge of concentrotions to use. You could systemoticolly dilute down the ocid provided using woter, whilst keeping the totolvolume the some. Five different concentrotions would be needed to drow o decent line groph of the results. These should be well spoced out. If there ore ony interesting ports on your groph, you con choose to test more concentrotions. These might be more repeots to test possible onomolous results. Or they might be grouped oround on oreo where the groph looks like it chonges, e.g. where the slope gets much steeper or levels off.

10

It's imporlant to get your range right ! Always quote your maximum and minimum values when asked for the range of your data (and don't forget the unit),

)

Different types of vorioble

We con clossify voriobles into the following types:

o Cotegoric voriobles:

These ore voriobles thot we cqn describe

using words. Exomples ore: 't5rpe of ocid' e.g. hydrochloric ocid, or 'type of corbonote' e.g. colcium corbonote.

o

Ordered voriobles: These ore o type of cotegoric vorioble thot we con put into on order. An exomple is 'surfoce oreo' of colcium corbonote, if you use 'lorge lumps / medium lumps / smoll lumps' os o woy of describing the volues of the vorioble.

1 had noid eq Vacia.[les c 6u a be quite5 o V a,f' o.ble.

6

o Continuous voriobles:

These ore voriobles thot we con describe by ony number, qs their volues ore meosurements e.g.

o c

17.5cm3. Exomples ore: 'temperoture' or 'concentrotion'. This type is the 'most powerful' to investigote. Thot's becouse the relotionship between the voriobles con be described by o mothemoticol equotion. You con use the equotion or the line groph produced (see poge 72) to moke the most occurote predictions to test.

o Discrete voriobles:

These ore voriobles thot con only hove whole number volues. An exomple is: 'the number of morble chips'.

'Not-so-foir' tests

!

In some investigotions it is eosy to chonge one vorioble of o time, ond keep oll the others constont, to moke o foir test.

Howeveq in other investigotions controlling ollthe voriobles thot motter is difficult (or even impossible). An exomple is on investigotion into the effects of fertiliser on plont growth. If this investigotion tokes ploce 'in the field', there ore foctors such os the weother conditions thot you con't control. But you should moke sure ollthe plonts tested experience the some weother.

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Evoluoting your doto Remember thot the doto you collect must be relioble (see poge 6). You should olso design your investigotion so thot the dotq will onswer the question posed. Consider the investigotion on the previous poge: Is it volid to judge the rote by timing how long it tokes to collect 20 cm3 of gos ? After oll, os soon os the reoction storts the concentrotion of ocid will stort to decreose !

This \sri b fai r!

a'nrr nob cornPlqrnrnal

You would olso use o lorge somple of the some types of plont to test. It's no good picking just one plont to test with the fertiliser ond one without it. There could be

differences between plonts which might offect the result.

Using o lorge somple size ond choosing your somple corefully will help to overcome the problems of setting up o foir test involving living things.

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Presenting your doto

Tobles As you corry out on investigotion, you con record your doto in o results toble Scientists orronge their tobles so thot the independent vorioble (the one you chonge deliberotely, step by step) goes in the first column.

The dependent vorioble (used to judge the effect of vorying the independent vorioble) goes in the second column. For exomple, if you were doing on investigotion like the one on poge 10, but voried temperoture, the toble would hove these heodings: lndependent variable: Temperature ("C)

Dependent variable: Time to collect 20 cm3 of gas (s)

If you decide to repeot your tests ot eoch temperoture to get more relioble doto, you con split the second column up: Time to collect 20 cm3 of gas (s)

Temperature ('C)

First test

Second test

-^

Third test

Mean (average)

-----_--

Grophs Then you con show the relotionship (link) between the two voriobles by drowing o groph.

The independent vorioble goes olong the horizontol oxis. The dependent vorioble goes up the verticol qxis. Look ot the oxes opposite: The groph you drow depends on the type of independent vorioble you investigoted. (See poge 11.)

If it is o continuous vorioble, you con disploy your results on o line groph. Thot's becouse the independent vorioble is meosured in numbers. You might choose to do the tests ot 20,30,40, 50 ond

60'c. However, you could equolly hove chosen ony points in between. Thot's why we con join the points with o continuous line.

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E 200 c o

o o

o (E 1

50

E

o N

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00

o o o o)

E

50

10 20

30

40 50

60

temperature ('C)

Look ot the groph opposite: In this cose, the independent vorioble is 'Type of metol'. If your independent vorioble is o cotegoric vorioble - you hove to disploy your results on o bor chort. Thot's becouse there ore no volues between eoch bor. (Remember thot cotegoric voriobles ore usuolly described by words.) Of course, the dependent vorioble (up the side) hos to be continuous (meosured), otherwise we con't drow ony type of groph

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tr

200

150 !

Spotting potterns in doto Once you hove your groph to refer to, you con see whot the relotionship is between the two voriobles.

zinc

Exomples you will find in chemistry include:

magnesium

calcium

iron

Type ol metal

!

o a (!

o o

o !q (!

0) (g

positive linear - a straight line sloping upwards

o)

o E f

o

negative linear a straight line sloping downwards

-

c F

o (0 o

! .s)

=

I

t

positive curve

o

o

(U

E P Mass of fuel

Time burning

Concentration of X

/n thrs case, the variables are directly proportional because the straight line passes through the origin (0, 0) on the graph.

The relotionship is only shown between the ronge of volues in your investigotion. The link moy or moy not hold true outside this ronge. This will be o limitotion of your investigotion. You con extend the line on your groph to moke predictions, but you connot be sure untilyou test them by experiment.

)

Evoluoting your whole investigation

You should consider the reliobility ond volidity of the meosurements you moke ond the method you used. You con olso improve reliobility ond volidity by:

o Looking up doto from secondory sources, e.g. on the Internet. o Checking your results by using on olternotive method. For exomple, in the investigotion on poge 10, you might meosure the rote by monitoring the loss in moss os the reoction progressed. You could then plot initiolrote ogoinst different concentrotions.

o

Try to use lines of best fit to give 'overoge' lines. You con olso plot oll your doto to show the ronge within sets of repeot meosurements. This indicotes the precision ond reliobility of your doto. The lorger the spreod of repeot reodings the less precise your doto is. Also the less relioble os other people ore less likely to get exoctly the some results crs

you.

c o o (g 0)

o

c

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C OJ

Seeing if other people following your method get the some results, i.e. ore your results reproducible ?

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time

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Society's influence on evidence

Some scientific studies ore of interest to society in generol - not just to the scientific community. For exomple, investigotions into:

New wonder drug con cure concer

o pollution from cors ond industry, o the sofety of food odditives, o the properties of new moteriols, o the purity of drinking woter. These will offect us oll. But how do we heor qbout the evidence these studies produce ? Often it is through the medio - TV, rodio, the Internet ond newspopers. So how relioble qre the reports we get ? Con we trust them ?

Tobloid newspopers ore likely to 'ploy up' score stories. Sensotionol heodlines willsell their newspopers. So often scientists willfind their reseorch reported bodly in the medio. Dongers con be exoggeroted. The very smoll chonces of hormful effects moy not be mentioned. On the other hond, successfulbreokthroughs on q smollscole moy be reported os findings thot will chonge the world - now These moke greot heodlines but ore often unreolistic. !

There ore lots of foctors thot influence the woy evidence is presented to us. If it is going to be unpopulor with the public, evidence might be 'wotered down' or hidden in publicotions. This might olso hoppen if the reseorch results show o problem thot willbe expensive to put right. The reputotion of the scientist doing the reseorch con olso influence people's response to reseorch findings. Fomous, eminent scientists ore likely to get their ideos listened to more fovourobly thon less

wellknown scientists. When we look of evidence for o certoin viewpoint we should olso consider ony bios. For exomple, do we know who poid for the reseorch ? If o food compony produce doto thqt o colouring is sofe, should we trust thot os much os doto from o government 'wotchdog' ? Or whot obout on independent consumer group ? Are they unbiosed ? The ideos we hove looked ot in this chopter should help you to consider evidence criticolly. You might wont to know obout the sensitivity ond occurocy of instruments used in tests. The somple size might be importont. How scientists chose sites to test ond how mony times they repeoted their tests could olso offect the trust you hove in their evidence.

Ihese protesto rs believe that genetically modified crops are a danger to the environment

In 1989 two electrochemists cloimed to hove mode o discovery thot would solve the world's energy crisis ! Their findings suggested thot they hod monoged to reproduce the nucleor reoctions thot produce energy on the Sun. The two scientists, Pons ond Fleischmonn of Utoh University in the USA, soid thot they hod ochieved 'cold fusion' in their lob. Pons ond Fleischmonn held o press conference to tellthe world obout their greot discovery. However, doubts soon begon to surfoce obout their cloims. The press conference hod been set up before their findings hod been published in ony scientific journol. They hodn't even presented their work to colleogues of o conference. This is not normol proctice in the world of science. Scientists usuolly submit new findings to o journol to shore with other interested scientists. But before they get published, fellow scientists check to moke sure thot proper scientific methods hove been used. So this hod not been done.

Physicisfs have built machines that can generate temperatures of over 50000000oC to make nuclear fusion happen on Earth, but they still can't produce energy economically. So imagine their surprise when a couple ol chemists said that they had managed to achieve fusion using only simple lab apparatus.

Once the detoils were out, scientists qll over the world tried to reproduce their results. Fleischmonn ond Pons cloimed to hove got o lot more energy out from their experiment thon they put in the first ploce. But other scientists foiled to get the some effect when they set up the experiment. They showed thqt the originol evidence wos unrelioble. It could not be reproduced, so it could not be trusted.

Noturolly, other scientists were scepticol. They put down the originol results to experimentol error. So cold fusion wos never occepted into the moin body of scientific knowledge. However, o few people ore still convinced in the technology thot could revolutionise the world. Of course, the rewords for inventing o cleon, cheop woy to produce energy would be incredible. So money is still invested in funding further reseorch. Conferences ore held ond fovouroble findings ore shqred by the foithful.

And so the seorch for the elusive 'fusion in o test tube' goes on. One doy it could moke somebody rich beyond their wildest dreoms. It could olso sove our environment from the pollution coused by most of our current sources of energy. But the lucky person who solves the problem must mqke sure their doto is relioble. Fellow scientists will then need to check their findings before 'going public' ond publishing results.

5L)re

L tt,irrk

godre cightl

Summory o

get involved in scientific issues thot willoffect

People need to understond their lives.

a o

o

questions but not with 'Should we

Sometimes they will corry out foir tests. To set these (the independent voriable) whilst keeping other judge the effect of vorying the independent

up, you chonge the vqrioble under vqriobles constont (the vorioble, you meosure the Scientists should moke sure octuolly onswers the

relioble (i.e. you cqn hust it) ond it is volid (i.e. it

a

)

?'type questions

e.g. funding, vested interests, reputotion of

o) i)

Questions

1. Copy ond complete: o) The o . . . . of o meosurement tells us how

neor the true volue it is. b) The s . . . . of on instrument tells us its obility to meosure smoll chonges in o vorioble. c) We con improve the r . . . . of doto by checking ogoinst other people's doto. d)We con describe our doto os p . . . . if repeot reodings ore grouped very closely together. e) The . . . . vorioble is the one we choose to investigote ond vory in on investigotion. f) In on investigotion we judge the effect of vorying the vorioble in port d) by meosuring the . . . . vorioble. g) In o foir test we must keep ollthe . . . . voriobles constont. h) If the design of on investigotion ollows you to onswer the originol question, we con describe the doto collected os v .. . .

Whose results ore likely to be the more occurote ? ii) Exploin your onswer. b) Did Pete ond Deon get the some order of ocidity? Write down eoch student's order. c) Soro used o different pH sensor to meosure the pH of the some solutions. Her results for A to D respectively were 3.8, 5.5,2.7 ond 3.7. Like Deon's, these numbers were reod off the computer screen.

Are the differences between Deon's ond Soroh's results likely to be through rondom

error? Exploin your onswer. Whot might hove coused the differences

?

3. A student

heoted somples of metol corbonotes to see which decomposed most eosily

.

2. A closs

wos given four solutions to test for ocidity. Pete decided to use universol indictor poper to dip in eoch solution. Then he motched the colour of the indicotor poper to the colours on the pH scole. Deon used o pH sensor ond doto logger to meosure the pH of the solutions. Here ore their results :

16

t

carbonate being tested limewater

heat

1.9

She used equol mosses of mognesium corbonote powder, o lump of colcium corbonote, zinc corbonote powder ond copper corbonote powder. When the corbonote decomposed it gove off

3.5

corbon dioxide gos.

Solution

Pete's pH values

Dean'E pH values

A

3

B

3.6 5.3

c

6 2

D

4

o) When she heoted copper corbonote it turned from o pole green colour to block.

direction of

r'

river llow

Mognesium corbonote olso decomposed, but there wos no colour chonge in the reoction. How did the student know there hod been o reoction ? (HINT: Look ot the diogrom ot the stort of the question.)

b) i) How

could she judge how quickly eoch corbonote decomposed ?

ii) Whot meosuring equipment would she need to moke her judgements ? iii) Do you think her judgements will be precise ? Exploin your onswer. iv) Whot could the student do to improve the reliobility of her doto collected ? i) c) Give one woy mentioned in the question in which the student tried to corry out o foir test. ii) Give one vorioble mentioned in the question thot the student foiled to control. Soy how this would offect her results.

d) i) Nome the independent vorioble investigoted.

ii) Is this o cotegoric, ordered, discrete or continuous vorioble ? e) i) Nome the dependent vorioble in her investigotion.

ii) Is this o cotegoric, ordered, discrete or continuous vorioble ? f) Whot type of groph should the student use to disploy her results ?

4.

The residents of o villoge on the bonks of o river ore worried obout pollution from o new foctory upstreom. Mercury, o toxic heovy metol, is involved in the monufocturing process in the foctory. Some people in the villoge enjoy fishing. They believe thot there ore less fish to cotch since the foctory opened o month ogo. The monogers in the foctory promised to corry out some tests.

They collected woter from the sites shown obove. Then they onolysed the woter in the lob. Two months loter they reossure the residents thot mercury levels ore perfectly sofe. TECHNICAL INFORMATION Mercury levels found in o woter somple token ot 8.00 o.m. on 5th Moy ot eoch site: Site A: 0.0000049/ litre Site B : 0.000 002s llitre Accurocy of method used to onolyse woter somples + or-50%. Sofe level of mercury in drinking woter is 0.000 0029I litre o) Some people in the villoge wont the

County Council or Environmentol Agency to corry out their own tests for mercury.

whv? b) When questioned, the foctory owners soid thot the mochine used to onolyse the woter somple wos 20 yeors old. Why did this worry the concerned villogers ? c) Give two woys in which the foctory could hove mode sure the dotq collected wos more relioble ond volid ? d) i) How could the foctory orgue thot levels of mercury were sofe ? ii) How could the villogers orgue thot they were not convinced even if the doto wos occurote ?

Further questions on poge 63.

77

Bmsfim nffimffis tin.C The oncient Greeks were the first to suggest thot everything is mode up from porticles.

15 rvrade

Aar ticleS

Txo.ts o,ll G(ee\


2H2O

./ 2H2 + 02

2H20

This is the bolonced equotion

Balanced at last ! left-hand side

rr+>

4 H'S 2 O's

right-hand side 4 H's 2 O's

The equotion reods: 2 hydrogen molecules plus 1 oxygen molecule gives 2 molecules of woter. Remember you should net)er change a formula when boloncing on equotion. You con only put numbers in front of o formulo.

o

Now you con try to bolonce these equotions

i) H2 + Cl2 --------> 1191 ii) No + Clz --------> NoCI iii) Li + 02 --------> lirQ ,,;!-.gy): ',,...t

,:

)

Stote symbols

Sometimes we find it usefulto odd even more informotion to our equotions. We con show the state of reoctonts ond products. Remember thot there ore 3 stotes of motter solid, liquid ond gos. It is olso usefulto know if ony substonces in the equotion ore dissolved in woter.

A balanced equation, Now what shall we do ? I know, we'll putin sfate symbols too.

Chemists use o short-hond colled stote symbols to show these things: stote symbol

solid liquid

(s) (1)

sos

(g)

(oq) solution (dissolved in woter) : (oq) comes from the Lotin word for woter, oquo.

States of matter There are three, We'llshow them by an s, / and g

Look ot this equotion with ol14 stote symbols: sodium 2No(s)

* woter --------> sodium hydroxide * hydrogen + 2H2O(l) --------> 2NoOH(oq) + Hz(g)

It tells us thot solid sodium reocts with liquid woter. They form o solution of sodium hydroxide ond hydrogen gos. Stote symbols ore olso usefulwhen substonces in equotions ore not in their normol stote of room temperoture. For exomple,

+

MgO(s) + Hz(g) --> Which substonce in the equotion is not in its usuol stote ?

Mg(s)

HzO(g)

The stote symbols tell us thot the mognesium hos reqcted with steom. Notice thot the H2O in the equotion is o gos,

not o liquid.

a a a

:28

Disso/ved in water? lVow this one is new. I know ! It's shown by the letters aq

!

)

4. Look ot this condle burning

Questions

1. Copy ond complete: o) The smollest port of on element is colled on .... . All the .... in on element ore

the some. Elements con't be broken down

into....substonces. b) Atoms joined, or bonded, together chemicolly ore colled . . . . . If osubstonce is mode from more thon one type of otom, it is colled o

...

.

Which lobel (A or B) shows o chemicol chonge ond which shows o physicol chonge Exploin your onswer.

.

c) In o.... chonge, new substonces ore formed. However, no new substonces ore

modeino....chonge.

5. Look

^q o9

2. The

density of o substonce is worked out using this formulo: density

.)o ICD

moss

volume

o) An 8cm3 block of iron hos o moss of 62.88g.

C

Work out the density of iron in (g/cms).

o

I

Look ot the densities in the toble below: ty (g/cwrs) oxygen

0.001 33 (at room temp. and pressure)

copper zinc

8.92

nitrogen

your onswer. d)WhV is the temperoture ond pressure importont when giving the density of oxygen ond nitrogen ?

3. Exploin eqch of the stotements below in terms of porticles : o)You con smell o fish qnd chip shop from ocross the rood. b)Sugor dissolves foster in hot woter thon cold woter. c) Condensotion forms on the inside of your windows in winter.

C o q o

'ccc C

c CO

C

D

@

@

@

@

@

Which box contoins: o) one element b) o mixture of elements c) o pure compound d) o mixture of elements ond o compound Whot might be hoppening in this box?

7.14 0.001 17 (at room temp. and pressure)

b) Whot is the physicolstote of eoch element in the toble at25"C? c) Exploin the big differences in the densities of the elements shown. Mention porticles in

ot the boxes below

6.

?

?

Some rescue flores contoin oluminium (Al) powder. It reocts with oxygen (Oz) in the oir to form oluminium oxide (Al2O3) - o white solid. o) Is this o physicol or o chemicol chonge ? b) Write o word equotion for the chonge. c) Now write o bolonced symbol equotion. Include stote symbols.

7. Bolonce these equotions: o) Hz + F2 --------> |JP b) CoCO3 + HCI -------> CoCl2 + COz c) CHa -t Oz CO2 + H2O t Oz d) NoNO3 -------> NoNO2 -->

+

H2O

Further questions on poge 64.

Ag l r

'l l

IG

STH )

History of the otom

HE

400

BC Democritus suggests that all things

are

made of particles. (See page 18.)

The word otom comes from o Greek word meoning 'something thot con't be split'. This fits in nicely with Dolton s ideos obout otoms. However, os you probobly olreody know, otoms con be split ! 1805

In the lote 1800s ond eorly 1900s, scientists hod to think up new pictures of otoms

John Dalton's atomic theory. Atoms of the same element are all alike. They combine to make compounds. (See Chapter 2.)

to exploin new observotions. For exomple, in 7897 J.J. Thomson

put forword his 'plum pudding' theory. He thought otoms were bolls of positive chorge with tiny negotive porticles stuck inside. The negotive porticles were colled electrons. He soid they were like the curronts in o bun or Christmos pudding. This model exploined Thomson's experiments with electricity very well. However, loter experiments using rodioqctive porticles needed o new picture. By 1915, scientists, like Ernest Rutherford ond Niels Bohr, hqd developed o modelthot is stilluseful todoy.

)

Inside the otom

There ore 3 types of porticle inside on otom. These ore

protons, neutrons ond electrons

The protons qnd neutrons ore found squoshed together in the centre of the otom The centre, colled the nucleus, is incredibly

smollond dense. The tiny electrons whizz oround this nucleus.

1

897

1909

J.J. Thomson finds the electron (See page 31.) Ernest Rutherford discovers the proton (See page 31.)

1911

Ernest Rutherford discovers the nucleus. (See below.)

1913

Niels Bohr suggests that electrons are found in shells around the nucleus. (See page 32.)

1932

James Chadwick proves that neutrons exist. (See page 31.)

This toble shows the chorge ond moss of the sub-qtomic porticles in qn otom

proton

1+

1

neutron

0

1

electron

1-

0 (almost)

Things to notice:

o protons ond neutrons hove the some moss o the electrons ore so light thot you con ignore their moss. In foct it tokes qlmost 2000 electrons to weigh the some os o proton or o neutron

o

remember the chorge on eoch porticle like this: protons ore positive, neutrons ore neutrol, (so electrons must be the negotive ones).

Protons I'm Penny the Proton and I'm pretty large, I'm considered a plus, with my positive charge. Itly friends and I, in the nucleuswe huddle, It's nice and cosy with neutronsto cuddle !

Neutrons I'm

Ned the Neutron and I'm pretty heavy, I'm fat and lazy and take things steady. You could call me 'cheap' - I've no charge at all, I really am just a dense, neutralball !

Electrons I'm Elvis the Electron and I'm pretty quick,

I fly round the nucleus

at a fatr old lick ! The protons and I, we tend to attract,

I'm negative you

see and that's a fact !

l$*r,;,,- ll,ir

)

Electron shells

The electrons in the otom ore orronged in shells oround the nucleus. The shells ore sometimes cqlled energy levels. The first shell (neorest to the nucleus) con hold just The second shell con hold up to 8 electrons. The third shell con olso hold 8 electrons.

2 electrons Electrons go round the nucleus in she//s /

1st shell holds 2 electrons

2nd shell hslds 8 electrons

3rd shell holds 8 electrons nucleus

Filling the shells The elechons stort filling up the shells from the inner shell outwqrds. They like to get os close to the nucleus os possible. You con see this from the exomples below:

helium

carbon

sodium

(has 2 electrons)

(has 6 electrons)

(has 11 electrons)

)

Describing otoms

You don't need to drow pictures of otoms every time. You con use o short-hond colled the electronic structure (sometimes colled the This just shows the number of electrons in eoch shell, working outwords from the nucleus.

electronic configurotion)

So the exomples drown on the previous poge con be shown os:

helium

o

corbon 2,4

2

sodium 2,8, 7

Con you write down the electronic structures of

:

o) nihogen (with 7 electrons) b) neon (with 10 electrons) c) oluminium (with 13 electrons) d) colcium (with 20 electrons -

the lost

2

electrons stort filling

the 4th shell)?

Atomic number (or proton number) Eoch element hqs its own otomic number, sometimes colled the proton number. It tells us how mony protons there ore in one otom of thot element. (All the otoms of o porticulor element hove the some number of protons.)

Atomic number

:

the number of protons (which is the sorne os the nurnber of electrons)

Atoms are neutraL The positive chorges ore concelled out by on equol number of negotive chorges. So the number of protons (+) in on otom must olwoys equol the number of electrons

(-

You have protons and 14 neutrons. Your mass number is 27.

).

13

Moss number You olreody know thot protons ond neutrons ore the heovy porticles which moke up on otom's moss. The moss number tells us how mony of these protons ond neutrons there ore in on otom.

Moss number

:

Try

Weight-watchers

AI

the number of protons

*

the numbet of neutrons

(N.B. Moss number is sometimes cqlled nucleon number.) You con work out the number of neutrons from this, os long os you know the otomic number os well.

Number of neutrons

: :

moss number moss number

-

number of protons otomic number ,59;1,

1, rLrrl,,1iiifii

)

Using qtomic numbers ond moss numbers

We con use the otomic number ond moss number to build up o complete picture of on otom. Let's look of on exomple:

,s

otomic number is 3 in alithium otom? 3 elechons.

lithlum

More short-hond

!

The otomic number ond moss number con be shown using chemicol short-hond. The informotion obout lithium in the exomple obove con be shown os: 7

3Li The top number is the moss number. The bottom number is the otomic number

number ----r- 27 otomic number ------>

mqss

AI "

o Work out the number of protons, neutrons 1s6

O,

ona l]

e.

ond electrons in Now show how the electrons ore orronged.

There ore often stories obout nucleor power ond otomic weopons on television. So you might hove heord the phrose 'rodiooctive isotopes'. But whot is on isotope ? Some elements ore mode up of otoms with different mosses. The number of protons in otoms of the some element is olwoys the some. So isotopes must hove different numbers oJ neutrons.

i, :., . , r r: , t. li,

I

:, r,. ri,ririi Lili :,ll,tr:, itltl Lrlli r, r,i,!at, lt|/,rt,,,. 1

We find thot some isotopes ore rodiooctive but mony ore

non-rodiooctive. Let's look ot this exomple: Example Corbon's otomic number is 6. Most corbon otoms hove q moss number of 12. A few hove o mqss number of L4. Drow the two isotopes of corbon c

o

6 protons and 6 neutrons

(,

o

6 protons and 8 neutrons

'o

"'c

'

Two isotopes of carbon

You con see thot the isotopes ore exoctly the some, oport from their numbers of neutrons. Isotopes of on element hove the some chemical reactions. This is becouse their electrons ore orronged in exoctly the some woy. (Chemicolreoctions only involve electrons. The protons ond neutrons in the nucleus toke no port in chemicol reoctions.) Isotopes ore sometimes written showing just their moss numbers. In the exomple obove the isotopes con be written os corbon-12 and corbon-14

::/. .., , I ,, .iri. ,.r'.. I .,:tir,r I liti:r,t.,iiit;i-, it.,,,., ,,'l I I ir ,, ,.rilli_ ..jri.ir l,|i t,1|r'r:,,i,,i r,trlttir:-'..1

Isotopes ore otoms with the some number of protons, but different numbers of neutrons. Rodiooctive isotopes hove mony uses. For exomple, they ore used in hospitols to kill concer cells. They ore olso used in industry to find leoks in underground pipes without hoving to dig the pipes up. Uronium-235 is the energy source in o nucleor power stotion. 35

)

Relotive otomic moss (R.A.M.)

Eoch type of qtom hos o different moss. However, the moss of qn qtom is too smoll to meosure. So we compore their mosses on q scole which gives the lightest element of oll, hydrogen, o moss of 1. This gives us o number colled the Relotive Atomic Moss (R.A.M.), sometimes given the symbolA,.

[;;ch e/errrrr:ll

rlaai a ,q..4

/'i.

/

Let's look more closely of the hydrogen otom: Hydrogen's qtomic number is 1. Its moss number is olso 1. This meons thot o hydrogen otom hos 1 proton, 1 electron, but no neutrons. You con see why it is so light I 1 electron

the hydrogen atom

-

the lightest of

1 proton

all atoms

You might think thot there is no point hoving Relotive Atomic Mosses qnd moss numbers. Both seem to tellus how heovy otoms ore. However, look ot the R.A.M.s in the tqble opposite: Do you notice onything stronge ? Could you ever get o moss number thot wos not o whole number ? You con't hove froctions of protons or neutrons in otoms. In foct, the Relotive Atomic Moss of qn element tokes into occount the element's different isotopes. Some elements ore found os mixtures of their isotopes. The R.A.M. is their overoge moss, toking into occount lhe different proportions of eqch isotope in the noturol mixture

chlorine-35

chlorine-37 chlorine-37

chlorine-35

chlorine-35 be chlorine-37 We

tl+ig'u;l,,u '

A carbon atom is 12 times as heavy as a

hydrogen atom. lts R.A.IVL is 12.

Element

ft.A.fitt-,(Ar)

chlorine copper

35.5 63.5 55.8

iron

)

Relotive Formulo Mqss

c 0,

Once you hove o list of relotive otomic mosses, you cqn work out the relotive mqss of ony molecule. You just need to know the chemicolformulo.

The formulo of corbon dioxide is CO2. It's molecules ore mode up of 1 corbon otom ond The R.A.M. of corbon is 12. The R.A.M. of oxygen is 16.

2

+

oxygen otoms

If we odd up the R.A.M.s qs in the formulo, we get the relotive formulq moss (or moleculor moss), sometimes given the symbolM,. So for CO2 we hove:

lcorbon : I x 72: 2oxygen:2x76:+32

I

/

Let's look of corbon dioxide os on exomple:

r\1,'ri rrir

t|e

P A.i,/ s io

gel the Relative

Flrrrri,ia /rlass

12

44 Therefore the relotive formulq moss of corbon dioxide is 44

How mony times heovier thon o hydrogen otom is o molecule of corbon dioxide ?

44H

1 CO2

atoms

molecule

These mosses ore usefulto chemists when working out the mosses of reoctonts ond products in chemicolreoctions. (See poge 350.)

Now let's try o horder exomple:

CO2 is 44 times as heavy as one H atom

Example Whqt is the relqtive formulo moss of oluminium sulfote, AI2(SO4)3 (R.A.M.s: Al 27, S 32, 16)

:

:

o formulo hos q This tells us thot oll the ore multiplied by the number So in oluminium sulfote. we 2 oluminiums,3 sulfurs ond

O:

?

of brockets

Now let's odd up their

2N:

2x27:

help us to do

moss of oluminium sulfote 237 and 350.)

oa

JI

Summory o Atoms contoin protons, neutrons ond electrons. o Protons ore positively chorged. Electrons ore negotively chorged. Neutrons hove no chorge - they qre neuhol. o Protons ond neutrons ore the heovy porticles in on otom. o o o o

They eoch hove q mqss of 1 otomic moss unit, ond ore found in the nucleus (centre) of on otom. We con ignore the tiny moss of the elechons. The elechons orbit the nucleus in shells (or energy levels). The 1st shell con hold 2 electrons. The Znd shell con hold 8 elechons, os con the 3rd shell. the number of protons (which equols the number of electrons). The otomic number the number of neutrons. the number of protons The moss number Isotopes ore otoms with the some number of protons, but different numbers of neutrons.

:

:

*

5.

l.

Copy ond complete: There ore 3 types of porticle found inside

otoms:o)

Sub-atomic particle

1

The protons ond neutrons ore found in the . . . . of the otom, colled the nucleus. The . . . . zoom oround the nucleus in shells. The 1st shell, which is . . . . the nucleus, con hold . . . . electrons, whereos the 2nd ond 3rd shells con hold .... electrons. o) Whot is the otomic number of on otom ? b) Whot is the mass number of on otom ? c) Whot is the otomic number of the otom below? Whot is its moss number ?

19e, Give the numbers of protons, electrons ond neutrons in the otoms below:

4.

i3x

b) e)

?3N"

c) 'f e

22c" r) 'liu

|rt"

b)

Za" .l

?3et at

Do you hove to look up the otomic number of lithium, given the informotion in the toble obove ? Exploin your onswer.

6. Hydrogen (otomic number 1) hos 3 isotopes. H. They con be shown o. ] H, ? H "na ? o) Whot ore isotopes? is the difference between the 3 isotopes? c) Hydrogen reocts with chlorine in sunlight, forming hydrogen chloride : Hz -t Cl2 -------'> ZHC| Would you expect the some reoction for eoch isotope of hydrogen ? Why ? d) Chlorine" exists noturolly os,2 isotopes. 75"/" is li Cl. ond 25"/" is \)Cl.

b) Whot

Show why the relotive otomic moss of chlorine is 35.5. e) The element chlorine is o gos. Its formulo is Cl2. How mony different mosses of the Cl2 molecule would you expect to find in o somple of chlorine gos ? Exploin your onswer.

7. Work out the relotive formulo moss of b) C2HsOH c) No2SOa o) H2O :

Drow fully lobelled diogroms of the otoms below

o) 38

'rnN

'19

(atomic mass units)

0 (almost)

o) d)

2,1 14

proton

3.

structure

lithium

Mass

Charge

Electronic

Atomic number

Element

....,b) ....ondc) .....

This toble shows their mqss ond chorge:

2.

Copy this toble ond fill in the gops. Use Toble 1 on poges 390 ond 391 to help you

13co

(R.A.M.s: H

:

1, O

:

16, C

S:32)

Further questions on poge 65.

:

12,No

:

23,

Ih

le

Sorting out the elements Scientists like to find potterns. Around 200 yeors ogo, scientists were discovering lots of new elements. However, they struggled to find ony links between the different elements.

Look ot the picture opposite:

Where shall we storf?

At the time, some substonces, which were thought to be elements, were in foct compounds. Other elements hqd not yetbeen discovered. No wonder finding o pottern wos tricky !

Finding the pottern Reolprogress wos mode oround 1865 by John Newlonds. He put the elements in order of their otomic moss. He found thot ev?ry eighth element wos similqr.

Unfortunotely, his pottern only worked for the first 15 elements known ot thot time. After thot, he could see no links between the rest of the elements. Other scientists mode fun of his ideqs. They suggested thot he could hove done better by sorting the elements into olphobeticol order I

How would you like to do a jig-saw with no picture to work from? Some pleces are missing and others don't belong in this jigsaw ! Ihls was the state of chemistry at the start of the 1 800s.

In 1869 the problem wos solved by o Russion chemist colled Dmitri Mendeleev. He olso tried putting the elements in order of their otomic moss. He mode q toble of elements. New rows were stqrted so thot elements which were qlike could line up together in columns. He wonted o toble of regulor (periodic) potterns. However, Dmitri wos not ofroid to toke risks. When the pottern begon to go wrong, he would leove o gop in his toble. He cloimed thot these gops were for elements thot hod not yet been discovered. He even chonged the order round when similor elements didn't line up. As you might expect, people doubted his 'Periodic Thble' However, he used his toble to predict the properties of elements which could fillthe gops.

In 1886, the element germonium wos discovered. The new element motched Dmitri's predictions. Finolly other scientists occepted his ideos.

Oo,.o,

I

oct"l

fotrr5

Dntitri 'was a chemistry teacher ln ,?ussia

I

)

The Periodic Toble

Although Mendeleev's toble wos occepted, there wos one thing thot he could not exploin. Why did he sometimes need to chonge the order of otomic mosses to moke the pottern corry on ? The onswer lies inside the otoms. The qtoms of elements in the Periodic Toble ore not orronged in order of moss. It is their number of protons (otomic number) which reolly motters. U

H

Group

numbers

1

1

2

LI

tse

34567

4

3 lihlum

,

bom

Na 't2 Mo "

l1

sodrium

t9

K

Rb

db&rim

Cs

55

66ium

r3

Wre$Ufi

Ca

20

38

Sc 21

tll

Ni

lulitanim

Sr

stJonlium

Ba

56

badum

Y lZr

sg

wim

l4o

la*i*

cTFiifl 172

t"nt

-r l

I

n*ar.

fi

Ta

g

/3

l€flElm

the alkaline eadh metals

Bdnium

@mlum

7

B

nilrog€n

Si

oxyg€n

F

I

16

sllur

As

34

Ne 10

,luoilne

cl

S

P

dfm

In

Sn

m

dn

indium

Sb

ct

antimony

Pb

T1 81 halllum

kidium

o

N

17 chlorine

Se

Br

dlium t9

ae€r

l4

,1 ztrc

Nb

rdobun

AI

erio

Ga 32Ge

30

28 nickd

sndim I

M 97

o

beryllium

h6llun

C

B

l@d

53

telluiium

Po

Bi 83

s2

84

bismuth

I

Te 52

rclonium

Xe 54

iodino

At 35 astatino

xM

Rn

86

BdOn

I

the halogens

the transition metals

1

the noble gases

the alkali metals

Groups

Each colour shows a chemical 'family' of elements with similar properties. You can see the full Periodic Table on pages 392-3.

There ore 8 groups in the Periodic Toble. A group is o uertical column. Allthe elements in o group hove similqr properties They ore o'chemicol fomily'.

Look ot the Periodic Toble obove: Some groups hove speciol 'fomily' nomes. Con you find Group 7 ? Whqt is the group cqlled ? Hove you met ony elements from this 'fomily' before? Other groups ore just known by their group number. Notice thot the tronsition metols form o block on their own

Periods Periods qre the rows across the Periodic Tirble. You reod the toble like o poge. Stort ot the top, ond work your woy down, reoding from left to right. So there ore 2 elements in the 1st period, H ond He. The 2nd period hos 8 elements, storting with Li. o Which is the lost element in the 2nd period ? o Count how mony elements ore in the 3rd period.

i,,

40

Groups are farnilies oI eiemenls Tlte rnentbers of ihe faniiy are -stntlar DLtt nat exactly [he s.1na

Example C is in Group 4. It is in the 2nd period. Al is in Group 3. It is in the 3rd period.

)

Metols, non-metols ond the Periodic Toble

As you know from the previous poge, the Periodic Toble hos 8 groups of elements. Groups 1 ond 2 ore oll metols, whereos Groups 7 ond 0

contoin only non-metols. However, the elements in the middle groups stort with non-metols ot the top, but finish with metols ot the bottom. For exomple, look of Group

4:

C

corbon

non-metol

5r

silicon

Ge

germonium

silicon ond germonium ore colled semi-metols or metolloids. They ore on the borderline between metols ond non-metols

Sn

tin

metol

Pb

leod

metol

Sr/icorr rs

a sertti tnc:tal

Silicon is the most well-known semi-metol. It behoves like o metol in some woys, but like o non-metol in others. For exomple, it is shiny like o metol, but brittle like o non-metol. Tin oxide reocts like o metoloxide, but olso reocts like o non-metol oxide It is on omphoteric oxide (behoves like on ocid ond o bose). !

This shows us thot science is not olwoys 'block ond white'. The semi-metols ore on exomple of o 'grey' oreo. However, we con drow on imoginory line in the Periodic Toble to divide the metols ond non-metols. You con think of the line os o stoircose. (See the bold line below.) Below stoirs you find metols, obove stoirs you find non-metols.

S/icon ls used rn the micro-electronic industry. /t ls a 'semr-conductor'. The silicon chip has made ltpossib/e to make circuits incredibly small.

metals non-metals

1H 4 liihium

11

5

beryllium

Na 12v Mo K

potassium

Rb

37

rubidium

AI

aluminium

Ca

20

calcium

38

Sr

slrontium

_^Ba --Cs 5b

b5

caesium

B ttur

13

sodium

19

berium

Sc 21

sndium

39

Y

Ti 22

23

litanium

40

Zr

vurium

zkconium

La

Hf

57 72 lilthanum halnium

V

vanadium

Nb 41 niobium

Ta

73

tantalum

24

Cr

Mn

25

Fe

Co

iron

cobalt

26

chromium

Mo

42

Tc

43

nolvbdenu[ €chnetium

74

W

tungsten

Ru

44

nithenium

Re _Os tb

75

rhenium

osmium

Rh

45

rhodium

Ir iridium

Ni 28

Cu

29

nickel

copp€r

Pd

Ao

46

palladium

78

Pt

platinum

silver

Zn

30

zinc

cd

48

cdmium

Au g0v Ho

79

mld

He h6liuh

semi-metals or metalloids

lWrogen

Be

Li

2

mercury

C

I

N 7

@lbon

si

l4

nitrcgen

P 1

.a'ilFrtn

o

F

oxyq€n

lluorire

I

16

S

sullur

^Ga JI oG" uA$ uSe oallium

49

In

solon,um

Sn

50

indium

TI

81 lhallium

tin

Pb

82

l€ad

Sb

51 antimonv

83

Bi

bismuth

39

le

'17

cl

chlorine

35

Br

bromine

53

I

iodine

Po

84

polonium

Ne 10

)5

At

astatino

.nsn

Ar

18

arcon

Kr

36. ikMton

Xe

54 xenm

Rn

86 Edc'ii

4-!'

:'

)

Group 1 - The olkoli metols

The elements in this first group don't hove mony uses os the metols themselves. They ore too reoctive. However, you will certoinly use some of their compounds every doy. You con reod obout these on poges 44,45,105 ond 254.

lithium sodium potossium rubidium coesium

You willfind the elements in Group 1 on exciting bunch I They ore metols, but they hove some very unusuol properties. You con see for yourself below :

DemonSrstion 4.1 Looking at sodium Your teocher will show you o piece of sodium. Whot is it stored under? Why?' Does the sodium look like o metol?

Sodium is stored under oil. This keeps it away from oxygen and moisture in the air.

A'oo,r,

Your teocher will cut o piece of sodium with o knife. o How soft is it? o Whot does it look like inside ? Is this more like o metol,'now? Your teocher will wqrm q smoll piece of sodium gen{y on q combustion spoon. o How eosily'does sodium melt?

shi ny surface

sodium at 98oC

Now you con see why sodium, ond the other olkoli metols, ore unusuolmetqls. They hove low melting points ond ore very soft. For metols, they olso hove very low densities. You will see in the next demonstrotions thot lithium, sodium ond potossium floot on woter !

H

Sodium can be cut with a knife. It's like cutting a piece of cheese.

The alkali metals can be cut with a knife

Look ot the toble below

lithium

sodium potassium rubidium caesium

o o

3

180

1360

11

98

900

19

63

37 55

39

777 705

Whot potterns con you see going down the group Tiy to predict the melting point of cqesium.

Typicol metols hove much higher melting points For exomple, iron melts of 1540 "C. l

[..=:

.w.

669 ?

Reoctions of the olkoli metols

Dit16€(00S

The olkoli metqls ore the most reoctive group of metols in the Periodic Toble. They ore too dongerous for you to use in experiments. However, your teocher cqn show you some reoctions of lithium, sodium ond potossium.

4,2

DO

rloT ToucH

Demonstration Ltthium with'water Your,teocher will,.drop osmoll piece of into o hough of woter. Whot do you see hoppen titnium The gcrs given off con be collected os strown : Test the gos with o lighted splint. o Which gos is given off ? Now odd q little universol indicotor solution to the kough. ro Is the solution left ocidic or olkoline ?

lithium ?

A

lithium

4.3

Sodium ond potossium with water Your teocher con now ky sodium ond potossium with woter' Demonstration

A

to

"ooir-oi*t potassium You con see:thot sodium gets hot enough melt itself os it reocts. Potossium gets so hot thot it lights the hydrogen gos given off. It burns with o lilqc flome.

o Whot

sodium reacting with water

hoppens to the reoctivity of the olkoli metols going down the group ?

The Periodic Thble is very useful. Its groups moke chemistry eosier You only hove to leorn the reoctions of one element in o group. The others ore usuolly similor. For exomple, lithium + woter --------> lithium hydroxide * hydrogen (*{$.r ru} imur x*:$ul {*tr )

Li(s)

water ' "

Group

1

!

least reactive

+

The olkoli metols get more reoctive going

the group.

Other reoctions The olkoli metols reoct wellwith non-metols. For exomple,

* oxygen ------> lithium oxide 4Li(s) + Oz(g) --------> 2Li2O(s) sodium * chlorine --------> sodium chloride 2No(s) + Clz(g) --------> 2NoCl(s) lithium

,iiidth

r'.1

2H2O(l) --------> 2 LiOH(oq) + Hz(g) Knowing this, we know the equotions for the other olkoli metols: sodium * wqter -------> sodium hydroxide * hydrogen 2No(s) + 2H2O(l) --------> 2NoOH(oq) + Hz(g) o Write o word ond symbol equotion for potossium reocting with woter 2

potassium reacting

most reactive

V

This pattern is explained on page 61

Compounds formed by Group I metole ore usuolly white solids (thot dissolve in woter to form colourless solutions).

Lithium Lithium gets its nome from the Greek word for 'stone'. As the metol itself, we use it to strengthen other metols, such os mognesium, in olloys. (Seepoge277.) It is olso used in botteries. Lithium botteries ore powerful ond lightweight. In foct you might be neorer thon you think to o lithium bottery now ! They ore suitoble for colculotors, wotches ond comeros They ore olso used in heort poce-mokers.

Lithium batteries are used in heart pace-makers

Lithium compounds Lithium compounds hove been used more ond more since the Second World Wor.

Look qt the diogrom below. It shows mony of their uses todoy

:

kill germs

medicine (lithium carbonate is used to treat mental illness)

hospital laundries)

glass (lithium carbonate is used in making tubes inside TV's and for lenses which darken in sunlight)

\\)l (\

/l

lithium compounds

ceramtcs dyes (lithium hydroxide helps to dye nylon and paper)

air conditioning (lithium hydroxrde is used in air condilioning systems and on submarines to remove carbon dioxide)

YELLOW PAGES

J

Potossium compounds Potossium is essentiol for the heolthy growth of plonts Potossium nitrote is used os o fertiliser. It is olso used in moking explosives ond fireworks. (See poge 197.)

M

(lithium oxide is added to ceramics, f rom oven-ware to the nose cones of rockets)

F

Chemistry of work: Group 1 metols ond their compounds

Sodium The element sodium is used in street lomps ond in nucleor reoctors. You con reod obout the uses of sodium on poge 106.

Sodium compounds The two most importont sodium compounds ore sodium chloride ond sodium hydroxide. Their uses ore covered in Chopter 8.

Food additives Do you eot cereol for your breokfost ? If you do, hove you ever reod the box? You will olmost certoinly find some sodium compounds Fast food contains additives. You can about E numbers on page 7 80. in the list of ingredients, even if it's only solt. Common solt, sodium chloride (NoCl), wos the first food odditive. You con reod obout it on poge 102. Nowodoys, we use mony other sodium compounds os odditives. Sodium sulfote(lV), sodium nitrite ond sodium nitrote ore ollpreservotives. They stop bocterio growing. Other sodium compounds improve the texture of foods. But perhops the most well-known (or infomous !) odditive is mono-sodium giutomote. It brings out the flovour in foods, ond is used o lot in Chinese restouronts. However, in some people it con couse dizziness, heodoches, nouseo ond is dongerous to osthmotics. Not surprisingly, it is bonned from boby foods !

Sodium carbonate The moteriols needed to moke sodium corbonote ore brine (sodium chloride solution), limestone ond ommonio. We moke obout 26 million tonnes eoch yeor Look ot the diogrom showing its uses:

!

washing powders and liquids it softens water (See page 293)

sewage treatment

dyeing textiles

it neutralises acid

sodium carbonate tanning leather

s!19: l (See page 1 14)

read

)

The tronsition metols

The tronsition metols lie in between Group 2 ond Group 3. They hove mony importont uses. (See poge 48.) Some well-known tronsition metols ore iron, copper, chromium, nickel ond gold. Metols in the whole block hqve similqr properties. As you know, this is stronge for the Periodic Tqble. Usuolly fqmilies of elements line up in the columns we collgroups.

WU;I, ffiiBffiffiffi ffi$h$$d[r1rfffiffiffiffiffi

ffiffii,:ffiffiI:ffiffiffi

Physicol properties The tronsition metols ore 'typicol' metols. They ore hord, dense ond shiny. They ore good conductors of heot ond elechicity. They ore molleoble ond ductile. The trqnsition metols qlso hove high melting points ond boiling points, except for mercury.

Why is

copper used for water pipes?

Experiment4.4

Magnetlc metals Try touching different tronsition metols with q mognet. o Which ones ore othqcted to it?

Iron, cobolt ond nickel ore the mognetic metols.

Chemicol properties

4.5

Heating copryr Hold o stuip of copper firil Heot it stongly for o Experiment

r

o o o

Does the copper burst into Whot does the copper look Which gos in the oir hqs it Whot do you think the block

copper loil

does? down? is colled ?

Copper, like mony tronsition metols, only reocfs slowly with oxygen in the oir. It forms o loyer of block copper oxide on its surfoce.

copper 2 Cu(s)

+ +

oxygen --------> copper oxide Oz(g) --------> 2 CuO(s)

il

Q. What does an alloy of nickel and titanium wear in bed

?

u-!N

ev

Experiment,4.6 Tiansition metals with water Put o tronsiti0n metol in the opporofus os shown

:

bu con repeot this using iron, copper, nickelond ony other somples you hove. o fue there ony signs of q reoction ?

funnel

Leove them in:the wcrter for o week.

water

o

Hqve ony honsition metols reqcted with the wqter? If they hove, hoLr cqn yoq tell thqt,there hos been o reoction

transition metal ?

The tronsition metols reoct very slowly, if of oll, with woter. You con reod obout iron rusting on poge 76.

The tronsition metols ore lecc seaetive thon Group 1 metols.

Tronsition metol compounds Look ot the compounds of tronsition metols Whqt do they hove in common ? Look qt the photo of the weothered copper roof on poge 203. The copper compound formed on it is green.

\a/ @/ \a/

coppe(ll) chloride

@/

cobalt(ll)

chloride

iron(lll) chtoride

nickel chloride

manganese(ll) chloride

Tronsition metols form coloured compounds. On the other hond, the compounds of Group 1 metols ore usuolly white.

Which formulo

?

Most tronsition metols form compounds which cqn hove more thon one formulo. For exomple, on the lost poge you sow copper oxide, CuO, formed. Howeveq there is qnother form of copper oxide whose formulo is Cu2O. The compounds ore different colours. Romon numbers in the nomes tellus which compound we meon. Copper(ll) oxide is CuO. Copper(l) oxide is Cu2O. Other exomples ore iron(ll) oxide, FeO, ond

The presence of chromium (Cr3+) makes this emerald green

iron(lll) oxide, Fe2Os. You con find out how to work out formulos on poge 251.

Cotolysts

ammonra sulfuric acid

vanadium(V) oxide

We use cotolysts in industry to speed up reoctions.

nitric acid margarine

platinum / rhodium nickel

(See poge

272.) Look qt the toble opposite:

The tronsition metols ond their compounds ore importont cotolysts.

iron

The tronsition metols ond their compounds ore widely used in industry ond in everydoy life. Iron is the most commonly used metol, mostly os steel. You con reod obout its uses on poge 78. Here ore some uses of the tronsition metols oround the home

copperwater pipes

zinccoaled water tank

ti m'

fungsfen filaments in lightbulbs

cobaltis copperwater tank

in the alloy used to make razor-blades

brass (an alloy of copper and zinc) door handles

copperwiring lor electricity

titanium oxide is the pigment used

in white paint chromium plaled laps

stainless steel radiators

stainless steel sink (an alloy of iron with chromium and nicke$

cast fon used for is

manhole covers

Other uses A rodiooctive isotope of cobolt is used to treqt potients with cqncer.

plastic-coated steel fridge

Plotinum

is used in cotolytic converters, fitted to cor exhousts. It cuts down the omount of pollution from cors. (See poge 148.)

)

Chemistry ot

Tronsition metols ond their compounds

Gold People often think it's just jewellers thot use gold. (See poge 273.) It is used for jewellery becouse of its ottroctive oppeoronce ond its

low reoctivity. Howeveq gold is olso used in o greot voriety of industries thot's despite its high price. Here ore some of the other users of gold:

-

ond

computer, telecommunication and home appliance industries

gold-coated electrical connections

satellite manufacturers

gold-plated shields and reflectors to protect equipment from solar radiation

the latest laser technology in

in lasers to perform eye operations and kill cancerous cells. The lasers use gold reflectors to concentrate light energy

hospitals

motor industry

Gold jewellery

gold-coated contacts in sensors that activate air bags

Mony of these ore 'new technologies', of the cutting edge of industry. o Whot properties of gold hove resulted in its vorious uses ? Link eoch use in the toble to gold's usefulproperties.

Silver Gold, like silver, hos been used to moke jewellery for thousonds of yeors.

o

r

o

Why is silver one of the 'jewellery metols'? Which metol, gold or silveq is more likely to tornish Nome onother expensive metol used by jewellers.

?

Gold helps to save lives. How

?

Silver olso shores mony of gold's other usefulproperties.

Did you know thot TVs, dishwoshers, telephones ond computers oll contoin silver in contocts ond switches ? A typicol woshing mochine will contoin more thon 15 silver contocts !

However, the biggest use of sllver (447o) is in the silver compounds in photogrophic film. (See poge 254.) The lotest developments use nono-scole, tiny porticles of silver. (See poges 336-7 .) These hove very effective onti-bocteriol, onti-virol ond onti-fungicide properties. They ore used in sproys to cleon operoting theotres.

o

Why ore moteriols with nonoporticles of silver used to line fridges

?

Sl/ver is the most reflective of all metals. We use it to plate the surface of cutlery and in mirrors.

49

Summory I The I I

Periodic Toble orronges the elements in order of otomic number.

properties line up in verticol columns. These columns ore cqlled groups. in the Periodic Toble. Thble is colled o period into metols ond non-metol s (with o few semi-metols or metolloids

a A row a The

ln a

Group

1under oil hove low densities ond low melting points quickly tornish in oiq but ore shiny when freshly cut ore the most reoctive get more reqctive

ore

-

Iionsition metqls

-

-

ore hord ond dense hove high melting ore less reoctive form coloured more thon one formulo, con form compounds for exomple, iron(ll) oxide, FeO, ond iron(lll) oxide, Fe2O3 ore importont cotolysts in industry.

2.

obove. o) Which olkoli metol is used in street tights

1. Copy ond complete: o) The elements line up in order of otomic . . . . in the Periodic Toble. There ore . . . .

groups. The elements in eoch group hove . . . . properties. Groups form v------columns, whereos periods ore rows. Most of the elements h_ con be divided into2 sets - the .. . . ond the non-metols. b) Group 1 elements ore colled the . . . metols. They hove . . . . melting points ond . ... densities. They ore the most.... group of metols, ond ore stored under .... . Lithium is the .... reoctive member of the group. They ollreoct with cold woter, giving off . . . . gos ond leoving on .

....solution. c) The . . . . metols ore typicolmetols. They ore hord, hove . . . . melting points ond .. .. densities. They ore .... reoctive thon the metols from Group 1. They form . . . compounds, which con often hove more .

thonone..... 50

Look of the cortoons in the Summory box ?

(See poge 106.) b) List some uses of nomed tronsition metols. (See poge 48.)

3. The

numbers in this Periodic Toble represent

elements. 2

J

4 tr

6 7

2 elements ore in the some group ? Give the nome ond number of this group. b) Which elements ore in the 2nd period ? c) Which elements ore metols ? d) Which group is element 7 in ? Which o) Which

period is it in ? e) Which element is o semi-metol (or metolloid)?

4.

Use Toble 1 on poges 390 ond 391 to help you onswer this question. o) Record the melting points ond otomic numbers of the Group 1 metols in o toble. b) Plot o groph like the one shown below:

6.

The olkoli metols, ond porticulorly their compounds I ore verg useful. Drqw o spider diogrom to show their uses. You could moke o poster from your reseorch. You will hove to refer to informotion in Chopter 8 to find out more obout sodium.

7.

o) Where in the Periodic Toble do you find the tronsition metols ? b)Nome 5 common tronsition metols. c) Moke o list of the properties of o typicol

Li

o c o

o.

c o)

E

3

atomic number

c) Whot pottern do you see going down Group

t? d) Look up the melting points ond otomic numbers of the Group 2 metols ond put them in o toble. e) Now do onother groph, showing the melting points of the Group 2 metols. f) Compore your grophs for Groups 1 ond 2. How ore they olike ? How do they differ ?

5.

o) Describe whot you see when sodium reocts

with woter. b) Write o word equotion for the reoction in o). c) When the reoction in o) hos finished whot would you odd to the solution left to test its pH ?

tronsition metol. d) Compore the reoctions of sodium (Group 1) ond copper (o tronsition metol) with oir. Whot con you soy in generol obout the reoctivity of the tronsition metols compored to metols from Group 1? e) Look of these two compounds: A

Which one is the tronsition metol compound, ond which is the olkoli metol compound ? How con you tell the difference?

8. I ook ot this toble of doto obout 4 metols, lobelled A, B, C ond D.

d)Whot is the pH of the solution left? e) Which substonce mokes the solution

on olkoli?

f)

We con collect the gos given off when lithium reocts with woter. How con you test thot the gos is hydrogen ? g) Why would it be impossible to collect the gos given off when potossium reocts with

woter

?

h) Predict whot would hoppen when rubidium, which is under potossium in

i)

Group 1, reocts with woter. Include o word ond symbol equotion in your onswer. Stote the pottern in the reoctivity of the Group 1 metols going down the group.

Metal

Melting point ('C)

A

63 1494 1060 98

B

c D

Use letters A, B, C or D to onswer o) qnd b). o) Which metols ore probobly tronsition metols ?

b)Which metols do you think ore from Group 1? c) Whot would the doto quoting the density of eoch metol show

?

Further questions on poges 66 to 68.

51

e a

Gt rmftmp*er,5 We hove looked of some groups of metols. Now let's move ocross to the other side of the Periodic Toble

ond look more closely of some non-metolelements

)

Group 7 - The hologens Halogen molecule

F

fluorine

CI chlorine

Br bromine I iodine At ostotine

Colour

State (at 25'C)

F2

pale yellow

gas

Clz

yellow / green

gas

Brz

orange / brown

liquid

l2

grey / black (violet vapour)

solid

The Group 7 elements ore colled the hologens. Look ot the toble obove: Notice thot ollthe hologens' otoms 'go round in poirs'. They form diqtomic molecules. In other words, 'two-otom' molecules, likeF2 ond Cl2. You con olso see some potterns in the toble going down the group. o Do they get dorker or lighter in colour ?

Look of their stotes: o Whot is the pottern ? o Do their melting points ond boiling points get higher or lower os we go down the group ? o Using the toble, moke some predictions obout ostotine (the element, ot the bottom of Group 7, below iodine). Now let's look of some of the reoctions of the hologens :

The hair-tqe:tt:; iitilir i,'i.rlr)ir-'il,'iirrri-i.']rif:' l (They are atott tit, lr'li/r: 1r

Q

Experiment 5.7 The halogens with water In this experiment you willuse hologens dissolved in wqter. Use o dropper to put o few drops of solution on to some universolindicqtor pqper crs shown: zi\ ll\ o Whot do you see hoppen? o Which hologen solution is most ocidic ? solutions of chlorine and bromine o Which is the shongest bleoch ?

Chlorine is used os o bleoch. (See poge 54.) It reocts with woter: hydrochloric ocid chlorine * woter

+ chloric(l) ocid (bleoch) --> Clz(g) + H2O(l)--------> HCI(oq) + HOCI(oq)

Bromine is less ocidic thon chlorine. It is olso o weoker bleoch. Iodine is even weoker.

isz

Why can iodine molecules see so wel/ ?

is,Io/i

aaeq Aeql

E solution of chlorine

asnecag V

Reoctivity of the hologens Demonstration

5.2

Chlorine with iron Your teocher will show you this experiment in q fume-cupboord. The chlorine con be mode by dropping hydrochloric ocid on to sodium chlorote(l). 7\ Heot the ironrwool strongly os the chlorine .+ chlorine posses over it. o Whot do you see hoppen ?

hydrochloric acid chlorine

out

r+>

t

iron wool glows brightly as it reacts with chlorine

heat

sodium

chlorate(l)

The iron ond chlorine reoct vigorously. Red/brown iron(lll) chloride is mode in the reoction.

iron f 2 Fe(s) +

The hologens olso reoct with other non-metols. For exomple : Hz(g) + Clz(g) -------> 2 HCI(g) The compounds formed ore mode of smoll molecules. They hove low melting/ boiling points.

chlorine --------> iron(lll) chloride 3 Clz(g) 2 FeCl3(s)

Notice how chlorine-> chonges to chloride in its compounds In generol, we soy thot the hologens form holides. Bromine forms bromides. Iodine forms iodides. Bromine does not reoct with iron os quickly os chlorine. The reoction with iodine is even slower. We find thot:

F

cr

The hologens get less reoctive going down the group.

o

Which is the most reoctive of oll the hologens

?

Hologens in competition

A

most reactive

I

least reactive

We con put the hologens into competition with eoch other to see which is more reoctive.

Experiment 5.3 Displacement from solution Add chlorine solution to o solution of potossium bromide o Whot do you see hoppen ? Do the some with o solution of potossium iodide. o Whot hoppens ? Now hy mixing solutions of bromine ond potossium iodide. o Whot hoppens ? If you hove time, mix solutions of bromine, then iodine, with potossium chloride.

A

This pattern is explained

on page 61

chlorine solution bromine solution

chlorine solution

potassium bromide turns yellow as bromine is

displaced

Chlorine is more reoctive thon iodine or bromine. It con 'push' (disploce) bromide ond iodide out of solution. chlorine * potossium bromide potossium chloride

Cl2(oq)

o

+

2KBr(oq)

:

* bromine 2KCl(oq) + Br2(oq)

Bromine is more reoctive thon iodine. Con it disploce iodide from solution Write o word ond symbol equotion for the reoction of bromine with potossium iodide in solution.

?

53

)

Chemietry of work: Hologens ond their compounds Fluorine Fluorine is the most reoctive of ollthe non-metol elements. It even ottocks gloss I However, some of ils compounds ore useful. Remember thot the properties of elements ore completely different from those of the compounds they form.

Teflon is a fluorine compound. lt is the non-stick lining on pans. (See page 155.)

l\lost toothpastes contain fluoride to prevent tooth decay. Some p/aces have fluoride added to their water supplies. (See page 254.)

Chlorine Chlorine ond its compounds hove mony uses antiseptics and disinfectants killing bacteria in swi mming pools

a

killing bacteria in drinking water

o

ffi solvents

pesticides and weedkillers bleach

to kill bacteria and to whiten paper

hydrochloric acid

The most common chlorine compound is common solt, sodium chloride. You con see some products mode from it on poge 105

Bromine Bromine is used in pesticides. It is olso used to moke medicines. Silver bromide is used in photogrophic film (See poge 254.)

Iodine Iodine is qn ontiseptic. It is dissolved in qlcohol, ond put on to cuts.

lodine can be used before operations

)

Hologens

- working for or ogoinst us ?

The hologens ond their compounds hove hod both good ond bod effects on the world.

Chlorine hos hod o bod reputotion since it wos used os the first chemicolweopon in the First World Wor. Its compounds ore olso used in biologicol nerve gqses. However, chlorine's use in killing bocterio in drinking woter hos soved millions of lives oround the world. It hos greotly reduced the number of coses of cholero. However, obout 25 000 people still die oround the world every doy from diseoses spreod in woter. Yet even this use is now being questioned. Scientists ore corefully meosuring the poisonous

compounds thot the chlorine mokes ofter it is odded to our woter supply. These poisons were first noticed in dischorges from poper mills. Chlorine is used to moke poper white. Poper monufocturers now use less chlorine gos, ond ore looking for new woys to bleoch pqper.

There are still many people who have to drink

untreated water

Hologen-bosed pesticides hqve reduced deoths coused by diseoses corried by insects, such os molorio. They olso reduce the loss of crops in storoge. On the other hond, these compounds con offect other wildlife in the food choin.

&

I

'$ $ I

Hologen compounds ore olso domoging the ozone loyer. This loyer in the upper otmosphere protects us from hormful ulko-violet roys from the Sun. (See poge 306.) CFCs (chloro-fluoro-corbons) were once hoiled os new wonder compounds. They ore very unreoctive ond were thought to be completely hormless to living things. They found uses in oerosols ond os coolonts in fridges. However, scientists in the 1980s discovered o hole in our ozone loyer - ond it wos growing. They predicted thot more coses of skin concer ond eye cotorocts would soon be observed. This hos led to o seorch for different compounds to do the jobs of the CFCs. CFCs ore now being phosed out, os ore other hologen compounds used in fire extinguishers, flome-proofing ond solvents. However, becouse they ore so long-losting, CFCs will remoin in the otmosphere for mony yeors to come.

r&ozoNt

(0ilTAut5 NO (Ht0t0ruu080

(tRg0il

PR0til.tAt{r

AittGt0

r0

DAMt6t 1ilr

OZONE

TRIENDI.Y

I.AYIR

ri

# Ihese aerosol cans contain no CFCs

, 6fi,,

:

l

)

Group 0 - The noble goses

0

tr

Q. What do you call a chemical element with no chemistry ? A. A noble gas! The most striking thing obout this fomily of elements is their lock of reoctivity. They used to be colled the inert gqses. Inert meons 'hoving no reoctions'. However, in 7962 their first compound

helium neon orgon krypton xenon rodon

hlc r*nnf- to be olone I

wos mode. They were then re-nomed the noble goses

As you know, most of the goses we hove met so for ore mqde up of molecules. Gqses like

The noble gases prefer to be alone

oxygen, 02; hydrogen, H2; ond chlorine, Cl2 However, the noble goses ore so unreoctive thot they ore found os the otoms themselves. They ore colled monotomic goses

(bne-otom'

goses)

\o

{^

.

The noble goses ore very unreoctive.

Why ore the noble goses so unreoctive

(/) The noble gases are 'monatomic'

?

Chemicol reoctions involve the electrons in the outer shells of qtoms. Most otoms hove o tendency to hove their outer shell completely fullof electrons. With/ull outer shells, otoms are stoble.

[f\ore

J

Q lect/ar:.s,

5t f ?

thaoks rT 'm

Atoms con give, toke or shore electrons with other otoms to get full outer shells. (See Chopters 19 ond 20.) So let's look ot the otoms of the first 3 noble gqses : (Remember thot the 1st shell con hold 2 eleclrons, the 2nd ond 3rd shells con eoch hold 8 electrons.)

helium

Whqt do you notice obout their outer shells

?

The noble goses ore stoble becouse their outer shells ore

l'',,,

,

s6,

Q

argon

neon

full.

Why are the noble gases so lonely?

iuobte spuouJ )taql osnecog v

Physicol properties of the noble goses Boiling points

0

Do you think thot it tokes o lot of energy to boil o noble gos ? Whot evidence hove you got for your onswer ? By the time we get to room temperoture the noble goses hove olreody boiled of much lower temperotures. In generol, the torces between molecules get stronger

-50

o

as the molecules get larger.

So whqt do you think hoppens to the boiling points (or boiling temperotures) of the noble goses os we go down the group ? Do you expect o pottern Look ot the groph opposite: So we con soy thot:

He Ne Ar Kr Xe

00

c oo)

50

.E

o

?

I)

-200

The boiling points (or boiling temperotures) of the noble goses increose going down the group.

-250

Liquid helium boils at That's only 4"C above the lowest temperature you could ever have in theory @alled absolute zero).

-269'C.

Density

1

x

1o-2

How would you expect the density of the noble goses to chonge os we go down the group ? Con you think why ? Look ot the groph opposite:

8

x

1o-3

E

6x1 6-3

o)

Helium has a very low density

=oc o)

4x1 g-s

2

The density of the noble goses increoses going down the group.

x

l0-3

0

He Ne Ar Kr Xe

Rn

Rn

)

Chemietry ot Helium If we cool down metols to very low temperotures, they lose their electricol resistonce. They become perfect conductors, or super-conductors. (See poge 269.) Liquid helium is used to coolmetols down. Remember the groph on the previous poge: Helium boils ot -269'C ! It is used to cooldown the coils in body sconners in hospitols. The coils con then moke the very strong mognetic fields thot sconners need. These mochines hove become very importont. Doctors con now see o complete picture of the orgons inside your body. This is very useful in finding concers ond helps doctors to judge whot effect their treotment is hoving on tumours.

Hove you ever seen on oirship ? Perhops of o sporting event? Comeros on boord provide those fontostic views looking down on the oreno ond crowds. As you know, helium is much less dense thon oir. It is used to fill oirships to provide lift. However, the first lorge oirships built in the 1920's used on even lighter gos - hydrogen. o Con you think of ony dongers using this gos ? Look ot the photo below: Helium is much sofer? Why ?

Hydrogen ls nol sale to use in airshps

Body scanners use liquid helium

Aerial view from

Helium is used nowadays

an airship

Chemistry of work: Noble goses Neon Lote in the 1800's scientists were investigoting goses ond electricity. They found thot o gos ot low pressure con be mode to glow if we opply o high voltoge to it. These dischorge tubes helped scientists, such os J.J.Thomson, find out more obout electrons ond otoms. Nowodoys, we use the noble goses to moke mony of the brightly coloured lights you see in cities. Neon is the gos used for red signs.

I'T!I

/t^t*

;-;;i-

IL ii

,1

I

'lli'i ,tS? t" 4v ltli lr ,J'-" "*... -{'fliEr

tl t1

f,n

"

-.--

' lt . 'rf ,;Tiq,

'l ,ii I

ti

t

{

Argon Light bulbs ore filled with orgon gos. Why do you think thot oir is reploced by orgon ? Argon won t reoct with the tungsten metol filqment inside the bulb, even when it is white-hot. Its lock of reoctivity olso helps in welding. It octs os o shield oround the hot metol in the weld. o Whot might hoppen otherwise ? Argon is used in the extroction of titonium metol. We olso pump the gos into the molten mixture to stir it up when moking steel.

t

t I I

g

Krypton Krypton gos is in the losers thot doctors use to operote on eyes. The loser opposite is being used to repoir the retino ot the bock of the eye: iv

Rodon There is hordly ony rodon gos in the oir. But in some ports of the country people hove hod to check the levels of this gos in their homes. In rocks, such os gronite, there ore smoll omounts of noturolly occurring rodium. This rodioocive element breoks down into rodon gos which is itself rodiooctive. So the gos con build up ond become o donger to heolth. Some houses hove pumps instolled to moke sure the oir inside is chonged regulorly. Ironicolly, rodon is used to help treot concer. o Reseorch ond write o brief report on 'The discovery of the noble goses'.

I

Estimatod propoftion of homes exceoding the Action Level in England

n

m 1.3

rI I

3-10

t0-30

)

Atomic structure ond the Periodic Toble

We olreody know thot the elements in the Periodic Toble

ore orronged in order of atomic number. The otoms of eoch element hove one more proton (ond electron) thon the one before it. The toble below shows the woy electrons ore orronged in the first 20 elements.(You don't need to know ony more thon this.) Electronic

Atomic number

Electronic

Atomic number Element

structure

1

H

1

1'l

Na

2,8,1

2

He Li

2

Be

2,2 2,3 2,4 2,5 2,6 2,7 2,8

12 13 14 15 16 17 18 19

Mg AI Si

2,8,2 2,8,3 2,8,4 2,8,5 2,8,6

K

2,8,8 2,8,8,1

20

Ca

2,8,8,2

3 4 5 6

1

structure

Element

2,1

B

C

7

N

8 9

o

0

Ne

F

Con you see ony potterns

P S CI

2,8,7

Ar

?

Look ot these otoms from the first ond lost groups in the Periodic Toble Group number

2 Li

7 Be

o

:.

a

_.

..

0

Ne

F

a

Ms

Ar

I.:

a

Con you see o link between the group number ond the number of electrons in the outer shell?

Atoms of elements tn hove the some number of For exomple,

N-2,5 ond P-2,8,5

Table shell. ore both in Group 5.

It is the electrons in the outer shell thot get tronsferred or shored in chemicolreoctions. This exploins why elements in the some group hqve similar chemicsl reactions. But whot obout the tronsition metols ? Theg ore ploced in the 4th period. Thot's becouse ofter the first 2 electrons go in the 4th shell, the next 10 electrons go into the inner 3rd shell. You con think of the 3rd shell os holding 8 electrons, but with spoce for onother 10 in reserve !

tlondr.rPrall rrr,th

electrons'rn outcr Although iodrne has 53 e/ectrons, you know it has 7 electrons in its outer shell because it is in Group 7

Exploining potterns in the Periodic Toble

No.1

Why are the alkali metals (Jrom Group 7) so reactioe?

Li

Like oll otoms, they wont to reoct to get o full outer shell. As elements, they hove just 1 electron in their outer shell. So when they reoct, they wont to lose thot 1 electron to leove o full outer shell.

n&fa'c! LJhg ore 5oo

q.

Group 1 elements ore so reoctive becouse it is eosy for them to get rid of just 1 electron. o Why do you think thot sodium, from Group 1, is more reoctive thon its neighbour from Group 2, mognesium ?

rne,

Sodi"""?

No to rid

Why do the metals get more reactive going down Group 7? The outer electron gets eosier to remove os you go down the group. Remember thot electrons ore negotively chorged. They ore ottrocted to the positive protons in the nucleus. As you go down the group, the otoms get bigger. Therefore the outer electron gets further owoy from the ottroctive force of the nucleus. This mokes it eosier for on electron to escope from o bigger otom (even though the positive chorge on the nucleus is greoter).

th-n

Sodium is more reactive than lithium

Why do the halogens get less reactive going down Group 7?

An otom of o hologen hos 7 electrons in its outer shell. It needs to goin 1 electron to fill up its outer shell. A fluorine otom is o lot smoller thon on iodine otom. Therefore, on electron entering the outer shell of o fluorine otom is neorer to the ottroctive force of the nucleus. The elechon is ottrocted more strongly.

Charged particles Remember thot when the olkoli metols reoct, they lose the electron from their outer shell. Once the electron is lost, the otom is no longer neutrol. It becomes o chorged porticle colled on ion. It hqs one more proton thon electrons, so its chorge is 1+.

On the other hond, the hologens goin on electron. o How mony protons ond electrons does fluorine hove ofter it hos goined on electron ? The hologens oll form 1- ions (F-, Cl-, Br- ond I-).

lluoride ion

tluorine atom

Allthe elements in o group form ions with the some chorge (for exomple,Li+, No+ ond K+). neutral

gains an electron 1

-

charge

on ion. F-

atom, F

-)> ,fifli

, ,, , ,.

.

Summory

I2 llodii)ne

The elements of Group 7 ore colled the hologens. They exist os diotomic molecules (F2, Cl2, Br2, ond I2). They ore o reoctive group of non-metols. They get less reoctive going down the group. The elements in the lost group (numbered 0) ore cqlled the noble goses. They exist os single qtoms. They ore ollvery unreoctive. Their otoms ore very stoble becquse their outer shells ore full of elechons.

\t

There are in iodine,

2l's

Its formula is It is diatomic.

12.

All the otoms of elements in the some group of the Periodic Thble hqve the sqme number of electrons in their outer shell.

)

3. Drow o picture in your book, or moke

Questions

1. Copy ond complete

:

The elements in Group . . . . ore colled the hologens. Fluorine ond .... ore goses, . ... is oliquid

ond iodine is o.... . They oll exist os .... molecules, e.g. Cl2 ond Br2. They get . . . . reoctive os you go down the group. Therefore, . . . . is the most reoctive hologen. The elements in Group 0 ore colled the . . . . goses. They ore the most . . . . group in the Periodic Toble, hoving olmost no chemistry ot oll. This is becouse the outer shell of their otoms is . . . . of electrons. The number of the group on element is in usuolly tells us how mony electrons ore in the . . . . shell of its otoms. For exomple, iodine is in Group 7; therefore it hos . . . . electrons in its outer shell.

2. Copy ond complete

these sentences obout

the uses of the noble goses o) Helium is used to filloirships ond bolloons becouse .... b) Liquid helium is used in body sconners becouse .... c) Neon is used in odvertising signs :

.

.

becouse

....

.

d)Argon is used inside light bulbs becouse

....

.

4.

o) Drow o toble showing the colour ond physicol stote of fluorine, chlorine, bromine ond iodine. b) Which is the least reoctive of the hologens in o)? c) You wont to collect o gos-jor of chlorine gos. Copy ond complete the diogrom below. (Hint: chlorine is more dense thon oir.) hydrochloric acid

? sodium

chlorate (l)

d) Write o word ond symbol equotion for the

reoction between chlorine ond iron. (No) reocts with chlorine (Cl), moking sodium chloride (NoCl). o) Write o word equotion for this reoction. b)Now write o symbol equotion. (Don't forget to bolonce your equotion.) c) Write word ond symbolequotions for the reoction between sodium ond fluorine. d) How would you expect the reoction with sodium to differ if you used fluorine insteod of chlorine. Exploin your onswer.

5. Sodium

Further questions on poge 69. 62

o

poster, showing the uses of the hologens ond their compounds.

Further questions on The Foundotions of Chemistry

ts How science works 1. A student is osked to study the rote ot which mognesium reocts with hydrochloric ocid solutions of different concentrotions. The time token for o piece of mognesium ribbon to completely disoppeor in the ocid is meosured. The experiment is repeoted using different concentrotions of ocid. o) Whot is the independent vorioble ? tll b) Whot is the dependent vorioble ? tll c) Suggest two controlvoriobles. t2l

2. A student plonned on investigotion to compore the temperoture rises which occur when different metols ore qdded to hydrochloric ocid. o) Suggest three voriobles which must be controlled so thot the investigotion is q foir

test.

t3l

b) Suggest two woys in which the student could moke the temperoture meosurements os occurote os t2l

The students oll hod slightly different results. Suggest three possible reosons for the sfudents not getting exoctly the some result. t3l

4. Tom works

os o scientist with o compony thot mokes rubber products. He corries out tests on two somples of rubber. Somple A hos been heoted with chemicols. This is colled vulconised rubber. Somple B hos not been heoted. This is unvulconised rubber. He tests the somples for the following: o the resistonce to breoking when it is stretched (tensile strength) The higher the volue, the less likely it is to breok.

.

hordness

The higher the volue, the horder the rubber is.

Tom does eoch test five times. The toble shows Tom's results. Tensile strength in MPa

possible.

3. A closs of students

were given the tosk of meosuring the volume of hydrogen gos produced whenZ4g of mognesium reocts with on excess of hydrochloric ocid. The opporotus shown in the diogrom wos used. hydrogen

hydrochloric

magnesrum

o They weighed

o o o

33 34 33 34

36

43 38 45 65 40

rubber)

Sample B (unvulcanised rubber)

34253

22 29 24 28 25

o) i) Work out the best estimote for the tensile strength of somple A by

colculoting on overoge volue. You must show how you work out your onswer. The unit willbe MPo. tzl ii) Exploin why Tom repeoted eoch test ond took on t2l iii) There ore smolldifferences in the repeot meosurements. Suggest one reoson t1l b) Look ot Tom's results for the hordness of somple A. Tom thinks thot the best estimote for the hordness of somple A lies in the ronge 38

overoge

acid

o

Sample A (vulcanised

Hardness

o smollpiece of mognesium

ribbon. The mognesium wos dropped into the ocid in the conicolflosk. The bung wos quickly ploced in the top of the flqsk. The hydrogen produced wos collected in the meosuring cylinder. The volume of hydrogen thot would be produced by 24g of mognesium wqs then colculoted from their results.

why.

to 45. Exploin

why.

t2l

c) The discovery of the process of vulconising rubber wos importont in the monufocture of cor tyres. How do Tom's results confirm this?

t2l

Notei although a question may be marked (AQA) etc., it ll/ill often be relevant to other examinations as

(ocR)

well.

63

Further questions on The Foundotions of Chemistry

9.

@ Bosic ideos 5.

ommonium nitrote (NH4NO3). Is this substonce on element or o compound ? Exploin your onswen [2] (AOA)

In the boxes below different otoms ore represented by o ond o

ABC o

L-)

o

10. Chemists often give nomes to compounds, which end in '-ide' or '-ote'. Whot ore the

CO

c

6^

o

correct nomes for these compounds ? c) MgO o) HCI b)CuS d)CuSO+ e) MgCOs fl KNO3 t6l

ao

CO E

D

Oa ooo

11. Bicorbonote of sodo is o compound used in cooking. The chemicol formulo of bicorbonote of sodo is:

o Motch the letter on the box to the following descriptions o) o mixture of goses b) o solid :

c) o goseous compound d)oxygen (Oz) e) o pure gos mode up of single otoms.

tsl 6.

(WJEC)

The list below contoins three elements ond three compounds.

oluminium ommonio corbon dioxide

woter

compounds

t3l

(AOA)

Choose words from this list to complete the tens

millions ninety

thirty

There ore obout

....

CoCOs(s) - CoO(s) + COz(g) Choose one of the following phroses to complete this sentence.

more

thon

the some

qs

less thon

corbon otoms, six hydrogen otoms ond one oxygen otom. Write the chemicol formulo of this compound. t7l

reoction.

t1l t1l

t2l

(AOA)

15. The reoction between sodium ond woter moy (AOA)

is o non-metol.

Exploin why it is eosier to seporote iron from o mixture of iron ond sulfur thon from o (AOA) compound of iron ond sulfur. t2l 64

is heoted it decomposes to form colcium oxide ond the gos colled corbon dioxide.

b) Briefly exploin why on unbqlonced chemicol equotion connot fully describe o

noturolly occurring

8. Iron is o metql ond sulfur

12. When colcium corbonote

14. o) Bolonce these chemicolequotions. i) H2 + 02 + HzO ii) Al + oz -------> A12O3

twenty

elements. From these elements ... . of different substonces ore mode. t2l

t2l

13. Eoch molecule of o compound contoins two

sentences below.

hundreds

NoHCO3 Nome ollthe elements present in bicorbonote of sodo.

The totol moss of the products formed will be . . . . the totol moss of the reoctont. [1]

copper sulfur

Soy which ore elements ond which ore

7.

The fertiliser o former uses is bosed on

be represented by the following equotion: 2No(s)

+ 2H2O(l) ----> 2NoOH(oq) +

Hz(g)

Write down the meoning of eoch of the stote symbols in brockets obove.

t2l

(WJEC)

Further questions on The Foundotions of Chemistry

) 16.

Atomic structure

I"9. Which two porticles W X, Y ond Zrepresent different isotopes of the some element

Element

Atomic number

Mass number

Oxygen

8

16

Chlorine

17

35 70 65

Gallium

31

Zinc Tungsten

30 74

184

In one otom of sodium

18.

Boron-1

ii)

the number of neutrons is

b)

the number of electrons is

c) (AOA)

?

proton ii)

electron

Relative charge Relative mass 1

zero (0) negative (-ve)

ii

i)

1

1

840

t3l

9

z

o

10

10

(AOA)

(A0A)

protons electrons neutrons

symbol

,,h

,je

1

c

boron otom

21. Look

?

t1l

t1l

(OCR)

ot the toble.

Substance

Formula

Decane

CrcHzz

Ethene

CzHq

Octane

CaHrs

Relative Formula Mass (Mr)

The relotive otomic moss (A.) of hydrogen is 1 ond the relotive otomic moss of corbon is 12. Work out the relotive formulo moss (M.) of

tll

i)

10

required.)

ethene ond

b) Copy ond complete the toble shown below. Name

9

c) Whot is the electron orrongement in o

Drow o diogrom to show the eiectronic orrongement of this otom. tll Whot is the moss number of this

otom

1

Y

o) Copy ond complete the tqble t3l b) The relotive otomic moss of boron meosured precisely is 10.82. Whot does this tell you obout the relotive omounts of the two different boron otoms in o somple of boron ? (No colculotion

o) A diogrom of the nucleus of on otom is shown below.

i)

'1

2

Boron-10

o)

tsl

1

1

atom

11I\ O

the number of protons is

1

is o non-metollic element The toble shows informotion obout two types of boron otom.

23r. r

proton (otomic) number

Electrons

20. Boron

otom to complete the toble.

number

Neutrons

t1l

Use the informotion given obout o sodium moss

Protons

w x

find in on otom of oxygen ? b)Where in the otom would the protons be found ? c) How mony neutrons would you expect to find in on otom of zinc ? d)Which element in the toble obove hqs otoms which contoin the some number of protons os neutrons ? [4] (EDEXCEL)

17.

Number in one particle Particles

Use the tobie obove, where necessory, to help you to onswer these questions. o) How mony protons would you expect to

?

22.

octone.

t2l

(OCR)

o) The formulo for ommonio is NH3. Whot does the formulo tellyou obout eoch

molecule of ommonio ? [3] b)Ammonio is used to moke nitric ocid (HNO3). Colculote the formulo moss (M,) for nitric ocid. (Show your working.) (H 1,N 14,O (AOA)

:

:

: 16) tsl

55

Further questions on The Foundotions of Chemistry

ts The Periodic Toble

Property

23. Port of the Periodic Toble which Mendeleev published in 1869 is shown below.

Group Period

1

1

Group 2 Group 3 Group 4

Group 5 Group 6 Group 7

H

Period 2

Li

Be

B

c

N

Period 3

Na

Mg

AI

Si

P

Period 4

Kcu c^

Period 5

Rb

ar Ag

Ti

zn

cd

,IN

Zr

o e

A5 Sn

Nb

F

They react with water to give alkaline solutions. They are gases. They are non-metals. They form an ion with a 1+ charge. They react with water and give off hydrogen They form an ion with a 1- charge. They are metals They react with water to give acidic solutions

ct

s, Mn

t3l

B,

I

Sb

24. Below

question.

x

o) i) Give the symbols of two elements in

z

Group 1 of Mendeleev's Periodic Toble which ore not found in Group

Toble. ii) Nqme these two elements.

not their

chemicolsymbols

Use poge 392 to help you qnswer this

1 of the modern Periodic

is the outline of o Periodic Tqble. The

letters represent elements but ore

t1l t2l

b)Which group of elements in the modern Periodic Toble is missing on Mendeleev's toble ? t1l c) Mendeleev left severolgops on his Periodic Tqble. These gops ore shown os osterisks (*) on the toble qbove. Suggest why Mendeleev left ,nn.n sops.17J

w V

Which two elements ore in the some period?

A WondX B WondZ

C XondY D Y ond Z

25. This

t1l

(AOA)

is on outline of port of the Periodic

Toble

B

D C

A d)Whot is the missing word in the following sentence.

In the modern Periodic Tqble the elements ore orronged in the order of

their....numbers.

tll

e) Mendeleev ploced lithium, sodium ond potossium in Group 1 of his Periodic Toble. This wos becouse they hove similor

properties. Some properties of elements ore given in the following toble.

Four of them ore properties of lithium, sodium ond potossium. One of these properties hos been ticked for you. Write down the other three properties. 66

The four letters show the positions of four elements. Which letter represents on element with one electron in the outermost shellof (AOA) eoch otom ? tll

26. The element potossium

is in the some group

of the Periodic Toble os sodium. Potossium reocts with chlorine to moke potossium chloride which is sometimes used insteod of common solt in cooking. o) kedict the formulo of potossium chloride. /7J b) By reference to the electronic structures of potossium ond sodium, exploin why the reoction of potossium with chlorine is similor to the reoction of sodium with (aonl chlorine. tll

27. Sodium reocts violently with cold woter. o) Complete the word equotion for the reoction. sodium

*

woter

-->

sodium hydroxide +

....fi1

wqter.

i)

iii)

shows some properties of

the Group 1 metols.

b) Describe in detoilwhot you would see when o smollpiece of sodium is ploced in o dish of cold t4l c) At the end of the reoction, the solution in the dish contoins sodium hydroxide. If universolindicotor is qdded to this solution it turns purple. Whot colour is universol indicqtor in water ?

ii)

29. The toble below

Exploin why the indicotor in sodium Suggest o likely pH hydroxide solution

Elem6nt

Reaction with water

Meltlng point

Density

(/cm3)

fc) Lilhium

Floats, forms hydrogen and an alkaline solution. Burns with a crimson tlame when lit with a splint.

Sodium

Floats, forms hydrogen and an alkaline solution. Burns with a yellow flame when lit with a splint.

0.97

Potassium

Floats, forms hydrogen and an alkaline solution. Burns with a lilac llame. Explosive reaction.

0.86

i)

Rubidium Caesium

180

0.53

1.53

Explodes on contact with water. Forms hydrogen and an alkaline solution.

1.88

o) Use the toble to predict: i) rubidium's reoction with ii) coesium's melting point.

t2l 28.

(EDEXCEL)

q) The diogrom shows the electronic strucfure of o porticulor element.

tll

b) In terms of electronic structure, whot do the Group 1 metols hove in common ? /7/ (EDEXCEL)

30. Which of the following

represents the electronic structure of three elements in the some group of the Periodic Toble ?

A 2.1 2.8.1 B 2.7 2.8

c 2.8 2.8.1 D 2.8.2 2.8.3

In q similor woy, show the electronic structure of onother element from some group in the Periodic nome the element you select. The element lithium gives o reoction with cold woter, hydrogen ond forming o lithium hydroxide. Describe how sodium is i) similor to lithium ond ii) how it is different from lithium, in its chemicolreqction with cold

2.8.8.7 2.8.1 2.8.2 2.8.4

31. G, H, J ond K ore four their elechonic strucfures

2.7 H 2.6 J 2.8.1 K 2.8.8 G

I

Which two elements hove similor chemicol properties ?

A GondH

woter.

Exploin ony similority or difference in terms of their otomic shucture.

t\l

(A0A)

B GondJ C HondJ D J ond K

t1l

(AoA)

67

Further questions on The Foundotions of Chemistry

32.

Use the Periodic Toble on

35. Iron, nickelond plotinum

poge392 to help

you to onswer this question. In the diogrom thot follows, e represents on electron, n represenh o neuhon ond p represents o proton

con oct os cotolysts. Severol industriol reoctions use cotolysts to lower the cost of the monufoctured products. o) Whot type of metols ore oble to oct os

cotolysts ? [1] b) Nome qn industriolprocess thot uses o

cotolyst ond nome the cotolyst.

t2l

(AOA)

36. Lithium, sodium, potossium ond rubidium o) Identify the element, the otom of which is

drown

obove.

t1l

b) Nome onother element thot is in the sqme

group.

tll

c) Whot do the outer electron shells of the other elements in this group hqve in (AOA) common with eoch other? tll

oppeor in this order in Group 1 of the Periodic Toble. This toble contoins doto obout three of these elements. Boiling point

Melting point in oC

Element

in

oC

330

Lithium

180

Sodium

98

890

39

688

1

Potassium

33. Look

ot the Periodic Toble on poge 392. o) Describe ond exploin the pottern in the electronic structure of the first 18

elements.

Rubidium

tsl

Which of A, B, C or D is most likely to be potossium ?

b) Exploin why the chorge on o sodium ion is + 1 but the chorge on o chloride ion is * 1. t2l (EDEXCEL)

34. Here

Melting point in oC

Boiling point

A

34

700

B

64

774

c

83

D

120

is some informotion obout the

elements vonodium, mongonese ond cobolt. Vanadium

Cobalt

23 6.0

7.2

1240

conductivity

good

good

Common oxides

Veos

MnO

Vzos

MnO2

oC

007 817

tll

25

1130

(A0A)

37. The toble below

lists some of the properties of the element silicon.

Electrical

Mn207

Property

Silicon

Appearance

black solid

Melting point

1410"C medium no reaction

Electrical conductivity Fleaction with dilute acid Type of oxide

o) Choose three properties from the toble thot show why these three elements ore exomples of transition metals. t3l b) Give two more properties of tronsition metols or their compounds not mentioned in the toble obove.

It is difficult to clossify silicon. Give two pieces of evidence, from the toble, for silicon being o metol ond two pieces of evidence

(AOA)

(EDEXCEL)

t2l

68

1

Mn

Symbol

Atomic number Density (g/cm3) Melting point ("C)

Manganese

in

for it being o non-metol.

acidic

[4]

Further questions on The Foundotions of Chemistry

)

Groups of non-metols

41. The toble below

shows the elements of Group 7 of the Periodic Toble.

38. o) Fluorine is the first member of o group colled the hologens. Give the nomes of two other hologens in this group. t2l b) Give two properties which the vopours of the hologens hove in common.

t2l 39. The toble

Name

Atomic number

Astatine

85

Melting point

('c)

F CI

Br

(WJEC)

I

shows observotions mode when

eoch of the hologens chlorine, bromine ond iodine ore odded to solutions of sodium holides. o) Whot ore the missing entries lobelled i)-iii) in the toble ? Sodium halide solution sodium

Symbol

chloride

sodium bromide

sodium iodide

Chlorine

no reaction

ii)

brown solution formed

Bromine

no reaction

no reaction

iii

lodine

i)

no reaction

no reaction

)

o) Copy the toble obove. Use Toble 1 on poge 390 ond the Periodic Toble on poge

3921o help you complete the toble. t2l b) The element ostotine does not exist nofurolly on Eorth. Drow q suitoble groph to enoble you to estimote its melting point. tsl c) Use your knowledge of the properties of the elements in Group 7 to predict: i) the number of electrons in the outer shell (energy level) of on ostotine otom, ii) the formulo of o molecule of ostotine, iii) the electricolchorge on on ostotide ion. t3l d) From o knowledge of electronic structure, exploin why scientists predict thot ostotine is the leost reoctive element in Group 7.

t3l

tsl

(AOA)

b) Fluorine is the element ot the top of

Group 7.

42. Look

ot the toble below. It shows some of the noble goses ond their otomic numbers.

Predict whot will hoppen when fluorine is odded to o solution of sodium

chloride.

t1l Noble gas

Atomic number

Helium

Name

Symbol

Fluorine

F

Chlorine

CI

Bromine

Br

lodine

I

Neon

10

Argon

18

Krypton

36

orgon.

o) Write down one use for t1l b) Write down the nome of one other noble gos from the toble. Write down one use of

this

These elements ore ploced in the some group of the Periodic Toble. Exploin why.

t3l

(EDEXCEL)

gos.

t1l

c) Which of the noble goses in the toble hos the highest density t1l d)Whot is the meoning of the term otomic (EDEXCEL) number

?

?

t1l

69

,i'

chapter6

OT

Chemistry is importont in ollour lives. We rely on chemicol reoctions to mqke most of the mqteriols thot we oll toke for gronted. Moteriqls like the metols used to moke bicycles, cors, ships, troins ond oeroplones. We willlook ot the chemistry involved in getting these metols from their row moteriols, ores, in this chopter. Ores qre rocks from which it is

economicolto extroct metols thot they contoin. With new techniques, we con now extrqct metols from rock once thought of os woste. (See poge 97.)

) I

The metols in ores qre chemicolly bonded to other elements. So how con we extroct the metols ? To onswer this we must understond the Reoctivity Series of metols The Reoctivity Series is like q 'leogue toble' for metols. The most reqctive metols ore of the top of the leogue. The leost reqctive ones ore of the bottom. We con stort putting the metols in order by looking ot their reoctions with the oxygen in oir, woter ond dilute ocid. Order of

reactivity

Reaction when heated in air

potassium sodium lithium calcium magnesium

burn brightly, forming oxide

aluminium zinc iron tin lead

copper silver gold

platinum

7A

oxide layer forms without burning no reaction

The Reactivity Series

Reaction with water tizz, giving off hydrogen; alkaline solutions (hydroxides) are formed

Reaction with

dilute acid explode

react with steam, giving off hydrogen; the metal oxide is formed (but no immediate reaction with cold water)

fizz, giving off

only a slight reaction with steam

react slowly with warm acid

no reaction, even with steam

no reaction

hydrogen

)

Displocement reoctions

We hove now seen how to use the reoctions of metols to get on order of reoctivity. We con olso judge reoctivity by putting the metols into competition with eoch other.

In the next two experiments the metols will 'fight' eoch other to 'win their prize' - oxygen. The more reoctive metolwillwin the competition.

Experiment 6.7 Metals in competition - iron v copper Mix o spotulo of iron filings ond copper oxide in o test tube. Heot the mixture shongly. o Is there o reoction ? Look for o red glow mixture of iron spreoding through the mixture. and copper oxide When the tube hos cooled, empty it into o dish o Cqn you see ony pink copper metolleft?

wool

heat

Copper storts off with the oxygen in copper oxide. However, iron is more reoctive, so it tokes the oxygen owoy from copper. You see o reoction toke ploce, ond copper is left by itself. We soy thot iron hos disploced the copper.

oxide + iro. --------- iron oxide This is o displocement reqction. copper

+

Ttre r^irnnefl

copper

-rr

It shows us thot iron is more reoctive thon copper. Why wouldn't you expect to see o reoction between iron oxide ond copper ?

iron oxide

*

copper

-X--*

no reoction

You con now try some other displocement reoctions. Experiment 6.2 Displacement reactions Tiy heoting the mixfures of metqls qnd oxides shown in the toble: Look for ony signs of o reoction.

{ : oreoction I :

Metal

ztnc

rron

Metal

oxide

oxide

zinc

x

noreoction iron (Be coreful when looking for signs of o reoction. you yellow heot it by itself. Zinc oxide turns when copper It turns white ogoin when it cools down.) o Why con you put some I's in the toble before you do the experiment? o Write word equotions for the reoctions you hove ticked.

copper oxide

x x

We find thot

o more reoctive metol con dloploce o less reoctive metol from its compounds.

77

)

Metols of lour reoctivity

Extracting metals from ores

You con now stort to understond how we get metols

from their ores. Most metols ore found noturolly in rocks colled ores. They ore in compounds, chemicolly bonded to other elements. However, the unreoctive metols of the bottom of the Reoctivity Series con be found os the elements themselves. We soy thot they ore found notive. We con find copper, silver, gold, ond plotinum os the metols in noture. (Copper ond silver compounds qre olso mined os ores.)

Look qt the photo below:

ORE

Purred+

,/--\

Hiiflf{#J?{*o*

{/\ ueri-l-conapoutto

"'""':!L[:r#kr:r':l METAL

ln this chapter, we will see how we extract metals

Go/d ls found as the metal itself

o Why con gold

be found notive

?

Gold is very expensive becouse it is difficult to find. For exomple,lhere is plenty of gold in the seq. Unfortunqtely, it is spreod ollround the world. This mokes it too costly to extroct from seo-woter.

These people are 'panning' for gold in Brazil

Roosting ores Mony metol ores contoin oxides or sulfides of the metol. Copper is found in on ore colled chqlcocite. This hos copper(l) sulfide in it. We cqn get the copper from this ore just by heoting it in oir. Look ot the equotion below:

* CuzS(s) +

copper(l) sulfide

yL

copper Oz(g) --------> 2 Cu(s)

oxygen

* +

sulfur dioxide SOz(g)

Cqre must be token to stop sulfur dioxide gos escoping into the otmosphere. This gos couses qcid roin. (See poge 148.) However, the gos con be piped to o neorby chemicqlplont thot mokes sulfuric ocid. (See poge 135.)

72

The copper in this ore is chemically bonded to sulfur and iron. We must heat it to extract the copper.

)

Metols of medium reoctivity

The metol obove copper in the Reoctivity Series is leqd. Leod con be extrocted from on ore thot contoins leod sulfide. Look ot the experiment below: Demonstration 6.3 Roosting lead sulfide This should be done in q fume-cupboord.

/i\

lead sullide

Turn on the woter-pump to suck oir over the leod sulfide. Now heot the leod sulfide.

alr+

o Whot hoppens to the indicotor solution ? e Whot does this tell you obout the gos given off ? o Cqn you see ony leod metol forming?

l_ oxygen --------> leod oxide * 2PbS(s) +3Oz(g) -------->2PbO(s) +

t

universal

indicator

heat

When we roost copper(l) sulfide, we get copper. However, when we roost leod sulfide, no leod is mode. Insteod, we get leod oxide (plus sulfur dioxide) : leod sulfide

potassium

sulfur dioxide 2SOz(g)

magnesium aluminium

ond how eosy it is to extroct:

iron

o metol is, the more is to extroct from its ore.

difficult it

^A.

hard to

sodium

The sulfur dioxide con be used to moke sulfuric ocid. (See poge 135.) There is o link between o metol's ploce in the Reoctivity Series

Ihe more reoctive

water-pump to suck air through

suttur dioxide sas

zinc

tin

compounds getting more stable

lead

Reoctive metols ore eoger to join chemicolly with non-metols Once they hove formed compounds, they don't wont to chonge bock into the metologoin Less reoctive metols ore eosier to persuode ! Their compounds ore eosier to breok down. !

copper

;

silver

easy to extract

gold

[F!!i

After our experiment obove, we ore left with leod oxide. How con we get the leod from the leod oxide ? This is where carbon comes into the story.

Leb us ?ol

s,iF,Q:ilssn$_*$

!

The whole story is on the next poge

!

+

r..i.3i""

Lead rs left by itself as carbon flies off wtth the oxygen

!

73

)

Extrqcting metols with corbon

Corbon ond the Reoctivity Series Corbon is o non-metol. However, we con put it into our leogue toble of metols. It slots in between oluminium ond zinc. This meons thqt corbon con disploce ony metolbelow qluminium in the Reoctivity Series.

potassium sodium magnesium

aluminium

CARBON

We get corbon from coql. Cool is cheop ond there's plenty of it of present.

zinc iron tin lead

Therefore, extrocting metols with corbon is not too expensive.

copper

You con try to extroct leod ond copper from their oxides in the next experiment:

6.4

Experiment Ertracting lead and copper Mix o spotulo of corbon powder with o spotulo of leod oxide. Set up,tfu,,apporotus os shown:

t

carbon cannot be used to extract the more reactive metals

T

A

these metals can be extracted using carbon

loose plug of mineral wool (to stop mi)Cure shooting out)

lead oxide

copper oxide

Heot it gently ot first, then more shongly. Look for signs of o reqction in the test-tube. o Con you see ony silvery beods left qfter the reoction This is leod metol.

mixture of carbon and lead oxide ?

Try the some experiment, using corbon ond copper oxide. e Con you see;ony copper metol (o pinkish brown powder)?

t

heat

Corbon is more reqctive thon leod. Therefore, it con disploce leod from leod oxide.

oxide PbO(s)

leod 2

* corbon leod * + C(s) ---> 2 Pb(s) + ----->

corbon dioxide COz(s)

Reduction ond oxidotion Look of the equotion obove. The leod oxide loses its oxygen. We soy thot leod oxide is reduced. The corbon goins oxygen. We soy thot

corbon is oxidised.

2PbO + C + COz + 2Pb Reduction and oxidation are chemical opposites. (For more detalls see page 99.)

74

)

Extroction of iron

Corbon is importont in the exhoction of iron. We use o giont blost furnqce to get the iron from its ore. The row mqteriqls ore fed into the top of the furnoce. The row moteriols qre :

iron ore coke limestone

o iron ore (moinly hoemotite, iron(lll) oxide), o coke (o cheop form of corbon, mode from cool), o limestone (to get rid of sondy woste).

The blast furnace hot waste gases (re-cycled to heat the turnace)

waste gases

Look ot the diogrom: Con you see why it is colled ablast furnoce ? It's q bit like o huge borbecue. The temperoture gets obove 1500"C.

Reoctions in the blost furnoce 1. The coke (corbon) reocts with oxygen in the

hot oir to moke corbon dioxide.

C(s) +Oz(g)

-->COz(g)

2. This corbon dioxide reocts with more hot coke to moke cqrbon monoxide gos.

COz(s)

+

C(s) --------> 2 CO(g)

3. The corbon monoxide then reduces the iron oxide to iron. FezOs(s)

+

3CO(g) --------i> 2Fe(ll

+

3COz(g)

4. Limestone breoks down into colcium oxide (o bose) This gets rid of the sondy bits (ocidic impurities) in the iron ore. They form o liquid slog. Notice thqt the iron oxide is reduced to

by corbon monoxide gos in step Fe2O3

+ 3CO

--->

2Fe

+

3.

iron

btasrs of hot air

hot air

*

molten slag

3CO2

We soy thot corbon monoxide is the

reducing ogent. molten iron

Reducing ogents toke owcy oxygen. At the high temperotures in the furnoce, the iron formed is molten (o liquid). It sinks to the bottom of the furnoce. The impure iron is run off into moulds. The molten slog floots on top of the iron. The slog is topped off, cooled ond used for moking roods.

75

)

Iron into steel

the furnace is tipped

up to pour off The iron from the blost furnoce is impure. t'""1 It contoins 3"/o to 4 % corbon, plus some other non-m"tolr.'h" The impure iron is very brittle. It smoshes eosily. Most of it gets turned into steelwhich is much tougher.

molten, impure iron

Steel is mode up moinly of iron. It hos o tiny omount of corbon left in it. Other metols con olso be odded. There ore 2 moin steps in turning iron into steel:

A basic oxygen

converter

1.

Removing most of the corbon This is done by blowing oxygen into molten iron from the blost furnoce. Cqrbon burns ond escopes os corbon dioxide gos. 2. Adding other metols We con olso odd other metols to give the steel

lron is turned into steel. The oxygen burns off the carbon and other non-metal impurities.

speciol properties. For exomple, we moke stoinless steel by odding chromium ond nickel. This type of steel does not rust. It is used to moke cutlery.

You con find out more uses of steel on poge 78.

)

Stain/ess stee/

does not rusl

Corrosion of iron

The rusting of iron costs us millions of pounds every yeor. Rust forms on the surfoce of iron (or steel). Unfortunotely, it is o soft, crumbly substonce. It soon flokes off, then more iron rusts. Let's find out whot couses iron to rust:

Experiment 6.5 What causes iron to rust? Set up the test-tubes qs shown: Tube A tesb to see if oir olone will moke iron rust. Tube B tests to see if woter olone will moke iron rust. Tube C tests to see if oir ond woter willmoke iron rust. Leove the tubes for o week. o Whot do you see in eoch test tube ?

Changing a rusty exhaust

Tube A

Tube C

oil

rron

calcium chloride to water

wool

water (to remove air)

water

Rust is o form of iron(lll) oxide. It hos woter

loosely bonded to it. It is colled hydroted

iron(III)

oxide.

Both oir (oxygen) ond woter ore needed for iron to rust.

ln order for iron to rust Both air and water's a must. Air alone won't do Without water there too, So protecf it, or get a brown crust

We con show the reoction os

iron

76

*

oxygen

*

woter -------> hydroted iron(lll) oxide

!

6.6

Comparing rates of corrosion Experiment test tubes os shown : Set up the for the tubes oweek. Leove

o

Which tube hos most rust in it?

Test some other metols, including oluminium,

in the some woy.

o

L fu**ffiwater

weakly acidic

solution (acid rain)

Compore their corrosion with iron's.

Solt speeds up the rusting of iron. o Cor owners who live neor the seo should wosh their cors regulorly. Why ? o Why is solt o problem for cor owners in winter ? Whqt con they do to reduce the problem ? Acid roin olso speeds up corrosion of metols. o Why does oluminium resist corrosion ? (See poge 89)

Preventing rust We know thot oir ond woter ore needed for iron to rust. Therefore, if we con keep these owoy from iron, it con't rust We con do this by cooting the iron or steelwith:

1. point

4.

2.

oil or

greose 3. plostic or 5. o more reoctive metol.

How has the fence around these tennis courts been protected ?

o less reoctive metol,

Let's look of how good these methods ore:

6.7

Stop the rust Experiment Set up the test tubes qs shown : The rust indicotor turns blue ot the first signs of rust. Look of your test tubes every few minutes.

o Which method is best ot preventing rust? o Exploin why we set up o control experiment.

E

water with rust indicator

/: groased nail

nail wrapped in zinc

nail

in

copper tin

magnesium experiment

Most methods for preventing rust rely on keeping the iron owoy from oir ond woter. The iron will rust if there is even o tiny gop in the cooting. Then the rust soon spreods under the cooting. However, this does not hoppen if you use o more reoctive metol. Even if the cooting is scrotched, the iron does not rust. Zinc is often used to protect iron. We soy thot the iron is golvonised. The zinc is more reoctive thon the iron. Therefore, ony woter or oxygen reocts with the zinc rother thon the iron. This is cqlled socrificiql protection. The zinc socrifices itself to protect the iron. (See poge 79.)

lf the tin coating is broken, the can will rust harmful bacteria will then get to the food. Why can't we use zinc to coat food cans?

-

77

of work: Uses

I

Steelis used more thon ony other metol. It is very importont in the building industry. It is used for girders ond for the rods inside reinforced concrete. You will hove seen the steeltubes, colled scoffold, used when buildings ore mode or repoired.

"\

I

I

,r'- ,-:

/-

I

It I

,l

-a

-

Different types of steel

,',,.

As you know from poge76, steelis mode moinly from iron. It hos o smoll omount of corbon in it. The qmount of cqrbon offects its properties.

|

tl

..,,

= ,"1"'

Workers erecting steel scaffold

Look ot this toble:

"!{

Corbon steels Type of stesl

r::Aittalllht of carbon

Hardness

Uses

mild steel

0.2%

can be easily shaped

car bodies, wires, pipes, bicycles

medium steel

0.37o to 0.60lo

hard

girders, springs

high-carbon steel

O.60/o

very hard

drills, hammers, other tools

o o

lo

1.5o/o

Whot hoppens to the hordness of the steel os we increose the omount of corbon ? Why do you think thqt mild steel is used to moke cors

?

Why

don't we use mild steel for rail tracks

Alloy steels You con chonge the properties of steel by odding other metols. For exomple, tungsten in steel keeps it hord ond tough, even when it gets very hot. It is used to moke high-speed cutting tools Mixtures of metols ore colled olloys. Steels with less thon 5 "/" other metols ore colled low olloy steels. Those with up to 25"/" other metols, such os stoinless steel, ore high olloy steels. You con reod more obout olloys in Chopter 21.

How can steel cutting tools be used to shape stee/ objects?

?

)

Chemistry of urork: Preventing rust Stoinless steel Unfortunotely, iron ond steelrust. (See 'Cors for scrop', poge 91.) However, we hove found some very effective woys to fight ogoinst rust. You hove just reod obout olloy steels. If chromium ond nickel ore qdded to steel,

you get stoinless steel, o steel which does not rust. Stoinless steel is expensive, but is used for smoll items, such os knives ond forks.

o Why don't we moke

Starn/ess stee/ is used to make a surgeon s instruments. lt is important that they do not rust

cors from stoinless steel?

Socrificiol protection You hove seen on poge 77 thot iron con be cooted in zinc (golvonised). This works even if the cooting gets scrotched

o

How does this method work

?

Mognesium con be used insteod of zinc. It is used in hqrsh conditions

Look qt the photos opposite:

o Why ore these things likely to rust very quickly without the protection of mognesium?

Magnesium bars are bolted onto this ship's hull This pier is built

on steel

Electricol protection

SHOCI(ING }rUST ! Concrete is the most widely used building material. It is reinforced by steel rods which

make

it

much stronger. However, some

concrete buildings and bridges are showing signs of weakness. The steel inside the concrete is rusting away

Rust takes up much more space than steel so the concrete cracks ! Scientists have found a way to stop this. A small electric current passing

through the steel will protect it. Many new structures will be protected this way.

!

79

)

The highly reoctive metols

The highly reoctive metqls ore the most difficult to extroct from their ores. These metqls qre found in very stoble compounds. Reduction by corbon won't work. You know corbon's ploce in the Reoctivip Series. It lies just under oluminium. Therefore corbon con't disploce the highly reoctive metqls from their ores. However, we do hove o woy to get these metols. It is colled electrolysis. We will look ot this in more detoil in the next chopter. You willsee how oluminium is extrocted by electrolysis. Once you hove seporoted the metqlcompound from the ore, the next 2 steps ore: 1. melt it, then 2. pass electricity through it.

Both steps use up o lot of energy. Therefore highly reoctive metols ore expensive to extrqct

P et

ookya.rl

Reactive metals iorm slab/e compoLinds fhrs makes them diffrcult to extract t

Et€cTRtctTY

e f,$ HEAl

/l Iakes a le:t of energy lo split Ltp compounds of reacttve rnelals. lrke potassrLtrn and thaf cosls a lot of money. makrng these melals expensive

Summory The woy we lxfuoct q metol from its ore depends on its ploce in the Reoctivity Series. The more reoctive o metol is, the hqrder it is to exhoct

Look ot the list of metqls below: Order of

reactiuity

Method of ertraction

potossium (K)

sodium (No) lithium (Li) colcium (Co) mognesium (Mg) oluminium (Al)

Electrolysis The metol compound is: 1. melted, then 2. hos elechicity possed through it.

zinc (Zn\ iron (Fe) tin (Sn) leod (Pb)

Reduction by corbon For exomple, ZnO * C

copper (Cu)

These metols con be found uncombined, os the metol itself. We soy thot they ore found notive. (Copper ond silver ore often found os ores but they ore eosy to extroct by roosting the ore.)

silver (Ag) gold (Au)

plotinum (Pt)

80

^l

-----> Zn + CO Corbon monoxide is formed when we extroct zinc. (lf the ore is o sulfide, it is roosted first to get the oxide.) easy to extract

)

4.

Questions

1. Copy ond complete: The method used to extroct q metolfrom its ore depends on itsposition inthe .... .... : o) Metols of low reoctivity con be found . . . . os the metql itself. b)Metols of medium reoctivity must be extocted from their ores by heoting with . . . The metoloxide hos its oxygen . . . . by the corbon. We soy thqt it hos been . . . . by the corbon. Iron is extrocted in o. . .. furnoce. Corbon, in the form of .. . . , is mixed with iron ore ond . . . . . The moin reducing ogent in the furnoce is .... .... gos. c) Highly reoctive metols qre extrqcted by . . . . There ore 2 moin steps: 1. the metolcompound is . . . ., then

Look ot this toble which shows how much some metols cost: Metal

Cost ($ per tonne)

lithium magnesium

61 500

aluminium zinc

1 650 980

2250

.

2. ....

2.

ispossedthrough it.

This toble shows when some metols were discovered: Metal

Known since:

potassium

1

sodium

zinc copper gold

o) Con you see o pottern between the position of these metols in the Reoctivity Series ond their cost ?

b) Con you exploin this pottern ? c) Gold costs $12 300 000 per tonne. Plotinum costs obout the sqme os gold. i) Is your pottern from o) true for the whole Reoctivity Series ? ii) Con you exploin the high cost of gold ond plotinum ?

5.

iron ore, coke and

blonks:

807 1807

blasts of

before 1500 in lndia and China ancient civilisations ancient civilisations

b)Which substonce is the moin reducing ogent in o blost furnoce ? c) Some iron(lll) oxide is reduced by corbon in the furnoce. i) Write o word equotion for this reoction.

o) Whot pottern cqn you see between o metol's ploce in the Reoctivity Series ond its discovery ?

b) Con you exploin this pottern

?

ii)

3. Leod is found

in the ore goleno. The leod is in o compound colled leod sulfide, PbS. To extroct the leod, we first roost the ore. It is then reduced by corbon. o)Write word ond symbolequotions to show whot hoppens when leod sulfide is roosted in oir. b) i) Whot usefulproduct con be mqde from the woste gos mode when leod sulfide

ii)

q) Copy this diogrom of o blost furnoce ond fill in the

is heoted ? Why is it importont to stop this gos

escoping into the otmosphere ? c) Exploin whot hoppens in the reduction with corbon. Include o word equotion ond o symbol equotion in your onswer.

Write o symbol equotion for this reoction.

d)Whot is the moin impurity in the iron we get from o blost furnoce ?

6.

o) How is iron turned into steel? b) List some uses of steel. c) Nome the metols odded to iron when moking stoinless steel.

7.

o) How could you show in on experiment thot

both oir (oxygen) ond woter ore needed for iron to rust ? b) List 5 woys to prevent iron rusting. c) Explain which method is best to protect i) o bicycle choin, ond ii) o dustbin. Further questions on poge ll9 to l2l. 81

chapter

0

r

El

I$

electrolysis in the lost chopter. probobly You've seen it in odverts for beouty shops. It con be used to remove unwonted hoir. More importontly for us, it is the woy thot we extroct highly reoctive metols from their compounds. We met the word

Electrolysls is the breok-down of o substonce by electricity. Now you con find out more obout electrolysis

)

AFTER

DEFORE '

Electrolytes

ExperimentT.T Electrolysis This con be shown in o circuit diogrom like this:

Set up the circuit os shown: power pack

4V

carbon rods called

bulb

electrodes solid sodium chloride sodium

o

Does solid sodium chloride conduct electricity ? Now qdd some wqter ond stir. o Does sodium chloride solution conduct electricity

I

?

/i\

chlorine sas

in afume-cupboard.

Your teocher will do the test shown below

zinc chloride

nc chloride

o

Does solid zinc chloride conduct? oromine sas Now heot the zinc chloride until it melts. o Does molten zinc chloride conduct? o Do you think electrolysis con hoppen in solids ?

I

r^fr

We find thqt electrolysis only hoppens in liquids.

Liquids which con be electrolysed qre colled electrolytes.

Electrolytes ore liquids (molten compounds or compounds in solution) which qe broken down when they conduct electricity.

82

Experiment 7.2 Which solutions are electrolytes? The substonces in the toble below hove been dissolved in wqter You con test which conduct electricity.

bulb

Set up the circuit qs shown:

Do not breothe in ony goses given off.

cathode

Moke sure you don t let the electrodes touch eqch other. Rinse your beoker ond elechodes well ofter eoch test. Put your results in o toble like this :

solution being

tested

What do you see at each electrode ?

+

Does it conduct ?

Solution

-

(anode)

(cathode)

potassium chloride (KCl) sucrose (C12H22O1r) ethanol (C2H50H) sodium iodide (NaI) zinc bromide (ZnBr2) calcium hydroxide (Ca(OH)z) dilute sulfuric acid (H2SOa) glucose (C6H1206) copper sulfate (CuSOa)

o

Which solutions conduct elechicity

?

These solutions qre the electrolytes. o Did you see the reqctions of the electrodes

?

Electrolytes usuolly contoin compounds of metols ond non-metqls. o Which is the exception in the toble qbove ? solid

When electrolytes conduct, we see reoctions of the electrodes. The reoctions qt the electrodes ore exploined loter in the chopter

Why do electrolytes conduct

?

Most electrolytes contoin metols qnd non-metols. These compounds qre oll mode up of ions. We hove met ions before on poge 61. Remember thot ions ore charged particles.

ions vibrate, but are fixed in position

We sow in Experiment 7.1 thot solid compounds

don't conduct elechicity. Solids like sodium chloride contoin ions, but they ore fixed in position. Their ions con't move to the electrodes. However, when they ore melted or dissolved in woter, the ions become free to mooe oround.

Electrolytes contoin ions. When molten or dissolved in woter, the lons are free to moae.

ofi dissolve in water

melt

on

ions free to move in molten compound

o ions free to move in solution

83

ln order to make your lamp brigh| You need an elec-tro-lyte. The ions must flow, Through liquids they go, /n so/ids they're just packed too tight !

We know thot liquids contoining ions conduct electricity. Yet solids which contoin ions don't conduct. We think it must be the mooement of ions in liquids thot is importont in electrolysis.

Let's look of some evidence for the theory of the moving ions:

ExperimentT.3 lons on the moue We con use coloured ions to see which woy ions move during electrolysis.

o) Potossium mongonote(VlD Set up the opporotus qs shown: Use tweezers to ploce the potossium in the middle of the domp Leqve the power pock on

potassium starts tn the

+

The potossium ions ore colourless. The mongonqte(Vll) ions qre purple.

o o

o o

damp lilter paper on a glass slide

Whot hoppens on the filter poper? Which elechode do the mongonote(Vll) ions move to? How con you tell? Do you think the mongonote(Vll) ions corry o positive or negotive chorge ? (Remember thqt opposite chorges othoct. ) Which woy do you think the potossium ions move ?

t4{- +

lons carry their charge to the electrode

b)Copper chromote(Vl) Your teocher will set up this qppqrotus: Leove the power on untilyou con see colours neor the elechodes.

dilute sulfuric

Copper ions ore blue. Chromote(Vl) ions ore yellow.

r

Which colour con you see neor the,positive electrode

?

o Which ion is ottrocted to the positive electrode ? o Which colour con you see neor the negotive eleclrode? o Which ion is othocted to the negotive electrode ? In generol we con soy thot:

metal ions are positive For example, Na+, K+, Ca2*, Al3+

(exceptions: H' , hydrogen ions and NHo+, ammonium ions)

84

non-metal ions are negative For example, Cl -, Br-, , 02 (exceptions : complex transition metal ions, like the ones in the experiment above, lrtlnOa-, CrOo2 )

I

Cotions ond qnions We know thot metol ions ore positively chorged We olso know thot opposite chorges ottroct.

ctro n 5

C ,A

'f

Therefore, os we hove seen on the previous poge

metql ions ce olwoys ottrocted to the negative electrode (cathode). Positive ions ore sometimes colled cotions. This comes from the word cothode - o negotive electrode

Cal ions are pLtssytive' ! Calions go ta ltte cathode. When they get there they receive electrons.

Negotive ions ore ottrocted to the positive electrode (onode). These ions ore sometimes colled onions Why ore they colled onions ?

+-

Why ore ions chorged?

e9

(See page 87 )

/+-\-

Lithium fluoride is mode up of ions. Let's look of the difference between the otoms of lithium ond fluorine qnd their ions :

anr0n

J-

Con you remember your work on otomic structure in Chopter 3 ? Atoms hove the some number of protons (+ ) os electrons Therefore otoms hove no chorge. They ore neutrol. Lithium atom, Li number of protons number of electrons

overall

charge

+'+ (-

)

Fluorine atom,

: 3+ : 3:

CATions -+ CAThode

ANions -+ ANode

The charge in an atom is balanced

F

number of protons number of electrons

overall

0

charge

: 9+ : 9:

0

However, in ions there ore different numbers of protons ond electrons. Metols lose electrons ond non-metols goin electrons. You con reod obout why this hoppens onpoge248.

Now count the electrons (-) oround eoch ion below Look ot the positive chorge in eoch nucleus. Con you see why lithium is positively chorged ? Lithium ion, Li+ number of protons number

overall

: 3+ of electrons : 2-

charge :

1+

o

The charge in an ion is un-balanced. Can you draw see-saws for F and F - ?

Fluoride ion, F number of protons number of electrons overall charge

Mognesium ions hove o 2+ chorge. o How mony more protons thon electrons does on Mg2* ion hove

:

9+

10-

't-

?

85

)

Electrolysis of copper chloride

We know thot ions ore ottrocted to oppositely chorged electrodes. But whot hoppens to the ions when they get to the electrode ? The next experiment

will help you to find out.

ExperimentT.4 Breaking down copper

chloride

Set up the circuit os shown in o

A 4V

tume-cupboqrdorwell-ventilqtedroom. *od?;i#ft3Xto,uton Wotch whot hoppens of eoch electrode. Test the gos given off obove the positive electrode with domp litmus poper. Turn off your power pock os soon os you hove detected the gos. o Whot hoppens to your litmus poper? o Which gos is this the test for ?

Lift the negotive electrode from the beoker. o Whqt does it look like ? o Whot do you think hqs formed on this eleckode

b

carbon electrodes

copper metal forms

damp litmus paper is bleached

copper chloride solution

?

Copper metolforms on the negotive electrode (cothode). Chlorine gos is given off ot the positive electrode (onode) The copper chloride is electrolysed. It is broken down into its elements, copper ond chlorine.

r+

electrolysis

copper chloride

il

ry

copper

+

chlorine

Exploining electrolysis

This carbon electrode has been coated with copper metal

To understond how copper chloride is broken down, we need to know how electricity flows oround o circuit. An electric current is the flow of electrons.

Look ot the diogrom opposite: Remember thot electrons ore tiny negotive porticles. As they ore 'pushed out' of the negotive end of the bottery, others ore ottrocted bock into the positive end.

During electrolysis, the electrons from the bottery go to the negotive electrode. Here they meet the positive ions. The ions then chonge into neutrolotoms. In the experiment obove, copper ions chonged into copper otoms.

86

electrons flow from the negative end ol the battery and others arrive back at the positive end

\

Electrons flow through the wires and bulb. This is an electric current.

Negotive ions gother ot the positive electrode. The ions ore negotively chorged becouse they corry extro electrons. (Look bock to the exomple of the fluoride ion on poge 85.) Their extro electrons ore removed of the positive electrode. These get 'sucked bock' into the bottery. In our experiment we sow bubbles of chlorine gos on the positive electrode.

Look of the cortoon opposite: Electrons leove the negotive end of the bottery. Electrons orrive bock ot the positive end of the bottery. Therefore we hove o complete circuit. A bulb in the circuit will light up. However, no free electrons poss through the electrolyte.

eleclrons

r:,lf,r iiitir.il

gliven

EAlrk

oul.

wE GIV 6

one el

YooP.

s,?!{n",s

ErEr{c#Loils

A

+

il o 0

-

E

Fleiii/.tii,.ii.:- \iioil t: ltke a t-tank. The torls are the alr.'tlit/rre/i. /ire e/eclrors are the rnaney. Ercrrlrcrr.: itc'.,,'tc and frr-trn ttte battery but not i ) -u i.,,i a) a: t't il-r e eiec lrodes.

Ions ccry chcge through electrolytes. No free electrons pqss through. Cu 2++

2{

Holf-equotions We con describe whot hoppens of the electrodes

using holf-equotions. These show whot hoppens to the ions during electrolysis

AT THE CATHODE

Let's look ot the electrolysis of copper chloride in more detoil:

,t!

+ 2e- --------> Cu

Cl

,

:

cl

n

---------t'

A chlorine otom is formed. However, chlorine does not exist os Cl otoms, but os Cl2 molecules. So two CI otoms join together ond we see chlorine gos:

Cl +Cl

I

t

t:

t:t-tI I t r-ttlc.

I

Fee.l

[rKe

a

.^-114o\€ neu)

C,)

o

6o

i r/r lire orrrr. /l gels lwo e/eclrons :rrrii clrartoes fron an tctn to an atom.

(ot the cothode)

At the positive electrode, the chloride ion, loses its extro electron

I

Cv

Copper ions hove o 2+ chorge. The originol copper otoms hove lost 2 electrons. (See the exomple of the lithium ion on poge 85.) At the negotive electrode the copper ions goin 2 electrons. The ion is no longer chorged. It becomes o copper otom. This con be shown by o holf-equotion:

Cu2+

(-)

itre r'olritlr ion r:; ieeltncl bltre. ll's lct:;t Irl,! -:ii-r.li rl/lr. Dut ttels-t t:; ttvatlable

Cr.r|r'r--i

AT THE ANODE (+)

:ieliloi..s g, rraCl

ir lir:

i-raiter;,'

/C(-7€ +

-Clz

Cb

These chonges ot the positive electrode (onode)

con be shown like this:

zC.l-

2e- -------->

Clz

(ot the onode)

i'.,,,'.; r.ir,,f

(.,i

;il(ri r

,rrr.s ai ta)

t.roh lose [tteir exlrtt ntake a Cl., noler:t tlt,

87

)

Electrolysis of molten compounds

In Experiment 7.1 we sow thot solid zinc chloride does not conduct electricity. However, it does conduct when we melt it. Con you remember why ? The ions must be Jree to move to the electrodes before we get electrolysis. In the next experiment you con look more closely ot the electrolysis of o molten compound.

7.5

A

Demonstration Electrolysis ot' lead bromide Your teocher will set up the opporofus os shown

bromine

in o fume-cupboord.

o When does the bulb light up ? o Whot do you see ot the positive

bromine motten bromide

After o few minutes, corefully pour leod bromide using tongs.

r

x

Whot is left in the bottom of the dish ?

o Whot hos leod bromide turned into?

t

molten lead collects under the cathode

heat

The electrolysis of leod bromide storts os soon os it melts. The ions ore then free to move between the electrodes. The leod bromide breoks down into its elements:

UD

electrolysis

lead +

lead bromide

At the cathode

(

-)

Pbz*

+ 2e

-------->

bromine

At the anode

Pb

Lead ions, Pb2+, gain 2 electrons. They form lead atoms.

electrons leave

(+)

2Br - 2e

Two bromide ions, Br-, each lose their extra electron. They form Br2 molecules.

electrons arrive at the battery

the battery

BrCATHODE

BrPb

88

Bro

Pbz* + 2e Pb2*

--------> Brz

2Br--

t2e

ANODE

) Extroction of oluminium As you know, highly reoctive metols ore extrocted by electrolysis.

The most importont of these metols is oluminium. Aluminium hos mony useful properties. It conducts heot ond electricity well. It hos o low density for o metol. It olso resists corrosion. Thot's becouse of the tough loyer of oluminium oxide on its surfoce which protects it. Look ot the pictures opposite: o Exploin why oluminium is chosen for eoch of these uses.

Getting the ore Aluminium is extrocted from its ore bouxite. This is moinly oluminium oxide. The impurities ore removed before oluminium is extrocted. Lorge omounts of bouxite ore dug up in Jomoico. Look ot the photo opposite: o Whot effect does the oluminium industry hove on our environment? Wil recyc ling help ? (See poge 90.)

Electrolysis of oluminium oxide The oluminium oxide is melted, then electrolysed o Why do we need to melt the oluminium oxide ? Energy is soved by dissolving the oxide in molten cryolite This lowers its melting point. The electrolysis is done in cells like the one shown: .

Open-cast mining of bauxite in Jamaica

an aluminium plant uses the same amount of electricity as a small town

the lining of the cell is a carbon cathode

carbon anodes

molten aluminium

o o o o

o

o o o

o oo

€

o

o

At the

cothode

onode

in molten cryolite)

o molten

molten aluminium

At the

oxide (dissolved

alumlnium is tapped or syphoned off from the cell

Aluminium ions ore reduced to oluminium otoms. (See poge 99.)

Al3+

2O2- - 4e-

..

02

The oxygen gos reocts with the hot corbon onodes It mokes corbon dioxide gos. This burns owoy the onodes, which must be reploced quite often.

89

)

Chemistry ot work: Recycling metols On poge 89 we looked of some uses of oluminium ond on poge 78 we sow how steelis used. Hove you ever recycled oluminium drinks cons ? How con you tell if o cqn is mode from steel or oluminium

?

Both oluminium ond iron require lorge omounts of energy to extroct the metols from their ores. o Con you think of ollthe woys in which energy is needed in o Blost Furnqce ond in moking steel? (See poges 75-6.) And whot obout extrocting oluminium from bouxite ? (See poge 89.) There is o 95

7o

soving in energy if you compore

recycled

:1"^"1::lt^?f

::f::!:!,:'m

atuminium

So this is good news for globol worming os we burn less fossil fuels, so less corbon dioxide is releosed into the oir. We olso reduce other pollutont goses in the extroction process.

There is olso the benefit of preserving the ore supplies ond less open cost mining meqns fewer scors on the londscope The qluminium thot would hqve been thrown owoy would olso tqke up precious spoce in our londfillsites. The process of recycling oluminium is shown below: aluminium

Fsdmwyor

Sh€dd€r

D6@rter

M€lling

fum@

Recycling reduces pollution from the extraction of the metal

lngots

Besides soving londfillspoce, recycling steel olso soves energy (obout 50To of the energy needed to moke steel from iron ore) ond our noturol resources. For exomple, eoch yeor in the USA, steelrecycling sqves enough energy to provide electricip for obout 18 million homes! Then there ore the sovings in coql (to moke coke), the iron ore, ond the limestone needed in q Blost Furnoce. Recycling olso meons less greenhouse goses releosed into the oir.

The recycling rote for steel cons is obout 60 %, hoving risen from 15 % in 1988. However, there is still o lot we con oll do to help our environment in the yeors oheod.

o Why do you think

90

it is importont to recycle metols

?

Many people recycle aluminium and

slee/

)

Chemistry of work : Cors for scrop People hove mode o living from scrop cors for mony yeors.

Eoch yeor obout 2 million cors come to the end of their useful life. At present oround 95% of the metal in o cor is reused or recycled. But thot still leoves olmost 500 000 tonnes of other moteriols thot get dumped in londfill sites. This tokes up voluoble spoce, so new Europeon torgets hove been set. By 2015 we willbe required to recover 95% of oll moteriols used to moke o cor. Look of the metols we find in o normol cor: Material Ferrous metal (steels) Light non-ferrous metal (mainly aluminium) Heavy non-ferrous metal (for example lead)

Average mass (kg)

o/o

IvoR

cARn

1I|8SS

780

68.3

72

6.3

17

1.5

Other moteriols used include plostics, rubber ond gloss. Cor mokers ore trying to ensure these ore oll recycloble. o Whot is the overoge moss of metol in o cor? o Whot percentoge of o cor's moss is mode up of non-metallic moteriols ? Discuss the problems in recycling these moteriols.

A cor of the 'end of its life' con go to dismontlers ond/or shredders. The dismontlers toke off ollthe things thot they con sell on. Shredders will recycle ony of the rest thot they get money for. However, they ore worried thot the new torgets connot be met while still moking money out of scrop. o Whot is the moin metol found in most cors ? Which of its properties ollows it to be seporoted eosily from other moteriols in the scrop ? o Discuss who should poy for meeting the Europeon torgets on recycling cors.

People can make money from scrap cars, but new recycling targefs will prove difficult to meet

Aluminium is o less dense metol thon steel. As it is lighter, o cor mode from oluminium uses less fuelthon o troditionol steel-bodied cor. However, oluminium is much more expensive thon steel. So, of the moment, only 'top of the ronge' monufocturers ore moking oluminium cors. Aluminium ports, though, ore getting more common os fuel economy becomes more ond more importont. This will help to reduce pollution from cors. Aluminium cors should olso lost longer thon steel cors becouse they will not corrode.

This aluminium car is expensive to buy !

91

.P: To get o highly reoctive metolfrom its compounds

o thonk5!

We like ib

we must melt the compound before we con electrolyse it. Don't you think it would be cheoper qnd eqsier to just dissolve the compound in woter, then electrolyse it ? After oll, solutions hove free ions, just like molten compounds However, you con't get ony reactiue metols from their solutions by electrolysis.

'rn'the

When electrolysing solutions, we hove to think obout the water molecules in the electrolyte. Woter (HzO) con offect whot is formed ot eoch electrode. Let's test some of the products we get from the electrolysis of solutions:

YoLi oar,. t

isortri

Cathode

potassium iodide (KI) potassium nitrate (KNO3) magnesium bromide (MgBr2) sodium carbonate (Na2CO3) calcium nitrate (Ca(N03)2) lithium chloride (LiCl) copper sulfate (CuSOa) sodium hydroxide (NaOH)

hydrogen hydrogen hydrogen hydrogen hydrogen hydrogen

copper hydrogen

(-)

extraci sodirrnr /ronr sea waler

irii ch ioriaie soiiiliort)

Experiment 7.6 Electrolysing solufions Set up the opporofus os shown: See if you ccrn identifu ony of the products shown below. Do not breothe in ony gos given off. Solution

uqtef

gases collected o

solution being

Anode (+)

o o .o

tested

"o

iodine oxygen bromine oxygen

oxygen chlorine oxygen oxygen

o Which gos is given off qt the cothode insteod of the reoctive o Where do you think this gos hos come from ? o Whot hoppens with o less reoctive metol, like copper?

+

metol? 4V

Look ot the toble obove: You con see thot lhe reactiue metals stay in solution. Hydrogen gos is given off insteod. The hydrogen comes from H2O.

@

%

-w-

When you electrolyse o solution of o highly reoctive metol, hydrogen - not tlre metol - is given off of the cqthode. The holf-equotion is:

H++e

-------->H

A hydrogen ion, H+, goins on electron to form o hydrogen otom, H. Then two H otoms join together to moke on H2 molecule:

H+H

-H2

These 2 steps ore usuolly shown os:

2H+ + 2e- ------> 92

H2

H'1tit ot.1t:r

i

It tt.ti :,ocltttrtt1 /u

i";c r, ier;1t oiy.se sodi

L//l r t:

I

t

qiyclt rtII v,tI tett kt

t

t

rl t- :;o

I

tt

t t

ct r t

Why is hydrogen given off?

Cothode

solution arntt ou6h faf +hebdh

Let's toke o solution from the lost experiment os on exomple. Let's look of colcium nitrote solution:

"S

In ony solution there ore o few woter molecules which hove split up:

H2O(l)

+

H+(oq)

+

oH-(oq)

Catho

They form hydrogen ions, H+, ond hydroxide ions, OH-. Let's think whot hoppens ot the cothode ( - ). Both colcium ions ond hydrogen ions ore qttrocted towords the cothode. However, colcium ions ore more stoble thon hydrogen ions. Remember thot colcium reocts with ocid (poge 70). Colcium con disploce H+ ions from on ocidic solution. So given q choice between H+ qnd Co2+ of the cothode, it's H+ ions thot hove to leove the solution !

Whot hoppens ot the qnode

? Order ot discharge

Hydroxide ions, OH-, ond nitrote ions, NO3-, ore both ottrocted to the onode (+). But which of the two ions is 'kicked out' (or dischorged) from the solution ?

carbonate, CO32nitrate, NO3sulfate, SOa2-

hydroxide, OH- ions from water

Look ot the brder of dischorge' opposite: If the negotive ion is obove the hydroxide in the list, it stoys in solution. So nitrote (NOs-) ions stoy in solution. Hydroxide ions from woter ore dischorged When this hoppens, we get oxygen gos (Oz) given off. Here is the holf-equotion:

oxygen

+ calcium and nitrate ions stay in solution

e

hydroxide ions are discharged at the anode

4OH-

- 4e- -+ 2H2O

+ 02

I

(O2)

hydrogen

these ions stay in solution; oxygen is given off

chloride, Clbromide, Briodide, I-

(H2)

OH- stays in solution; the halogen is given off

bulb

( calcium nitrate solution hydrogen ions are discharged at the cathode 2H+ + 2e- --> H2

93

)

Active electrodes

We hove now seen how electrolysis con be used

to extrqct highly reoctive metols, like oluminium The other uses of electrolysis depend on electrodes which reoct - octive electrodes.

,*

,$

In oll our experiments so for, we hove used corbon electrodes. These ore colled 'inert' electrodes. They toke no port in the electrolysis. The corbon electrodes just corry electrons to ond from the electrolyte.

=---';tE

Platinum ls used to make inert electrodes. Why do you think we've used carbon but not platinum electrodes in our experiments?

N

I

C

t( E

However, some metqlelectrodes do toke port in electrolysis. These ore colled octive electrodes.

L

tl

Let's look of copper os on exomple of on octive electrode. We will electrolyse copper sulfote solution.

Experiment

Ihese meta/s form active electrodes

7.7 Electrolysis

of copper sulfate solution using copper electrodes Moke sure your copper elechodes qre cleqn ond shiny. Use o pencilto mork one elechode ond the other

*

Weigh them with on occurote bolqnce. Set up the opporotus qs shown

4V

-.

+

:

After 10 minutes, rinse the electrodes with distilled woter. Dry them by dipping in proponone qnd letting it evoporote. When dry, re-weigh the elechodes. o Whot do you find? o Why would it be o good ideo to repeot your experiment? Look bock to the elecholysis of copper sulfote solution

onpoge92.

o Whot difference

I

copper anode loses mass

copper

copper sulfate solution

cathode gains MASS

do you notice qt the onode (+)?

When we electrolyse copper sulfote solution using copper electrodes, the moss of both eleckodes chonges. Remember thot metols ore olwoys formed ot the cothode So not surprisingly, the cothode gets heovier.

+(-)

The stronge thing is thot the onode loses moss. The copper onode is on ocfiue electrode. We find thot:

loss in mosa at the onode

=

goin in moss of the cothode

A 94

|

| 1 C)t : L.

'r llte , .ttlto.le

. eotr

t

Comporing inert ond octive electrodes Let's compore the electrolysis of copper sulfote solution using corbon ond copper electrodes: Carbon electrodes At the cathode

(-)

Cu2+(aq)

+ Ze-

Copper electrodes

I Cu2nlaq; + 2e- ------->

--------> Cu(s)

Cu(s)

the reactions are the same

At the anode

(+)

4OH*(aq)

- 4e- ------->

2H2O(l)

+ Oz(g)

oxygen gas is given off

- 2e

--------> Cu2+(aq) no oxygen is seen; copper atoms from the anode lose 2 electrons and enter the solution as Cu2* ions Cu(s)

ute

The copper onode is on octive electrode. As copper otoms form on the cothode, copper otoms ore lost from the onode. As copper ions leove the solution of the cothode, they ore reploced in the solution of the qnode.

Copper ions, Cuz+, moke copper sulfote solution blue. o Whot do you think would hoppen to the colour of the copper sulfote solution using corbon electrodes o Why won't the colour fode using copper electrodes ?

3et

?

Getting pure copper Hove you ever wired o plug or seen inside on electric coble The metol wire is copper. Copper is on excellent conductor of electricit5i. However, it must be very pure to do its job well.

?

/)\.:.

(.i)i)i )( / rlr/r! u/tlg/ tlt-- ::OlLtttctt t at tlle ano(je.

Copper extrocted from its ores is not pure enough to be used for electricolwiring. It con be mode pure using electrolysis.

Look ot the diogrom opposite: In indushy o thin cothode of pure copper is used. The onode is mode of impure copper. o Whot do you think hoppens ot eoch electrode ? The cothode slowly gets bigger os the onode gets smoller ond smoller. (See toble qbove.)

The impurities from the onode drop to the bottom of the cell. This sludge contoins voluoble metols, like gold ond silver.

+ impure copper anode gets

smaller

very pure copper at the cathode

sludge containing precious metals

solution containing copper ions

Many of these cells operate at the same time in industry. The cathodes are removed about every two weeks

95

On the previous poge you sow how we purify copper. This is especiolly importont for electricol copper wires. But where does the copper onode come from ? Where do we get the impure copper from ?

1. Recycling copper High quolity copper from wires con be recycled by melting ond/or re-using it. With just o few impurities, the copper con be mode the qnode ond purified by electrolysis (os on poge 95). However, o lot of old copper is mixed with other metols in olloys. These ore not so eosy to recycle. You hove to onolyse the olloy to see whot percentoge of eoch metol is in it. You might then just melt the mixture of metols ond re-use os the olloy.

If the percentoge of copper is low, you con't use the olloy os the onode to purify it. The process does not work. You might be oble to odjust the percentoges of metols to get onother useful olloy. Or you could odd more copper to the impure copper by melting them together. This roises the percentoge of copper in the olloy so then you con purify it electricolly. But this mokes the copper more expensive to recycle.

2. Smelting copper

Some copper scrap can be recycled to pure copper

ores

Some copper ores con be heoted to leove copper by itself. (See poge 72.) In this experiment you con extroct copper from one of its ores. Molochite ore contoins o form of copper corbonqte.

Experiment 7.8 Extracting copper from malachite Heot two spotulos of copper corbonote,in o test tube o Whot do you see hoppen ? The reqction you see is q thermol decomposition. (See pqge 111.) Allow the copper oxide formed to cool down.

A

copper compounds sulfuric acid

Pour the block powder into o boiling tube. Then odd 10 cm3 of dilute sulfuric ocid. Stopper the tube ond shoke.

You con worm the boiling tube in o woter bqth (with the stopper removed). This gives o deeper blue solution os more Cu2+ ions go into solution. Filter off ony excess block powder. You con get the copper from the blue copper sulfote solution by: EITHER Plocing on iron nqil into the solution in o boiling tube.

o 96

Exploin whot hoppens.

iron nail

copper sulfate solution

\

OR Electrolysing the solution in o smoll beoker. Combine your copper sulfote solution with q couple of other groups ond poss electricity through it. Use corbon electrodes so you con see where the copper forms cleorly.

o

4V

...t.,.

+

Exploin whotihoppens.

Smelting copper ores still provides the moin source of copper.

3. Rock-eoting bocterio (bio-leoching) The extroction of copper involves open-cost mining thot scors the londscope. (See next poge.) The sites hove lorge woste tips of rock thot contoin too little copper to moke it worthwhile extrocting by smelting. Fortunotely, there ore bocterio thot feed on the iron ond copper compounds found in the 'low grode' ore.

carbon electrodes

copper sultate

solution

Co? q of h 5 de\isi ou 5 fo q k

>/,..rrn

t

-

By o combinotion of biologicol ond chemicol processes, the copper ions in the ore dissolve in sulfuric ocid. Then the solution of copper ions runs off the slog heops. The solution con be collected ond the copper extrocted from it (by displocement or by electrolysis os in the previous experiment). So now we con extroct copper from woste ond from new deposits of low grode ores thot were thought to be uneconomic. At present obout 20% of copper is produced by leoching out copper with bocterio.

Advontoges of bio-leoching

o o

o

The cost of setting up this bio-leoching process is low. It does not need huge open-cost mines thot scor the londscope. As mentioned, bocterio con get the copper from low grode ores or wqste. It uses o lot less energy ond does not produce sulfur dioxide gos os in smelting sulfide ores. It con be used on ores thot would pollute the oir when smelted. For exomple, you con use copper ores thot contoin toxic orsenic.

Disodvontoges of bio-leoching

o o o o

Bio-leoching does not recover precious metols. (See poge 95.) So this reduces profits for the copper refiners. Sometimes ocid hos to be qdded to the ore - which costs money. Sometimes the bocterio themselves produce too much ocid which hos to be neutrolised. Agoin this costs more money. It con toke yeors to extroct only 50 7o of the copper from the ores So reseorch continues to speed-up the oction of the bocterio. However, os sources of high grode copper ore run out, bioleoching will get more ond more importont.

Bio-leaching in action, By using waste rock from old copper mines we reduce the area of land scarred by the opencast mining of high-grade ores. (See next page.)

97

)

Chemistry of work: The costs of exploiting metol ores Metqls ploy o vitol role in our technologicol society. Without metols the electricol devices we depend on would be useless However, whenever we extroct the metqlfound in the Eorth's crust there is o price to poy. Thot price is not just the money we poy out. There is usuolly q cost to the environment.

Mining the ore As you sqw on poge 89, open-cost mining is often used to get the metol ore from the ground. As well os oluminium, 90 7" of. copper comes from open-cqst mines. These huge pits scqr the londscope. They olso destroy the hobitots of plonts ond onimols. The mining produces lorge unsightly slog heops of woste rock.

Ihis is an open-cast mine in Zambia.

The mining componies con help to solve these problems once o mine hqs been stripped of its useful ore. They con londscqpe the site, plonting trees ond perhops creoting o loke. The hole con qlso be filled with our rubbish before covering it with eorth. This is useful os it is difficult to find new lond-fill sites. The wqter in on oreo cqn olso be offected by mining, especiolly if the ores contoin sulfides. Roinwoter seeps through the exposed ore qnd woste. The woter ond oxygen (plus the oction of bocterio) turn the metolsulfides to sulfuric ocid. This runs down into the groundwoter ond ocidifies it.

Processing the ores Sulfide ores ore heoted strongly in the process of smelting. This releoses sulfur dioxide gos into the oir, cousing ocid roin. (See poges 72 ond148.) Strict controls ore now enforced by low Mony smelters con stop more thon 997o of the sulfur dioxide they moke from escoping. Almost hqlf the cost of producing copper goes in controlling pollution. However, the high cost of updoting smelters hos meqnt mony hove hod to close down, resulting in thousonds of job losses.

In developing countries, pollution control is not os tight ond lqbour costs ore cheoper. So the copper industry in richer countries struggles to compete.

o

98

Discuss the issues focing the people who live in o town thot relies on extrocting copper. The town is in Arizono, USA where the Environmentol Protection Agency insists on strict pollution control meqsures.

This mine is in Zambia. Many African nations have rich mineral resources. M u lti -national companies often set up mines and processlng plants there. o What lssues does this raise?

)

Redox reoctions

You hove olreody seen how we extroct metols from ores. Often o metol oxide is reduced. Look bock to page74. Whenever o substonce is reduced, something else is oxidised. We coll the reoction o redox reqction. Con you see why ?

Look ot on exomple from the blost furnoce on poge 75:

+ Fe2Os +

iron oxide

iron + corbon dioxide --------> 2 Fe + 3 CO2

corbon monoxide --------> 3

CO

Iron oxide is reduced by corbon monoxide. It loses oxygen. The corbon monoxide itself gets oxidised. It goins oxygen. The corbon monoxide is colled o reducing ogent. Con you remember how we extroct highly reqctive metols Corbon or cqrbon monoxide connot reduce their oxides. We hove to use electrolysis. Look of the extroction of oluminium on poge 89. The oluminium oxide is reduced.

(-) Als+ + 3e- ------->

?

At the cothode

41

The Al3+ ions goin electrons. They ore reduced. So we con soy thot:

Reduction is the galn of electrons.

Ihrs b/asf furnace is about 50 m high lnside it, iron oxide is reduced to iron

o

D

The Al3+ ions hove been reduced to Al otoms ot the cothode Oxidotion ond reduction ore chemicol opposites. So whot do you think hoppens to the number of electrons in on ion thot gets oxidised ?

Oxidotion is the loss of electrons. For exomple, 2O2-

- 4e-

-

02

We con olso write this qs:

2O2-

-------->

on

of electrons uction

of electrons

02 + 4e

So oxide ions ore oxidised ot the onode.

OIL-RIG will help you to remember 99

!

Inuestigation 7.9 Inuestigate electrolysis ! You cqn now use your ideos obout electrolysis to find out:

Which factors affect the rate of electrolysis? You cqn investigote copper sulfote solution.

Think obout these things: o How con you speed up the electrolysis of copper sulfote ? r Use your ideos obout ions to exploin why it is speeded up. o How ccrn you meosure or judge how quickly it hoppens ? (Hint: on qmmeter might be useful.) o How con you moke it o foir test? o Is your plon sofe ? o How con you collect relioble doto thot you con trust? Show your plon to your teocher before you stort.

Summory o Electrolysis

is the breqkdown of o substonce using electriciU.

exomple, copper chloride -------> copper * chlorine o Ions ore chorged porticles. Metql ions ore positive. Non-metql ions qre negotive. o The negotive electuode is colled the cothode. The positive elechode is the onode For

o Solid compounds o

o

o o

mode from ions connot be elecholysed. They must be melted or dissolved in wqter first. The ions then become free to move to the electrodes. Metols forrn otthe cothode (-). Non-metqis forrn qt the onode (+). For exomple, in the electrolysis of copper chloride : Cu otthecothode Cu2* + 2Cl- 2e- --------> Clz In solutions, reoctive metols ore not formed of the cothode. They stoy in the solution qnd hydrogen (from the woter) is given off : otthecothode 2H+ + 2e- -------> Hz Reoctive metqls ore exhocted from molten compounds. For exomple, oluminium is extrocted by electrolysing molten qluminium oxide. We olso use electrolysis to purify copper.

qttheonode

-

2e +

D Questions 1. Copy ond complete: When we breok down o substonce using electricity it is colled .. . . . The . . . . electrode is colled the cothode. The . . . . electrode is colled the onode. The ions in o. . . . ore not freeto move. However, when the substonce they ore in is molten or . . . . in woteq electrolysis con toke ploce.

100

Metols form of the . . . . , ond non-metols of the

.....Forexomple,

+ . ..------> ottheonode 2Br - 2e -------->

ot the cothode Pb2+

Pb

When solutions of reoctive metol compounds ore electrolysed . . . . is formed ot the cothode, not the metol. Electrolysis is used in industry to extroct reoctive metols, ond to purify .. . . .

2. Liz ond Jobeen set up the experiment

below

:

7. Jo ond Tim set up this experiment

sodium chromate(Vl)

carbon electrodes copper sulfate solution

damp filter paper

They left it for 15 minutes. Sodium ions ore positively chorged. They ore colourless. Chromote(VI) ions ore negotively chorged. They ore yellow. o) Whot did they see hoppen ? b) Exploin the results of their experiment.

3. Whot do these words meon: o) cothode, b) onode, c) cotion, d)

4.

onion?

Complete this toble:

Substance electrolysed

What is formed at cathode ?

What is formed

molten lead bromide

a)?

b)?

potassium

chlorine

d)?

e)?

t)?

s)

c)? calcium nitrate solution

copper chloride solution

h)? sodium iodide solution

aluminium

i)?

at anode ?

?

oxygen

i)?

5. Copy ond complete these holf-equotions ot the cothode: o)No+ + ....--------> No

b)Li+ e --------) .... c) Mg2* + .... - Mg d) .... + 2e- --------> Co

6. Copy ond complete the onode:

these holf-equotions ot

2ClClz b) .... - 2e -> - B.z c) 2I- - 2e--------> d)ZOz- - 4e--=> o)

o) Drow o circuit diogrom of their opporotus. b) Whot did they see ot the cothode ? c) Complete this holf-equotion ot the cothode: Cu2* + .... e- --------> Cu d) Whot did they see ot the onode ? e) Jo ond Tim did the experiment ogoin, but this time they used copper electrodes insteod of corbon. Whot differences did they notice between their two experiments ?

8. Look

ot the experiment below:

lead bromide

o) The bulb does not light up when you dip

the electrodes into the solid leod bromide Exploin why not. (Use the word ions in

your onswer.) b)You wont to electrolyse the leod bromide. Which opporotus is missing from the diogrom ? c) Copy ond complete: . . . . moving through the wires moke the bulb light up, whereos . . . . corry the chorge through the leod bromide.

9. Exploin why reoctive

metols con't be extrocted from their solutions by electrolysis.

10. o) Whot difficulties do we hove recycling scrop thot contoins copper ? b) WhV willbocterio become increosingly importont in the extrqction of copper?

Further questions on poge

ll9 to l2l. 101

r# SCr

chapter 8

Do you like o little solt on your food ? Even if you don't odd it yourself, just look ot the lobels on the pockets ond tins ot home. Solt is odded to mony foods to bring out the flovour.

Satt a^ 4?

It con olso help to preserve food. Eorly explorers, like Coptoin Cook, took meot rubbed in solt on their long voyoges.

vineXo'r

The chemicol nome for solt is codlum chlorlde. Its formulo is NqCl. Hove you ever been swimming in the seo? If you hove, you willknow how solty seo-woter is. Imogine how much solt must be dissolved in the world's oceons ! It's no wonder thot chemists coll solt 'common solt' !

T.r 5t

aad

aciA, g le4ta

In hot countries solt is extrocted from seo-wqter. The seo-woter is left in huge shollow lokes. Then the Sun's energy evoporotes the woter. (See poge 131.) Why don't we get much solt this woy in Britoin ? Fortunotely, we hove found thick loyers of solt under the ground in this country. Most solt lies under the Cheshire countryside. How do you think it got there Sqlt is o very useful row moteriol. It hqs ottrocted the chemicol industry into Cheshire. So how do we get the solt up to the surfoce There ore two methods:

?

7. digging Jrom mines, ond

2. pumping

?

up salt solution (brine).

People think that millions of years ago there was an inland sea where Cheshire is today. lt dried up leaving salt behind. The seam r,s up to 2000 metres thick in places !

First of oll, let's look ot mining solt.

Solt mining The solt is found obout 300 m below ground. In its noturol, impure form it is colled rock solt. It is drilled ond blosted out, then brought to the surfoce The underground coverns formed do not cove in if pillors of rock solt ore left in ploce. The rock sqlt is sold to councils oround the country It is used to grit roods in winter. o Why is rock solt put on roods ? Whot is the disodvontoge for cor owners ? (See poge 77 .)

102

:w-

Rock salt can be dug from underground

)

Brine (solt solution)

The second woy thot we con get solt from the ground is solution mining. This method relies on solt dissolving in woter Look ot the diogrom below:

water pumped down outer pipe

Hot woter is pumped down the outer pipe. It dissolves the solt. The solt solution is then forced up the smoller, inner pipe by the pressure of woter. The solt solution is colled brine. The brine gets stored in lokes until it is needed. It is then pumped stroight to the chemicolplont.

When mining in on oreo hos finished, the holes left under the ground must be filled. If not the lond obove con collopse ond slide into the old mines. This is colled subsidence. Look ot the old photogroph opposite: Subsidence used to be more of o problem in Cheshire. Nowodoys the holes crre more corefully spoced out.

Subsrdence was a problem in Cheshire

103

We hqve now seen how brine (solt solution) is brought to the surfoce.

At the chemicolplont it is electrolysed (broken down by electricity). You cqn try this yourself in the next experiment:

ExperimentS.T Breaking down brine

shown,

Set up the opporotus qs Test the gos you collect ot the cothode with q lighted splint. Whot hoppens ? Test the gos given off ot the onode (+)

(-)

A

hydrogen

chlorine gas o

$\

brine (sodium chloride

o

damp blue litmus paper

with domp blue litmus poper. Whot hoppens? (Switch off your power pock os soon os you hove detected the gos. WhV ?)

o

oo

Test the solution neor the cothode with

universol indicotor poper. Whot hoppens

Products from brine

?

brine (sodium chloride solution)

+

-

sodium hydroxide chlorine gas

solution (alkali)

hydrogen gas

You con reod obout the uses of chlorine, hydrogen ond sodium hydroxide on pqges 54,105-7,177 ond2OO. Remember Look of this picture , It might help you to remember which gos is given off ot eoch electrode when we elecholyse brine.

: catHv's

Ancl

Cathy's ankle Cathode 4Hydrogen Anode *Chlorine

In industry

chlorine

There ore severoltypes of cell used in industry. The most modern is colled o membrone cell. Look ot the diogrom opposite: A plostic membrone divides the cell in two. This keeps the chlorine ond hydrogen gos oport ond stops chlorine reocting with the sodium hydroxide. The goses leove from the top of the cell.

+

Sodium ions con poss through the membrone. Hydroxide ions con't get through. This gives us sodium hydroxide on the negotive side of the cell. 1&t

hydrogen membrane

brine

Only positive ions can pass through the membrane

o o sodium o o

hydroxide

o solution

Exploining the electrolysis of brine Let's see if we con work out how we get hydrogen, chlorine ond sodium hydroxide from brine. You might hove reqd obout the electrolysis of solutions on poge 92. It exploins why reoctive metols, such os sodium, ore not freed from solutions during electrolysis. Remember thot brine is sodium chloride solution. Insteod of sodium we get hydrogen forming ot the cothode (- ).

paper (using chlorine)

rayon fibres (using sodium hydroxide)

Con you recoll where the hydrogen comes from ? H+ ions come from the woter (HzO) in the solution. A few woter molecules split up into hydrogen ions (H+) ond hydroxide ions (OH-):

H2O(l)

+

H+(oq)

+

ffi

OH-(oq)

Therefore, when we electrolyse o solution of sodium chloride we con think of 4 different ions

:

bleach (using chlorine and sodium hydroxide)

soap (using sodium hydroxide)

sodium No*, hydrogen H+, chloride Cl-,

ond hydroxide OH- ions. The H+ ond

Cl- ions ore dischorged ot the electrodes.

Hydrogen comes off ot the cothode

2H+(oq) Chlorine 2

+ 2e2

:

-------> Hz(s)

comes off ot the onode

Cl-(oq)

(-)

e- ----+

(+) Clz(g)

margarine hydrogen)

(using

The No+ ond OH- ions stoy in solution. They form sodium hydroxide solution in the cell.

Sodium hydroxide is o very importont olkoli. Look ot the diogrom

PVC (using chlorine)

These are some everyday products made using salt as a raw material

hydrogen gas

chlorine gas

estay in solution

2Cl-

-

2e-

-;

Cl2

2H'

+ 2e- -+ H2

105

Here ore the chemicols we con get from solt:

diesolved in water

heat molten

/\

electrolysis

@/ \o

chlorine

./t\

eodlum chloride

@/erectrorvsis

\"

chlorine mdlum hydrorldc hydrogen

codlum

Eolution (an alkali)

-solution Uses of sodium Street lamps Hove you ever noticed the yellow glow of night in o lit-up oreo? We con thonk sodium for this effect. A smoll omount of sodium vopour is inside the yellow sheet lomps.

Heat transJer

Sodium vapour ls used in street lamps

Sodium is olso used in some nucleor reoctors. You might think it is stronge to use such o reoctive metol in o nucleor power plont. However, sodium hos some usefulproperties. It is o good conductor of heot qnd hos q low melting point. This is why it is used to tronsfer heot from the reoctor to the steom generotors. It is pumped oround the power plont in seoled pipes.

o

r

Why is it importont to keep the pipes seoled ? Why con't o sofer, less reoctive metol, such os copper, be used to tronsfer the heot ?

Sodium ls used in nuclear reactors

Uses of sodium hydroxide The solt industry is known os the 'chlor-olkoli' industry The olkoli, sodium hydroxide, is the most importont of the products from solt. detergents Look ot the ronge of and things it is used to soaps to

moke:

tuffi

ceramrcs rayon and acetate fibres

remove grease

@@ makins new &:$ Lj$ chemrcars & _-$ &J

sooruil paper

&_.u &_, pu

106

aluminium

Using hydrogen in fuel cells Hydrogen is used in spoce-croft to power fuel cells. Fuel cells ore o very efficient woy to use the chemicol energy stored in fuels. The conventionolwoy to honsfer the energy stored in fuels is to burn the fuel. It reocts with oxygen ond releqses energg os heot. Bosicolly, in o fuel cell the some reqction hoppens, but the chemicol energy in the fuel is tronsferred directly into electricol energy. Advontoges of fuel cells over conventionol woys of generoting elechicity o They ore more efficient becouse there qre fewer stoges in releosing the stored chemicol energy. Fuel cells are used in space-craft to o There is less pollution os the only woste product is woter. transfer chemical energy into electrical However, the hydrogen used in o fuel cell must be energy produced from somewhere, e.g. from electrolysis of woter. This requires energy which is often supplied by burning fossil fuels, so there con still be indirect pollution of the otmosphere :

The hydrogen fuel cell

+ hydrogen gas out

+

hvd rogen gas (fuel)

'-+

oxygen gas out

potassium hydroxide solution

+

+oxygen

porous graphite electrode coated in nickel

gas

porous graphite electrode coated in nickel and nickel(ll) oxide

This cell uses hydrogen os the fuel: ot the negotive electrode:

2Hzk) + 4OH-(oq)

+

4H2O(l) -t 4e- (hydrogen is oxidised)

of the positive electrode:

Oz(s) + 2H2O(l) -t

4e-

-------->

4OH (oq) (oxygen

is reduced)

So overollwe get: 2Hz@)

o

+ Oz(g)

--------> 2H2O(l)

Discuss how hydrogen fuel cells could be mode to reduce pollution from cors

to7

Summory o o o o

)

Common solt is sodium chloride, NoCl. It is found in the seo or in underground seoms Sqlt is dug up from mines os rock solt. It is olso pumped to the surfqce qs o solution. Solt solution is cqlled brine. When molten sodium chloride is elecholysed we get: sodium qt the cothode (-), ond chlorine ot the onode (+). When o solution of sodium chloride (brine) is electrolysed we get : hydrogen ot the cothode (-), chlorine of the onode (+), ond sodium hydroxide solution (an alkali) formed.

4. Sodium metol is extrocted in o Down's

Questions

1. Copy ond complete:

chlorine gas

The chemicol nome for common solt is .. . Its chemicql formulois .... . When molten sodium chloride is electrolysed, . . . metol forms otthe .... (-) ond .... gos is given off ot the onode (+). Solt solution is colled . . . . When it is electrolysed . . . . gos forms ot the cothode (- ) ond . . . . gos ot the onode (+). The solution becomes on .... os sodium .... is left.

+

molten sodium

chloride (with calcium chloride added to lower melting point)

sALr

/ @

3.

\ @

graphite anode

.

/+\ solution

-l o@@

This diogrom shows the solution mining of solt.

Copy the diogrom ond exploin whot hoppens ot A, B ond C.

108

steel gauze

o) Complete this word equotion to describe whot hoppens in the Down's Cell: electrolysis sodium chloride .... + ... b) It tokes o lot of energy to melt the sodium chloride. i) Why con't we use sodium chloride solution to get the sodium metol? ii) Which substonce is odded to the sodium chloride to lower its melting point? Exploin why sodium would cost more to buy if this substonce wos not odded.

Copy ond complete this flow diogrom. It shows the chemicols we con get from solt

molten

molten sodium metal steel cathode

.

2.

Cell

5.

Compore the use of hydrogen fuel cells with electricity produced by burning fossilfuels.

6.

o) Describe how brine is electrolysed in industry. Include o diogrom in your onswer. b) Imogine you ore o sodium ion, No+, in o seom of rock solt. Describe your odventures on the woy to finding yourself os sodium hydroxide in on oven cleoner.

Further questions on porge 122.

chapter 9 Colcium corbonote Hove you ever seen the 'white cliffs of Dover'? If you hove, you've seen lots of colcium corbonqte. Cholk is one form of limestone, mode from oround 98% colcium corbonote. You might olso find other rocks contoining colcium corbonote

oround your school. Limestone itself is q common building moteriol. It might be spreod on the schoolroods or roofs os chippings.

A school built from limestone

Another source of colcium corbonote is morble.

The chemicol formulo of colcium cqrbonote is CoCOs. Mony rocks with colcium corbonote in them were formed from the shells of seo creotures thot died millions of yeors ogo. The sediments built up on the seobed ond slowly formed limestone. Morble is formed from limestone crushed by powerfulmovements in the Eorth's crust ond/or by very high temperotures neor molten rock (mogmo) underground.

Limestone quorries Hove you ever visited the Peok District or the Yorkshire Doles? If you hove, you will hove enjoyed the beoutifulviews from the limestone hills.

Limestone is a raw material for making concrete and g/ass

You might hove been pot-holing or visited the coves there. These coves hove been weothered out of the limestone by roinwoter. Roinwoter is slightly ocidic becouse corbon dioxide dissolves in it os it folls. You con see how limestone reocts with ocid onpoge204. Limestone is o common rock in Britoin. It is blosted from the hillsides in huge quorries. Look ot the photo opposite:

o Why do you think thot mony people

ore ogoinst ony plons for new quorries ? These orguments hove to be bolonced ogoinst the benefits. Limestone is o vitol row moteriol for industry. Look ot its uses on poges 112 ond 113. New jobs ond money ore creoted for the oreo. o Whot ore your views on quorrying ? (See poge 117.) A limestone quarry 'scars' the landscape

109

)

Looking of limestone

Once limestone is quorried, it is chonged into

#,.,'!\.

mony usefulmoteriols. Is your home mode from bricks ? If it is, they ore fixed in ploce by mortor. Mortor is mixed using cement, which we get from limestone. Or perhops you live in o building mode moinly from concrete ? The row moteriql for concrete is olso limestone.

ik

{

r17rV I

\,

$fu"-"

;.er;!6pr

Limestone and its products are used a lot in the building industry

In this experiment you con moke some new substonces from limestone:

Experiment 9. 7 Changing limestone Follow the steps shown below. r Record whot hoppens os you go olong. Step

Step 2

1

dropper limestone chip

water tin lid

Heqt o piece of limestone shongly for ot leost 5 minutes, os shown qbove. Moke os much of the limestone glow os possible. (This is where the word 'limelight' comes from.)

Let it cooldown. Then odd o drop of wqter os shown. Keep odding woter, o drop of o time, until the reqction stops.

Step 3

Step 4

Use o gloss rod to push 50 cms of wqter.

ollthe white solid into

Stir ond then filter.

Pour holf your cleor solution into o conicol flosk. Blow genfly into it with o stuow.

r

Whot hoppens to the solution

l

Step 5

Add o few drops of universql indicotor solution to the other holf of your filtered solution. o Whot is its pH ? Is it on ocid or on qlkoli ?

E

110

?

)

Reoctions of limestone

The reqctions in the lost experiment con be shown like this calcium carbonate limestone

step 4 add carbon dioxide (this is the test for COr)

step

7

heat

carbon dioxide given off

calcium hydroxide

calcium oxide

sol ution

quicklime

limewater step 3 add more water and filter

step 2 add a little water

calcium hydroxide slaked lime

Equotions step 7 CqCOs(s) --------> CoO(s)

+

step 2 CoO(s)

Co(OH)z(s)

+

H2O(l)

---->

COz(s)

step 4

Co(OH)2(oq)

The lime

+

CO2(s) --------> CoCOe(s)

+

H2O(l)

waste air and carbon dioxide

limestone

gas

carbonate)

(calcium

kiln

In industry the limestone is heoted in lime kilns. The limestone is broken down by heot in the kiln. This reoction is colled thermol decomposition.

heot- colcium oxide * CoCOs(s) --------> CoO(s) +

colcium corbonote

fire-brick

corbon dioxide COz(g)

It's like Step 1 in Experiment 9.1 on o lorge scole. The kiln is lined in fire-bricks. They hqve to withstond very high temperotures (qbout 1500'C). Rototing kilns ore used to turn limestone into cement. The powdered limestone is heoted with cloy. Most cement goes on to moke concrete. You con reod more obout these ond other uses of limestone on the next few poges.

hot air

hot air

quicklime (calcium oxide)

111

)

Uses of limestone

Look of the uses of limestone below

buildings and roads steel (limestone removes

glass (limestone is heated with sand and sodium carbonate)

impurities in furnace) heat with clay limestone (calcium carbonate)

gravel + sand +

l}rryconcrete cement

+*t

neutralise acidic soil and lakes affected by acid rain

>cr

mortar

paper (used to whiten and provide bulk)

Cement Hove you ever wotched brick-loyers ot work ? They use o mixture of cement ond sond, with woter odded to moke o thick poste. This is colled mortqr. It tokes o lot of skill to set the bricks in the right position. Whot do you think would hoppen if their mortor wos too runny ? Whot if it wos too dry ? Cement is mode by heoting limestone ond cloy (or shole). They ore ground up ond heoted in kilns which rotote. A little gypsum (colcium sulfote) is odded. This stops the cement from setting os soon os you odd woter. Cement sets os it reocts with woter. This is colled hydrotion. The reoctions ore complex. We con think of it os 'fingers' of crystols growing out from eoch groin of cement. These interlock ond bind the mixture together. Mortor will set overnight. However, it corries on reocting ond getting stronger for severol months.

lnuestigation9.2

Mortar

n

^/l\

cement

Why don t you hy some brick-loying yourself ! ' ' ' Experiment with different mixtures of cement ond sond. See which mixture mokes the best mortor.

tt2

,?O(f C e

€ G \-/

Hzo grarns oJ cement

Crystal fingers (of calci um hydroxide) hold the structure together as lt sets. Calcium hydroxide can react with CO2 in the air to form calcium carbonate: ca(oH)2+ co2----> caco3+ H2o

Concrete Whot ore the poths oround your school mode from ? Some willbe mode from concrete. Concrete is mode by mixing cement, sqnd ond smqllstones. If you look closely, you will see the smoll stones set in position

Concrete is the most widely used building moteriol in the world. Thot exploins why we produce obout 1000 million tonnes of cement in the world every yeorl Inuestigation

9.3 Concrete

sond,

Concrete is delivered to customers readymixed in trucks. Why does the large drum on the back rotate continuously ?

n

l\

cement

You con test different mixtures of cement, ond grovel to see which mqkes.,,the strongest concrete. You con moke your mixtures in yoghurt pots. o Evoluote:rtfui:,reliobility ond volidip of your investigotion. (See pagq6.)

Reinforced concrete Concrete is o relotively cheop building moteriol. As o moteriql itself it is hord, but o beom will snop if put under tension. We con moke it stronger by moking reinforced concrete To moke reinforced concrete, the mixture is ollowed to set oround o steel support. Its increosed strength ond flexibility meons thot we con use it to moke buildings ond bridges. You've probobly seen lots of

concrete on motorwoy bridges. The bridges would not be oble to spon ocross gops without the embedded steel.

However, corrosion of the steel inside the concrete con be o serious problem, weokening q skucture.

In Use the

rembed

concrete two smoll beoms- In one beom with reinforced

mx

Reinforced concrete being laid

n

/!\

cemeil:

poper clips.

,.,,r, ,Test

113

)

Gloss

Limestone is one of the moteriols thot we use to moke gloss. Gloss is importont in oll our lives. Think of ollthe things we use every doy thot ore mode from gloss. Look qt the photos:

s\l

,

ar. !*mffi o

List some other things mode from gloss.

Whot is gloss

?

Gloss is o stronge moteriql. Con you remember the 3 stotes of motter? (See poge 19.)

Some people collgloss the 4th stote of motter. It's like o 'solid liquid' ! The row moteriols (see below) ore heoted to 1500'C. At this high temperoture, they melt ond reoct to form molten gloss. As it cools down, the gloss turns into o solid. However, the porticles don't form o regulor pottern. It's os if the porticles in the molten gloss ore frozen in ploce. Look qt the diogrom: Con you see how the structure is jumbled up ?

The disorderly structure in borosr/rcate g/ass

Whot's in gloss ? Did you know thot gloss is mode moinly from sond ? Gloss hos been oround for o long time. It wos probobly discovered by occident in the sond underneoth on oncient fire ! The first gloss object hos been doted ot obout 4500 BC. The Egyptions used gloss contoiners oround 3000 BC. As well os sond (SiO2), the other row moteriols qre

- sodo - (No2CO3) (sodium chloride) solt common You hove seen some of the uses of mode usefulproduct poge is onother 106. Sodium corbonote on from solt. Re-cycled gloss (cullet) is becoming more importont. It con moke up to 30 7o of some gloss-moking mixtures. limestone (CoCOs) ond sodium corbonote

114

The composition of g/ass

Different types of gloss Hove you ever seen o cor window thot's been smoshed ? The bits of gloss look very different from the pieces you get when o bottle smoshes. Bottles ond cor windows ore mode from different ppes of gloss There ore mqny different gpes of gloss. Scientists hove tried chonging the gloss-moking mixfure. They've olso found woys of treoting the gloss to chonge its properties. For exomple, windscreens ore usuolly mode like o gloss sondwich - with o thin sheet of plostic os the filling ! This is colled lominoted gloss. How does this help if o stone hits your windscreen ?

Look ot the toble below: Do oll these ppes of gloss hove ony properties in common

Ihis g/ass had not been laminated

?

Type of glass

Use

soda-lime boro-silicate lead-crystal glass fibres

windows test-tubes, beakers, etc. (heat-proof, chemical resistant) decorative glasses, bowls and vases fibre optics, fibreglass lenses in spectacles, cameras, projectors, etc. opaque oven-ware

opticalglass glass ceramic

Ihese g/ass fibres carry information in the form of light. A single fibre can carry 10 000 phone calls at once.

Coloured gloss Hove you token ony gloss to be recycled ot o bottle-bonk ? The bottles ore sorted out into different colours. Whot ore the most common colours of gloss bottles ? Green ond brown bottles get their colour from iron impurities in the sond thot it is mode from.

rYY

On poge 47 we found out thot the transition metals form coloured compounds. Adding smollomounts of their oxides mokes gloss coloured.

Experiment9.S Make your own glass

A

1. Sugor, like sond, is mode of crystols. You con moke sugor-gloss (toffee) by melting some sugor. Heqt it until its colour is pole brown. (Do not touch !) Then cool it quickly to mqke o cleor, hord toffee.

Z.Heotsome borqx on owire loop os shown: This meltsto form q stuucfure like gloss. When molten, dip it in atiny omo-unt of q trsnsition metol oxide. This will moke o beod of coloured gloss when cool.

molten borax

metaloxides borax

glass or wooden handle

wire loop

H 115

'...,

)

Chemistry of work: New developments in concrete ond gloss New types of concrete Some form of mortor hos been in use for thousonds of yeors. Do you remember how you investigoted the effect of vorying the mixture to see how it offected the strength (poge 112)? Then on poge 113 you investigoted reinforced concrete. People hove olwoys tried out new woys to improve the properties of mortqr ond concrete. For exomple, oround 400 BC the Romons

were trying out onimolfot, milk qnd even blood in their mortor. The experiments continqe todoy with ollthe support of modern science to help. Concrete wos first reinforced in Fronce in 7867 .

i

They used o wire mesh to strengthen it. Nowodoys we con use:

o o o o

gloss fibres

tr

corbon fibres steelfibres

poly(propene), nylon, polyesters ond Kevlor.

The latest High Performance Concretes make new, creative designs possib/e

Some of the lotest reseorch uses pulp from wood, plonts ond recycled poper. The moteriols ore shredded ond sliced into smqll pieces before odding them to the concrete mixture.

reinforced concrete composites. A 'composite' is o combinotion of moteriols, mixed to get improved properties for o certoin use.

We cqllthese

A little recycled poper con improve concretes resistonce to crocking, impoct (moking it tougher) ond scrotching! Using industriolwoste qs odmixtures ('odditives') to concrete mokes economic sense. New developments use gronuloted slog from o blost furnoce or osh from coql-fired power stotions to moke High Performonce Concrete.

A scientlsf testing a new

concrete composite

Gloss in concrete We con even substitute ground-up woste gloss insteod of sond in concrete. However, the cost of cullet (recycled gloss) does not moke this worthwhile of present.

However, reseorch of the University of Sheffield, hos shown thot there could be o mqrket for 'ConGlossCrete'. They embedded lorger pieces of gloss ond polished the surfoce to get q very ottroctive finish. Look ot the photo opposite: A decorative concrete composite made with scrap g/ass

116

New uses of gloss The gloss we collect from recycling con now be used for: o obrosives o loying foundotions in ploce of grovel ond smoll stones o filtering ond for the droinoge of woter o tronsporent bricks o insulotion fooms mode with gloss fibres. By bonding gloss to other moteriols, such os wood or metol, we olso get interesting composites. The new moteriol mode is stronger thon the originolmoteriols we storted with. o Design o morketing leoflet for either the lotest developments in gloss or concrete. Corry out your reseorch using the Internet.

G/ass is finding many new uses

work: The limestone for oll these uses is quorried out of the ground. Hove you ever seen o quorry? They ore not o pretty sight! They produce o huge scor on the londscope' rhrs is

a

rimestone

quarry' Workers use build o quorry in o beoutifulpiece of countryside. 7;:'f;!;:;"ni#frz rock face. Look of some of the orguments below:

Imogine o limestone compony wont to

The dust will settle on my crops ond they won't grow as well

The quorry will destroy the hobitots of birds ond onimols

Ihe lorries corrying limestone will go right through the villoge post our primory school

We mighf get thot by-poss for these lost 10 yeors

we've been osking

Yes, but

think I'll get o lot more business from the workers ot the quorry - snd there will be more jobs for youngsters like you

I

don't know

if

my

heort will stond those explosions when they blost fhe rock out !

o

We'll be oble to supply limestone for the gloss, steel ond cement industries in this regron now

Discuss the issues involved in goining plonning permission for o new quqrry.

777

9.6

Thermal decomposition You hove seen on poge 110 whot hoppens when we heqt colcium corbonote. The reqction is colled thermol decomposition. Now investigote this problem. lnuestigation

Which corbonotes breok down most eosily ? You con investigote some of the corbonotes of : colcium, mognesium, sodium, potossium, copper, ond zinc. Design q fqir test to find out which of these decomposes most quickly. o How con you moke it sofe ? Ask your teqcher to check your plon before you try it.

t

carbonale being tested limewater

heat

Summory o Colcium corbonote (CoCOs) is moinly found in noture in limestone, cholk ond morble. o It is broken down by heot (thermol decomposition), to give colcium oxide ond cqrbon dioxide o Colcium oxide (quicklime) reqcts with wqter to form colcium hydroxide (sloked lime). This con be used to roise the pH of qcidic soil in o neutrolisotion reoction.

o Cement is mode from crushed limestone ond cloy in o rotory kiln. o Mortqr is mode from cement ond sond, mixed into o thick poste with woter. o Concrete is olso mqde from cement ond sond, but qlso hos smollstones (or grovel) mixed in. o Gloss is mode by heoting limestone, sond qnd sodium corbonqte (sodo).

)

4.

Questions

1. Copy ond complete

limestone

:

The chemicolnome for limestone is

....

.

Itsformulois..... When heoted, limestone breoks down in o reoction colled . .. . decomposition. The productsformedore .... .... ond corbon dioxide. Quicklime is onother nome for cqlcium . . . . It mokes . ... lime when we odd woter, ond this is used to . . . . the pH of ocidic soil. Gloss is mode by .. .. o mixture of limestone

slaked lime

Motch the numbers to D u

;

2. Drow o toble with 2 columns. 3.

118

Limestone is roqsted in o lime kiln. o) Write o word ond symbol equotion for the reoction in o lime kiln. b) Whot do we coll this type of reoction ? c) Drow o diogrom of the opporotus you could use to show thot corbon dioxide gos is given off when colcium corbonote is heoted.

below:

c"(cjHi;(,

I to 4 with the letters A

tr&

CoCO:(s1 heot

co(oH)z(oq)

+ COz(g) C Co(OH)2(oq) + COz(g)-+ CoCOe(s) + H2O(l) D CoO(s) + H2O(l) -------->go,OH)z(s)

B

ond..... Use it to show the odvontoges ond disodvontoges of storting o limestone quorry in o Notionol Pork.

quicklime (or lime)

limewater

5.

CoO(s)

o) Describe how we furn limestone into cement.

b)Whot is the difference between mortor ond concrete?

6.

Imogine thot you work for on odvertising compony. You ore given o job to design o poster to show the public how importont limestone is. Use informotion from this chopter ond other sources to creote your poster.

Further questions on Products from Metol Ores ond Rocks

)

Exhoction of metols ond Electrolysis

4.

1. Mony iron

ores contoin iron(lll) oxide. Iron con be extrocted from iron(lll) oxide by heoting it with corbon. o) Copy ond,complete this equotion for the reoction. ZFe2Os+.... C -*-*-> .... Fe* .... .... t3l b) This reoction is described os q reduction of the iron(lll) oxide. Exploin why. tll c) Nome two other metols thot ore obtoined by o similor reoction. t2l

2. Look ot this list of metols: oluminium copper iron

?

b) Exploin why reduction with corbon connot be used to exhoct this c) Whot method is used to extroct this metol?

metol.

3.

?

zinc

o) Which of these metols connot be extrocted from its ore by reduction with corbon t1l

tll tll

Tungsten is used for the monufocture of filoments for light bulbs. Tungsten moy be obtoined by heoting its oxide, WO3, in hydrogen. The equotion for this reoction is: WOs(s) + ....H2(g) ----+W(s) + .... HzO(g) o) Whot is the chemicol symbol for tungsten used in the obove equotion ? b)Bolonce the obove equotion. c) Whot does H2O(g) in the equotion suggest qbout the temperofure of the reqction ? d) Whot is reduced in this reoction ? e) Whot is oxidised in this reoction t6l f) Do you think thot the obove method would be suitoble for the extuoction of potossium from potossium oxide? Exploin why.

t2l

5.

o) A student wos trying to exhsct the metqls from leqd oxide ond oluminium oxide. She heqted eoch oxide with corbon in q fume

cupboord: lumps of charcoal (carbon)

The toble gives informqtion qbout some metqls.

Name of

the metal

Cost of one lonne Percentage of the metal in the crust of the metal in December 2003 (e)

Aluminium Platinum

of the Earth

1

6 720

000

0.000 000

216

lron Gold

8

0.000 000

1

She wos oble to extroct leod from leod oxide

1

but not oluminium from oluminium oxide. i) Exploin the results of these

o) Use informotion in the tqble to suggest why gold ond plotinum ore very expensive

metols.

b)Aluminium ond iron ore mode by

i) ii)

t1l

Use the reoctivity tqble on poge 70 to suggest o metol thqt would

tll

experiments.

t4l

Complete this word equotion for the reoction between leod oxide qnd corbon.

* corbon

----->....

* .... tll

b) Copper con be exhocted os shown below.

H positive electrode

negative electrode

nl

reduce oluminium c) Aluminium is mode by the reduction of molten oluminium ore, using o very lorge omount of electricip. i) How is iron ore reduced in o blqst furnoce to mqke iron t2l ii) Suggest why oluminium is more expensive thon t1l

? iron.

ii)

leod oxide

Nome the element thot is removed from the ores when they ore reduced.

ore.

mixture of powdered carbon and the metal oxide

very strong heat

4.1

236 800

tt

(o/o)

8.2

883

(EDEXCEL)

solution of copper(ll) chloride

Copper chloride is on ionic compound. Stqte where the copper would collect ond (AOA) exploin your onswer fully.

t2l

Note: although a question may be marked (AOA) etc., it will olten be relevant to other examinations as

well.

119

Further questions on Products from Metol Ores ond Rocks

6.

Copper metql con be extrocted from the ore molqchite. o) Whot is on ore

?

tll

b) Molochite contoins copper(ll) cqrbonqte. This is roosted in oir to obtqin copper(ll) oxide. How is copper obtoined from this copper(ll) oxide t2l c) The copper obtoined by this process is not pure. Whot method con be used to purifu the

?

copper?

tll

7. It is thought thot

oncient Britons first mode o useful substonce by occident, when they mixed some mqlqchite - on ore of copper

with formulo Cu2CO3(OH)2 - with some chorcool, ond heoted them together. o)Whot useful substqnce wos mqde? ttl b)Whot might this substqnce hqve been used

for?

ii) iii)

At which electode will mognesium metql be formed during elecbolysis ? [7/ Nome the substonce formed qt the

other elechode. t1l c) Sodium chloride lowers the melting point of mognesium chloride so less energy is needed to melt the mognesium chloride. Suggest two odvontoges of using less

en€rgy.

t2l

(EDEXCEL)

10. Copper sulfote solution con be electrolysed. Whot forms ot the cqthode A Copper B Hydrogen C Oxygen

D Sulfur

11. The following opporotus

?

tll

(AoA)

is used to purify o

somple of copper.

tll

+

c) Whot type of reoction took ploce during heoting [1]

dc

?

8.

In which one of the following sets ore qll the metols so reqctive thot they oll hove to be exhocted by electrolysis ?

A Co :Cu Pb BCqMgNq CCuMgZn DCuKMg E Mg Pb Zn

9.

t1l

(ocR)

Mognesium metolis monufoctured by electuolysis of the solt mognesium chloride. This solt is obtoined from seo woter. Before electrolysis, mognesium chloride is mixed with sodium chloride ond the mixture is heoted to melt it. Adding sodium chloride lowers the melting point of the mognesium chloride without offecting the products of the electrolysis. Whot is the stote of mognesium chloride in seo t1l Whqt is the stqte of mognesium chloride during the elecholysis

o) i) ii) b) i)

woter?

process

?

720

copper

dilute sulfuric acid

During the electrolysis copper leoves the positive electrode ond joins onto the negotive electrode. o)Write o hqlf equotion for the reoction ot the positive electrode (onode). tzl b)Write o hqlf equotion for the reoction ot the negotive electrode (cothode). t2l c) During the electrolysis the negotive electrode goins less moss thon the positive elechode loses when the electrodes were weighed before ond ofter the experiment. Exploin why. t2l

12. Window fromes mode from iron corrode

t1l

fqster thon those mqde from oluminium. This observotion does not follow the order of the reoctivity series. Exploin the reosons

tll

for

Whot type of porticle is present in mognesium chloride which ollows it to be elecholysed

?

impure copper

this.

t3l

(AoA)

Further questions on Products from Metol Ores ond Rocks 13. The diogrom shows o method used to purify

15. The toble gives informotion obout five metols

copper. Density Tensile strength Resistance to

Metal

o@

(/cm3)

(MPa)

corrosion

Aluminium

2.7

195

good

Copper

8.9

224

good

Mild steel

7.8

450

poor

Titanium

4.5

460

Cast iron

7.8

150

very good poor

o)Aluminium is used for overheod power cobles. These cobles hove q steel core. i) Aluminium ond copper ore both good elecfuicol conductors.

Choose words or phroses from the box to complete the sentences below.

bottom of the

tonk

crocking

displocement electrolysis negotiveelectrode positiveelectrode surfoce of the solution This method of purifuing copper is colled . . . . . The impure copper is mode the . . . . ond the pure copper collects of the . . . . The impurities collect ot the . . . t4l

.

14. The toble shows informotion qbout different types of steel. Type of stee!

Percentage of carbon

b)The properties of oluminium ond mild steel con be modified by olloying. Whot is meontby olloying? c) Cost iron con be converted into mild

tll tll

steel.

Why is mild steel more usefulthon cost iron ? t1l d)The following is qn exhoct from on orticle in o science mogozine. Titonium is fontostic. It is lighter thon steel yet stong ond tough enough to survive the extremes of spoce

Description

Mild steel

o.25

can easily be bent into shape

Medium steel

0.45

harder than mild steel

High carbon steel

0.80

hard and brittle

Cast iron

3.00

very brittle and easily cast

or the corrosive solb ond pressures of the deep oceon with hordly o blemish. In foct, just obout the only dror,vbock with the mqteriol is ib price. But this looks set to chonge, with the discovery of o new woy to extoct titqnium metol thot requires little more thon blqck sond ond electricity. Best of oll the process promises to lower the price of the metol by up to three-quorters.

o) Whot is the effect of increosing the

percentoge of corbon in steel? tl b) Impure iron from the blost furnqce is cqlled pig iron. Exploin how this is chonged into mild

steel.

ii)

Exploin why oluminium rqther thon copper is used for overheod cobles. [{ Why do the cobles hsve q,steel core ?

l

t3l

c) Mild steel is o mixture of substonces but is not on olloy steel. Exploin this stotement. tsl (EDEXCEL)

Titonium is the ninth most qbundqnt element in the Eorth's crust with on estimoted 10000 yeors supply of ore. Until now, the cost of exhoction hos mode the metol very expensive. i) Why is it likely thqt the discovery of the new method of extrocting titonium will increose demqnd for the

metol?

ii) Whot ore the benefits to society of

tll

this new method of exhoction of

titonium

?

t1l

(EDEXCEL)

721

Further questions on Products from Metol Ores ond Rocks

)

Solt

o) Nome the type of process used to obtoin

chlorine, hydrogen ond sodium hydroxide from brine. tll b) Describe o test for chlorine. t2l c) Give o use of sodium hydroxide. tll

16. Look qt the diogrom. It shows how sodium hydroxide solution con be monufoctured. It is monufqctured by the elecholysis of sodium chloride solution. hydrogen

chlorine

(EDEXCEL)

18. The diogrom below shows the electrolysis of sodium chloride solution, in the loborotory.

sodium

chloride+ solution

power supply

oo

oo O6

solution

positive electrode (chlorine formed here)

negative electrode

+ electrode (anode)

porous membrane

sodium chloride solution

electrode (cathode)

o) Whqt is the meoning of the word

'electrolysis'?

b)Sodium hydroxide

is produced when

t2l

sodium chloride solution is electrolysed. Give the nomes of the other two produch.

o) Which gos forms ot the negotive

t2l c) Sodium chloride solution contqins porticles colled ions. Exploin how sodium chloride solution conducts d) The cost of moking sodium hydroxide includes the cost of the row mqteriols used. Write down three other costs involved in moking sodium tsl e) The elecholysis of sodium chloride solution con olso be corried out in the loborotory. Describe whot you would observe of the positive (OCR)

electricity.

? positive electuode. electrode

b)Exploin why chlorine gos forms ot the c) Stote one use of chlorine

tll

t1l

17. Rock solt is on importont row mqteriolfor the chemicql industry. Rock solt is extrocted by dissolving the solt in woter to form brine. The brine is pumped out qnd converted into chlorine, hydrogen ond sodium hydroxide.

722

t1l

t2l (AOA)

19. Whot ore the odvontoges ond the disodvontoges of using hydrogen fuel cells to power motor cors ? t4l

hydroxide.

electrode.

gos.

t1l

)

Limestone

20. The diogrom ot the top of poge 123 shows q lime kiln. This is used to moke cqlcium oxide from limestone (colcium corbonote). o) Use informotion from the diogrom to help you to write o word equotion for the reoction which tokes ploce in the lime

kiln.

t1l

Further questions on Products from Metol Ores ond Rocks d)Why is leod oxide qdded to some types of

carbon dioxide

t

gloss ?

e) Borosilicote gloss is often found in the kitchen. Whot is it used

for?

calcium carbonate

22. a) Limestone is o very useful moteriol which

1500"c

!

hot air

tsl

hotair

is reqdily ovoiloble in the United Kingdom. When it is heoted, it is broken down into simpler substonces. Whot is the nome for this type of chemicql b) Limestone con be used for mony purposes. Some uses ore shown below.

reoction?

tll

making sodium carbonate

T

calcium oxide

making cement

b)The diogrom below shows qnother process thqt uses limestone.

limestone building roads

mixture of powdered

Nome one more use of limestone.

i product

Nome the product mode in this process.

t1l

(AoA)

shows the composition of some

types of gloss. si02

iron

kiln

ilfl.llfl"+

21. This toble

6xtracling

Sodium carbonate

Soda lime glass

75o/o

15%

Lead glass

60%

157o

Borosilicate glass

75o/o

SYo

Lead

oxide

Other oxides

Other

1OYo

25/o 20o/o

o) Whot is the common nqme for the

chemicql SiO2

?

b)Which type of gloss contoins the leost omount of sodium corbonqte ? c) Whot might be included in the bther' cotegory for sodo lime gloss ?

tll

(AoA)

23. Limestone (mode moinly of colcium corbonote - CoCOs) is heoted with sond (silicon dioxide) ond sodq osh (sodium cqrbonqte) to moke gloss. o) When limestone is heoted it decomposes to moke quicklime, which is colcium oxide, CoO, ond corbon dioxide. Write o bolonced equotion for this

reoction.

t2l

b) Quicklime is reocted with woter to mqke slqked lime, which is colcium hydroxide, Co(OH)2. Sloked lime is often odded to soils thqt qre too qcidic. How does the sloked lime cure this problem ? ttl c) Limestone (colcium corbonote) wos formed in the tourist oreo now colled the Peok District, obout 300 million yeors ogo. Todoy limestone is mined neor Buxton, in one of the lorgest limestone quorries in the United Kingdom. Suggest three sociol or environmentol issues which might be involved in the mining of limestone in the Peok District.

tsl

(ocR)

723

chapter 7O

ACIDS AND ALI(ALIS

Acids oll oround Whot do you think of when you heor the word ocid Most people think of o fuming, corrosive liquid which is very dongerous.

?

However, not oll ocids ore like this. Most of us like q little ocid on our fish ond chips ! Look ot the cortoon on poge 102. o Which ocid does vinegor contoin ? Vinegor hqs the shorp, sour toste of ocids. (The Lotin word for 'sour' is ocidus.) Citric ocid gives oronges ond lemons their shorp toste These fruits olso contoin qscorbic ocid. We know it better os vitomin C !

Did you know thot even roinwoter is slightly ocidic. (See poge 291.) Corbon dioxide gos dissolves in the roin os it folls This is olso the gos in fizzy drinks, such os colo, beer ond sporkling minerolwoter. Why do you think these drinks toste tongy ? These qre oll exomples of

These teenagers are enjoying a little ethanoic

acid on their chips!

weok ocids thot we meet every doy.

Acids in the lob You will hove used ocids in your science lessons. The 3 common ocids found in school ore:

hydrochloric ocid sulfuric ocid

nitric ocid These ore

HCI H2SO4 HNO3

strong ocids.

Did you know thot we oll hove one of these strong ocids in our stomochs ? Hydrochloric ocid helps to breok down our food

into smoller molecules qnd kills bocterio. You con reqd more obout sulfuric ocid on poge 134 Nitric ocid is on poge 235.

124

Fizzy drinks are acidic

What's the formula ? 3 strong acids we should know, Learn this rhyme and have a go! Nitric acid's firsf we see Its formula's HNO3 The next one you should learn as well ls hydrochloric*HCl Sulfuric leaves usiust one more, That famous H2SO4

)

Neutrolisotion

Hove you ever hod indigestion ? The 'burning' feeling comes from too much hydrochloric ocid in your stomoch. You con cure the poin quickly by toking o toblet. The toblet contoins on olkoli (or bose) which gets rid of the ocid. ffiiluml

Acids ond olkolis ore chemicolopposites. They reoct together ond 'concel eoch other out'.

'/'/e aii ita',tt: ityclror:Itk'trrc ,t,' ali,t

If we mix just the right omount of o strong ocid qnd o strong olkoli togeth er, we get o neutrol solution.

The reoction between on ocid ond on olkoli is colled

itc:tc1

:-lutllachs

neutrollsdion.

The pH scole

These antacid tablets can neutralise excess acid in your stomach

You hove used universol indicotor before to meosure pH. Do you know the pH of o neutrol solution ? Here is o reminder of the pH scole :

11 12 13

012

14

iron(lll) chloride 2 Fe(s) + 3 Cl2(g) -------> 2 FeCIs(s)

lron and chlorine can make the salt iron(lll) chloride by direct combination

127

)

Preporing solts

You hove now seen how to moke o solt by reocting on ocid with on olkoli. But olkolis ore port of o lorger group of compounds colled bqses.

copper oxide

iron oxide

Look ot the diogrom opposite: An olkoli is just o bose thot con dissolve in woter. Do you think boses will reoct with ocids, os olkolis do The generol equotion is:

ocid * bose

--->

o

solt *

?

All metal oxides are bases. The soluble ones are alkalis

woter

For exomple,

* zinc oxide --------> zinc sulfote * + ZnO(s) ZnSOa(oq) + --> As in oll neutrolisotion reoctions, o solt is mode. sulfuric

ocid

H2SOa(oq)

o

woter H2O(l)

Whot is the nome of the solt in the reoction obove

? Sa/ts have many uses. This farmer is treating his vrnes

with copper sulfate to kill pests. Why must grapes be washed well before we eat them ?

Experiment 70.3 Making a salt from an acid and a base 1. Put 25cm3 of sulfuric qcid in o smoll beoker. Add blqck copper oxide qnd stir with o gloss rod. Keep odding the copper oxide until no more will dlssoloe (react). Worm gently (do not boil). o How do you know when qll the ocid hos reocted? o Work out whot is formed in the reoction. 2. Filter the mixture in your beoker. You should get o cleor, blue solution. r Whot should you do if you still hove some block powder in your solution ?

ocid

128

* +

copper sulfate solution

copper oxide copper sulfate

copper oxide --------> copper sulfqte

CuO(s)

warm sulfuric acid

acid

--------> CuSO+(oq)

* +

3

H

water bath

2 copper sulfate solution

The sulfuric ocid is neutrolised by the bose, copper oxide:

H2SOa(oq)

glass rod copper oxide

A

3. Pour your solution into on evoporqting dish. Then heot it on o woter both os shown: Stop heoting os soon os you see some crystols qround the edge of the solution. Leove the solution for q few doys to crystollise slowly. o Whqt is the nome of your solt? o Whqt do the crystols look like ?

sulfuric

1

woter H2O(l)

t

heat

More soluble solts Acids con olso be neutrolised by reocting them with corbonotes. You hove olreody seen how limestone (colcium corbonote) reocts with ocid In generol we con soy:

ocid + o o

o corbonote

----i>

o

solt + woter *

cqrbon dtoxide

How is this different from the equotion for on ocid reocting with o bose ? How could you test for the gos given off ? This lake has become acidic It is being neutralised by

We con use the some method os Experiment 10.3 to prepore o solt from o corbonote. This is becouse most corbonotes ore insoluble in woter.

calcium carbonate released from a helicopter.

Experiment 70.4 Preparing a salt from an acid and a carbonate Collect 25 cms of hydrochloric qcid in o smoll beoker. Add o spotulo of copper cqrbonqte. o Whot hoppens? Whot is the gos given off ? A

copper carbonate

acid

Add more copper corbonote until it stops fizzing. copper carbonale Filter to remove the un-reocted copper corbonote. Repeot step 3rfrom the end of Experiment 10.3 to get some crystols of your solt. o Whqt is your solt colled ? o Whot do its crystols look like ? The hydrochloric ocid is neutrolised by copper corbonote:

* HCI(oq) +

hydrochloric ocid 2

copper chloride t woter -t corbon dioxide --------> CuCl2(oq) + H2O(l) + COz(g) CuCO:(s) ------>

copper corbonote

Metols ond ocid We hove olreody seen how some metols reoct with ocid. Con you remember which gos is given off ? Do oll metols reqct with ocid ? (See the toble on poge 70.) If o metoldoes reoct, the generol equotion is:

ocid + smetol

--+

osolt +

hydrogen

You con use the method from Experiment 10.3 to prepore the solt. o Why would it be dongerous to use this method to prepore potossium chloride ? o Which ocid ond metolwould you stort with to moke mognesium sulfote ?

Here is magnesium reacting with

dilute sulfuric acid. How can you remove any excess magnesium after the acid has been neutralised ?

.

729

F

Acids need uroter

!

Allthe ocids we hqve used so for hove been solutions. The ocid molecules ore dissolved in woter. Acids need woter before they con show their ocidic properties Let's look ot citric ocid (the ocid in oronges) os on exomple: Experiment

1.a.5

Tbsting citric acid

You con compqre solid cihic ocid (which hos no woter odded to it) to q solution of the ocid Write down your results in o toble like this:

/\

acio

Results for citric acid solution

Results for pure citric acid

Test blue litmus paper sodium carbonate magnesium ribbon does it conduct electricity

?

o How does woter offect the properties of citric ocid ? o Think of onother test to show if o substonce is qcidic. Without water, subsfonces are not acidic. Look qt these properties of o typicol ocidic solution: o turns litmus red, ond hos o pH less thon 7, o reocts with o bose, o fizzes with o corbonote, giving off corbon dioxide, c fizzes with o metol, such os mognesium, giving off hydrogen

hydrogen chloride gas

dissolve in water

Let's see whot difference the woter mokes: In woter, the ocid molecules split up. We con look ot hydrogen chloride, HCl, os on exomple:

lunnel

Hydrogen chloride is o gos. It only shows its ocidic properties when we dissolve it in woter. We collthe solution formed hydrochloric ocid: HCI(g)

dissolve in woter

H*(oq)

+

hydrochloric acid

Cl-(oq)

Remember thot oll ocids contoin hydrogen. When dissolved in woter, the hydrogen is releosed into the solution os H+(oq) ions.

The hydrogen chloride gas sp/its up (dissociates) in water into lons. You can read more about this on page 226. The solution is called hydrochloric acid. (The gas is very soluble in water.) Why is a funnel used when disso/vtng the gas?

.

It is H+(oq) ions thot moke o solution ocidic. Acid plus alkali gives salt and water, H + ions are led to the slaughter I

Exploining neutrolisotion When we neutrolise on ocid, the H+(oq) ions ore removed from the solution. Alkoline solutions contoin hydroxide ions, OH-(oq)

fg+

H*(oq) + oH-(oq) neutrolisotiglr H2O(l) The H+ ond

130

OH- ions 'concel eoch other out', forming

H+

oH- oH-

H+

+

woter.

Hzo

oH-#

)

Solubility of solts

Do you remember how we get o soluble solt from its solution ? If we heot the solution, woter evoporotes off. Smoll crystols of the solt stort to form. This is colled the point of crystollisotion. We now hove o soturoted solution. No more solt con dissolve in the solution. As more woter evoporotes, the crystols of the solt grow bigger.

You can get the salt from sea-water in hot countries. As the water evaporates, the solution becomes saturated. Then salt cnTstal/r,ses out and is collected.

Solubility curves We meosure how soluble o solt is by seeing how much dissolves in 100 g of woter. (100 cm3 of woter hos o moss of 100 g.) For exomple, the solubility of copper sulfote is 19 g per 100 g of woter, ot 15 "C. 120

Notice thot the volue for the solubility obove is given ot 15 "C. Do you think thot temperoture offects how soluble o solt is ?

c)

(! = o

o) o o

100

80

0)

Look ot the groph: o Which of the 3 solts is most soluble ot20"C? o Which solt is most soluble ot 60'C ? We collthe lines on the groph solubility curves. They show us how much solt dissolves

of different temperotures. You con find out more obout solubility curves on poge 295. lnuestigation

70.6

o)

60

=

40

f

Eo

sodium chloride

20 0

0204060

80

100

temperature ('C)

Solubility curves (also see page 295)

Which solt is mosf soluble?

You con test the solubility of these solts : copper sulfote, sodium chloride, colcium chloride ond zinc sulfote. Design o foir test to see which of these solts is most soluble. Use 10 cm3 of woter for eoch test. Whot other voriobles must be kept constont for o foir test? o How con you tell when your solutions ore soturoted? o How will you meosure how much of eqch solt dissolves ? Your teocher will check your plon before you stort.

r

lnuestigation 10.7 Which factors affectthe solubility ot' copper sulfate? Your teqcher will check your plon before you stort. o Why is it difficult to collect precise ond occurote dotq?

/\

.opp", sutfate

131

>

Moking insoluble solts

The solts we hove mode so for ore oll soluble in woter, To get the solt, we crystollise it from its solution. However, some solts ore insoluble.

An exomple of o solt which does not dissolve well in woter is colcium sulfote. We con prepore on insoluble solt by o precipitotion

reoction. Do you know whot o precipitote is ? Sometimes, when we mix two solutions we get on insoluble solid formed. The solid is o precipitote.

Barium su/fate ls a salt which does nol dissolve well in water. /t is used in a'barium meal' which enables doctors to see your digestive sysrem using x-rays.

Look ot the cortoon below: It exploins whot hoppens in o precipitotion reoction

+ it antl D ltave:;waltlteri

1.r;rtlrrer;

i.ila,rirrlltr;r.r i r/i i

70.8

Making an insoluble salt by precipitation 1. Toke 5 cm3 of leod nitrqte solution in o test tube. Add 10 cm3 of sodium iodide solution. rr

Experiment

o whot hoppens? o Whqt is the precipitote cqlled ? o How cqn we seporote the precipitote

l\

lead

tl

nitrate

sodium iodide

lead salts

from the solution

?

2. Filter your mixfure.

The solid leod iodide is left on the filter poper. Rinse it with distilled woter. o Why must we rinse the leod iodide ?

lead iodide

3. Scrope the sqlt mode on to some fresh filter poper, Leove it to dry.

The leod nitrote ond sodium iodide reoct to moke o precipitote, leod iodide. leod nitrote

(oq)

+

sodium iodide (oq)

leod iodide

(s)

+

sodium nitrote (oq)

The leod iodide must be rinsed with woter- to wosh owoy ony soluble solts. 732

)

Precipitotion

In the lost experiment we mode on insoluble solt from two soluble solts. To help us choose which solts to mix, we need to know which solts dissolve in woter. Look ot the toble below:

AB(oq)

CD(oq) -----> AD(s) + CB(oq) A precipitotion reqction

+

Salt

Solubility

chlorides

soluble (except for lead chloride, silver chloride)

sulfates

soluble (except for barium sulfate, calcium sulfate, lead sullate)

nitrates

all soluble

Any solts of lithium, sodium or potossium ore olso soluble

o

Nome two solt solutions you could mix to moke

o

borium sulfote. Which ocid would you odd to borium nitrote solution to moke borium sulfote ?

mrx

c

o (U

-_ o_

'o

o

Look of the word equotion for the lost experiment. The bolonced equotion is: Pb(NOs)z(oq)

+

2Nol(oq)--------> Pblz(s)

+

o_

lead nitrate solution

2NoNOa(oq)

sodium iodide solution

We con olso show whot hoppens like this:

Pb2+(oq)

+ 2l

This is colled on

Na+ (aq)

and NOt(aq) are spectator

(oq)--------> Pblz(s)

ions

ionic equotion.

It shows us which ions stick together to form the solid in the precipitotion reoction. The sodium ions, No+(oq), ond the nitrote ions, NO3 (oq), stoy in the solution. They ore not chonged, so they don't oppeor in the ionic equotion. They ore colled spectotor ions.

precipitate of lead iodide A precipitation reaction

The centrifuge The solids in precipitotion reoctions ore formed os very smoll groins. The mixture is colled o suspension. A centrifuge is o mochine which spins test-tubes oround ot high speed. Whot do you think hoppens to the fine porticles of the precipitote ? Think obout whot hoppens to you

A centrifuge spins test tubes at high

on o ride thot spins oround quickly ot o foirground

speed

!

precipitate -qf

After centrifuging the so/id is packed at the bottom, The

solution above can be poured off (decanted). The precipitate is then washed and dried.

133

)

Chemistry of work: Sulfuric ocid, H2SO4 Uses of sulfuric ocid Sulfuric ocid is one of the most importont products of the chemicol industry.

Look ot its uses below: Which products mode from sulfuric ocid hove you used todoy ?

fertilisers

libres and

dyes paints and pigments chemicals and plastics

sulfuric acid tanning leather

4soo ACID conosNo

cleaning metals

soapless detergents (see page 179)

134

)

Chemistry of work : Sulfuric ocid, H2SO4 The Contoct process Sulfuric ocid is mode in the Contoct process The row moteriols ore sulfur, oir ond woter. Look ot the diogrom below: molten

stage

sullur

air

l

98% sulluric acid 2o/o

layers oI vanadium(V) oxide catalyst

+

soz(s)

1

waste gases

sulfur burner

450''c

sos(g)

stage 3

stage 2

*il0*,s4 Stoge

walet

99.5% sulfuric acid H2S04

1

Sulfur is burned to moke sulfur dioxide. We con import the sulfur on ships from Polond or the USA. It con olso be extrocted from impurities in crude oil or noturol gos. However North Seo gos contoins very little sulfur, so it con't be used. The sulfur burns in oir :

* oxygen - -----> sulfur dioxide + Oz(s) --------> SOz(g) S(l)

sulfur

Stoge 2 The sulfur dioxide is turned into

dioxide * 2SOz(g) +

sulfur

sulfur trioxide.

chimney fitted with basic 'scrubbers' to stop acidic gases escaping

Economic ond

o

The sulfur dioxide mode in Stoge supplied directly from thot contoin sulfides. So often mqke sulfuric ocid ot the

oxygen * sulfur trioxide 2SOs(g) Oz(g) +

Notice thot the reoction is reversible. You con reod more obout this type of reoction in Chopter 17. A cotolyst, vonodium(V) oxide, is used to speed up the reoction. Why do you think there ore 4 loyers of cotolyst ?

Stoge 3 In the finol stoge, sulfur trioxide is chonged into sulfuric ocid. The sulfur trioxide gets obsorbed into o mixture of 98 % sulfuric ocid ond27o woter.ln effect, the sulfur trioxide reocts with the woter:

ocid would be condensed qnd chemists found thot into o mixture of 987o

* woter --------> sulfuric ocid SOs(g) + H2O(l) ------> H2SO4(I)

sulfur trioxide

135

)

Chemistry ot work

:

Neutrolisotion

Acid soil If soil is too ocidic, most crops will not grow well. Formers con spreod powdered limestone (colcium corbonote) or sloked lime (colcium hydroxide) on the soil to roise its pH.

Experiment 70.9 Roising the pH of soil Add 50 cm3 of distilled woter to some ocidic soil. Stir it well, filter, then odd o few drops of universql indicotor. Add powdered limestone untilyou neutrolise the solution. o How con you see when you hove odded enough ?

Sodium hydrogencorbonote Boking powder helps coke-mix to rise. It contoins sodium hydrogencorbonote (known os bicorbonote of sodo) ond o weok ocid. When woter is odded the two reoct. The reoction is like on ocid plus o corbonote. Do you remember which gos is mode ? (See poge 729.)

ocid +

o hydrogencorbonote

Baking powder helps a cake rise to the occasion !

----> o sqlt + woter +

For exomple with hydrochloric ocid (but don't odd to your coke mix!)

HCI(oq)

+

NoHCOs(oq)

+

NoCl(oq)

+

H2O(l)

+

corbon dioxide :

COz(g)

The corbon dioxide gets tropped in the coke-mix. Self-roising flour hos boking powder olreody odded. The sodium hydrogencorbonote olso undergoes thermol decomposition in the hot oven:

2NoHCOs(s) 2No2CO3(s) + H2O(g) + CO2(g) This olso helps the coke to rise. - hydrogencorbonote in cleoning ogents qnd in some We olso use sodium toothpostes. It neutrolises ocidic solutions.

Tieoting stings Bee stings qre soid to be ocidic, olthough this is debotoble However, you con eqse the poin with bicorbonote of sodo (sodium hydrogencorbonote) - o weok olkoli. Wosp stings ore olkqline. You con neutrolise them

with vinegor (ethonoic ocid).

136

!

Summory Acids form solutions which:

o turn blue litmus red o hove o pH less thon 7 o reqct *ith on olkoli (or bose) to give o solt qnd woter - this is colled neutrolisotion o reoct with o cqrbonote to give o solt, wqter ond corbon dioxide o reoct with metols to give o solt ond hydrogen (the metol must be obove copper in the Reoctivity

Series)

Solts ore compounds mode when we reploce the hydrogen in on ocid by o metol. Hydrochloric ocid (HCl) mokes solts colled chlorides. Sulfuric ocid (HzSOa) gives sulfotes. Nitric ocid (HNO3) gives nitrotes. Exomples of soltJin-clude sodium chloride (NoCl), copper sulfote (CuSO+) ond silver nitrote (AgNOs)

)

3.

Questions

indicotor poper. He wrote down their pHs:

1. Copy ond complete

1,5,7 ,14

Acidic solutions turn blue litmus Their pH is olwoys . . .. thon 7. Here ore their common reoctions:

....

but forgot to write the nomes of the solutions. Con you help him by motching the pHs to the correct solutions ?

.

ocid ocid

f *

bose(orolkoli)------r-osolt * .... corbonote --------> o solt + woter

ocid

*

metol -------->osolt

+ .... .... + ....

When on ocid ond olkoli reoct to 'concel eoch other out', we coll it o . .. . reoction. A solt is mode when the . . . . in on ocid is

replocedbyq..... Salt

Acid hydrochloric acid

acid --> -----> _> nitric acid

2. Copv ond complete

Joe tested some solutions with universol

sulfates

these word equotions

Solution tested

pH

distilled water sulfuric acid sodium hydroxide vinegar

4. Morie ond

Sokib wont to moke some crystols of copper sulfote. They hove dilute sulfuric ocid ond block copper oxide powder. o) Describe how they con get copper sulfote crystols sofely. b) How con they tellwhen the sulfuric ocid hos been neutrolised ? c) Whot type of substonce is the block copper oxide powder - on olkoli or o bose ? d)Write o word equotion ond o symbol equotion for the reoction.

:

+ .... ocid ----> sodium chloride t woter .. + ..'. t sulfuricocid -------> .j .opp"r.... + hydrochloricocid ------> copper.... + woterf corbondioxide mognesiumsulfote * hydrogen d) .... t sulfuricocid .. + ... nitric ocid --------> e) sodium hydroxide -l ---->

o) sodium hydroxide

b)copperoxide

.

737

5. The toble below

shows the conditions some

plonts prefer: Plant

pH

apple potato

- 6.5 - 6.0 - 8.0 7.0 - 8.0 6.0 - 7.0 5.0 - 7.0 6.0 - 7.0

blackcurrant mint onion

strawberry lettuce

below.

It shows the solubility of potossium nitrote ot different temperotures. Temperature

5.0

('c)

4.5 6.0

o) Which plonts grow well over the lorgest range of pH vqlues ?

b)Which plont con grow in the most ocidic soil

8. Look ot the toble

?

c) Describe how you con test the pH of o soil.

d) How con you roise the pH of on ocidic

soil?

Solubility

(fl00g

of water)

20 40 60 80

110 169

100

246

32 64

o) Drow o solubility curve for potossium nitrote. (See poge 131.) b) Whot pottern con you see from your groph ? c) Whot is the solubility of potossium nitrote ot

i) 50 "c ii) 70 "c ? d) Whot does o 'soturoted solution' meon

?

e) How con you moke o soturoted solution of potossium nitrote ? No solid should be present.

6. Sulfuric ocid is mode in the Contoct

process. o) Whot ore the row moteriols for the process ? b) Drow o flow diogrom showing the steps in

moking sulfuric ocid. Include word equotions. c) Whot is the cotolyst used in the process ? d) In the lost step, why don't we dissolve the sulfur trioxide in woter ? e) Drow o spider diogrom showing the uses of sulfuric ocid. 7

. Liz wos investigoting which of four indigestion toblets wos most effective. She crushed eoch toblet ond odded it to 25 cm3 of woter ond on indicotor. Then she odded dilute hydrochloric ocid 1cm3 of o time, untilthe indicotor chonged colour. Here ore her results : .a

o) Put her results in o suitoble toble. b) Whot type of groph would you use to show Liz's results ? c) Which toblet wos the most effective ? d) How could she hove mode her results more relioble ?

138

9. o) Voni hos o solution which she thinks might be ocidic. Describe 3 tests she could do to see if it is ocidic or not. b) Exploin why woter is needed before o substonce con show its ocidic properties.

10. Here is o list of soluble solts: sodium nitrote - NoNO3 potossium chloride - KCI mognesium sulfote - MgSOa colcium chloride - CoCl2 leod nitrote - Pb(NO3)2 o) Choose o poir of solts you could mix to moke the insoluble solts: i) leod chloride ii) colcium sulfote. b) i) How would you collect opure somple of eoch solt mode in port o) ? ii) Write o word equotion for eoch reoction. iii) Write o symbol equotion for eoch reoction. Include stote symbols. iv) Write qn ionic equotion for eoch reoction.

I 1. Look through this chopter (ond others if you hove time) ond design o poster showing some uses of solts.

Further questions on poges 187 ond 188.

PRC/DUCIS FRc/II

)

chapter 77

Hydrocqrbons

Imogine you could vote in o'Molecule of the Century' competition. A vote for o hydrocorbon would stond o good chonce of winning ! So whot is o'hydrocorbon'? And why ore they so importont? As the nome suggests:

A hydroccbon is o compound contoining only hydrogen ond ccbon. One of the world's most importont row moteriols is crude Crude oil is o mixfure of mony hydrocorbons.

oil

The hydrocorbons in crude oil ore not only vitolfuels. They ore qlso the storting moteriols for mony new products, such os

We get petrol from crude oil

plostics.

The olkones There ore lots of different hydrocorbons in crude oil. Most of them ore colled olkones.

Nqturol gos, which is found with crude oil, is moinly methone. This is the smollest olkone, CHa. Irtly

The olkqne molecules hove o'bockbone' of corbon otoms. Their corbon otoms ore surrounded by hydrogen otoms.

+

Look ot the pictures of some olkones below

methane

Just light the gas And turn me higher ! :

+|" {+I-. +ffi{-" elhane

You con see the nomes ond formulos of the first few olkones in this toble. Notice thot olltheir nqmes end in -qne. Con you see o pottern in their formulos ? Con you work out the formulo of hexone Con you drow the structure of hexone ?

Name

Formula

methane ethane propane butane pentane

CH+

hexane ?

pentane

butane

Propane

Notice the bonds thot join the otoms together : Corbons hove 4 bonds. Hydrogens hqve 1 bond. (See poge 257.)

o o o

name is methane'

lf you want a fire,

CeHo CsHa

CaHro CsHrz

(D:

carbon

o

hydrogen

:

The generolformulo

of on olkone is: CnHz, * z where n con be ony number.

139

Most of our common fuels ore Con you nome ony ?

fossil fuels.

Cool, crude oil (which gives us petrol), ond noturol gos ore ollfossilfuels. Cool is the odd one out os it is not o hydrocorbon. It does contoin corbon ond hydrogen. However, there ore olso other ppes of otoms, such os oxygen, in some of its molecules. Fossil fuels hove token millions of yeors to form. Cool come from trees ond ferns thot died ond were buried beneoth swomps. Crude oilwos formed from tiny onimols ond plonts which lived in the seo. The plonts ond onimols got their energy from the Sun. So when you burn o fuelyou ore using energy thot storted off in the Sun ! the plankton in the sea which went on to make oil got their energy from the sun

Fern lossrh are found in coal

the trees that made the coal got their energy from the Sun (in photosynthesis)

oil rig

?:

Fossil fuels ore colled non-renewqble fuels. Thot's becouse once we use up our supplies on Eorth they willbe gone forever.

Scientists predict our supplies of crude oil could run out within your lifelime (in about 50 years time). Coal could last another 300 years.

The story of oil begins

dead sea creatures and plants collected on the sea bed

Crude oil wos mode from the bodies of tiny seo creotures ond plonts in plonkton thot died obout 150 million yeors ogo. These were buried under loyers of sond

ond silt on the seo bed. They did not decoy normolly os the bqcterio feeding on them hod little or no oxygen in these conditions. As the pressure ond temperoture slowly

increosed, they were chonged into oil.

Noturol gos is usuolly found with the crude oil.

140

new layers of sedimentary rock lormed on top of the original sea bed

oil started to form

Finding oil

When looking for oil you need a sign, Always look for an anti-cline !

Oil supplies ore scorce. Oil componies, like BP ond Shell, ore looking for new oilollthe time. So how do they find their oil?

signs ol oil

First of oll scientists look for clues on the Eorth's

surfoce. Look of the diogrom opposite:

"'xn'

Crude oil sooks into porous rock, just like woter sooking into o sponge. The oil rises towords the surfoce but is usuolly stopped before it gets there by o loyer of non-porous rock.

sensors to pick up echoes

The oil is usuolly found under o dome shoped loyer colled o cop rock or onti-cline. (See poge 316.)

Seismic survey If on oreo looks good, scientists con find the structure of the rocks underground. They do this

A seismic survey

by o seismic survey. Smoll explosions ore set off on the surfoce. These send out shock woves. The woves thot bounce bock from eoch loyer ore picked up by sensors. A computer helps to onolyse these echoes. It then drqws o mop of the rocks beneoth the surfqce. If the loyers ore like the ones shown obove, there might be oil. The scientists do not know for sure until they octuolly drill down. If rock contoining oil is found, more wells ore drilled. This helps the compony see if it is worthwhile going into full

production. A mistoke qt this stoge is very costly

!

An exploration rig

Tionsporting oil There ore two woys to move the oilfrom the

oilfield to the refinery: i) by pipeline or ii) by oil tonker. Pipelines ore often used when the oil is found reosonobly close to the refinery. For exomple, North Seo oil is piped to Aberdeen in Scotlond.

Giont ships colled oil tqnkers toke oil oll over the world. However, occidents con hoppen of seo ond the oil con be spilled. The effects on wildlife ore disostrous. (See poge 338.)

Oil tankers can be 400 m long. The crew sornetlmes use bicycles to get around the ship.

747

) Distilling crude oil At the refinery When crude oil reoches the refinery it is o thick block, smelly liquid. It is not much use to onyone. You leorned on poge 139 thot crude oil contoins o mixture of different hydrocorbons. At the refinery these ore sorted out into groups of usefulsubstonces colled frqctions. These froctions ore seporoted by

froctionol distillotion.

An oil refinery at night

We con distilcrude oilin the lob to help you understond whot hoppens in the refinery.

o

o

Demonstration 77.7 Distillation of crude oil The opporotus is set up os shown in q fume-cupboord.

Where do you think would be the best ploce to build on oilrefinery? Why? How could the refinery horm our environment?

/i\

crude oit

Heqt the crude oil gently ot first. Collect q few drops of the first liquid thqt collects. Keep heoting ond chonge the receiving tube. Now collect,the,liquid thqt distils up to 150 "C. Agoin chonge:lthe,tube ond collect the liquid when you heot strongly.

(which can to 35oC)

Pour eoch fiuctibn,collected onto q wotch gloss.

o

receurng

Note its colour qnd how thick it is.

Tiy to light eoch froction with o lighted splint.

o Whot hoppens? o Why is the receiving tube kept ih cold woter? o You need o fuel for o cor. Why would you use the first froction collected

?

'),,.

o Why would you use the lost froction to lubricote o cor engine

?

cold

crude soaked

water

into

eramic wool

t

heat

1st

lractions

Q. What do you call a hydrocarbon who tells rude jokes?

ilto epruc 'v

There was a young girl called Eve, Who boiled oil with a friend called Steve Small molecules flew

Up out from the brew As they were the firsl ones to leave.

142

Looking for potterns Fraction

Size of

Colour

How it burns

Thlckness

(vlscoslty)

molecules low boiling point (up to 80'C)

small

colourless

runny

lights easily (highly flammable), clean flame

medium boiling point

medium

yellow

thicker

harder to light, some smoke

large

dark orange

thick

difficult to light (not very flammable), smoky flame

(80-150'C) high boiling point

(viscous)

(above 150'C)

The froctions get less volotile (ore horder to evoporote) os the molecules in their compounds get lorger.

o Look down eoch column in the tqble

obove: Whot potterns con you see os the boiling point of the froction gets higher ?

Exploining the distillotion If you hove o plote of spoghetti, you find thot the short stronds ore eosier to pull out thon the longer ones. This helps to exploin the distillotion of crude oil, Insteod of spoghetti, think of molecules ! As the oil is heoted, the smollmolecules boiloff first. These gos molecules ore then

condensed (turned bock to liquid) in the cold receiving tube.

Smoll hydrocorbons hove lower boiling points thon lorge ones. They ore eosier to seporote from the mixture of molecules in crude oil.

The long pleces of spaghetti get tangled up. They are harder to separate out, iust like the long molecules in crude oil.

As you corry on heoting, the temperoture of the crude oilrises. The lorger molecules qre then

boiled off ond ore collected. Remember: small hydrocarbons boil

Smqll hydrocorbons hqve lower boiling points thon lorge

first

onea.

larger hydrocarbons have higher boiling points (their molecules tend to get tangled up and need more energy before they can escape)

The lorger the molecutes, the stronger the forces of ottroction between molecules.

heat

t43

)

Froctionol distillotion in industry

In on oilrefinery the crude oil is seporoted into its frqctions This hoppens in huge frqctionoting columns. Remember thot o froction is o group of hydrocorbons with similor boiling points. Just like distillotion in the lob, they use the different boiling points of the hydrocorbons to seporote them. But there is o difference. In Demonstrotion 11.1 we boiled off eoch froction in turn. In industry, they boil up ollthe froctions together. Then they condense them of difference temperotures of the some time. You con see this in the column shown below.

A froctionoting column 70'c

*

temperature

petroleum gases (such as propane and butane)

r+

petrol (gasoline)

*

kerosine (paraffin)

r) crude oil is heated and enters as a vapour

'"t::

:) temperature

diesel

:il

lubricating

rI)

heavy tuel oil

ffig Ilm*

-r

@

oil

large molecules . high boiling point . dark in colour . hard to light . viscous or thick (if still a liquid at room temperature - bitumen is a solid)

360'C

;:)

small molecules . low boiling point (volatile) . light in colour ' easy to light and burn well (flammable) . runny

bitumen

Explanation The crude oil is heoted up ond evoporotes. It enters the column os o vopour. The froctionoting column is hot ot the bottom ond cooler ot the top. This meons thot the lorger hydrocorbons, with the high boiling points, turn bqck to liquids neorer the bottom.

At the high temperotures there, the smoller hydrocorbons stoy os goses. They rise up the column. The different froctions now condenie ot different levels. At the top of the column there ore hydrocorbons with low boiling points. At 70'c these hove still not condensed, but come out of the top os goses. TM

petroleum gases petrol

kerosine

Cr-C+ C+- Ctz

fueloil

- Crs Crs - Crg Czo - Ceo Cso - C+o

bitumen

C56 and

diesel lubricating oil

Crr

above

+

small molecules (which include some hydrogen)

After distilling the crude oil, the oil componies find thot they hove too mony lorge hydrocorbons. We just don't need thot much of the heovy froctions Yet the smoller hydrocorbons, like petrol, ore in greot demond. So scientists hove found o woy to

+

large molecules

chonge the lorger, less useful molecules into smoller, more useful ones.

A cracker in an oil refinery

The reoction used is colled crocking.

+

The big molecules ore broken down by heating them os they poss over o cotolyst. A cotolyst helps to speed up o reoction. (See pose 212.) In the refinery this hoppens inside o crqcker

-..,>

It s a cracker !

Ac

c

Mo!(N5

ln '---> MoLicU!45

ouT

+

Q. What do you call two mad scienfists in an orl refinery?

isrs\cetc 'v

L)o ti yottrst:iiiri aa(ef

Experiment 17.2 Cracking In this experiment you cqn crock o lorge molecule (poroffin) into smqller ones.

paralftn soaked into

Set up your qpporotus os shown:

delivery ft You must take the end of theyou tA the water before stop heating. tube out of (You don't wont cold wqter to be sucked bock into your hot tube !) Stort by heoting the oluminium oxide skongly. Then just move the flome onto the poroffin every now ond ogoin. This is just to moke sure thot some vopour is possing olong the tube. (Don t collect the first few bubbles thot oppeor. This is hot oir inside the tube exponding.) Collect two test tubes of gos. The gos is ethene. Test the ethene with q lighted splint.

o

Whot hoppens

?

Test the other tube by odding q little bromine

wqter. Reploce the bung quickly ond shoke.

o

Whqt hoppens

?

wool

t heat

catalyst ol aluminium oxille (orporous pot)

ethene sas

o o o o o o

safety valve

o

A

o

ethene bromine water

Remember

Crocking is when we breok doum lorge hydrocorbons into smoller, more useful ones. This is done by possing the vopours over o hot cotolyst or mixing them with steom at very high temperotures. Crocking is on exomple of o thermol decomposition reoction.

t45

)

Ethene ond the olkenes

Name

Formula

ethene

CzH+

Picture of molecule

You hove seen how elhene con be formed in crocking. For exomple:

CrcHzz --------> CsHrs

decqne

+

octone

H

-H

CzHs

H

ethene

H

(used in petrol)

propene

Their nomes stqrt off like the olkones, but end in -ene insteod of -one. Remember the olkones hove only single bonds joining their otoms together. The olkenes hove ot leost one double bond between corbon otoms. (lf you wont to know more obout bonds, reod Chopter 20.) bond

H

H

I

I

c- C_ H

CgHo

I

Notice thot ethene is o hydrocorbon. Like the olkone fomily on poge 139, it contqins only hydrogen ond corbon otoms. However, they ore joined together differently. Ethene belongs to o fomily of hydrocorbons colled the olkenes. Look ot the toble:

H

H

butene

H

C+Ha

The table shows the first three members of the

alkenefamily. c Can you see a pattern in their formulas?

. . .

Can you guess the names and formulas of the next two alkenes ? (Look at the table of alkanes on page 139 for c/ues.) Can you draw a molecule of butene? Why is there no alkene with just one carbon atom ?

The generol formulo of on olkene contoining one corbon-corbon double bond is:

an ethene molecule

CnHzn

A double bond mokes o molecule reqctive. Ethene even reqcts with itself to moke poly(ethene). (See poges 153 ond 154 for detoils.)

Soturoted ond unsoturqted molecules Ethene qnd the other olkenes ore colled unsoturqted compounds. They hove one or more double bonds between cqrbon otoms in their molecules.

add unsaturated compound

+

shake

On the other hond, the olkones ore soid to be sqturoted. They contoin only single bonds. You con test to see if o compound is unsoturoted:

bromine

water

Unsoturoted compounds (contoining corbon-corbon double bonds) turn yellow bromine woter colourless.

bromine water turns

colourless if double bonds are present

When we crock lorge hydrocorbons, we get o mixture of smoller soturqted ond unsoturoted hydrocorbons. o Look ot the equotion ot the top of the poge: Lqbel eoch hydrocorbon os sqturoted or unsoturoted.

145

The test for an unsaturated compound For example C2H4

+ Br2 -------->

C2HaBr2

This is called an addition reaction

)

Combustion

As you know, the fuels we get from crude oil ore colled

hydrocorbons. Petrol is o mixture of hydrocorbons. Con you remember which 2 elements moke up o hydrocorbon ? Petrol contoins octone. Con you guess how mony corbon otoms there ore in octone

?

When we burn o fuel, the reoction is colled combustion. The fuelreocts with oxygen gos from the oir ond heot is given out. But whot is mode in the reoction ? You con find out in the next experiment:

Experiment 77.3 Products of combustian Set up the opporofus os shown Let it run until you see some chonges in the U-tube sand ond in the lit*ewqter.

Combustion is a useful reaction

+

to water pump (to arckthe

gases through the apparatus)

limewater

l3,llfl'f'n,,.*,

o o o o o

crushed ice and water

blue colbalt ctloride paper (whir$ tums pink in water)

Whot do you see inside the U-tube ? Whot hoppens to the limewoter? Which gos mokes limewoter go milky? Why should you repeot the experiment with just oir being sucked through ? Whqt is your conclusion ?

When hydrocorbons burn, they ore oxidised. We get corbon dioxide ond woter formed (never hydrogen

hydroccbon

* oryg€r

-------+. corbon dioxide

*

!)

wcter

Incomplete combustion There is only q smoll omount of oxygen inside o cor engine. There is not enough to turn qllthe corbon in the hydrocorbons into corbon dioxide. Some corbon monoxide, o toxic gos, is olso mode. Cotolytic converters on exhousts, once wormed up, con turn corbon monoxide into corbon dioxide. Sbmetimes fuels burn with o smoky flome. Incomplete combustion meons thot cqrbon itself is given off os soot. Porticles from diesel ore olso polluting the oir in our cities. Unburnt hydrocorbons in porticulotes con couse concer.

Carbon monoxide is given off from car exhausts. Ihis gas reacts with haemoglobin. /t stops your blood carrying oxygen around your body. This toxic gas can kill unsuspecting people when given off by faulty gas heaters.

747

)

Acid roin Burning fossil fuels couses ocld rofln.

Most fossilfuels contoin sulfur in compounds present os impurities. When we burn the fuel, the sulfur is oxidised. It turns into sulfur dioxide (SOz) gos. Power stotions burning cool or oil give off most sulfur dioxide. This is the moin couse of ocid roin. The gos dissolves in roinwoter, qnd reocts with oxygen in the oir, to form sulfuric ocid.

Coallired power statlons give off sulfur dioxide gas. Ihis causes acid rain.

Cors qlso moke our roin qcidic. Most petrol is sulfur-free now. However, cqr exhousts give off nitrogen oxides. In the high temperotures inside on engine, even unreoctive nitrogen gos will reoct with oxygen. The nitrogen oxides formed moke nikic ocid when it roins.

Experiment 71.4 Effect of sulfur dioxide on plants Set up the opporotus os shown: The sodium compound gives off sulfur which is toxic. sodium metabisullite Leove the seeds for o few doys. o Exploin why we need to ,"t ,p both tests. sulfur dioxide o Whot effect does sulfur dioxide hove on the growth of the seeds?

A

sodium metabisullate

crossi

seedB

added to

make sulfur dioxide

wool

Effects of ocid roin 1.

Forests - Trees ore domoged

2.

Ftsh

-

3. Buildings

-

ond even killed. Over holf the forests in Germony qre deod or dying. Hundreds of lokes in Norwoy ond Sweden now hove no fish left in them ot oll. Aluminium, which is normolly 'locked' in the soil, dissolves in ocid roin. It then gets woshed into the lqkes, where it poisons the fish. Acid roin ottocks buildings ond metolstrucfures. Limestone buildings ore most bodly offected.

Whot con be done

Acid rain damages buildings

?

We con burn less fossilfuels by using energy more efficiently. Or we could use olternqtive forms of energy. We qre now storting to remove sulfur from fossilfuels before we burn them. The sulfur con then be used to

mqke sulfuric

ocid.

(See poge 135.)

We con olso get rid of the ocidic goses before

they leove power stotions. A mixture of limestone ond woter neutrqlises ony oxides of nitrogen ond sulfur dioxide e.g. CoCO3(s) + SO2(oo) --------* CoSO3(s) + COz(s) 748

Nitrogen oxides are changed into harmless nitrogen gas by catalytic convefiers in car exhausts. The reaction is: 2CO(g) + 2NO(g)+ Nz,s.)+2Co2@)

)

Greenhouse effect :-

The Eorth's otmosphere octs like o greenhouse. It lets roys from the Sun through to worm the Eorth. But goses, such os corbon dioxide ond woter vopour, obsorb some of the heot woves given off os the Eorth cools down.

some heat escapes into space

Hzo

'co, the Sun heats up lhe Earth

o

We ore lucky to hove these noturol 'greenhouse goses'.

Without them, the Eorth would be obout 30'C colder How do you think thot would offect life on Eorth ?

greenhouse gases absorb heat

!

However, we ore moking more ond more of these goses. Whenever we burn o fossil fuelwe moke corbon dioxide. And we ore now burning up fossil fuels of on incredible rote. This disturbs the noturolbolonce of corbon dioxide. (See poge 304.)

Although plonts obsorb corbon dioxide, we ore cutting down huge oreqs of forest every doy. The trees ore often just burned to cleor lond for forming. This mokes even more corbon dioxide. More corbon dioxide, plus other 'greenhouse goses', such os methone from cottle, seem to be moking the Eorth hotter. We collthis globol worming.

o

Look ot the groph opposite: o Whot is the generol pottern ? But some scientists ore not sure if these chonges ore just port of the Eorth's noturol voriotions. However, if temperotures go on rising, it will offect the Eorth. Agoin, scientists disogree on the chonges ond how long they willtoke to hoppen.

ci E o

o O) c(! c

o) O) (U

Carbon dioxide and water vapour are the main 'greenhouse gases'. Methane from cattle and decomposing vegetation is another greenhouse gas.

0.6 U. 4

o.2 0

-o.2

6) (u

Ice cops ore melting. Wormer oceons could olso expond, cousing o rise in seo levels. The shope of the world mop would chonge qs low londs

4.4 -0.6 '1920 1930 '1940 1950 1960 1970 1980 1990 2000 2010 year

Changes from average temperatures, 192U2005.

flood. Climotes could chonge oround the world. However, scientists ore not sure exoctly how different ploces willbe offected. An experiment on o globol scole is not eosy to predict, even using the most powerful computer models.

Whot con be done

?

As with ocid roin, burning less fossilfuels will help. But cleqning the goses given off will not reduce the omount of corbon dioxide releosed into the oir.

However, nitrogen oxides, which ore olso 'greenhouse goses', con be removed from cor exhousts by cotolytic converters. (See poge 148.)

Like the g/ass in a greenhouse, the atmosphere lets light in but heat energy is trapped inside.

restore the Eorth's noturqlbolonce. (See Corbon Cycle,

However, sclenfists think that tiny solid particles in the atmosphere (from incomplete combustion of fuels) are also affecting climate. Ihese slop energy from the Sun reaching the Earth's surface causing a cooling effect. This is known

poge 304.)

as global dimming.

Plonting trees to reploce those cut down will help to

749

)

Chemistry ot urork: Nophtho A source of new moteriols You hove olreody seen some uses of the froctions we get from crude oil. (See poge 1214.) You con olso get o light froction colled nophtho. It is used to moke mony new products.

^ -{-lldrrrt

rubber

.h€+,-

fabrics and fibres

hthav

p/astics

crude oil vapo

u

chemicals for farming

r

so/venls medicines

So you see thot the moteriols we get from oil ore very importont. We qll use some of these products every doy of our lives. o Discuss the consequences for us when the world's supplies of

crude oilrun out.

150

detergents

Summory o o o

o

o o

Crude oil contoins o mixture of hydrocorbons. Hydrocqrbons ore compounds mode of hydrogen ond corbon only. Crude oil is seporoted into groups of useful substonces (froctions) by froctionol distillqtion. This works becouse different hydrocorbons hove different boiling points. The smoll hydrocorbons o hove lower boiling points, . ore lighter in colour, o ore eosier to light, burning with o cleqner flome, o ore thinner qnd more runny. The lorge molecules from crude oilcqn be broken down or crocked into smoller]more usefulmolecules. This is done of high temperofure, using o cotolyst. qnd woter formed. When o hydrocorbon burns in enough oxygen, we get corbon dioxide gos. The CO2 is o greenhouse If o hydrocorbon burns in o limited supply of oxygen, we olso get corbon monoxide gos. Tiny porticles of corbon ond unburnt ioxic hydrocorbons ore qlso releosed. These porticles con couse

)

globol dimming.

3.

Questions

1. Copy out ond complete

o) Copy ond complete this toble Alkane

:

o) A hydrocorbon is o compound contoining

methane

....

ond corbon otoms onlY. b) Crude oil is o . . . . of hydrocorbons. In on oil . . . . , the crude oil is seporoted into its froctionsby... . The heotedoil enters the froctionoting . . . . os o gos. The hydrocorbons hove different .. . . points ond condense of different temperotures. The smoller hydrocorbons, with the lower boiling points, ore collected neor the . . . . of the column. c) Lorge hydrocorbons con be crocked by heoting them with o . . . .'. The new molecules mode ore . ... ond more useful. d)When o hydrocorbon burns in plenty of oxygen, it gives cqrbon dioxide ond. . . This reoction is colled . . . . (or oxidotion). In o limited supply of oxygen, we olso get toxic corbon . . .. gos ond . . . .porticles. e) Burning fossil fuels couses . . . . roin becouse of . . . . dioxide gos given off from impurities. Scientists ore olso worried obout the lorge volumes of . . . . dioxide gos produced. This hos been linked to . . . ' worming coused by the . . . . effecf.

Structure of molecule

(CHr)

{+

{+t-

butane (C+Hro)

pentane (CsHrz)

"Hfi{+

.

b) Petrol contoins the olkone with 8 corbons. Con you guess its nome ? Drow o diogrom to show the structure of the molecule.

4.

2. Corlo distils

some crude oil. She collects 3 frqctions in different test tubes. But ot the end of her experiment, the tubes get mixed up. Give 3 woys thot Corlo could find out which order they were collected in.

Imogine you ore o smoll hydrocorbon molecule in crude oil. Describe whot hoppens to you from the time you ore discovered by on oil compony, to the time you end up heoting beons on o comping stove.

5.

Design o leoflet for your porents which exploins obout the greenhouse effect ond its possible consequences for our plonet. 151

6. Look ot the diogrom of o cotolytic converter below.

9. Zoro ond Lee wont to test the products formed when o hydrocorbon burns. They set up the experiment below:

*to water pump sand

tray limewater

tce

o) Exploin how o cotolytic converter helps to reduce ocid roin. b) Does o cotolytic converter help to reduce the greenhouse effect? Exploin your onswer. c) Exploin whot hoppens to the corbon monoxide ond nitrogen oxides in the cotolytic converter. Include o word ond symbolequotion.

7. o) Finish off this equotion :

HHHHHH

tttttt tttttt HHHHHH

10. o) Complete this generolformulo for the

H-C-C-C-C-C-C-H HHHH

tttt

olkones,

t

*?

Alkane methane ?

c) Whot ore the nomes of the 2 compounds mode in the reoction ? d)Whot must you do to moke this reoction hoppen ? e) Describe ond exploin o test ond its results to distinguish between the products formed in the reoction. fossil fuels.

o) Nome 3 fossilfuels. (See poge 140.) b)Which gos given off from power stotions con couse ocid roin ? c) Moke o list of the things we con do to reduce the problem of ocid roin.

152

lrlumber

ol

c8fhon atoms

b) Whot is this type of reoction colled

8. Mony power stotions burn

CnH,

b) Whot is the formulo of the olkone with 9 corbon otoms ? Look ot the boiling points in this toble

H-C-C-C-C-H

tttt HHHH

o) Why do they put ice oround the U-tube ? b) How con they test thot the liquid formed in the U-tube is woter ? c) The other product is corbon dioxide. Whot hoppens to the limewoter ? d)There is o smoll omount of corbon dioxide in the oir. How cqn they show thot the corbon dioxide they test for is not just the corbon dioxide in the oir ? e) Give the word ond symbol equotion for the complete cumbustion of methone, CHa.

ethane propane butane pentane hexane

1

2

3 4

Boiling polnt

fc) -

161

-88 -42 -0.5

5 6

69

c) Drow o groph of their boiling points (verticol oxis) ogoinst the number of corbon otoms (horizontol oxis). d)Whot is the generolpottern you see from your groph ? e) Use your groph to predict the boiling point of pentone.

Further questions on poges 188 ond 189.

chapter 72

>

Mqking plostics

Whenever oil componies crock lorge molecules into smoller ones, ethene is mode. Ethene is o very useful little molecule. It is the storting moteriol for mony plostics. Plostics were first mode on o lorge scole in the 1.930s. They ore now o very importont port of our modern world. Look of the picture of o toddler's bedroom from oround 1900. Nothing in it is mode from plostics

Polymers Plostics ore huge molecules. They ore usuolly long choins, mode from thousonds of otoms. These long

choin molecules ore colled polymers. (Poly meoningmany e.g. o polygon is o mony sided shope.) Polymers qre mode by joining together thousonds of smoll, reoctive molecules cqlled monomers. (Mono meoning one e.g. o monoroil is o roilwoy with only one trock.) It's o bit like stringing beods together to moke o neckloce. But using reol beods, your polymer neckloce would be obout holf o kilometre long

a

What things would be made from plastics nowadays?

beads

o o

necklace

U

O.^,+>

!

o

Lots of smoll, reoctive molecules colled monomers ioin together to moke o polymer.

oo

monomers

polymer

You con olso get the ideo by using shopes polymerisation +

+

+

+

etc.

+

monomers

polymer

The reoction is colled polymerisotion. The most common monomer is ethene. When it joins together in o long choin it mokes poly(ethene). We know it better os polythene

PREaTY PoLLY

lots of ethenes --------> poly(ethene)

monomers -------> polymer

Poiy parrot 2

153

)

Polymerisotion

I really teel I have to

You con now look of polymerisotion in more detoil. There ore two types of reoction to moke polymers. These ore oddition reoctions ond condensotion reoctions.

A life ol

cme just does

While yau are

lree

We're chained

up

1. Addition reqctions The diogrom of the shopes joining together on the previous poge is on exomple of oddition Here is onother with more detoil odded. addition

+> polymerisation

ethene

etc.

poly(ethene)

In oddition reoctions the monomers hove of leost one double bond between corbon otoms. The polymer is the only thing formed in the reoction. The reoction of ethene to moke poly(ethene) is the best known exomple, os shown obove. The reqction con toke ploce ot high pressure, using o cotolyst. It con be shown like this: n C2Ha -------->

where

{CzHq+"

n : olorgenumber.

Tltese supermarket trolleys make a polyner ! What are [he monamers in lhls

Look ot the diogrom below:

polymer?

What wotrld yau call the polymer 2 Poly(trolley) ?

The double bonds in ethene bpen up' ond neighbouring molecules join end to end.

ethene

t t etc

double bonds 'open up'

then molecules join together

etc. poly(ethene) An additrort reactron ?

154

say nat pay

a monamer a polymer.

Other oddition polymers Some of the hydrogen otoms in ethene con be swopped for different otoms. You con then get o new polymer with new proPerties:

rE+ (D

+>

n

Teflon (PTFE)

Teflon is the non-stick lining on pans

(D"

poly(tetraf luoroethene)

tetrafluoroethene

PVC

n n vinylchloride

->

poly(vinylchloride)

2. Condensotion reoctions This is the other type of polymerisotion. Nylon is on exomple of o polymer mode in o condensotion reoction.

Nylon is very strong

Experiment 12.7 Making nylon Put o thin loyer of monomer A into the bottom of o very smoll beoker. Corefully pour o loyer of monomer B on top of this. o Whot do you see hoppen ? Gently drow o threod out of the beoker using o poir of tweezets. Wind it oround o test-fube os shown [ ,onor",. Do not touch the nylon formed.

c

nylon

monomer B monomer A

I

You see fumes given off os the two different monomers reoct together. The fumes ore hydrogen chloride (HCl) gos. A smollmolecule is olwoys given off in q condensotion reoction.

A+B+APB+A n

The monomers hqve reoctive ports ot both ends of their molecules. They join together, end to end, to moke o long choin

il

,I

A corrdelsairo

reactive ends

+ ArB=A'E* t

q

reacltor't ?

MONOMERS +

condensation

etc.

+

+

A

B

t

+

reaction

A-B-A

POLYMER etc.

( + D * { * D:-small moleculesgiven

off

155

)

Properties of plostics

Why ore so mony things mode out of plostics ? They ore certoinly cheop to moke. However, lots of plostics do the job they ore designed for better thon troditionol moteriols.

r

Whot odvontoges do: o)PVC gutters hove over iron ones ? b)melomine kitchen work surfoces hove over wooden ones ? c)poly(propene) milk crotes hove over metol ones ?

The driver of this car escaped without serlous burns thanks to Kevlar. Racing drivers wear fireproolsuits made from this new polymer.

We con moke plostics thot do their jobs well in oll sorts of woys. For exomple, poly(styrene) is the plostic used to moke yoghurt pots. But if some gos is blown

into it during moulding you get 'exponded' poly(styrene) This is the plostic thot crumbles very eosily. It is used to hold hot drinks ond 'fost food'. The gos tropped inside mokes it on excellent heot insulotor.

o Whot ore the disodvontoges

of plostics in

house fires or in rubbish dumps

?

Structure of plostics Experiment 72.2 Heating plastics Heot o somple of o thermoplostic ond o thermoset on otin lid in oJume-cupboard. o Which melts more eosily? When the thermoplostic softens, use o gloss rod to drow out o threod- You ore remoulding your plostic.

o

Whot evenfuolly hoppens to your thermoset?

Thermoplootlcc soften ereily be remoulded into new shopes. sometlmes colled Ihermocets (or thermosetting ploetics) do not soften. If you heot them strongly

thermoplastic (or thermosoftening plastic)

A

thermoset

t

(or thermosetting plastic)

heat

toxic gases

relatively weak forces between the separate polymer chains

chains fixed together by strong bonds - this is called

Thermoplastic

Thermoset

cross-linking

enough, they eventuolly breoh down ond chor. They ce hord ond rtgid. These different properties con be exploined if you

look ot the orrongement of the polymer choins 156

:

)

Chonging the properties of plostics

On poge 155 you hove seen how using different monomers will produce o new polymer, with different properties. Thot's not surprising if you think obout the different shopes of the monomers

joining together. Some plostics ore mode of polymers with very stroight choins. Others hove polymers with lorge groups of otoms sticking out ot rondom. Stroight choins con pock together neotly. This is olso true of polymers with side-groups if the bits sticking out ore the some ond occur of regulor intervols down the 'spine' of the polymer chqin. Regulor pocking of polymer choins mokes o plostic denser thon those contoining polymers with rondom side-choins. Look ot the diogroms opposite: We con moke two forms of poly(ethene). Low density poly(ethene) is mode up of polymer choins with rondom side-bronches. But using ethene os the monomer with o speciol cotolyst odded in the reoction vessel, mqkes high density poly(ethene). The reoction tokes ploce ot lower pressure thon used to moke low density poly(ethene). o Why do the two types of poly(ethene) differ? o Which type of poly(ethene) will soften ot o lower temperoture? o Which type willbe stronger?

Low density poly(ethene)with its random branching on polymer chains

High density poly(ethene) with straightchain polymers

Mixing odditives with plostics As well os chonging monomers ond reoction conditions, we con olso odd things to modify the properties of plostics. There is o wide ronge of odditives to mix with q plostic.

Exomples include:

r .

o

Plosticisers - these moke o plostic eosier to mould ond more

flexible. Their molecules get in between the polymer molecules ond stop then lining up so neotly. Preservotives - these stop the plostic breoking down in horsh conditions or when it is being heoted os it forms. Some stop the plostic reocting with oxygen (ontioxidonts). Others stop sunlight offecting the plostic (UV stobilisers). Flome retordonts - these moke it more difficult to ignite o plostic ond more difficult for flomes to spreod.

Some substonces ore olso odded to moke plostics impoct resistont or horder weoring. For exomple, if you odd sulfur to rubber, it becomes much more duroble. Thot's becouse the sulfur forms cross-links between the rubber polymer choins. Look ot the diogrom opposite: By bonding neighbouring choins together, the rubber is now suitoble for moking pres. We soy thot the rubber hqs been

vulconised.

We can get doors and windows made from UPVC (unplasticrsed PVC). Yet cling film is

made from PVC with a plasticiser added.

sulfur 'bridges' between rubber polymers

Vulcanised rubber

r57

)

Developing new polymers

Chemists con often predict how to moke new polymers. They look ot reoctions thot moke similor polymers ond chonge things slightly. But sometimes whot they moke surprises them !

o. In1938 Dr Roy Plunkett wos reseorching

substonces to use in fridges to keep them cold. By occident, he found o woxy solid wos blocking one of his gos cylinders. This turned out to be

poly(tetrofluoroethene) or PTFE. (See poge 155.) The Americon compony he worked for morketed the new polymer os Teflon. This versotile polymer hos speciol 'non-stick' properties. It is olso very unreoctive. These hove led to o wide voriety of uses, including Goretex. (See below.)

b.

In the 1960s, the some Americon compony were trying to discover o new polymer to mqke lighter weight tyres. This would help sove fuel. Stephonie Kwolek ond her teom worked on the problem. One doy the chemicols she mixed formed o milky liquid, unlike the cleor liquid she wos expecting. But she didn't just throw the liquid owoy ond stort ogoin. She sent her discovery to the test lob. This stuff wos incredible It formed o plostic thot wos 9 times stronger thon o similor moss of steel. Yet it wos only holf the density of fibregloss. Eventuolly it wos morketed os Kevlor. Its strength, low density ond heot resistonce led to mony uses. These include bullet-proof vests, oeroplones, motorcycle 'leothers' ond tennis rockets omongst other things !

Kevlar has saved millions of lives

!

Rrd aont Com urrt l you

urocks!

c. In 1970, Spencer Silver wos trying to invent o super-strong glue. He did moke o glue. However, the glue he come up with wos even weoker thon existing glues. But ten yeors loter, the glue found world-wide fome os the sticky bond ot the top of Post-its. It is strong enough to stick to poper but weok enough not to domoge the poper when it is removed.

Goretex It is eosy to produce o cheop woterproof coot from o plostic like nylon. However, if you exercise in the coot you soon get uncomfortoble. Sweot condenses on the inside moking you wet onywoy !

raindrop- |

-fl water droplets can't get lhe Goretex are 2000

water can

the

Goretex is o moteriol thot solves this problem. It is mode of exponded PTFE. (See poge 155.) The PTFE polymer hos gos blown into it os it forms. This produces fine fibres with tiny gops between its stronds. Look ot the diogrom opposite:

The 'pores' ore 700 times the size of o woter molecule. So drops of woter con't get through, but woter vopour con. Thot's why Goretex is described os 'breqthoble'. You stoy dry inside your woterproof protection.

158

fabric layer of Goretex

skin

nylon mesh support

How Goretex works - it is waterproof but also 'breathable' (allowing water vapour to escape)

The breothoble polymer is sondwiched between o nylon mesh support ond on outer fobric. Not surprisingly, Goretex is used widely wherever people need to work hord but stoy protected ogoinst the weqther.

Medicol ond dentol opplicotions New polymers ore now being designed to improve our medicol core. Mony of these ore colled 'smort' moteriols. These con respond to chonges in their environment outomoticolly.

Goretex ls used throughout the worlds of sport, work and the

military

More ond more operqtions ore now done through 'key-hole' surgery. But imogine trying to stitch inside o potient through the smoll incision.

fibre tor stitches made of shape

Shope memory polymers ore now being developed thot con help. These con 'remember' their originol shope when heoted to o certoin temperoture. In this cose the originol shope of the fibre is the knot to be inserted in the stitch. Look ot the diogrom opposite: The threod is pulled through the wound. Then, os it worms up to body temperoture, it chonges bock to its knotted shope, opplying just the right pressure. The polymer is biodegrodoble so thot it just

memory polymers fibre knotted at

37'C cut

B

surgeon inserts straightened fibre at room temperature

dissolves ofter o few doys.

U

Hydrogels ore polymer choins with o few cross-linking units. This motrix con trop woter. (See Experiment\2.3, poge 160.)

Iibre warms up to body temperature (37'C) and takes up its knotted shape again

These hydrogels hove found use os wound dressings to ollow the

body to heol in moist, sterile conditions. They ore useful for treoting burns. The hydrogel con deliver teo tree oil os well os woter to treot the burn. The polymer con olso be used to grow new tissue on. The lotest 'soft' contoct lenses ore olso mode from hydrogels.

needle

>c

sides of cut

pulled together

Smart polymers help surgeons to stitch in awkward operations

To vory its properties, scientists con insert onywhere between 38% ond 80% woter in o hydrogel. Smort gels con shrink or swell up to 1000 times their volume due to chonges in pH or temperoture.

New polymers willeventuolly toke over from mercury omolgoms for filling teeth. Working with the toxic mercury every doy is o potentiol hozord to dentol workers. Other developments include new softer linings for dentures, os well os implonts thot con slowly releose drugs into o potient.

New so/f contact /enses use a silicone polymer to trap water in the structure

Active ond intelligent pockoging Active pockoging con chonge the conditions inside

o pock. Exomples include: o Ethene scovenging (to stop fruit ripening too quickly). . Oxygen scovenging (to stop oxidotion of o food). o Humidity control (to remove woter thot encouroges mould to grow). o Microbiolinhibitors (To stop bocterio, fungus ond mould growing). These con be included in sochets in the pock or built into the plostic pockoging. Intelligent pockoging con sense its environment (possibly using microelectronics) ond respond or poss on the informotion. For exomple, diognostic lobels will chonge colour when o food goes off. Thermochromic inks will olso chonge colour of pre-set temperotures.

Active and intelligent packaging is helping shoppers. Now we have the 'instant check-out'

159

Allplostics ore mode by smollmolecules (monomers) reocting together to moke very long molecules (polymers) The plostic is olwoys nomed ofter its monomer. You just put poly- in front of the monomer's nome. Look of these exomples: Monomer

Polymer

___l------->

ethene styrene vinyl chloride -------->

poly(ethene) poly(styrene) poly(vinyl chloride)

Special plastics have been injected into the timbers of the lrrlary Bose to preserve them. The ship sank rn 1545 and was raised to the surface in 1982.

As you con see, the nomes con get quite long ! So mony plostics ore known by their trode nomes. Well-known exomples ore Perspex, Teflon ond Kevlor (Nylon gets its nome from two fomous cities. Con you guess which ones ?)

Here ore some common plostics ond their uses:

Rt]

ffi tr

s ffi

fl

*r W #ffi poly(ethene)

nylon

poly(styrene)

melamine

C'

poly(vinyl chloride)

o

PVC

poly(propene)

o

t

t

Which of these plostics ore thermosetting plostics ? You know thot the world's crude oil will probobly run out within your life-time. Look of ollthe uses of moteriols we get from oil: . How would your life chonge without plostics ?

o

B phenolic resins

72.3

Slimy polymer from PVA - poly(ethenol) Gently heot 100 cm3 of woter in o beoker. Do not boil. Slowly odd 4g of PVA glue to the wqter while stirring. When oll the PVA hqs dissolved, stop heoting. Then odd o few drops of borsx solution ond stir. You moy odd o food colouring if you wish. Different groups cqn odd different omounts of borox. Leove to dry. Experiment

.

3

160

How does the omount of borox offect the polymer mode Trg to think of o use for your polymer.

?

.

Lookbqckotpoge 159: Whot type of polymer is slime

?

)

Plostic woste

Do you ever think obout how much plostic you throw owoy os woste ? Whenever you go shopping you notice how much pockoging is used on everything from foods to clothes. Plostics hove token the ploce of mony troditionol moteriols becouse they lost o long time. They don't rot. However, this becomes o disodvontoge when it comes to getting rid of the plostic. Most of our rubbish ends up in lond-fillsites. These ore huge holes in the ground thot ore covered with soil once the site is full. Plostics toke up much of the spoce ovoiloble, ond mony types toke q very long time to rot owoy. But we ore running out of ploces to dump our rubbish. So scientists ore trying to help reduce the problems we hove disposing of plostics. We need to moke sure thot new developments in plostics ore sustoinoble. Our environment must be protected.

Recycling On poge 156 we looked ot the two types of plostics thermoplostics ond thermosetting plostics.

-

We con melt thermoplostics ond remould them into new shopes. This meons thot we con recycle mony of the plostics we use. But we do need to sort them into their different types. Look qt the symbols opposite: Objects with these signs on them should be recycled. Do you recycle plostics ? Do you hove o recycling point neor your home ? Some ploces hove different bins for different types of rubbish. Whot do you think of thot ideo?

Space rn landJill sltes

.

Discuss the issues involved for o locol council plonning to build

on incinerotor of o woste tip.

running out

A A A A A A A

PET (polyethene terephthalate)

HD PE (high density poly(ethene))

PVC

LD PE

PP

PS

Others

Recycling symbols for plastics. o Whatdo LDPE, PVC, PP andPS stand for?

Burning plostics Burning plostics will reduce the volume of woste. However, mony plostics produce toxic goses os they burn. We need very high temperotures in incinerotors to breok down some of the polluting goses. Others need to be removed in chimneys fitted with 'scrubbers'. These contoin o bosic moteriol, such os colcium corbonote, which removes ony ocidic goses like sulfur dioxide. If the plostic burnt contqins chlorine, then poisonous hydrogen chloride gos is given off. Hydrogen cyonide is produced when plostics contoining nitrogen burn in o limited supply of oxygen.

r,s

75 000

P o)

50 000

c o o

-Y

25 000

1

kgof 1 kgof 1 kgof

coal oil

plastics

Energy available from different fuels. Switzerland burns most olits waste

to ge ne rate electricity.

161

)

Chemistry ot work: Getting rid of plostic woste Degrodoble plostics More ond more plostics ore now designed so thot they do not lost forever. They rot owoy, or degrode, noturolly. Normolly o thermoplostic willbreok down over mony yeors ond eventuolly decompose. Now chemists hove worked out vorious woys to help plostics breok down more quickly.

... by lisht Chemists con design polymer choins thot contoin certqin groups of otoms thot obsorb light energy. This energy splits the choin ot those groups. The plostic breoks down into smollbits which rot owoy more quickly. This is used in the plostic mesh used to hold some types of beer cons to eoch other.

,l/?

'ru-

, " +.to

i

: -)

4,

A degradable plastic

... by bocterio New plostics hove been mode by bocterio. The bocterio ore grown ond they produce gronules of o plostic. The new plostic is totolly biodegrodoble. It breoks down in noture completely in obout 9 months. One problem is thot the new plostic costs obout 15 times qs much qs normolplostics. o Would you poy more to be environmentolly friendly ? Scientists in the USA hove used genetic engineering to grow plonts which moke the new plostic themselves. But the yield of plostic from crops, such os pototo, is

A biodegradable plastic at

stilllow.

o Whot do you think of reseorch

in this oreo?

different stages in its breakdown

Other plostics hove been developed thot hove cornstorch built into their structures. The microbes thot decompose rubbish in lond-fill sites feed on the storch ond breok down the plostic. It is then eosier ond quicker for microbes to work on the bits of plostic rother thon lorge chunks.

... by woter Do plostics usuolly dissolve in woter ? Mony of their uses depend on their woter-resistonce. o Think of some of these uses. But now o new plostic hos been designed thot is soluble in woter. By chonging the reocting mixture, you con get plostics thot dissolve of different temperotures. . Tiy to think of some uses for o soluble plostic.

762

Ihese p/astlc bags in hospital dlsso/ve in the hot water in a washing machine. . Why are they used ?

Summory o o o

o

e

o o Smqll, reoctive molecules, colled monomers, con join together to o moke very lorge molecules colled polymers. The reoction is colled polymerisotion. The type of polymer we get depends on: o -the monomer(s) o -the conditions of the reoction monomers - odditives used. New polymers ore stillbeing developed, for exomple smort polymers These con respond to chonges in their environment. Degrodoble plostics con help us reduce the problems of plostic woste.

o

oo

rr+> polymer

4. Look ot this key to identify plostics 1. Copy ond complete Obiect

Does it bend easily?

this toble

Traditional material

a) drain pipe

tron

b) disposable

paper

Plastic used

cup

c) blouse

YES

NO

does it lloat in water?

does it float in water?

YES

NO

low density poly(ethene)

PVC

YES

high density poly(ethene)

cotton

d) disposable

NO

does it go soft when you heat it?

poly(ethene)

bag

Whot ore the odvontoges of the plostic in eoch exomple ?

2.

o) Whot hoppens in o polymerisotion reoction ? Use the words monomers ond polymer in your onswer. Include equotions if possible to help exploin. b)Whot ore the monomers colled thot moke:

i) poly(styrene)? ii) poly(propene)?

3.

o) How con you tellthe difference between o

thermoplostic ond o thermoset

?

b) How do their structures help to exploin these differences

?

c) Whot ore the most importont properties for the plostics used to moke: i) o light switch ? ii) ofizzy drinks bottle ? iii) o poir of sondols for the beoch ? iv) o wind shield for o motor-bike ? d) Corry out some reseorch to find the uses ond properties of Lycro ond Thinsulote.

YES

does it burn with a sooty flame?

NO

phenolic YES

NO

poly(styrene)

acrylic

o) Which plostic bends eosily ond sinks in

woter ? b) Which plostic does nof bend eosily, floot in woter or go soft when you heot it ? c) Use the key to soy os much os you con obout ocrylic. d)Notice thot in the key, it soys thot poly(styrene) does not floot. However, it con be chonged in its monufocture into o

form which does floot. i) Whot is this type of poly(styrene) colled ii) How is it mode ? iii) Whot ore its useful properties ? iv) Whot is it used for ? Further questions on poge 190.

?

163

I

I

cI

cI

chapter 73

ffi

I

tt In Chopter 11 we looked qt crude oil ond hydrocorbons. Con you remember the nomes of two fomilies of hydrocorbons ? The olkones ore soturoted hydrocorbons. They hove o corbon 'skeleton' or 'bock-bone', surrounded by hydrogen otoms. These compounds, bosed on corbon ond its obility to form 4 bonds, ore colled orgonic compounds. By replocing hydrogen otoms, we get lots of different orgonic compounds. Orgonic compounds ore very importont becouse they moke up oll living things. The olkones, ond the olkenes, ore exomples of homologous series. Members of the sqme series, or fomily, hqve similor chemicol properties. They reoct in o similor woy.

)

Organic compounds form the basis o/ all living things

Alcohols

If you reploce o hydrogen otom in on olkone by on -OH group, you get on olcohol.

HH

tt

H-C-C-O- H

tl

H H

ethanol is an alcohol (its structure can be shown as C2HsOH or CH,CH,OH)

The olcohols ore onother homologous series. The olcoholshown obove is the compound most of us think of when we use the word 'olcohol' in everydoy life. Ethonol is the qlcoholthot we find in beer, wine qnd spirits. Con you see how we nome on olcohol ? The number of corbons gives us the stem from the motching olkone Then the -e ot the end of the olkone is reploced by -ol.

You have probably heard of cholesterol. lt is an alcohol and an essenfr,a/ steroid in our diet, but too

much can 'fur up'your arteries and cause heart disease.

Look ot the first five members of the olcoholfomily:

HHH

H H

-O-H

H

H

I

ttt

I

butanol, C4HeOH

propanol, CaHTOH

ethanol, C2H50H

HHH

H-C -C-C-C-O-H ltl H HHH 1@

ttt

HHH

H

methanol, CH3OH

H

-o-H

ltt H- C-C-C -o-H HH

H

HH C-C

tt II -C-C tt tt HH HH

-o-H

pentanol, CsHTOH

Physicol properties of olcohols The -OH group increoses the boiling points of the qlcohols compored to the olkqnes with the some number of corbon otoms. Look ot the groph opposite:

100

alcohols

O

The -OH groups olso meons thqt the smoller olcohols ore soluble in woter, unlike hydrocorbons. They form neutrol solutions.

alkanes

c 0

o-

2

3

4

5

number of carbon atoms

o

_o

)

Isomers

Look ot the five olcohols ot the bottom of the previous poge:

-

100

The -OH group is ot the end of eoch molecule. Would we hqve the some molecule if the -OH group wos positioned somewhere else on the corbon choin ? Look ot proponol below H

HH

tl

: :

alcohols alkanes

I

HOH

H

H- C-C -c-

ll HH

key

I I

I

o-H

I

H

propan-1-ol

ttl H- C-C-C ttt HHH

-H

Propan-2-ol

Count the corbon, hydrogen ond oxygen otoms in eoch molecule Whot do you find? The two molecules obove ore colled isomers.

Isomers hove the some formulo, but their otoms ore orr(mged differently. These isomers of proponol ore both olcohols, but their physicol properties ore different. Look ot the toble opposite: Notice the woy the nome of eoch isomer tells you lsomer where the -OH group is on the corbon choin. propan-1 -ol The numbering olwoys storts of the end neorest the -OH group. propan-2-ol Why ore there only two olcohol isomers of proponol? Con you see thot it doesn't motter if the -OH group is on the first or the lost corbon ? It's the some molecule flipped over ! (Moke o 'boll ond stick' model to convince yourself !)

o o

Boiling polnt ('C) 97.5

82.5

How mony different positions con the -OH group occupy in butonol? Drow on isomer of butonolwith o bronched corbon choin. 165

)

Fermentotion

People hove used enzymes to moke new products for thousonds of yeors. Alcoholic drinks ond breod ore both mode using the enzymes in yeost.

Moking olcohol (ethonol) Yeost is o type of fungus. Like oll living things, it contoins enzymes. Yeost feeds on sugors, in the obsence of oxygen, turning them into olcohol.

The reoction is colled fermentotion. You con ferment o sugor (glucose) in the next experiment

Experiment 73.7 Fermentation Set up the opporofus qs shown: Put it somewhere worm. (Neor o rodiotor is o good Leove it for 10 minutes to stort o Whot hoppens inside the flosk? You con now leove your experiment until the next lesson. o Whot hos hoppened to the limewqter? o Which gos is given off during fermentotion ?

glucose solution and

The enzymes in yeost breok down the sugor, glucose, into ethonol (which we know os olcohol). Corbon dioxide is olso given off

:

glucose fermentotion ethonol (sugor) -.-------------(olcohol) C6H12O6

#trY

*

2C2HsoH

corbon dioxide

+

2Co2

The qmount of ethonol in the fermenting mixture connot rise obove obout 15 %. At this level, the ethonolpoisons the yeost. We hove to disfil the mixture to get purer ethonol

Froctionol distillotion will seporote the ethonol off. You con use the method on poge 175, but you will need o froctionoting column ottoched to the flosk used in simple distillotion.

766

lvlany people brew their own wine or beer. The air-lock at the top of the flask /ets CO2 gas

escape, but won't let bacteria or oxygen from the air in. Why is this impoftant?

There was an unfortunate beast. Who fermented some sugar with yeast When he swallowed the brew His stomach, it grew 'Til BANG ! CO2was released.

Moking breod Hove you ever wondered how the tiny holes get inside breod ? By 4000 BC, the Egyptions hod found out thot yeost mokes breod rise. The yeost feeds on sugor, os in brewing. Which gos is given off in fermentotion ? The corbon dioxide gos gets tropped in the dough This mokes the breod rise.

Look ot this recipe for moking breod

Can you see the holes where carbon dioxide gas was trapped in the

Home-made bread 1. Mix dried yeast with some sugar in warm water' 2. When it has a froth, add it to flour with a little salt. 3. Mix and knead the dough.

dough ?

4. Leave the mixture in a warm place for at least an hour The dough should rise to about twice its volume. 5. Bake in a hot oven at 200'C.

o Why must you odd sugor to the yeost in step 1? o Whot couses the froth in step 2? o Why do you leove the mixture in o worm ploce o

for of leost on hour before it goes into the hot oven ? (Think obout the effect of temperoture on enzymes.) Whot do you think hoppens to the size of. the gos bubbles in the breod os it is bqked ? (Think obout the effect of temperoture on goses.)

Expe.yjirnent

This baker is kneading dough. lt is then left to rise, before being baked.

1.3'.2' Rising dough !

Put 20g of flour in o beoker. Add 1g of sugor. Slowly pour in 25 cms of yeost solution, stirring os you odd it. You should get o smooth poste. Pour the poste into o lorge meosuring cylinder, without letting it touch the sides.

mixture of flour, sugar and yeast

--=-

your mixfure every 2 minutes. minutes. Time (mins)

Volume of mixture (cm3)

your results qs o line groph. (Put volume of mixture"up the side ond time olong the bottom.) o Exploin the pottern you see in your grqph

o

Comment on the reliobility of your doto.

167

)

Which method to moke ethonol

?

Do you know onyone who likes home brewing? You con buy kits to help you moke your own beer or wine. The kits hove brewers yeost in them. Yeost is o type of fungus You mix this with woter, sugor ond ony flovourings you like. The ethonol, which mokes o drink olcoholic, is mode when the yeost feeds on sugor, in the obsence of oxygen.

A chemicql reoction tokes ploce with enzymes in yeost. Glucose (o type of sugor) is broken down to ethonol. We collthe reoction fermentotion. (See poge 166.) Look of the equotion below: yeost C6H12O6(oq) 2C2HbOH(oq) + 2COzk) glucose ethonol corbon dioxide

-

The alcoholic solution is syphoned off before bottling beer or wine

Fermentotion of glucose

Ethonolcon olso be mode in industry from ethene. In Chopter 11 we sow how ethene is mode when we crock lorge hydrocqrbons found in crude oil. (See poge L4S.) Look of the reoction below: CzH+(g)

+

ethene

phosphoric ocid cotolyst

HzO(g) steom

C2H5OH(g) high pressure

ethonol

Hydrotion of ethene

Moking ethonolfrom ethene relies on crude oilsupplies. As you know, crude oil is q fossil fuel thot is running out. However, while supplies lost, we mqke our 'lower grode' ethonol from ethene. The process con be run continuously. Although the reoction is reversible, unreocted ethene is recycled bock into the reoction vessel. The reverse reoction is colled dehydrotion (i.e. removol of H2O): dehydrotion

C2H5OH(g)

czH+(g)

+

HzO(g)

Fermentotion is olwoys used to moke the ethonolin olcoholic drinks In countries, like Brozil, with no noturol oil supplies of their own, ethqnol is monufoctured on o lorge scole by fermentotion. They hove o climote thqt is ideql for growing sugor cone. So olthough the fermentotion process is o slow reoction, it is the cheopest woy for them to mqke ethonol used os o fuel. The ethonol hos to be mode in bqtches ond left to ferment. The ethonol is distilled off, then used to run some Brozilion cors. This helps preserve fossil fuel supplies, os petrol ond ethene come from crude oil. It olso reduces corbon dioxide releosed into the otmosphere. o Why should we wont to reduce CO2 emissions ? (See poge 749.) Ethonol does give off corbon dioxide when it burns, but the sugor cone removes CO2 gos os it grows ! (Remember photosynthesis ! ) 168

Sugar cane grows well in Brazil but needs large areas of fertile land. Why is this causrng concern in the Amazon rainforest?

.

Cars in Brazil can be adapted to run on ethanol or a mixture of petrol and ethanol (called' gasohol'). Ethanol produces about 70Y" of the energy released by the same volume of petrol.

)

Chemistry of work : Uses of ethonol Hove you ever looked ot the lobel on an alcoholic drink? Spirits, such qs gin or vodko, ore mode up of between 35% ond 407o ethonol. You used to get on ideo of the strength of o drink from its 'proof' volue. The word 'proof is used from olden doys when tolls hod to be poid on olcoholic drinks. The 'proof' or test of whether or not the duty wos poid used gunpowder. If gunpowder sooked in the drink still ignited when lit, this wos 'proof' thot the drink wos olcoholic ! The copper vessels shown opposite ore used to distil olcoholwhen moking whisky. This is needed to increose the concentrotion of ethonol. The yeost in the initiolbrew will not survive beyond obout o75% solution of ethonol. The whisky con be stored for yeors in ook borrels which help give it its chorocteristic flovour.

Less lhan half of the volume of this whisky is ethanol

Pure ethonol is poisonous. Do you know which orgon of the body removes hormful ethonol from your blood ? Too much olcoholover time will domoge your liver ond 'binge' drinking cqn leqd to olcoholic poisoning.

Alcohol is o legolised drug. It modifies the woy your body functions. A little con help people relox ond relieve stress. Excess dulls the senses ond your reoctions slow down. This is why it is so dongerous to drink ond drive. Alcoholics ore oddicted to ethonol. This oddiction leods some people to drink meths. This is much cheoper thon on olcoholic drink becouse there is no tox to poy on it. However, it hos o purple dye odded, os well os methonol. Methonol is more toxic thon ethonol. It is meont to stop people drinking meths. Meths drinkers ore often the poorest members of society whose oddiction con quickly leod to blindness, liver foilure qnd deoth.

Alcohol abuse can lead to addiction, liver failure and anti-social behaviour

Used properly, meths (or methyloted spirits) is o useful solvent. Hove you seen ony methyloted spirits in your home ? Whot is it used for? Ethonol is used os o solvent in the perfume industry.

r

It con olso be used os o/uel in spirit burners (or mixed with petrol in some Brozilion cors - see previous poge). Ethonolburns with o 'cleon', blue flqme. You con see the equotion on the next poge.

769

)

Reoctions of olcohols

Combustion Alcohols ore flommoble. They burn to produce cqrbon dioxide ond woter. You con use the opporotus on poge 147 to test for these products.

Experiment 13.3 Combustion of ethanol Set up the opporotus os in the diogrom on poge L47 with ethonol in the spirit burner. . How con you test for cqrbon dioxide ? . How con you test thot woter is formed? o Is the flome cleon or sooty ? . Write o word equotion for the reoction.

A

ethanol

,r r3 Ethanol burning

The equotion for the complete combustion of ethonol is shown below

c2HsoH(l) +3oz(g) --------> 2cozk) +3Hzo(g) It burns with o 'cleon' blue flome. Alcohols ore sometimes odded to petrolto moke it eosier to ignite.

Adding sodium Demonstration 1.3.4 Sodium and ethanol Wotch your teocher qdd q smoll piece of sodium metol to some ethonol on o dish.

o Whot do you see hoppen ? o Is this o more vigorous reoction

A

sodium ethanol

thqn when sodium

reqcts with wqter ? Sodium reacting with ethanol

The gas glven off ls hydrogen.

Oxidotion Do you know whot hoppens to the toste of beer or wine if you leove it open overnight ? Which gos in the oir do you think might reoct with the ethonol in the drink? The sour, shorp toste results from o reoction with oxygen coused by microbes in the oir. Thot's why you need on oir-lock if you brew your own beer or wine. The oir-lock lets the bubbles of CO2 escope, but stops microbes ond oxygen from the oir entering the jor. Con you remember which type of substonces moke things toste sour or shorp ? (See poge 124.) The ethonol hos been oxidised to form ethonoic qcid. Where hove you met this ocid before

oxidised

ethonol

----------->'

ethonoic ocid

?

Can you see how these air-locks keep air out from the fermenting mixture,

but let CO2escape?

770

)

Corboxylic ocids

H

H-C

Ethonoic ocid is the moin ocid in vinegor. It is olso used to monufocture the fobric colled royon. Look of its structure opposite: Con you see how it differs from ethonol? And why we soy thot ethonol hos been oxidised ? Ethonoic ocid is one of the homologous series of corboxylic ocids. Look of two other corboxylic ocids opposite: Other corboxylic ocids include citric ocid, found in oronges, lemons ond limes. These citrus fruits ore olso good sources of vitomin C. This is onother corboxylic ocid cqlled oscorbic ocid.

I

I

ethanoic acid

_H

(cH3cooH)

H

HH

tl H-C-C-

HH methanoic acid (HCOOH)

tl

HH

H

propanoic acid

(crH5cooH)

Aspirin is a carboxylic acid used to relieve pain and reduce risk of heart attacks.

The corboxylic ocids ore weok ocids, but do show the typicol reoctions of ocids.

(See page 330.)

Experiment 73.5 Reactions of carboxylic acids 1. Add o piece of mognesium ribbon to 5 cm3 of ethqnoic ocid solution. Test the gos given off with o lighted splint. 2. Add o spofulo of sodium corbonote to 5 cm3 of ethonoic ocid solution. Test the gos with limewqter. (We use this os the test for corboxylic ocids.) 3. Repeot test 2 with sodium hydrogencorbonote. As with other ocids, corbon dioxide is given off in reoctions with corbonotes

ond hydrogencqrbonotes. A solt ond woter is olso formed. With mognesium, o solt is mode ond hydrogen gos is given off.

Esterificotion Demonstration 13.6 Alcohol plus corboxylic acid Add 2 cm3 of ethqnol to 1 cms of concentroted ethonoic ocid in o test tube. Add 3 drops of concenkoted sulfuric ocid to oct os o cotolyst (to speed up this reversible reqction). Worm the reoction mixture gently in q hot woter both for 5 minutes. Pour the reqction mixture into q smqll beoker contoining sodium hydrogencorbonote solution, qnd stir well. This gets rid of excess ocid. . How do the products smell compored to the reoctonts ? The new products include on ester. In this cose the ester is colled ethyl ethonoote:

i ethonol *

cH3cooH+c2H5oH

ethylethonoote

*

concentrated acid ethanol

In generolwe con soy eulfuric ocld

qlcohol * ccboxylic ocid * ester * wqter

sulfuric ocid

ethonoic ocid

A

woter

+ cH3cooc2H5 +H2o

177

)

Chemistry of work : Uses of esters Food flovourings Hove you ever eoten sweets colled peor drops? If you hove, you will know the fruity smell of esters. The smoller esters qre oolatile. They evoporote eosily. Fruits, such os pineopple, peor, bonono ond strowberry, owe their smell ond toste to complex mixtures

thot contqin mony esters. Scientists con imitote the smells using simpler mixtures of esters. It would cost too much to try to motch

the exoct mixtures we find in noture. The esters ore then used os qrtificiolflovourings in foods

Perfumes You won't be surprised thot we olso find the sweet-smelling esters in perfumes. Cosmetic chemists creote new scents by blending esters olong with other ingredients. They ore mode to stimulote the sense cells in your nose.

Many drinks haye esters

added for flavour. Plastic drinks bottles can be made of polyesfer. Ihese can be recycled and made into new products.

The chemists hove to design o mixfure thot not only smells greot, but olso hos the right volotility. If the perfume evoporotes off too quickly, the smell will not lost long enough If it isn't very volotile, the smell will not be strong enough. So they foce o tricky boloncing oct to find the right mixture. The cosmetic chemist must olso moke sure the perfume: . is non-toxic (you don t wqnt to be poisoned!) P e rf u m e contains eslers o does not reoct with woter (otherwise it would There was a young compound named Ester chonge when you sweot) Who molecules would frequently pester . does not irritote your skin (you must be oble Asked "What's the attractton?" to opply it directly on to your skin without horm) They replied in a fraction . is insoluble in woter (so it is not wqshed off too "She sme//s sweef like a good perfume tester !" eosily).

Solvents Do you remember the smell of ethyl ethonoote from poge 171? You might hove recognised it from the smell of some glues. The ester is used os o solvent to dissolve o plostic in the glue. When the glue is opplied, the ester evoporotes off, ond leoves the solid plostic behind to stick objects together. This ester is olso found in noilvornish removers. The ester molecules ore strongly ottrqcted to noilvornish molecules, unlike woter molecules. So they oct os o solvent ond dissolve the noilvornish.

172

You might see 'ethyl acetate' written on the contents of nail varnish remover. This

is the old name for ethyl ethanoate.

Summory o Ethonol (C2HsOH) is o member

o o

.

)

of the olcohol fomily. It is mode by fermentotion of sugor using yeost in the brewing industry. Industriqlethonolis mode by possing ethene gos ond steom over o hot cotolyst (phosphoric ocid) ot high pressures. Ethonol is oxidised to form ethonoic ocid. Ethonoic ocid is o corboxylic ocid. These ore weqk ocids, ond show the typicol reoctions of ocids. (See poge 226.) An olcohol qnd o corboxylic ocid reoct together to form on ester Woter is olso formed in this reversible reoction. A cotolyst of concentroted sulfuric qcid is needed to speed up the reoction. Esters qre used os perfumes, food flovourings qnd solvents.

Questions

industriol process. If you leove on olcoholic drink in the oir too long, it tostes This is becouse hos formed in on .............. ocid reoction.

reoctions of both the olcohols ond corboxylic ocids in this chopter.

4.

5.

sweet smells

?

c) Describe how the smell of perfume spreods through o room. (See pqge 18.) d) Give two other uses of the compounds nomed in port b).

o) Nome this corboxylic ocid

H-C

,//,,o

\o-u

b) Nome ond drqw the structure of the corboxylic ocid which hos 3 corbon qtoms c) Which olcoholwould you use to reoct with ethonoic ocid to moke methyl ethonoote ?

o) Whot ore the foctors thot moke o good

perfume ? b)Which compounds give perfumes their

o) Nome the corboxylic ocid we find in vinegor.

b) Give 3 sources of cihic ocid. c) Whot is oscorbic ocid commonly known os? d) Stote two uses of ospirin.

Alcohols con reoct with ............. ocids to form sweet smelling compounds colled . A cotolyst of concentroted ...... ocid is used in the reqction.

2.

oof !

3. Drow spider diogroms to show ollthe

1. Copy ond complete: The olcoholwe find in beer, wine ond It is mode by spirits is colled f..................... sugor with ............ (o type of fungus). During the process, ............ gos is given off. We con olso moke this qlcoholby reocting ond steom in o continuous

\rJ

6.

Discuss the odvontoges ond disodvontoges of producing ethonol for use os o fuel by fermentotion ond by hydrotion of ethene using steom.

Further questions on poge 191.

t73

chapter 74

)

Plont olls

Oils in plonts

Do you enjoy olives on your pizzo? Some people like olives, but others hote them. Most olives ore used to moke olive oil. The olive trees grow well ollround the Mediterroneon. People who live in the wqrm countries of Southern Europe often soy thot it's the olive oil in their diet thot keeps them heolthy. It provides nutrients os well os lots of energy. Like onimols, plonts olso store excess energy they toke in os chemicolenergy in fqts. The fots in plonts ore often liquids ot20'C so we collthem oils. Mony of the compounds in plont oils ore esters. (See poges 177-2.) This group of corbon compounds olso contoin hydrogen ond oxygen otoms. Lots of oils con be extrqcted from o wide voriety of plonts. Fruits, seeds ond nuts ore good sources of oil, for exomple peonut oil. Polm oilis found in oround 7O7o of products in supermorkets. Some oils ore used in oromotheropy treotments. Some people think thot these 'essentiol oils' hove speciol heoling properties.

Olives are the source of an important plant oil. Plant oils contain unsaturated oils that result in low-density cholesterol that is good for you. Safurated lats p rod u ce h i g h -de n sity ch ol este rol th at clogs up your arteries.

People ore not only interested in plont oils in their diet ond in oromotheropy products. The oils qre olso being hoiled os new sources of olternotive fuels. (See poge 183.)

Extrocting the oil from plonts Oils extracted

In order to get the oil from o plont, we hove to breok open its cells to releose it. There ore two moin woys to breok down the cellwolls o pressing (opplying pressure) o distillotion (heot using steom). Then wqter ond other impurities ore removed.

from plants are used in aromatherapy

a:

Pressing In this method we squosh the plont moteriol. Then we collect the liquid. The oilond the woter-bosed solutions ore immiscible. They do not dissolve in eoch other ond willseporote out into two loyers.

This is the woy we extroct olive oil. After collecting olives from the trees, they ore crushed. Then the 'mosh' is spreod out on thin mots in o press. When the pressure is opplied, the liquid droins out. Then the oil ond woter ore seporoted by centrifuging (spinning the mixture ot high speeds) or just by deconting (pouring off).

174

,ti .;. .

.*Xhll. - ." soop

+

glycerol

(fotty qcid) We soy thot

oilis hydrolysed by the olkoli. The soop formed

is the sodium solt of the fotty ocid. Moking soop is colled soponificotion. Which plant oils do you think this soap is made from? Oils or fats are heated with sodium hydroxide to make soaps. lf potassium hydroxide ls used to make the soap, we get a soap which r,s a potassium salt of a fatty acid. (Remember that all alkali metal salts are soluble in water)

Soopless detergents Soops ore detergents. Troditionolly, they ore mode from onimolfots ond plont oils. Using soop in oreqs with hord woter couses 'scum' to form. (See poge 290.)The white bits of 'scum' con stick to clothes when they ore being woshed. However, soopless detergents from crude oil do not hove this problem. (See Experiment25.5, poge 338.) Soopless detergents do not moke 'scum' in hord woter. No detergent is wosted reocting with the hordness, so you sove money os well. About 80 % of oll detergents mode ore soopless detergents.

Treoting oil spills As you know from poge 141, crude oil is tronsported in giont oil tonkers. If these ships hove on occident, the crude oilcon escope. It floots on top of the seo, forming on oil slick. Soopless detergents ore used to cleon up the mess.

The detergent breoks up the slick. Then the oil is spreod out by the oction of the woves.

This oil tanker was grounded on the rocks near

Shetland 779

)

Food odditives

STMRBET FRU]TS .,11;1;{n assortrnent of

Do you ever reod the list of ingredients on food before you buy it? Hove you noticed how mony E numbers we hove in some foods ? Does it worry you ? Look ot the lobel opposite from some sweets:

'$git flavou1q{eets with a stdrbet cracknel centne

Permitted food odditives ore eoch given on E number. Mony ore extrocted from noturol products, such os seoweed. However, some people ore concerned obout their effects on our heolth. So why do we odd them ot oll?

Yegetable

Advontoges of food odditives Additives con colour, preserve ond odd flovour to our foods. There is o system used to give on odditive its porticulor E number Look ot the toble below: E number range

Use of additive

E296 E400 E500 E100

E181

colouring

E200

E290

preservatives

E385

anti-oxidants and acids emulsifiers and stabilisers

E495 E585

E620 - E640 E900

-

E1

520

2509 Permitted food additives are given an E number

anti-caking agents and mineral salts flavour enhancers others (such as wax glazes on fruit)

Let's look of eoch use in more detoil

Colourings When we process foods much of the noturol colour is lost. The food does not look oppetising. So food chemists hove seorched for substonces to put the colour bock into processed food. Other compounds ore used to odd vivid colours. For exomple, sweets ond soft drinks ore more ottroctive to children if they ore brightly coloured.

B ri g

htly co I o u red sr4/eels

Preservotives ond onti-oxidonts Fresh foods soon 'go off' os they ore ottocked by bocterio or oxygen in the oir. For exomple, fots in food ore oxidised to ocids, moking it roncid However, preservotives ond onti-oxidonts protect the food. They hove o longer 'shelf life' which is better for shops ond consumers. E300 is oscorbic ocid which is Vitomin C. This is odded by low to flour to reploce the vitomin lost in processing.

180

This margari ne contains presenratives E200 (sorbic acid), E270 (lactic acid)

and Vitamin E

Emulsifiers ond stobilisers We hove met emulsifiers before in this chopter These help fots ond oils to mix with woter. For exomple, o Coromel coke bor contoins

emulsifiers E471 ond E475. Look ot the lobel on the next bor of chocolote you eot to find the emulsifiers used.

Flovourings On poge 772,we sow how chemists use esters to flovour foods. We con't reproduce the exoct mixture of compounds thot moke up noturolflovours. For exomple, the smell of o strowberry is mode up from obout 280 different compounds. But the moin compounds ore identified ond mode os ortificiolflovourings. We olso looked of flovour enhoncers on poge 45. These oct, like sqlt, to increose our toste sensotions. Con you remember some of the concerns surrounding the use of monosodium glutomote (E627)?

Chocolate and ice cream contain emulsifiers. But do the delicious textures made possible by emulsifiers encourage people to eat unhealthy foods?

Eslers are used lo add flavour

Disodvontoges of food odditives People ore becoming more ond more owore of heolth issues. They ore looking more closely

of the things they eot ond wont more informotion obout the odditives in food. We hove seen the odvontoges of using E numbers, but there ore worries obout some compounds used. For exomple, tortrozine (E102) is o yellow colouring. It is used in sweets, joms, drinks ond snock foods.

However, it con provoke osthmo ottocks ond hyperoctivity in children. There ore olso cloims of other side effects. E102 hos now been bonned in Norwoy ond Austrio.

Some colourings have been linked with hyperactivity in children

Butyloted hydroxyonisole (E320) is onother controversiol compound. It wos bonned in Jopon os eorly os 1958 ond experts recommended its bon in the UK. However, due to pressure from industry it wos not bonned. Interestingly, McDonold's stopped using this odditive in Americo in 1986. You might not recognise E954, but you've probobly heord of socchorin. It is on ortificiolsweetener. It wos bonned in the USA in 7977, but wos loter reinstoted provided monufocturers print o heolth worning on lobels. o Whot do you think obout these issues ?

Do you check the ingredients of the drinks you buy?

181

)

Identifying odditives in food

We con use

chromotogrophy to seporote

smoll omounts of dissolved solids. For exomple, you hove probobly seporoted the dyes in inks.

Now try to seporote the dyes in food colourings: Experiment 74.7 Chromatograph;y Set up o piece of chromotogrophy poper

paper

os shown:

Let the woter sook up the poper until you hove seporoted the colours. Leove it to dry ond stick the poper, colled o chromotogroffi, into your book. Moke o toble to show which colours moke up eoch food colouring.

o

Which food colourings contoin only one dye

labels and line drawn in pencil

?

The more soluble o substonce, the further up the pqper it is corried by the woter. The soluble substonce is colled the solute. Woter is the solvent in Experiment 14.7. Other solvents, such os ethonol, con olso be used. Do you think you would get the some results?

paper clip solvent front

Chromotogrophy con olso be used to identify unknown substonces. We con look of chromotogrqms for substonces we know ond compore these with results for the unknown substonce. Look of the exomple shown:

water (the solvent)

The technique con olso be used with colourless substonces. The spots qre mode visible by sproying with o locoting ogent. front

We cqn olso use the lotest onolyticolmethods to identify unknown odditives in foods. These

mochines ore expensive but con detect ond identifu the tiniest omounts of unknown substonces. (See poge 366.) They include moss spectrometers ond infro-red spectrometers. This chromatogram shows that the unknown food colouring C is a mixture of A and B. lt should not be used in food because colouring B has been banned.

782

known colourings (A is a permitted colouring but B has been banned from use.)

unknown colouring being tested

)

Bio-diesel

Hove you seen the spectoculor bright yellow fields os you drive post forms in spring ond eorly summer ? These ore fields of the rope plont. Its seeds ore one source of on exciting new development in fuels. We use oilseed rope to moke bio-diesel. Sunflower oil is olso used. Even recycled oilfrom chip shops cqn be used os the storting moteriol for bio-diesel! Plont oils qre o reol olternotive to the diesel we get from crude oil. As you know, our supplies of fossil fuels qre running out. So getting fuel from o source thot con be re-grown every yeor will help to solve this problem. In other words, we con reploce o nonrenewoble energy source with o renewoble one.

The wonderful sight of oilseed rape growing could become more common as crude oll supp/ies run out

The bio-dieselcqn be odded to normoldieselto moke it lost longer. In Fronce, obout 57o of. their diesel is mode up from bio-diesel. Engines don't even hove to be chonged to run on bio-diesel.

Pollution is olso reduced by burning bio-diesel. It stillgives out corbon dioxide, o greenhouse gos, just like diesel. But this is lorgely bolonced by the CO2 obsorbed os the plonts grow. Whot's more, bio-diesel does not produce sulfur dioxide. The fuel does not contqin impurities of sulfur compounds like those from crude oil. Therefore, it helps people with breothing problems ond reduces ocid rqin. (See poge 148.) The porticulotes thot diesel engines give out, contoining volotile un-burnt hydrocorbons thot couse cqncer, ore olso reduced.

Mony boots on inlond woterwoys use diesel os their fuel. If there is on occident the diesel pollutes the woter ond endongers plont ond qnimol life. But bio-diesel is biodegrodoble, so it breoks down if spilt in the wqter. As dieselprices rise, bio-diesel is getting more ottention os the cheoper option. People ore even odding vegetoble oil from the supermorket to their tonks of diesel. After poying tox, it hos been worked out thot this soves you obout €10 per tonk. Its fons soy thot their cors even run more smoothly on their 'bio-diesel mix'.

Bio-diesel is a'cleaner' fuel than diesel from crude oil

However, bio-dieseldoes hove problems ot high ond low temperotures.lt freezes of o higher temperoture thon normol diesel, turning to sludge, Then of high temperotures the oil molecules con oxidise ond form polymers thqt con 'gum up' engines. On o globol scole, the use of lorge oreos of formlond to produce fuel insteod of food could pose problems if we stort to rely on it. People ore olso worried obout the destruction of hobitots of endongered species. For exomple, orong-utons ore under threot of extinction. Lorge oreos of tropicol forest where they live ore being turned into polm plontotions to extroct polm oil.

The habitats of endangered specles are under threat from plantations that supply the demand for plant oils

183

)

Chemistry ot work: Cooking Kitchen chemistry! Cooking could reolly be colled 'kitchen chemistry'. It's oll obout: o moking ond seporoting mixtures (physicol chonges). o moking new substonces (chemicol chonges). In cooking, we often mix oil-bosed ingredients with woter. You hove seen how emulsifiers help us ochieve thot. Egg yolk is on excellent emulsifying ogent.

But the chemistry reolly storts when you turn on the heot ! Thot's when we stort chonging one substonce into onother. In cooking these chonges ore not possible to reverse - o sure sign thot o chemicol reoction hos token ploce.

We can cook food in many ways, including microwave, baking. boiling, steaming, grilling and frying

We cook foods to:

o killbocterio in the high temperotures. o improve the texture, flovour ond toste. o moke them eosier to digest. Cooking meot ond eggs

Meot ond eggs ore rich sources of proteins. We need these to build muscle ond to help repoir our bodies. To understond whot hoppens when we cook them, you need to know o little bit obout the structure of protein molecules. Proteins ore noturol polymers mode from omino ocid monomers. You hove looked of monomers ond polymers in Chopter 12. The long protein molecules ore held in shope by forces within ond between their choins. When we cook meot or eggs, their protein molecules stort moving oround more vigorously. Once the temperoture gets high enough, they lose their originol shope. We soy they hove been denotured. (See poge 215.) Once denotured, the proteins connot chonge bock ogoin.

A body builder's diet contains a higher proportion of protein than that of most people. What food might they eat? 3rf?oSC

be Setjcec tho m;auttlrbot tl.rls ri 04oce ,(J.1l

In cooked meot, the proteins seporote from eoch other ond it becomes tender. In o row egg, the proteins in the egg white ore

coiled up ond flooting oround in o wotery solution. When fried or boiled, the proteins 'uncurl' ond stort forming bonds between eoch other. The woter in the egg white gets tropped between the open structure thot builds up. It's o bit like the slimy polymer on poge 160. The longer you heot the egg, the more bonds form between choins. Then the less woter con be tropped. Thot's why overcooking mokes the egg white more rubbery !

184

Boiling an egg is harder than you think !

)

Chemistry of work: Cooking Cooking pototoes If you osk people whot their fovourite food is, mony will reply 'chips' or 'French fries'. But doctors ore worning people thot too much of this type of 'fost food' is creoting heolth problems. More people thon ever ore obese ond of risk from heort diseose, shokes ond diobetes. Howeveq pototoes ore o good source of corbohydrotes. They provide us with the energy we need. Pototoes contoin plenty of storch. Storch is onother noturol polymer. It is mode up of lots of sugor (glucose) monomers. We need to cook pototoes before we eot them to help us get ot

the storch. The storch is stored inside pototo cells. Cooking helps to breok down the tough cellwolls ond releose the storch. Then we con digest the lorge storch molecules, breoking them down into glucose molecules. Plont oils ore used to fry pototoes, but doctors would prefer us to boil our pototoes. Frying in oilmeons you con cook of o higher temperoture (plont oils hove much higher boiling points thon woter). Like oll chemicol reoctions, the rote will increose os we roise the temperoture. So cooking is quicker. Not only thot, people like the toste better becouse of the flovour odded by the oil. The crispy cooting ond the soft pototo in the middle is onother ottroction.

French fries are very popular in 'fast food' outlets

However, the fried pototoes will obsorb some of the oil. This increoses the energy input of the pototo significontly. Thot's whot couses the link to be mode with obesity. If you don't exercise enough to use the extro energy, your body willstore it os fot.

Not only thot, of the higher cooking temperotures, Swedish scientists hove shown thot ocrylomide forms. This compound hos been linked to concer, olthough some orgue thqt this hos not been proved yet. The Swedish scientists did not find ocrylomide in boiled pototoes. Reseorch like this con often indicote links (correlotions) between voriobles. However, this is not necessorily o cousol link. For exomple, people who eot chips regulorly might be more likely to get o certoin diseose. But is it the chips or some other foctor thot couses the diseose ? o Discuss the issue of eoting pototoes os port of your diet. Point out the good points ond the bod points. Then form your opinions.

Polaloes absorb some of the oil when we fry them, This can cause health problems. However, the high energy content of plant olls is an advantage in some uses, such as the bioJuels on

page 1 83.

185

Summory o We con extroct plont oils by pressing or distillotion. o Oil ond woter qre immiscible. When shoken together they form on emulsion. o Emulsifiers keep the oil qnd woter from seporoting out into loyers. o Plont oils ore unsoturoted compounds. They contqin corbon-corbon double bonds

o o o o

)

in their molecules. You con test for these with bromine or iodine solutions (which turn colourless). Plont oils con be hqrdened ond turned into morgorine by reocting them with hydrogen. Processed foods con contoin permitted odditives thot ore ossigned E numbers. We con use chromotogrophy to detect ond identifiy colourings odded to foods. We con qlso use modern onolysis techniques using expensive mochines, such os o moss spectrometer. Plont oils con olso be used to moke renewqble bio-fuels.

3.

Questions

1. Copy ond complete :

.... from plonts by ... . or distillotion. When we mix up plont oils ond woter we get o mixture colled on .... These oils con be converted to . . . . in o We con get the

.

reoctionwith....gos. Permitted food

....

ore given E numbers.

4. A food scientist

colourings thot were bonned. Look ot the

Here ore the ingredients

chromotogrom below:

8 large eggs yolks of French vonillo ice cup sugar t creom: 221 cups heavy cream Creom is on emulsion contoining lots of foVoil 121 cups cold milk Pinch of fine salt mixed with woter. Milk 1 vanilla bean is o much more wotery emulsion with much less foVoil mixed in. Creom ond milk seporote out into two loyers in o bottle of full-creom milk. Using the informotion obove where necessory: o) Give the nome of on emulsion thot contoins moinly woter. b)Whot is the missing word below? Two liquids thot seporote out into loyers

I ril

I

186

t

I I

, colouring from sweet

c

A

banned dyes

oresoidtobei.....

c) Ice creom does not seporote out into loyers like full-creom milk. Which ingredient in the list octs os on emulsifier? d)Which substonces ore used to improve the toste of the ice creom ?

wos testing o new type of

sweet. She decided to moke o chromotogrom of the colouring used with some known

We con seporote the colours in o food dye by

2.

Plont oils con be used to moke morgorine. o) Which gos is odded to the morgorine ? b)Whot conditions ore needed for the reoction to toke ploce ? c) Exploin why this con be colled on 'oddition reoction'. d) Exploin why it is necessory to corry out this reoction ond how it solves the problem.

Whot could o food scientist deduce from the chromotogrom ?

5.

List the odvontoges ond disodvontoges of using plont oils to moke bio-fuels.

Further questions on poge 191.

Further questions on Chonging Moteriols

)

Acids ond Alkolis

1. This question

4. An ocid ond on olkqli reoct

is obout ocids qnd olkolis.

toble.

o) Copy ond complete the following Colour for universal indicator

o)

red 11

green

b)The reoction between on ocid ond on olkoli con be summorised os: ocid * olkoli --------> solt * woter i) Nome this type of reqction. t1l ii) Nome the solt thot would be formed by reocting dilute hydrochloric ocid with potossium hydroxide solution. t1l iii) Nome the ocid ond olkoli needed to produce the solt sodium nihote.

2.

Acid

Salt

nitric acid

sodium nitrate

Alkali

hydrochloric acid

barium hydroxide

potassium sulfate

t4l c) Describe how you could prepore o solution of mognesium chloride storting with dilute hydrochloric ocid. Include in your onswer whot you would do, whot you would see ond how you would mqke sure thot qllthe hydrochloric ocid hod been used up.

(WJEC)

o) Clore mode sodium chloride solution by odding sodium hydroxide solution, on olkoli, to hydrochloric ocid. Whot nqme is given to substonces, such os sodium chloride, formed from the reqction of on ocid with qn olkoli? Nome the process toking ploce in this

i)

Whot nome is given to the reoction between on ocid qnd qn olkqli? ttl ii) Whqt substonce, other thon o solt, is olwoys formed when on ocid reocts with on olkoli ? tll b) Copy ond complete the following toble to show the solt formed on mixing the olkqli ond the qcid.

[3J

pH of solution

t2l i)

tll ii) reoction. tll iii) Whqt should Clore use to find out

when she hos odded enough sodium hydroxide solution to reoct with ollthe hydrochloric ocid ? tll iv) Describe how she should use this to moke sure she odded the correct omount of sodium hydroxide. t2l b)Sodium chloride con be seporoted from its solution by evoporotion. Drow o lqbelled diogrom to show how this is done. tsl c) Milk of Mognesio cqn cure indigestion. Exploin how Milk of Mognesio works.

t2l

3. Sodium corbonote

(EDEXCEL)

reocts with ocids.

: [1] r '-?ij--" + + woter * -------> ;hffi; "" ;;;;i" o) Complete the word equotion sodium - hydrochloric sodium

b) Nome the solt produced if sodium corbonote (AOA) reocts with dilute nitic

ocid.

together to form o

solt. These reoctions ore olwoys exothermic.

t1l

tsl 5.

(EDEXCEL)

Complete the following word equotions o) zinc*sulfuricocid --------> .... + ....

b) sodium

nitric

hyciroxide- ocici +

c) mognesium . hydrochloric + corbonote

6. A student

ocid

tll

"" + ""

ttl

+..... *woter

-->..... ttl

(AOA)

mode o somple of zinc sulfote

crystols.

She odded excess zinc metol to qcid ond wormed the mixture. When the reoction wos finished, she filtered the mixture. She left the solution to ollow crystols to form. o) Nome the ocid she used. t1l b)Nome the gos formed by the reoction. tll c) i) Why did she use excess zincmetol? [1] ii) Why did she worm the mixture? tll iii) Why did she filter the mixture? t1l (EDEXCEL)

Note: although a question may be marked (AQA) etc., it will often be relevant to other examinations as

well.

187

Further questions on Chonging Moteriols

7.

The diogroms show whot hoppens when on ocid is odded to on qlkqli. St

age

9.

Crude oil is o mixture of hydrocorbons. o)Nome the two elements found in every

hydrocorbon.

1

b)To turn crude oil into useful products, it hos to be seporoted into different

t2l

froctions.

beaker contains dilute hydrochloric acid St

age

i) Nome the method used to seporote different froctions in crude oil. tll ii) Exploin how this method of seporotion works. t2l (OCR)

flask contains dilute sodium hydroxide + universal indicator. lndicator is purple

10. The demond for the froctions contoining smoller hydrocorbons, e.g. petrol, is higher thqn for those contoining lorger hydrocorbons. Smoller hydrocorbons ore produced from lorger ones by the process colled crocking. o) Stote two conditions which ore required for the crocking of lorge

2

dilute hydrochloric acid added to the

flask and mixed

hydrocorbons.

b) Octone ond ethene moy be mode from decone, CrcHzz, by crocking. Write o bqlonced symbol equotion for this

reqction.

indicator turns green

hydrocorbon compound into two different compounds, A ond B.

tll

b)Write on ionic equotion to show how woter is formed in this reoction ond stote the sources of the ions. t3l (A0A)

o) Give the symbolfor the ion which is produced when:

ony ocid ony olkoli dissolves in woter.

t2l

b) Copy ond complete the following word equotion. colcium - hydrochloric -----) l

188

+""+""

t1l

H

HHH HH II C-C-C -C-CHHH HH

rtt ttt

lt

H I

C

H

I

H

HHHHHH C: C + H-C-C-C-C-H HHHHHH CompoundA CompoundB

tttttl ltlttt

i) ii)

corbonote+ ocid

(OCR)

11. The equotion below shows the crocking of o

q) Whot is present in the flosk of stoge 2, besides universol indicotor ond woter ?

8.

tll

t2l

(WJEC)

o) Stote two differences between the strucfures of compounds A ond t2l b)Why is compound A useful in indushy?

B.

tll

(AoA)

Further questions on Chonging Moteriols 12. Methqne (CHa) contoins the elements corbon ond hydrogen only. A student wonted to find out which new substqnces ore produced when methone is burned. The student set up the opporofus shown below.

Name of

Formula

Structural

Use

formula

substance

H I

methane

H_C_H

CH+

fuel

I

suction pump

t

H

o)

CsHe

b)

c)

ethene

CzHt

d)

e\

o) Complete the

ice + water

toble.

tsl

b)Whot feoture of on ethene molecule tells you thot it is unsqhrrqted? t1l (AOA)

15. The diogrom below represents o methane gas

liquid collects here

limewater turns milky

o) Which gos in the oir reocts with methone

when it burns? b)Nome the liquid collected. c) Nome the gos which turns limewoter

milky.

froctionoting column used of on oilrefinery. The points numbered 1 to 4 show the levels ond temperqfures ot which different froctions qre collected.

t1l t1l

less than 40'C

t1l

40'-170"C

2

d)When methone burns on exothermic reoction tokes ploce. Whot is meont by on exothermic reoction

13. Orimulsion

is o

?

[2]

(AOA) 4

fossil fuel.

iii)

mode.

heater

bitumen

At which points would butone (boiling point 0'C) ond octone (boiling point 126"C) be collected

environment. t2l

Describe how corbon dioxide con hove q bod effect on the environment. (ocR)

t2l

14. The toble ot the top of the next column shows three of the substonces which con be

obtoined from crude petroleum.

?

Butane collected at point

Octane collected

A

1

2

B

2

1

c

2

3

D

3

2

E

1

4

t1l

Describe how sulfur dioxide con hove q bqd effect on the

250"-320'C

crude oil

It is o mixture of tor ond woter. Orimulsion is much cheoper thqn cool. When Orimulsion burns it gives out energy. There is o lot of sulfur in Orimulsion. q) i) Fossilfuels store energy. Where did this stored energy first come from? [1] ii) Will supplies of Orimulsion ever run out? Exploin your onswer in detoil. t3l b)Severolgoses ore mode when Orimulsion burns. Corbon dioxide ond sulfur dioxide ore two of the gqses. i) Exploin how the sulfur dioxide is

ii)

3

170'- 250'c

at point

tll

(ocR)

189

Further questions on Chonging Moteriols 17. Ethene

is used in the monufocture of the plostic poly(ethene). Ethene is heoted under high pressure in the presence of o cotolyst. Mony ethene molecules join together to form o giont molecule of poly(ethene). The diogrom below shows whot hoppens in the

16. John reods this orticle in o mogozine New Polymer Developed Dr Philip Green is o chemist working for o mojor oil compony. He hos reported the development of q new biodegrodoble polymer. This polymer hos similor properties to poly(ethene) but, when it is left in the environment, it is quickly broken down by bqcterio. Tests hove shown thot o supermorket bog mode from the new polymer disoppeors when buried in soil for eight weeks. Dr Green believes thot oll mojor supermorkets will use his polymer insteod of poly(ethene) within the next few yeors. He soid to our reporter, 'ln the post, chemists hove been blomed for developing moteriols such os poly(ethene) thot couse mojor pollution problems. My teom of chemists hos spent 10 yeors trying to put this right. We think our new polymer will hove o mojor impoct on the litter problem in this country. The doys of poly(ethene) bogs spoiling the oppeoronce of our countyside will soon be over. Everyone in my teom is delighted thqt our efforts to moke o non-polluting polymer hqve been successful'.

Use informotion from the qrticle to help you onswer these questions.

q) i) Exploin why using the new polymer

reoction: H H I

ii)

b) i) John shows

ii)

190

H

H

_ -C

C

I

I

I

I

I

I

H

H

H

H

n

q) Whqt is the nome of this type of reoction

?

t1l

b) Describe how the ethene molecules join together to form poly(ethene). tsl c) The poly(ethene) wos heoted qnd moulded into the shope of o bucket. The design of the bucket wos chonged. All the buckets were heoted ond then remoulded. Whot type of plostic is poly(ethene)? (EDEXCEL) Exploin your onswer. [2]

18. This diogrom shows port of o molecule of the polymer PVC.

CIHCIHCIH

tttttt

tsl

Supermorket bogs mode from the new polymer toke much longer thon eight weeks to breok down when not in contoct with the soil. Suggest why this is importont for

supermorkets.

C ____>

n C

insteod of poly(ethene) will reduce

environmentolproblems.

I

ttttrr

-C-C-C-C-C-CHHHHHH o) Whot is the structurol formulo of the

monomer from which PVC is mode? t3l b) PVC is used to mqke 'ortificiqlleother' for use in clothing, furniture, hondbogs etc. PVC is not o biodegrodoble moteriol. i) Exploin the meoning of the term

tll

the mogozine orticle to his

friend Holly. Holly soys thot oilcomponies ore only interested in profit, ond do not core for the environment. John hies to convince Holly thot environmentol issues ore on importont port of the job of chemists in the 21st century. Whot informotion from this orticle con he use to convince Holly? t2l Holly tells John thot the problem of litter from plostic rubbish could be solved by recycling oll of the plostics thot we use. John soys thot we ore never likely to rccycle oll plostics. Exploin why John is correct. [2] (OCR)

ii)

biodegrodoble. these

19.

tll

Describe the problems thot might be coused by the disposol of the PVC in

products.

tsl

Plostic bottles qre sometimes mode of the

oddition polymer poly(propene). o) Whot is meont by cddition polyner? [2] b) Drow the stuucfure of o propene molecule showing oll covolent bonds. t2l c) Show how two propene molecules ore joined os port of o poly(propene) molecule. Show oll covqlent bonds.

t2l

(EDEXCEL)

Further questions on Chonging Moteriols

)

)

Corbon chemistry

22. Surrflower -_*t"":lr*.r_-*-*rorine

20. The structurol formuloe of severol orgonic compounds qre shown below.

HO til H-C-C-O-H

HH

II oH-C-C-

lt HH

H

tt H-C-C-H

H

tt HH

H

ta:/ ,/\

c

extrocted from sunflower

c) Describe how sunflower oilcon be hordened to form morgorine.

H

ttt ttt

HHH E

undergoqdditionpolymerisotion?

t2l t3l

obtoined from plonts such os oil-seed rope. Some scientists think thot biodieselmoy hove odvontoges over diesel mode from crude oil. Biodiesel is o renewqble source of energy, is biodegrodoble ond contqins no sulfur. o) Describe how vegetoble oilcon be exhocted from seeds. tll b) Exploin why: i) Biodiesel is o renewoble source of

HHH H-C-C-C-H

b)Which is the only compound thot con

l

23. Biodieselcon be mode from vegetoble oil

D

?

tl

Whot type of chemicolbond is present in qn unsoturoted molecule? tll Describe how you could show thqt sunflower oil contoins unsoturoted

molecules.

H

o) Which of these compounds ore: i) olkones, ii) olkenes, iii) olcohols

seeds.

b) Sunflower oil contoins unsoturoted molecules.

ii)

B

HH

o) Suggest how sunflower oil cqn be

i)

I

H

A

Plont oils

energy.

ii) A spilloge of biodiesel into the seq t4l

tll

c) Which of the other four compounds con be dehydroted to moke compound D? 17l

21. Ethonol con be mode by fermentotion or by the reqction between ethene ond steom.

tll

moy couse less horm thqn q spilloge of dieselmqde from crude oil. t1l iii) A fuelwhich contoins sulfur moy hqrm the environment. tll c) To provide enough vegetoble oilto moke o lorge qmount of biodieselwould meon plonting lorge oreos of counhyside with plonts such os oil-seed rope. Suggest why some people moy object to this use of the countrysidet2l

24. Some foods

o) Write q bolonced equotion for eoch

method.

t4l b)Whqt qre the ideolconditions needed for production of ethonol by fermentotion ?

tsl c) Give on odvontoge ond o disodvontoge of eoch method. t4l d) Describe two uses of ethonol. t2l

need to be cooked before they ore eoten, others do not. o)Nome two foods thot do not hove to be cooked before they ore t2l b) Give three reosons why some food should be cooked before it is t3l c) When meqt is cooked proteins undergo

eoten. eqten.

chemicolchonge. Describe how the proteins

chonge.

t3l

791,

chapter 75 We oll need the energy we get from chemicol reoctions

Energy heots our homes ond powers industry. Energy from the chemicolreoctions inside our bodies keeps us ollolive.

Whenever chemicols reoct, we get o tronsfer of energy. The energy usuolly ends up os heot. Sometimes we olso get light energy or sound energy qs well. Con you think of o reoction which gives out heot, light ond sound ?

F

Fuels

The chemical energy in these fireworks is transferred to heat, light and sound energy

Fuels store chemicol energy. When we burn o fuel, it reocts with oxygen ond its chemicol energy is releosed. We con use this energy to give us heot or light.

You need 3 things to moke o fire:

Food is the fuel for our bodies. We 'burn' sugor by reocting it with oxygen in our cells. Luckily for us, in respirotion the reoctions ore corefully controlled. We don t burst into flomes I But fuels often do.

o fuel o hed

.

oxygen.

Choosing o fuel When choosing o fuel you should consider its o energv content r ovoilobility/cost

o toxicip o pollution effects (see poges 1.47 lo 749) o eose of use/storoge.

Heat

15.1

Comparing Bunsen llames Design on investigotion to find if o yellow or a blue Bunsen flome provides more energy. Moke sure your plon is os sofe, relioble ond foir os possible. Check your plon with your teocher before you stort your tests. o Which type of flome is better? Why? lnuestigation

Notice the soot produced by the yellow Bunsen flome. This is o sign of incomplete combustion. (See poge 147.) The gos we burn in o Bunsen burner is usuolly methone, CHa. Complete combustion: CHa(g) + 2Ozk) --------> COz(g) +

The fire triangle Whenever you come across heat, And tuel and oxygen meet. You're sure lo getfire, The flames will lick higher The fire triangle's complete I

2H2O(g)

Incompletecombustion:2CHak) + 3Oz(g) ------> 2CO(g) + 4HzO(g) andlor CH+(g) + Oz(s) --------> C(s) + 2HzO(s) corbon (soot) 792

This gives out most heot.

One of the moin foctors to think obout when choosing o fuel is its energy content. To compore this ocross different fuels we should look ot the energy releosed per grom of fuel burned. To get this informotion by experiment, you need to corry out o foir test. The only vorioble thot should chonge eoch time we collect

doto is the type of fuel. To moke the investigotion volid, we wont the energy releosed os the fuelburns to heot up the woter. (See Investigotion 15.2 below) Therefore we use o copper beoker (colled o colorimeter).

o o

Why is the beoker mode of copper? Why do you think thot the copper beoker is colled o 'colorimeter'?

You will olso need to weigh how much fuel is used in eoch test.

Then you con work out how much energy (in joules) is tronsferred to the woter using this equotion:

Energy = moss of woter

(J)

(d

The energy content of food is somellrnes expressed in caloiles per

1009.

1

calorie

:

4.2

joules. Fats, otls

and carbohydrates are'high energy' foods and too much in your diet can cause obesity. That's why we can now

buy 'low fat'crisps.

x specific heot copocity of woter x rise in temperoture

Q/s/"cl

('c)

To convert this energy into the qmount of energy per grom, we use

this equotion:

Energy per grom

energy releosed (J) moss of fuel used (g)

lnuestigationlS.2 Comparingfuels You con compore the heqt content of difterent olcohols using the opporofus opposite. o Design o foir test. Remember to weigh your spirit burner ond its fuelbefore ond qfter heoting the woter. Work out the energy content of eoch qlcohol in joules per grom. o Con you see ony pottern in your dotq? (Look of the formulo of eqch olcohol.) Use secondory doto if necessory. o Whqt ore the mqin sources of error in your investigotion ? o How could you improve the reliobility of your doto?

theimomster

water

copper calorimeter

alcohol

block of wood

Apparatus for comparing fuels

193

tr Exothermic ond endothermic reoctions Exothermic reoctions We looked ot the combustion of o fuel on poge 147. Think obout whot hoppens when we burn o fuel: o Is energy given out or token in os the fuel burns ?

Reoctions which give out heot qre colled exothermic. Combustion, plus mony oxidotion ond neutrolisotion reoctions ore exothermic.

The charcoal (carbon) reacts with oxygen in this barbecue. Heat from the exothermic reaction cooks the food.

Experiment 75.3 Feeling hot! Collect 25 cm3 of copper sulfote solution in o smoll beoker. Add o spofulo of zinc powder. Stir it with o temperoture sensor Corefully touch the outside of the beoker. o Whot do you see hoppen ? o Does the beoker feel hot or cold? o Does the reoction give out he colcium chloride 2

HCI(oq)

-------->

reoctonts

products

How con we meosure the rote of this reoction ? We con meosure how quickly one of the reoctonts is being used up. However, it is not eosy to meosure the omount of colcium corbonote or hydrochloric ocid os the reoction is hoppening. Let's think obout meosuring one of the products. Look of the equotion obove: Which one of the products is o gos ? It is much eosier to meosure how much gas is being mode os the reoction goes olong. Try one of the next experiments to meosure the rote of this reoction :

Experiment L6.1 Volumes of gas giuen off (7) Set up the opporotus os shown: Meosure the volume of gos collected every 30 seconds. Stort your timing os soon os you put

l[:3:x;:jl,lli,,tllXiqbre Time (s)

rike this

:

/i\

acio

Volume of gas (cm3)

0 30

measuring

50cmo of dilute hydrochloric acid

0

o o o o o o o

o

chips

,-A

Plot q line groph of your results. Put 'time' olong the horizontol oxis qnd 'volume of corbon dioxide gos' on the verticql oxis.

Experiment 16.2 Volumes of gas giuen off (2) Set up the opporotus os shown: Repeot the method obove. Tqke the bung out of the flosk when you hove collected 100 cm3 of gos.

/!\

Record your results ond plot o groph os obove. o Exploin why you cqn use o line groph to disploy your results. (See poge 12.)

204

+

acio syringe dilute

hydrochloric acid

marblo chlps

Experiment 76.3 Measuring the mass of gas giuen off Set up the opporotus qs shown: Meosure the mqss every 30 seconds. Record your results in o toble like this

/i\

cotton wool to stop acid 'spray' escaping

acio

50 cmo

Time (s)

Mass (g)

Loss in mass (g) 0

0

ol

dilute hydrochloric acid

30 marble chips

Some bolonces hove o TARE button. You con press this crs you stort timing. The bolonce will now give you the loss in mqss directly. Plot o line groph of your results. (Put loss in moss up the side ond time olong the bottom.) The loss in moss is the mqss of gos given off.

balance (reading to 0.019)

Alternotivelg, gou moy be oble to link your bolonce to o computer. This will plot your results directly on to o groph for you.

reaction has

Grophs qnd rotes of reoction

f

Are your grophs shoped like the one shown here? We con use grophs to meosure the rote of o reoction of ony given time. The slope (or grodient) of the line tells us how quickly the reoction wos going of thot time.

inished

no more product is formed

the reaction is slowing down here

o

f E

The steeper the slope, the foster the reoction.

o o-

o c f

Look ot the groph:

o When is the reoction fostest ? o How con you tellthot the reoction is slowing os time posses

o

E

(6

down

?

How do you know when the reoction hos stopped ?

the reaction is fastest at the start time

205

tr Effect of surfoce oreo Hove you ever hied to light o bonfire or o comp fire ? Which burns more quickly o block of wood or o pile of wood shovings ? We find thot smoll pieces of solids, especiolly powders, reoct foster thon lorge pieces.

It's like frying two pons of chips. One hos pototo cut into smoll, thin chips. The other pon hos bigger, thicker chips. Which chips will be cooked first ? Which chips hove the lorger surfqce oreo ? Lumps of coal burn slowly on a coal fire. However, coal dust in the air down a mine can cause an explosion !

Surfoce oreo is o meosure of how much surfoce is exposed. So for the some moss of pototo, smoll chips hove o lorger surfoce oreo thon big chips

r-

r+

I+

You increase the surface area of the potato each time you cut it smaller

Let's look of the effect of increosing surfoce oreo on the rote of o reoction :

Experiment 16.4 The effect of surface area on rate of reaction Set up the opporotus os shown: Use the sqme method os Experiment 16.3

/i\

Repeot your experiment twice. The only thing you should chonge is the size of the morble chips. Do it once with 5 g of smoll morble chips, then ogoin with 5 g of lorge morble chips.

r

o

cotton wool

acio

marble chips

Which hove the lorger surlace sreo'the srnoll or the lorge chips Why is it importont to keep qll other voriqbles constont?

dilute hydrochloric acid

?

Print or plot both sets of results on the some groph. Lobelthe oxes os in Experiment 16.3.

o o o

Which line on your groph rises more steeply ? Which size of morble chip reocts fqster ? Whot hoppens to the rqte of reoction qs we increose the surfoce qreo?

balance (reading to 0.019) (connected to computer if possible)

As we lncreose the surfoce ored, the rote of reoction increoses.

206

The collision theory As you know, oll substonces ore mode up of porticles. The porticles might be otoms, molecules or ions. Bef.ore we con get o chemicol reoction, porticles must crosh together. They must collide with enough energy to couse o reoction.

This is colled the

collision theory.

Think obout the rote of o reoction. Whot do you think hoppens to the number of collisions between porticles if you speed up o reoction ?

The more collisions between porticles in o given time, the foeter the reoction.

Particles ntrst colltde hard enoLtclh t-tefore they cart react i Ttte rnrntmum amounl of ertergy requtred to resr//l i/r a reaclion ts called the activation energy lSee page 213.)

Exploining the elfect of surfoce oreo Iron reocts with oxygen when you heot it in oir. Whot do you think it forms ? Experiment 76.5 Sparklers ! Compore whot hoppens when you heot: 1. on iron noil 2. iron wool 3. iron filings. Hold the iron noilond iron wool in tongs os you heot them. Gently sprinkle o few iron filings into q Bunsen flome from the end of o spotulo.

o Put the 3 types of iron in order of increosing surfoce oreo. o Whot effect does increosing the surfoce oreq of the iron hove on the rote of its reoction

W

?

Think obout burning iron filings. Powders hove o very lorge surfoce oreo. There qre lots of iron otoms exposed of its mony surfoces. The oxygen molecules in the oir con qttock ony of these iron otoms. With iron filings, there ore lots of collisions in o given time. The reoction is very fost. Compore this with heoting the iron noil. The iron noil hos o smoll surfoce qreo. It only reocts slowly. ln a lump, most particles are locked up inside, ln order to react, they have to collide ! But powders have lots of particles exposed, lf cut fine enough, they might even explode ! Explosions sometimes hoppen in flour mills or down mines. The fine powders of flour or cool dust reoct ropidly if exposed to o

only iron atoms on the surface can react

you cut the nail up, more iron atoms are exposed and ready to react

spork. 207

Look of these instructions from o woshing powder The woshing powder dissolves into the woter in your woshing mochine, moking q solution. The woshing powder contoins substonces which reoct with stqins to remove them.

Whot hoppens to the concenhotion of the solution in your mqchine os you odd more cups of powder?

Lighfly soiled Normal wash Bad stains

FOB USE cup ot Powder cups cups

If your woshing is not bodly stoined, you con sove money by odding less powder.

1 cup

But whot do you think hoppens if you use just 1 cup of powder on woshing with difficult stoins ? You willprobobly hove to wosh the clothes severoltimes. It is better to follow the instructions given on the pocket ond just wosh them once !

2 cups

3 cups

@s@

Which solution of washing powder is most concentrated ?

As you odd more cups of powder, you ore increosing

the concentrotion of the solution. So whot hoppens to the rote ot which the woshing powder reocts with stoins, os you increose the concentrotion ?

Experiment 16.6 Effect of concentration on rate of reaction In this experiment you will uarg the concentration of the ocid eoch time. o Whot other voriobles must be kept constont? Set up the opporofus os shown: Time how long it tokes to collect 20cm3 of gos. Record your results in o toble like this:

/i\

carbon dioxide

dilute hydrochloric

acio

acid

o o o o

o o

Acid (cm3) 10

20 30 40 50

Water (cm3)

marble

Time to collect 20 cm3 of gas (s)

40 30 20

chips

Iess

concentrated

10

more concentrated

0

o Which test gove the fostest reqction ? o Whot hoppens to the rote of reoction

os you

increose the concentrotion of ocid ?

As we increose the concentrotion, the rote of reoction increoses.

208

o

Exploining the effect of concentrotion You olreody know obout the collision theory from page 207 We con use it to exploin why more concentroted solutions reoct more quickly. Let's think obout the reoction in the lost experiment: The ocid porticles con only reoct with the morble chips when they collide. Look of these diogroms: acid

particles

Otr ,(o

'C

d

marble chip

,970 7oo 6

o o

69or,

Which beaker has the faster reaction ? Why?

lfthisisalMsolutionofacid.......thisisa2Msolution.Therearetwiceasmany acid particles in the same volume of solution (We often use the units mol/dm3 instead of M for concentration

- see page 344.) The ocid porticles move rondomly through the woter. As you increose the concentrotion of the ocid, there ore

more acid particles in the same oolume of solution. Therefore there is o greqter chonce of ocid porticles colliding, ond reocting, with porticles on the surfoce of the morble. You increose the rote of the reoction.

It's o bit like doncing ot o club. When o populor record is ployed, lots more people crowd on to the dqnce floor. The concentrotion of people on the donce floor increoses. There is now o lot more chonce of bumping into onother doncer !

Gqs reoctions Look ot the syringes opposite: If the end is seoled, how con you increose the pressure of the goses inside the syringe ? By pressing the plunger in, you now hove the some number of gos porticles in o smoller volume. In other words, you hove increosed the concentrotion of the gos. Therefore:

In reoctions between goses, increosing the pressure, increoses the rote of reoction.

sealed syringe

There are more collisions in a given time when you increase the pressure of a gas

209

tr Effect of temperoture Why do we keep our food in o fridge ? Some of the substonces in food reoct with oxygen in the oir. Hove you ever tosted milk thot hos gone off ? If you hove, you will know the sour toste of ocids Oils ond fots in mony foods turn 'roncid' when left in oir. They reqct ond turn into ocids.

!

The low temperature in your fridge slou.rs down the reoctions thot moke food go off. Let's look of on experiment to meosure the effect of temperoture on rote of reoction :

What happens to the rate of chemical reactions inside a fridge ?

Experiment 76.7 The et'fect ot' temperature on rate of reaction Mix equolvolumes of so(ium thiosulfote solution ond hydrochloric qcid in o flosk. n jdilute Whqido you see? l\

get

The solution goes cloudy becquse we "rrru?I**io" o precipitote of sulfur qs the solutions reoct. We con time how quickly the solution gets cloudy to meosure the rote of reoction. The diogrom opposite shows you how to do this:

Worm 50 cm3 of sodium thiosulfote solution to one of the temperotures in the toble below. Then ploce the flosk on your cross. Add 5 cms of hydrochloric ocid ond swirl. Time how long it tokes for the cross to disoppeor Record your results in q tqble like this Temp. ('C)

add dilute acid and start timing

I

sodium

thiosulfate solution

Time how long it takes for the cross to

disappear

:

Time lor cross to disappear (s)

sodum

thixullate

20 30 40 50

o How did you moke this q foir test? o At which temperoture did the cross disoppeor o Whot is the pottern in your results ?

sohnifi

most quickly?

From this experiment we find thot

As we increqse the temperoture, the rote of reoction increoses.

21.0

a cross drawn on paper

t heal

Exploining the effect of temperoture Whot hoppens to the woy porticles move when you heot them up ? The porticles hove more energy. They move oround more quickly. As they trovel foster, there ore more collisions in o certoin time. Therefore, reoctions get foster os we roise the temperoture.

an6,

a****

zffiffa

..@*

\%R m

-q* ,r*/d'(@ @r

"'@"'

ru, @\ @@/

But there is onother reoson why the rote increoses. Some colliding porticles just bounce off eoch other They don't bong together hord enough to stort o reoction. They don't hove enough energy.

Reaction at 30'C

However, of higher temperotures, the porticles ore moving foster. They crosh together horder. Therefore, more collisions produce o reoction.

@uw,%

So, rqising the temperqture: 1. mokes porticles collide more often in o certoin time, ond 2. mokes it more likely thot collisions result in o reoction. Becouse there ore more, effectiue collfsions temperoture hos o lorge effect on rotes of reoction If you roise the temperoture by 10 oC, you roughly double the rote of mony reoctions !

-"@

#)'e"..4| -,,# "[$^.w% Reaction at 40'C

notice that you get the same final amount of product at temperatures

ln the groph

40

Notice thot you

oto qulclcer.

You

rls

foster ot

o

How con you tell

o

If you whot

o

30'C or 210 "C ?

on the time

2tr

F Cotolysts You hove olreody met cotolysts on poges 47 ond 745. Con you remember which type of metols (ond their compounds) moke good cotolysts ? We use cotolysts to reduce costs in the chemicol industry.

A cdolyst is o substonce which speeds up o chemicol reoctlon. At the end of the reoction, the cotolyst is chemicolly unchonged. The filler sets in a few minutes once the catalyst is mixed in

So we con get more product in o certoin time using o suitoble

cotolyst. Hove you ever seen o domoged cor thot hos been repoired with filler ? Cor repoir kits use o cotolyst to horden the filler quickly. Look ot the instructions from q repoir kit: o Do you need to use o lot of cotolyst ? o Why must you prepore the surfoce before you mix the filler ond cotolyst ? o Why should you only mix the omount thot you

INSTRUCTIONS FOR USE:

1. Prepare the surface 2.

to be repaired Make sure it is clean and dry. Mix the filler and catayst as shown iller catalyst f

3.

Apply the filler immediately

plon to use ? You con see o cotolyst in oction in the next experiment:

76.8

Breaking down hydrogen peroxide Pour some hydrogen peroxide solution into o boiling tube. o Whot do you see oround the inside of the tube ? o Are the bubbles forming quickly ? The solution gives off oxygen gos qs it breoks down. Tiy testing for oxygen gos with o glowing splint. Whot hoppens? Experiment

manganese(lV) oxide

/!\

hydrogen peroxide

Now odd o little mqngsnese(lV) oxide, ond test for oxygen ogoin. o Whot hoppens os soon os you qdd the mongonese(lV) oxide ?

o

Did your glowing splint reJight this time

?

The mongonese(lV) oxide is o cotolyst for this reoction mongonese (lV) oxide hydrogen peroxide woter t oxygen 2HzOz@ql

MnOz(s)

2

H2O(l)

+

Oz(g)

We soy thot the mongonese(lV) oxide catalyses the reoction.

Notice thot the cotolyst does not octuolly oppeor in the equotion. We con write it obove the orrow, showing it is there during the reoction. o How con you get the mongonese(lV) oxide bock to use ogoin ofter the reoction ? (Hint: It is insoluble in woter.) 272

catalyst added

I hydrogen peroxide breaks down slowly by

itsell

oxygen is given otl rapidly with the

How cotolysts work activation energy without a catalyst

Do you remember the energy level diogroms from poge 796?They show us the energy chonge when substonces reoct together. But before reqctonts con turn into products, they need enough energy to stort off the reoction. On poge 217 we soid thot sometimes porticles with low energy con collide, but not reoct. It's like lighting o gos cooker. We need to supply energy (from o spork or o motch) before the gos

lower activation energy with a catalyst o)

reactants

0)

o

storts to burn. products

The minimum energy needed to stort o reoction is colled its octlvdlon energy. Look qt the energy level diogrom: Once on exothermic reoction storts, it provides the energy itself to keep the reoction going.

reaction pathway

A cotolyst lowers the octivotion energy. Cotolysts mqke it eosier for porticles to reoct. You con think of it like o high-jump competition. If you lower the bor, o lot more people con jump over it. With o cotolyst, o lot more porticles hove enough energy to reoct.

RoUTE

Jusl use a tvvist Of your catalyst And reactions wtll shoof Through an easier route !

ur€3ol

Inuestigation 76.9 Catalysts Here ore two problems to investigote:

T t\,^ink I'tl trb

1. Which metol oxides cotolyse the breokdown of hydrogen peroxide ?

2.Does the omount of cotolyst offect the rote qt which hydrogen peroxide breoks down

.

?

o

a Whot do yoU predict will hoppen ? a How will,,lpu moke it o foir qnd sofe test? a How

Sor|,le

transiEion Ptetnl oxideS

wiil,'pu judge how quickly the hydrogen peroxide breoks down

?

Check,your,plan with your teocher before you stort. Wos your prediction correct?

273

Hove you ever seen odverts on TV for 'biologicol' woshing powders ? (See poge 276.) These contoin enzymes which breok down stoins.

Enzymes we blologlcal catalysts. An enzyme is o lorge protein molecule. Enzymes help reoctions toke ploce of the quite low temperotures inside living things.

Allplonts ond onimols, including ourselves, depend on enzymes to stoy olive. Eoch enzyme cotolyses o porticulor chemicol reoction. For exomple, on enzyme colled omylose is in our solivo. It storts to breok down storchy foods in our mouths. Enzymes help to break down our food

On poge 272 we sow the breokdown of hydrogen peroxide using o cotolyst. Hydrogen peroxide is o poison. It con build up inside living things. However, we hove on enzyme in mony of our cells which con breok down the poison. You con wotch the reoction in the next experiment:

Experiment 1,6,,1,!0 Breaking down hydrogen peroxide using dn enzyme Collect 25cmi hydrogen peroxide solution in o conicol flosk. glowing Add o smoll piece of iresh liver. o Whot hoppens ? Test the gos given off with o glowing splint.

r

Whot hoppens? Which gos is given off

/N

splint

nyorogen peroxide

?

Some plonts cqn olso breok down hydrogen peroxide.

Chop up opiece of pototo or celery into smqll bits. Add them to 25 cm3 hydrogen peroxide solution. o Whot hoppens? o Is the hydrogen peroxide broken down os quickly this time

hydrogen peroxide

liver

?

Enz'ymes help trs lo

break do'urilar.cle

molecules

An enzyme in the liver con breok down hydrogen peroxide very quickly. Like qll enzymes, it is very efficient. Eoch enzyme molecule con deol with thousonds of reocting molecules every second ! enzvme in liver

hydrogenperoxide "

;

colled cotolose

274

)/

woter

*

oxygen

rrt fooc1

How enzymes work Enzymes ore lorge protein molecules. Eoch different enzyme hos its own special shape. The reoctonts fit into the enzyme, Iike q lock ond key. The reoctont slots into the enzyme of its qctive site.

Look ot the diogrom below active site

e

reactant breaks

reactant slots into active site

down into new

J

reactant

Other enzymes con build up big molecules from smqllones

Effect of temperoture on enzymes Look ot this box of biologicol woshing powder: At which temperoture does it work well? The enzymes in the powder don't work if you use woter thot is too hot. Tiy this experiment to see how temperoture offects enzymes Experiment 76.71 Heating enzymes nyotogen peroxide You con compore how well the enzymes in /i\ fresh liver qnd boiled liver work. See how quickly they breok down hydrogen peroxide. Repeot Experiment 16.10. Then hy it ogoin using liver you hove boiled in wqter for 5 minutes. o How did you moke it o foir test? o Whqt difference do you notice between fresh liver ond boiled liver?

Enzymes don't work of high tempercrtures. optimum temperature

As the temperoture rises, whot do you think hoppens to the woy on enzgme molecule shokes qbout?

If the enzyme gets too hot, it chonges shope. So the reoctonts will no longer fit snugly into the enzyme's octive site. It con't cotolyse the reoction. We soy thot the enzyme is denotured.

(the enzyme

works best at C

o o (u

this temperature)

0)

o o (s

Look ot the groph opposite: o Whot do we collthe temperoture of which on enzyme works best ? o Whot is your body temperoture ? Why do you think thot most enzymes work best of oround 40'C ? You cqn find out how we use enzymes on the next2 poges.

10

20

30

40

50

60

temperature (C)

Changes in pH also denature enzymes

275

F Chemistry of work : Uses of enzymes /Yoghurt For thousonds of yeors, people hove mode cheese ond yoghurt from milk. Howeveq they didn't know obout enzymes ond how they helped !

Milk contoins o sugor colled lactose. Noturol bocterio in the milk turn this into lactic acid. It is the first step in moking cheese or yoghurt. The loctic ocid mokes the milk toste sour ond it helps to preserve it. Nowodoys cheese ond yoghurt mokers use posteurised milk. This hos been heoted to kill ony bocterio. So they odd their own bocterio to stort off the process. Enzymes in the bocterio breok down loctose into two simpler sugors. Then other enzymes convert the sugors into loctic ocid.

It is thought that yoghurt was first made in the ltrliddle East

e After the milk hos gone sour, cheese mokers odd rennet. We get this from the stomochs of colves. The enzymes in it clot their mothers' milk. But now you con buy 'vegetorion' cheese. The enzymes used for clotting this cheese come from fungi (yeost).

,

The soggy lumps formed contoin curds (the solid) ond whey (the liquid). The curds ore pressed into blocks ond left to moture. In this finol stoge, other enzymes work on proteins ond fots to give the cheese its toste ond texture. like cheddor, ore left up to 9 months to moture. new enzymes con do the job in holf the time

fl I

2t6

,.: ,i i :

!., ,:,

:

G

Ll

The holes in this cheese were made by bacteria giving off carbon dioxide

Biologicol woshing powders contoin enzymes to breok down stoins. You con sove energy by operoting your woshing mochine of lower temperotures. They use proteoses to breokdown proteins ond liposes to ottock fots. They olso hove celluloses to soften fobrics by breoking down 'bobbly' bits thot con form. These woshing powders olso contoin: o detergents (see poge 178) o woter softeners (see poges 292-3) o bleoch (to remove coloured stoins) o opticolbrighteners (to give thot 'whiter-thon-white' look). . rl

ri

o;

woshing powders

'r"

*+'

t,

)

Chemistry of work: Uses of enzymes More uses of enzymes We hove olreody seen how enzymes ore used

nQ\)

(4!e i6nJ r.^ritl" t\,e At

in the brewing, boking ond doiry industries. (See poges 1,66-7, ond216.) But enzymes olso hove mony other uses.

Lett!

An eorly exomple is in moking ledherfrom onimol hides. In olden times, hides were softened by smeoring them with dog ond pigeon foeces (poo!). Fortunotely, enzymes come to the rescue of the stort of the lost century. A Germqn chemist, Otto Rohm, found out why dog foeces worked. It wos enzymes colled proteoses thot were breoking down proteins. These could be extrocted from the poncreos of o cow or pig. A lot less smelly ! It wos from the 1950s thot enzyme technology reolly storted. There ore greot benefits in using enzymes os cotolysts. They ore over 10 000 times more efficient thon other cotolysts used in industry. One enzyme molecule con cotolyse 10 million reoctions in o single second ! They olso work of lower temperotures, soving enerEg. Do you like those chocolotes with the soft, gooey centres ? Hove you ever wondered how they ore mode ? The chocolote is poured over o solid mixture which contoins sucrose (the sugor we odd to teo or coffee) ond on enzyme. The chocolote sets qnd then the enzyme breoks down the sucrose into glucose ond fructose. These smoller sugqrs ore much more soluble thon sucrose ond dissolve in the smoll omount of woter in the originol mixture. Look ot the toble opposite: We looked ot the good points obout using enzymes, but scientists hove hod to overcome some problems. For exomple, if you wont to cotolyse one porticulor reoction you need apure en4lme (not the mixture found in cells). This con be tricky, which mokes pure enzymes expensive.

You olso need to use expensive enzymes over ond over ogoin. But it is hord to remove enzymes from liquid products. So the enzymes con be stuck to plostic beods. We soy thot they ore immobilised. They do not get woshed out with the product, ollowing o continuous process. Biotechnologists hove olso found other woys to immobilise enzymes. For exomple, they con be tropped in tiny pores inside inert structures or in beods of colcium olginote.

treat cancer / make penicillin

medical

confectionary/ break down starch syrup into glucose syrup sweets (carbohydrases are used)/change glucose into fructose which is sweeter so less is needed and is used in stimming foods (isomerase) / break down sucrose into glucose and fructose / make artificial sweeteners meat

make the meat tender

baby food

start off digestion of food (proteases and lipases)

H"tel

U5

ouUl

@ @ 217

Inuestigation 16.72 Magnesium and acid Mognesium ribbon reocts with dilute qcid, giving off hydrogen gos.

/r.

/i\

acio

Use your ideqs from this chopter to investigote the foctors whrich offect the rote of this reoction.

o e o

Choose which vqrioble you will investigote. Predict ond exploin whot you think will hoppen. Plon o fqir ond sofe test to collect relioble dotq. Show your plon to your teocher before you stort.

Summory

rn&

Chemicolreoctions ore speeded up by increosing

Snail

o surfoce oreo o concentrotion (or pressure if goses ore reocting) o temperoture. The collision theory exploins why these foctors offect the rote or speed of o reoction. When porticles collide more often in o certoin time, reoctions speed up. With higher temperotures, the collisions ore olso horder. This meons thot more collisions produce o reqction.

tooA rrratcr

.tsnc sorrc

q toocl^ qnd

o0 -WAt

alEw

Some reqctions ore olso speeded up by o cotolyst. The cotolyst itself is not chemicolly chonged of the end of the reoction. o Enzymes ore biologicolcotolysts. They ore protein molecules.

F Questions

2. Explain how the witch in the cortoon obove

L. Copy ond complete:

mokes her potions so quickly

o) Smoll pieces of solid, especiolly powders, hove o . .. . surfoce oreq. The . . . . the surfoce oreo, the foster the

3.

reoction. b) The more concenhoted o solution is, the . . it reocts. This is becouse there ore more porticles in the some . . .. . Therefore, the porticles . . . . more often in o certoin time. c) The . . . . the temperoture, the foster the reoction. Hot porticles hove more energy, so they move oround more .... . This meqns thot they collide . . . . often. The collisions ore olso . . .. ond more effective. d) A . . . . is osubstonce which speeds up o reoction, but is chemicolly . . . . itself ot the end of the reoction. e) An . . . . is o cotolyst found in living things. .

278

!

Imogine thot the pupils in q school ployground ore reocting porticles. A reoction hoppens eoch time the pupils bump into eoch other hqrd enough to soy 'Ow !'. o) Whot hoppens to the pupils os the temperoture goes up ? b) Exploin how o) offects the rote of their reoction. c) Think of 2 woys to increose the concentrotion of pupils in the school ployground. d) Exploin how c) offects the rote of their reoction. e) Think up your own model, using pupils, thot could help to exploin the effect of surfoce oreo on rote of reoction.

4. Hosson andZoe wont to meosure the rote of

6. A group of students

ore studying the effect of surfoce oreo on rote of reoction. They use morble chips (colcium corbonote) reocting with dilute hydrochloric ocid.

reoction between zinc ond dilute sulfuric ocid. They set up their opporotus os shown below:

1

E

piece of cotton

2

N

o

O o q)

1. small marble chips 2. medium marble chips 3. large marble chips

E

6= dilute sulfuric acid

zl

time (mins)

o) Whot did the students investigoting the

o) Why is the zinc in o test tube ? b) How could they stort the reoction

reoction hove to do to moke lt ofair test? b) Which size of morble chips hos the lorgest surfoce oreo (given the some moss of eoch)? c) Which morble chips reocted fqstest ? How con you tell? The students doing the experiments olso tried d) reocting the some moss of pourdered colcium corbonote with the ocid. Whot would their results look like on the groph obove ?

?

Zoe reod the volume of gos collected every minute. Hosson recorded the results, qs shown below: Time (mins)

0

1

2

3

4

5

6

7

8

Volume of gas (cm3) 0 15 24 32 33 39 40 40 40

c) Plot Hosson's results on o groph. Put o circle oround the point on your groph which seems to be o mistoke. Whot do we coll this type of result? (See poge 9.) Now drow o 'line of best fit'. d) During which minute wos the reoction fostest ?

e) How long did the reoction toke to finish ? f) Nome the gos given off in the experiment. g) If you odd o little copper sulfote, the gos is given off more quickly. Drow o dotted line on your groph to show whot would hoppen.

5.

o) Whot is o

cotolyst

?

b) Hydrogen peroxide decomposes to form woter ond oxygen gos. The reoction is cotolysed by some tronsition metol oxides. You ore given oxides of copper, mongonese ond nickel. Describe how you con test which is the best cotolyst. c) How con you get the metol oxides bock to use ogoin when the reoction hos finished ?

7

. The

reoction in question 6 con olso be followed by recording the moss of o flosk contoining the reoctonts. o) Why is there o groduol loss in moss ? b) Drow the opporotus you would use to do this experiment. Why do you use cotton wool in the mouth of the flosk? Here ore some results obtoined of 20"C: Time (mins) Mass of flask and its contents (g)

2 3 4

80.00 78.50 77.50 76.95 76.60

5

76.41

6

76.33

7

76.30 76.30

0 1

I

c) Drow o groph of moss ogoinst time. d) Drow o dotted line on your groph showing the reoction ot 30'C.

Further questions on poges 244 olnd 245. 279

chapter 77

r+> ommonium sulfote NH3(oq) + H2SOa(oq) --------> (NHa)2SOa(oq)

2

Notice thot compounds of ommonio qre colled ommonium solts. Inuestigation

1.8.4 ksting: your own fertiliser

Plon on investigotion to see if your ommoniumrsulfote offects the growth of o seedling. fuk your teocher to check your plon before you stort.

236

ilil

Ammonium nitrote fertiliser Ammonium nitrote is o very importont fertiliser. Do you know which ocid reocts with ommonio to moke ommonium nitrote ? On poge 235, we sow how ommonio is turned into nitric ocid. Most of this nitric ocid is used to moke ommonium nitrote fertiliser. Look ot the diogrom

below,

IflH:,;r?,X,?ffi,;t"Jii:1

Making ammonium nitrate spray of molten ammonium nitrate

ammonta

nitricacid

+

pellets of

ammonium nitrate

Which fertiliser contoins most nitrogen

air blown in

?

Ammonium nitrote ond ommonium sulfote ore common 'nitrogen' fertilisers. Ureo is olso used in poorer countries. But which of these contoins most nitrogen Con you remember how to colculote relotive formulo mosses. (See poge 37.) Look ot the exomples below:

?

2x Formulo moss

14

:

+s4

XO

1XC

1

t6

16

28

132

So ureo hos the highest percentoge of nitrogen. Ureo is found in monure. It is not os soluble os ommonium fertilisers so it tokes longer to releose its nitrogen. On the other hond, it is not woshed out of the soil (leoched) so eosily. The leoching of fertiliser couses pollution problems. (See pose 240.)

237

tr

Nitrog€tr, phosphorus ond potossiuffi - N, P ond K

Plonts olso need other elements, besides nitrogen, for heolthy growth. Phosphorus (P) ond potossium (K), like nitrogen, ore often odded to the soil in fertilisers.

nitrogen is needed for the proteins in leaves and stalks

Look ot the diogrom of the plonts opposite: Eoch one hos missed out on one of the 3 essentiol elements. o Whot hoppens if o plont does not hove enough: - nitrogen ? - phosphorus? - potossium ? Formers con buy fertilisers which provide nitrogen, phosphorus ond potossium. Nobody hos ever mode o compound of these 3 elements thot plonts con use. Therefore, the bogs of fertiliser contoin mixtures of compounds.

potassium protects plants against disease and frost damage. lt promotes seed growth

You con find out obout your soilwith o speciol soil-testing kit. It tells you which element(s) your soil needs. You con then buy o fertiliser to suit your soil.

Look ot the bogs of fertiliser below : The percentoge of nitrogen is the first number, followed by phosphorus, then potossium. These numbers ore colled the N : P : K volue of the fertiliser 8:

phosphorus speeds up the growth ol roots, and the ripening of fruit

There was a young man from Leeds Who swallowed a packet of seeds With N, P and K

And pesticide spray He's now fully covered in weeds

!

14:14

14

ABC

o

Which fertiliser would you use: - if your soil needed topping up with oll 3 elements - if your soil wos very low in phosphorus ?

Inuestigation

78.5

?

Fertilisers

Plon on investigotion to onswer one of these problems: o How does the omount of fertiliser offect plont growth ? o Whot effect do nihogen, phosphorus ond potossium hove on plont growth? o Which mixfure of nitrogen, phosphorus ond potossium is best ?

Moke sure thot you plon o fqir test. Is it sofe ? Check your plon with your teqcher before you stort.

238

Here sre some compounds thot you could use crs fertilisers: o qmmonium nitrote, NH4NO3 o cqlcium phosphote, Cos(PO+), o potossium chloride, KCl. Test if ony of these offect the pH of the soil. Wllthis offect your test?

> A fertiliser foctory There is o lorge fertiliser foctory ot Billinghom on Teesside. On this poge we con see why this is o good ploce to hove the foctory. The foctory con moke its own ommonio ond nitric ocid. These reoct with eoch other to moke ommonium nitrote, NH4NO3. o Which essentiol element does this give to plonts ? There is olso o sulfuric ocid plont on the site. The sulfuric ocid is used to moke phosphoric ocid from phosphote rock. The phosphoric ocid reocts with more qmmonio to moke ommonium phosphote fertiliser, (NH4)3PO4.

You

can see how large the site at

Billingham is

Look ot the formulo of qmmonium phosphote obove: o Which fuo essentiol elements does it provide ? Potossium is put into fertilisers os potossium chloride, KCl, or potossium nitrote, KNO3. o Which potossium compound provides fu.ro essentiol elements

Look ot the mop

-

motorway

r-+-+ railway

E

?

main road Freight terminal

ICI built up areas

I -I

power station oil and gas pipeline

So why build the foctory ot Billinghom ? There ore lorge towns neorby thqt con supply the work-force. It is neor the North Seo. This is importont for o supply of noturolgos. Remember thot noturol gos is o row moteriol for the Hober process. (See poge 231.) o Which river is neorby ? Plenty of woter is needed to moke steom. Whot is steom used for when moking ommonio?

o

Is the foctory neor o port to bring in phosphote rock ond sulfur (to mqke sulfuric ocid) from other countries ? The compony con olso export their fertilisers from o port. o Why ore good roqd ond roillinks importont? o Discuss the issues thot outomotion (replocing workers with mochines) would roise for o compony ond the locol community. o Whot would be your concerns if o lorge fertiliser foctory wos built neor your home ?

You need

good transporl syslerns to uct

d istri bute you r prod

239

tr The trouble with fertilisers . . . As you know from poge230,

most plonts toke up nutrients through their roots. So fertilisers hove to be soluble in woter. Sometimes too much fertiliser is odded to the soil Sometimes it is odded ot the wrong time of yeor. (Why do you think thot spring is the best time ?) This con couse pollution in rivers.

Fertiliser is'leached from the soil

Some fertiliser is woshed down through the soil by roin. lt is leached out of the soil. The dissolved fertiliser droins from the fields

into rivers. Tiny plonts, colled olgoe, thrive on the fertiliser. They stort to cover the surfoce of the woter. This cuts off light to other living things in the river.

Algae thrive

When the olgoe die, bocterio decompose them. The bocterio multiply quickly with so much food They use up much of the oxygen dissolved in the woter. This meons thot fish ond other woter onimols connot get enough oxygen. Soon they die. This choin of events is colled

eutrophicotion.

Nitrote fertilisers ore very soluble. They ore finding their woy into our drinking woter. People ore storting to worry obout the possible heolth risks.

Bacteria decompose the algae and use up the dlsso/ved oxygen. Fish die without oxygen.

In this country, os mony os 5 million people ore of times drinking more thon the recommended omount of nitrote. There is concern obout stomoch cqncer ond 'blue boby' diseose (when o new-born boby's blood is storved of oxygen). However, others orgue thot there is no evidence. Links between the levels of nitrqte in our woter ond diseose hove not been proved. But most people ogree thot it is wise to limit the omount of nitrote we drink.

o Why is it difficult to prove

beyond doubt thot

nitrotes in drinking woter couse certoin diseoses

240

?

Plants in this polluted river are thriving on fertilisers leached from fields

Summory c Formers odd fertiliser to their soil to provide nutrients.

nitrogen in the air

Nitrogen, phosphorus ond potossium ore oll needed for heolthy plont growth.

r

l'*"'

Nitrogen fertilisers ore mode from ommonio (NH3). Ammonio is mode in industry by the Hober process:

* hydrogen ommoniq Nz(s) + 3Hz(g) 2NH3(g)

nihogen

ammonta

t

o Ammonio

is on olkoli. It reocts with ocids, moking the solts we use os fertilisers. For exomple,

ommonio NHs(oq)

r

* +

nitric ocid -------> ommonium nitrote HNO3(oq) --------> NH+NOs(oq)

Fertilisers con be woshed out (leoched) from the soil. They get into rivers ond lokes cousing eutrophicotion. (See poge 240.)

tr Questions

3. Ammonio

Formers odd 3 essentiol nutrients to their soil:

.... (N), ....

(P) ond

moking ommonio. b)Whot qre the row moteriols for the nitrogen ond hydrogen used in the process? c) Whot is the cotolyst used ? d)Whot temperoture ond pressure ore chosen for the process ? e) Look bock to poge 233. Exploin why the conditions in d) ore used.

....

(K). Ammonio is mode by the . . . . process. Nitrogen ond . . . . ore reocted together to

moke the ommonio. Ammonio reocts with . . . . to moke solts. For exomple, qmmonio + .... ocid ------>ommonium nitote Fertilisers con be woshed out, or l------, from the soil. Then they con couse in rivers ond lokes. e ------o) Drow o flow diogrom of the nitrogen cycle. b) Formers odd nitrogen fertilisers to their soil. Exploin why they hove to do this when there is so much nitrogen in the oir. c) In olden doys formers used to 'rotote' their crops, os do some orgonic formers. One of their fields wos left without o crop every few yeors. Clover wos grown in the field. This wos ploughed into the soil before seeds were plonted the following yeor. Why wos this o good ideo?

is mode in industry by the Hqber

process. o) Write the word ond symbolequotion for

1. Copy ond complete:

2.

process

4.

Describe how we mqke nitric ocid in indushy. Include o flow diogrom of the process.

5. Whot foctors would you look for in siting fertiliser foctory

6.

o

?

Rivers ond lokes con be polluted by fertilisers.

Design o leoflet for formers exploining the problem. Suggest how they might help reduce the problem.

Further questions on poge 247.

241

Further quections on Rotes ond Energy

F Energy chonges l.

SAFETI

The opporofus wos used to meosure the temperoture chonge of 1009 woter thot resulted from burning fuel.

WARNINE! Asphca oBge cap cyllndd is 6mpty.

ffis

6 calor

$l6ty l6af6t.

Calor Gas Ltd, Slough

CYTII{DER SAFETY RUTES

i. lfflame

do6s not go od when regulalorswilch is lumd l6ave appliancs alight and cdl Cdor re61d. Do nol atemptto disconn€ct.2. Do nol stoG or us6 in changing cylindoB. 4. updght 5. Ensure good vontilation.

Results of this experiment ore shown in the

Temperature of 1009 waterfC

before

233.75

after fuel burned

232.25 1.5

after

64

before

31

temperature rise

33

4.20Jlgl"C.') t3l b) Colculote the energy releosed per grom of fuel. t2l c) This volue is less thon the theoreticqlvolue colculoted using bond energies.

why.

2. o)Whot piece of opporotus

tll is needed to

?

show thot o reoction is exothermic t1l b)How could you show thot the reoction

between borium hydroxide solution ond dilute hydrochloric ocid is exothermic ?

t4l

3. Color gos is o convenient

(EDEXCEL)

energy source for booting, comping ond corovoning. It is qvoilqble os butone Cqlor gos or propone Color gos. The following lobel hos been tqken from o cylinder contoining butone Cqlor gos, CaH16.

242

lights'.

tll

bosements,

t1l

chonged neqr'noked b) From your knowledge of the properties of hydrocorbons suggest why propone Color gos, C3Hs, is preferred os o fuel in winter rother thon butone Color gqs even though it is more expensive ond gives out less heot per grom thon butone Color t2l c) The following equotion represents the complete combustion of the formulo moss in groms of butone in oir. The structurol formulos of the chemicols involved ore shown.

gos.

o) Colculote the energy releosed by burning the fuel. (Specific heot copocity of woter is

Suggest

not be:

ii)

toble. Mass of burner and fueUg

o) Suggest why these cylinders should i) stored or used in cellqrs or

I nHHH

'F-i-t t i

I

I

+ 13(O:O)

8(O:C:O) + 1 Bond

Enersy (kJ/mol)

C_H

413

C{

498 743 464

o:o G_H

Colculote: i) the enerry needed to breok qll the bonds in the reoctonts, t3l ii) the energy releosed os new bonds ore formed in the products, t2l iii) the energy chonge. tll (AOA)

Noter although a question may be marked (AOA) etc., it will often be relevant to other examinations as well.

Further questions on Rotes ond Energy

4. The symbol equotion below

6

shows the reqction when methone burns in oxygen. CH4+ 2O2 --------> CO2 + zHzO An energy level diogrom for this reoction is shown below.

methane +

HYDROGEN FUEL OF THE FUTURE It hos been suggested thot hydrogen could be used os o fuel insteod of the fossil fuels thot qre used of present. The equotion below shows how hydrogen burns in oir.

x

oxygen (reactants) level

carbon

dioxide + water

(products)

energy.

o) Hydrogen wcrs successfully used os o fuel for o Soviet qirliner in 1988. Why would hydrogen be o good fuel for use in on oeroplone t2l

o)Which chemicol bonds ore broken ond which ore formed during this reoction ? /4J b) Exploin the significonce of x, y ond z on the energy lwel diogrom in terms of the energy

?

b)The woter splitting reoction is shown in the equotion below.

hqnsfers which occur when these chemicql (AoA) bonds ore broken ond formed.

zHzO ------+ 2H2+O2

[6J

5. Hydrogen (Hz) ond

chlorine (Clz) reoct together to moke hydrogen chloride (HCl). The reoction is highly eu

H-CI+ H-Cl

o) During the reoction some bonds ore mode ond others qre broken.

i)

Copy the equotion below ond put o ring oround the bond(s) which is(ore)

Copy the equotion below ond put o ring oround the bond(s) which is(qre)

H

H

H

i)

2H2O ------+

ii)

exothermic?

tll

(OCR)

iii)

4H+2O

t2l

Cqlculote the energy chonge when the H ond O otoms join to form H2 ond 02 molecules.

4H +

iii) Whot energy

v)

Colculote the energy neededto split the woter molecules in the equotion

intoHondOqtoms.

tll ----+ H-Cl + H-Cl H-H + Cl-Cl iv)

H

H-H +O:O H-H

Use informotion from the tqble in question 8 on poge 202to help you onswer this question.

mqde.

chonge (tronsfer) tokes ploce when bonds ore broken ? tll Whot energy chonge (tronsfer) tokes ploce when bonds ore mqde ? tll How does the difference in the energy involved in breoking ond moking bonds exploin why the reoction between hydrogen ond chlorine is

----->

+

broken. fl H-H + Cl-Cl ------> H-Cl + H-Cl ii)

heot

The hydrogen would be mode from woter using energy obtoined from renewoble sources such os wind or solor power. The woter splitting reoction requires o lot of

v

energy

H-H + Cl-Cl

02 ------> 2H2O+

2H2+

20 -----+ 2H2+ 02

Is the

t2l

overollreoction:

zHzO

--------->

2H2+ 02

exothermic or endothermic ? Use your onswers to i) ond ii) to exploin your choice.

t4l

(AoA)

28

Further questions on Rotes ond Energy

F

8. A student

Rotes of reoction

used the following opporotus to corry out on investigotion of the reqction between mognesium ond dilute hydrochloric ocid.

7. Colcium cqrbonote

reocts with dilute hydrochloric qcid os shown in the equotion below.

CoCOs(s) + ZHCl(oq)

measuring

cylinder

->

CoCl2(oq) + HzO(l) + COz(s) The rqte qt which this reoction tokes ploce con be studied by meosuring the omount of corbon dioxide gos produced. The grophs below show the results of four experiments, I to 4. In eoch experiment the qmount of colcium corbonote, the volume of qcid ond the concentrotion of the qcid were kept the some but the temperoture of the ocid wos chonged eoch time. The colcium corbonote wos in the form of smoll lumps of morble.

hydrochloric

magnesrum

The student put 50cm3 of dilute hydrochloric qcid into the conicol flqsk, qdded o 3 cm length of mognesium ribbon qnd inserted the bung. The student recorded the time to produce 50 cms of hydrogen gos. The student repeoted the experiment four more times using hydrochloric ocid solutions of different concentotions mode by using different volumes of the dilute hydrochloric ocid ond woter. Experiment

Volume ol dilute

Volume of

hydrochloric

water(cm)

c

Ec dE o.!)

0

23456

1

50

2

40

0 't0

3

30

20

4

20

30

60

5

10

40

145

o) Aport from oltering the temperoture, suggest two woys in which the

ii)

reoction of colcium corbonote ond hydrochloric ocid could be speeded

b) i)

up.

b) Which groph,

t2l

I

to 4, shows the results of the experiment in which the ocid hod the highest temperoture ? Exploin fully how you know. t2l c) i) In experiment 2, how does the rqte of reoction qfter one minute compore with the rqte of reoction qfter two minutes?

ii)

trl

Exploin, os fully os you con, why the reqction rote chonges during

experiment2.

ol

20

45

66

o) One time oppeors to be inconsistent. i) Which time oppeors to be inconsistent?

time (mins)

2M

'l

50cm3

gas (s)

acid (cm3)

Eo oP E5 BE

Time to collect

t2l

(AOA)

ii)

Suggest q time thot is consistent with

results.

tll tll

the other Use the results to stote how the rote of reoction chonges with decreosing concentuqtion of hydrochloric qcid. t2l Exploin, in terms of porticles, how decreosing the concenhotion of the hydrochloric ocid offects the rote of

reqction. tsl of meosuring the volume ofgos produced. ttl d)Suggest onother woy to chonge the rote of o reoction. tll c) Suggest onother woy

e) Copy ond bolonce the equotion below, ond fill in the missing stote symbols.

Mg(

)

+ HCI(qq) ------->MgCl2( ) + Hz(s)

t2l

(EDEXCEL)

Further questions on Rotes ond Energy

9.

v)

Some students hove sfudied the reqction between some metqls ond dilute hydrochloric ocid. The metols reoct with the qcid until they cqnnot be seen. Bubbles of gos ore produced during oll the reoctions. The students know thot: o metol

vi)

ocid.

'Definitely not!' Use your knowledge of the reoctivity series to exploin why the teocher wos (OCR) very wise to soy

ocid to produce mognesium chloride ond hydrogen. Write q bolonced symbol equotion for this

Time taken for magnesium to react completely/seconds

2.O

13

1.5 1.2 0.8 0.6 0.5

22 30 70 145

iii) iv)

250

t2l

tll

Use your grqph to help you to describe

how increosing the concenfuotion of ocid offects the rote of reoction. Use your groph to predict the time token for the reoction if the concentrotion of qcid wqs 1.0 moles per

ttl

dm3.

reoction of excess morble chips (colcium corbonote) with (A) 20 cm3 of dilute hydrochloric ocid, (B) 10 cm3 of the dilute hydrochloric ocid +10 cm3 of woter.

ttl

(A) 20cm3 dilute HCI

1

0.00 0.54

2

0.71

3 4 5

o.78 0.80 0.80

0

Finish the groph by drowing the best

curve.

1O. The toble below gives the results from the

Time in minutes

PIot the points on o groph to show the

bottom).

t2l

Total mass of carbon dioxide produced in grams

time tqken for the reoction to finish when different concentrotions of ocid ore used (reoction time up the side, concenfuotion of qcid olong the

ii)

this.

t2l

c) They corried out on investigotion to discover whether the concentotion of ocid used hod ony effect on the time token for the mognesium to reoct completely. Equol volumes of ocid ond equol lengths of mognesium ribbon were used in eoch test. The toble shows o set of results.

i)

t2l

Use the ideo of porticles to exploin

reoction.

o) Write oword equotion for the reoction of zinc with dilute hydrochloric t2l b)Mognesium reocts with dilute hydrochloric

Goncentration of acid/ moles per dm3

chonge.

the effect of chonging concenfuotion on the rote of t2l d) One student osked if the closs could repeot their experiment using potossium insteod of mognesium. The teqcher soid

* on ocid --------> q sqlt + hydrogen

reoction.

Write down two other foctors which could chonge the rote of this reoction. In eoch cqse stote how the rote would

(B) 10cm3 of dilute HCI + 10 cm3 of H2O

0.00 o.27 0.35 0.38 0.40 0.40

o) Plot the two curves on o groph (time olong the bottom). Lobel the first curve (A) ond the second curve t3l b)Sketch, on the some grid, the curve you might hove expected for reoction (A) if it hqd been cqrried out ot o higher temperoture. Lobel this curve c) Sketch, on the some grid, the curve you might hove expected for reoction (B) if the morble chips hqd been ground to o powder. Lobelthis curve d) Explqin your onswer to port

(B).

(C). ttl

(D). c).

tll tll

(WJEC)

245

Further queetions on Rotes ond Energy

F

Reversible reoctions

13. In the Contoct process for the monufqcture

11. Ethonol (C2H6O) is monufoctured from ethene (CzH+) ond steom (HzO). The equotion for the reoction is: C2H4+ H2O -.- C2H6O o) The sign indicotes thot this is o reversible reoction. Whot is meont by o reversible reoction? [2J b)The groph shows how the conversion of ethene into ethqnol, ot three different temperotures, will chonge os the pressure

+

chonges. tt

o o trl o c

E c

20OEE

()

260t8

E o o E 6

320Etr

+

2SOs

temperoture pressure cotolyst.

is mode from ethene in q two-stoge process. The first stoge is to convert ethene to 7,2dichloroethqne. 2C2Ha@l + 4HCl(s) + Oz(g) -2C2HaCl2@)+2H2O(g)

ethene

1,2-dichloroethone

Stote ond exploin the effect of increosing the pressure on: o) the yield of 1,2-dichloroethone, t2l (AOA) b) the rote of

tr

o E o o.

reoction.

pressure EatmosptreresE

ii)

2SO}+O2

This equilibrium reoction is exothermic from left to right. Stote ond exploin the effect of eoch of the following conditions on the rote ond yield of this reoction. o) increose in tsl b) increose in t2l c) use of o t3l

14. The monomer chloroethene

c

.9

i)

of sulfuric ocid, sulfur dioxide is oxidised to produce sulfur trioxide.

How does the conversion of ethene into ethonol chonge os the pressure

?

increuses How does the conversion of ethene

t2l

15. A student heoted some blue copper sulfqte

tll

cnTstols. The crystols hrmed into white copper

sulfote

into ethonol chonge os the temperoture increoses

?

t1l

iii)

Whot is the percentoge conversion of ethene ot 260'C qnd 55 otmospheres

iv)

A cotolyst is used in this reoction. Why is o cotolyst used ? nl Whot effect does o cotolyst hqve on the percentoge conversion of ethene ?

pressure

?

tll

ttl

is oxidised to nitrogen monoxide.

+

aNO(g) + 6HzO(g)

The reoction is exothermic.

In industry o mixture of dry ommonio ond oir qt qbout 7 otmospheres pressure is possed over o plotinum cotolyst ot 900'C. Exploin how chonging the conditions used could offect the yield of nitrogen monoxide.

t6l

246

continuously to chonge it into white copper sulfote. Stote whether the reoction wqs exothermic or endothermic.

(ocR)

12. In the mqnufqcture of nihic ocid, ommonio 4NHs(g)+ SOz(s)

o) The blue copper sulfote hod to be heoted

(AoA)

Exploin your onswen [1] b)The word equotion for this reoction is shown below:

hydroted [+heotenergy] € onhydrous + wqter sulfote copper sulfote (blue) (white) i) Whot does the symbol + tell you

copper

obout this reoction ? tll ii) How could the sfudent turn the white powder bock to blue

? ttl

(AoA)

Further questions on Rotes ond Energy

F

Products from qir

16. Ammonio

Effect of temperature and pressure on the amount of ammonia at equilibrium 100

is mqnufoctured by the Hober

process, in which nihogen ond hydrogen reqct qccording to the equotion shown below.

N2+3H2 +

symbol

+ ?

t1l

b)Nome one compound monufoctured on o lorge scole from ommonio. tll c) Why is iron used in the Hober process ond whot effect does it hove ? t2l d)The toble lelow shows the percentoge of ommonio present of equilibrium when nitrogen ond hydrogen reoct qt different temperofures ond different pressures. Pressure Ammonia present at equilibrium (%) (atmosphere) Temperature ("C)

100 200 300 400 10 25 50 100 200

88.2 91.7 94.5 96.7 98.4 99.4 99.9

400 1000

i) ii) iii)

E80 (d

50.7

14.7

63.6 74.0

27.4 39.5

81.7

52.5

89.0 94.6

66.7 79.7

98.3

92.6

3.9 8.7 15.3 25.2

38.8 55.4 79.8

ommonio?

1.2

2.9 5.6 10.6 18.3

31.9 57.5

tll

Use the toble to soy how the

percentoge of ommonio present ot equilibrium is offected by: increosing the temperoture increosing the

;

pressure

t2l

e) How willthe rote of reoction of nitrogen with hydrogen be offected by increosing the temperoture f) The moximum yield of ommonio shown in the toble occurs of 1000 otmospheres pressure ond 100'C. Why ore these conditions not used commerciolly t2l

?

tll

?

(EDEXCEL)

is mode from nihogen ond hydrogen in the Hober process. Nz(g) + 3Hz(g) + 2NHe(g)(+ heot)

g8,

oo

400

"c

500

"c

6so c

8.

40

5so

2zo 5 Bto 0 0

100 200 300

400 pressure in atmospheres

500

The Hober process uses o temperoture of 450'C ond o pressure of 200 otmospheres. Exploin why these conditions ore chosen.

tsl

500

Whqt is meqnt by the stotement thot o reoction hos reqched equilibrium ? [7J Whot will be present in the equilibrium mixture with the

17. Ammonio

o c

100'c "c 300'c 2oo

90

b70

2NH3

q) Whqt is meont by the

(E 'E

18. Reod this orticle obout

(AoA)

coffee production in

Costo Rico, o country in CenholAmericq. Answer the questions thqt follow. Coffee is one of the most voluoble crops of Costo Rico. Coffee

production occounts for neorly o fifth of the country's exports. The coffee plontotions ore found moinly in the Cenhol Volley of Costo Rico. Lorge omounts of nitrote fertilisers ore used throughout the yeor in the production of the coffee. Scientists hove shown thot coffee plonts toke up obout 407o of the nitrote fertiliser during the moin growing seoson. Towords the end of the growing seoson the plonts only toke up obout 67o oI lhe nihote fertiliser. Underneoth the Centrol Volley, there ore nqturol undergtound reservoirs in the rock which hold lorge volumes of fresh woter. These reservoirs supply woter to more thon one million people, obout o quorter of the populotion. Scientists hove found thot nihotes hove contominoted the underground woter. They hove olso shown thot o lorge omount of this nihote contominotion hos come from fertilisers used in coffee production.

o) Why do formers use nitrote fertilisers ? [7J b) How does the use of nitrote fertilisers help the people of Costo c) Suggest how the nitrotes got into the

Rico?

ttl

underground woter. t1l d)WhV ore scientists concerned obout pollution of the underground woter? t1l e) Suggest how the problem of nihote pollution could be reduced in Costo Ricq.

t2l

(AoA) 247

ch:optar 19 This section exploins the properties of moteriols. To understond the ideos, you need to know obout the shucture of otoms. (See Chopter 3.) When we look ot the Periodic Toble, we find o group of elements with olmost no reoctions of oll. o Con you remember the nome of this group ? Whot con you soy obout the orrongement of electrons in their otoms ? We hove seen on poge 56 thot the otoms of these very stoble noble goses oll hove/ull outer shells of electrons Other otoms would olso become stoble with full outer shells.

In this chopter we will see how metols ond non-metols bond together in compounds.

Metals, like sodium, react with non-metals, like chlorine. The compound formed is made of ions.

) Ionic bonding Let's look of sodium chloride os on exomple

lonic bonds form between metals and non-metals

Na atom. It has 1 electron in its outer shell

A sodium atom has 11 electrons (2,8,1)

Cl atom. It has 7 electrons in its outer shell

A chlorine atom has 17 electrons (2,8,7)

Both otoms would be more stoble if they hod full outer shells. They will olwoys toke the eosiest woy to fill their outer shell with electrons. Notice thot sodium hos just 1 electron in its outer shell. o How do you think it could get o full outer shell ? Would it be eosier for sodium to lose just 1 electron, or to goin 7 electrons ?

Look qt the chlorine otom obove: It hqs 7 electrons in its outer shell. o How do you think it could get o full outer shell? Would it be eosier for chlorine to lose 7 elechons, or to goin just 1 more electron ?

28

catch

I

n@ {hoaK5

',/etal ato,tt . OA e e/r I'.

lt

t. " t c

rlO

When sodium reocts, it loses its 1 outer electron This leoves o full shell. Where do you think sodium's electron goes to ?

Chlorine occepts the electron from sodium. It gofns the 1 electron it needs to fill its outer shell. Look ot the diogrom below: sodium gives its outer electron to chlorine

Remember thot oll otoms ore neutrol. They hove on equol number of positive protons ond negotive electrons. So the chorges concel out' However, qfter sodium hos given on electron to chlorine, the electrons ond protons in both otoms no longer bolqnce.

Let's odd up the chorges:

sodium 10 electrons 11

protons

: :

10-

: 17 protons :

chlorine 18 electrons

11+ 1+

1877

+

1-

The otoms, which we now coll ions, become chorged: No+ ond You con show the ions like this:

+

Na+

Cl-

this is the lrom sodium

[2,8]+

Cl- [2,8,81-

As you know, opposite chorges ottroct.

Therefore, the No+ ions ond Cl- ions ore strongly othqcted to eoch other. This electrostotic othoction sticks the ions together, qnd is cqlled qn ionic bond. Millions of ions bond together to form crystols os the ottroction octs in oll directions. You cqn see o diogrom of this on poge 253.

Opposites attractt Bttt why vtill Na- and Cl never be aione ?

A{Sit

,:,

r,.;a,i:]il;:r .,i:

)

More ionic compounds

We hove looked ot sodium chloride os on exomple of on ionic compound. When sodium ond chlorine reoct together, eoch sodium otom gives 1 electron to eoch chlorine otom. The otoms reoct together - one-to-one. So the formulo of sodium chloride is NoCl.

When metalmeels non-metal, the sparks they do fty "Give me electrons !" non-metals do cry. "You've got a deal !" the metalresponds, Then ions attract to form their bonds.

Mognesium is in Group 2 of the Periodic Toble Therefore, we know thot it hos 2 electrons in its outer shell. (See poge 60.) How could it get o full outer shell? Whot do you think hoppens if we reoct mognesium, insteod of sodium, with chlorine ? Look ot the diogrom below:

Mg atom (2,8,2)

Cl atom (2,8,7)

2+

Cl- ion

[2,8,8]-

Mg2+ion [2,8]2+

Cl- ion [2,8,8]-

The mognesium otom loses 2 electrons when it reocts. Therefore, its ion hos o 2+ chorge, Mg2*. You con see thot eoch mognesium otom con give on electron to eoch of 2 chlorine otoms. So the formulo of mognesium chloride is MgCl2.

Now let's look ot sodium reocting with oxygen: An oxygen otom hos 6 electrons in its outer shell. How con it get o full outer shell? Look ot the diogrom below:

[2,8]+

O2-ion [2,812-

The oxygen otom goins 2 electrons, eoch with o negotive chorge Therefore its ion hos o 2- chorge, 02 It tokes 2 sodium otoms to fillthe outer shell of 1 oxygen otom. So the formulo of sodium oxide is No2O.

l.,.

ll,.'l,,i11i1:,,rr11,,

.

ffi

O atom (2,6)

2-

+

Na+ ion

Na atom (2,8,1)

+

Na+ ion [2,8]+

2-

+

['"]

Iul

[-"].

'Dot and cross'diagram for NarO. It shows only outer shell electrons.

Working out the formulo You hove now seen how 3 ionic compounds ore formed. Look of the ions which moke up eoch compound:

sodium chloride magnesium chlsride sodium oxide

Na+ :1 Cl-

NaCl

1

MgC12

1Mgz+'ra,2Na+:102-

Na2O

Now qdd up the chorges on the ions in eoch compound. o Whot do you notice ? Do they bolonce out ? Ionic compounds ore neutral. The chorges on their ions concel eoch other out. Knowing this, ond the chorge on the ions, we con work out the formulo of ony ionic compound.

Notice thot the metol olwoys comes in front of the non-metol in the formulq. o Copy ond complete the toble below:

NaCl

Na2O

MgCl2

Al203

,li$'iffih##ti

ffiiltl#ulffir*

)

Properties of ionic compounds

You hove now seen how metols bond with non-metols Metols give electrons to non-metols. This meons thot:

Metols olwoys form positive ions, ond non-metols form negotive ions. Look ot the photo of two ionic compounds Con you see ony similorities ? You con test on ionic compound in the next experiment:

Here are crystals of two ionic compounds

Experiment 19.1 Testing tonic compaunds 1. Spreod o few groins of sodium chloride on o microscope slide. Focus your microscope on the groins. o Whot shope ore the groins ? o fue the ongles ot the surfoce of the grcins similqr? We collsolids with regulor ongles crystals. 2. Heat some sodium chloride crystols strongly in o test tube. o Whot hoppens? Does sodium chloride hove o high melting point? 3. Add 2 spotulos of sodium chloride to holf o beoker of woter. Stir it with o gloss rod.

o

4V

Whot hcppens? Is sodium chloride soluble in water?

4. Set up the circuit ss shown: Dip the electrodes into some solid sodium chloride. o Does the solid conduct?

carbon

test solid sodium chloride, then its solution

Now holf-fill the beoker with woter, ond stir. A o Does the bulb light up now? chtorine oas " r Does the solution conduct electricity? Switch off your power pock os soon os the test is completed. Here is o list of the properties of ionic compounds

:

Ionic compounds:

i

o

ore mode of crystols (which con be split olong certoin ongles)

o

hove high melting points

.

ore often soluble in woter

o

conduct electricity when molten or dissolved in woteq but not when solid. (Poge 83 exploins why.)

I

252

We transferred electrons and lost our hearts, 'Til electrolysis do us part. QO

+

(Let's hope it dr,te:-;rt ! ratrt t)i iite marriage could :;cton llc rlissr;,rr:1,'

,;

)

Giont ionic structure

Scientists need to know how the ions ore orronged in ionic compounds. This helps to exploin how

ionic compounds behqve.

Dorothy Hodgkin used X-rays to help show the structure of materials

We con get informotion by firing X-roys of o crystol. The X-roys moke o pottern os they poss through the crystol. The pottern gives us clues obout the orrongement of the ions. Scientists hqve found thot the ions form giont Millions of positive ond negotive ions ore

structures.

fixed in position. Look ot the diogrom below:

Cl-ion

Part of the giant

ionic structure of sodium chloride. It is called a giant ionic

lattice Nation

Con you see thot the ions ore orronged in o regulor pottern This exploins the regulor ongles of ionic crystols.

Why do you think thot ionic compounds hove high melting points ? Remember thot opposite chorges ottroct, forming strong ionic bonds. These forces of othoction oct in olldirections. Imogine trying to seporote oll the ions in the giont strucfure obove ! It tokes o lot of energy to overcome oll thqt electrostotic qthoction. Mony ionic compounds dissolve in woter. To exploin this we need to look ot o woter molecule in more detoil: The elechons in H2O ore not evenly spreod. One end of the molecule is slightly negotive compored to the other end.

?

the orygen end of a water molecule is slightly negative compared to the hydrogen end

,'1.

Look ot the diogrom opposite: The woter molecules ore ottrocted to the ions ond pullthem from the giont structure (lottice). The compound dissolves. Its ions ore then free to move oround (The electrolysis of ionic compounds is exploined in Chqpter 7.)

4-& ffi db 4-&

s? (+l

M

An ionic compound disso/vtng in water

1,;t.,

Affi|

rii..lii:1;ili;:.'lr:li.ii1;,,

- holides We hove olreody met lots of importont ionic compounds

in this book. For exomple, Chopter 8 is obout solt (sodium chloride). Look bock ot some of its uses.

Here ore some other useful ionic compounds of the hologens - the hqlides.

Sodium fluoride If you eot sweet, sticky food, it con rot your teeth. Bocterio in your mouth feed on the sugor, moking ocid os they do so. This ocid couses

tooth decoy. Fluoride ions help to prevent tooth decoy. As children grow, the fluoride forms port of the colcium compounds in their teeth. This mokes it more difficult for ocid to ottock teeth. Some woter outhorities odd fluoride to their woter supplies This greotly reduces the number of fillings children hove. However, too much fluoride con octuolly horm teeth. Sugary foods cause tooth decay In foct, higher doses ore toxic (poisonous) This hos led to mony orguments obout fluoride in woter. e Whot do you think obout odding fluoride to our woter supplies ? o How would you set up o survey to test if fluoride is effective ond sofe ? !

Silver holides These ore used on photogrophic film ond poper.

Silver holides ore offected by light. Try the experiment below:

Experiment 79.2 Effect of light on siluer halides Add silver nitrote solution to two test tubes, eoch contoining sodium chloride. Whot hoppens ? The white precipitote is silver chloride. Do the some with two test tubes of sodium bromide, then sodium iodide. Ploce o test tube of eoch silver holide in o dqrk cupboord for 5 minutes. Leqve the other 3 silver holides in the light. o Describe the differences you see. The silver holides ore reduced to silver in sunlight This exploins their use in photogrophy.

Deve I opi n g a ph otog raph

r

When metols reoct with Metqlotoms give This t The

r

a

compounds.

ond negotive non-metol ions. otkqcted to eoch other

ore mode hove ore rcnlc

ts Questions n

4.. Here ore 3 metol ions:

" Copy ond complete . . . . compounds ore mode from metols ond non-metols. Metols olwoys form . .. . chorged ions, ond non-metols form . . . . chorged ions. These ions ore orronged in . . . . ionic structures. Their crystols hove . . . . melting points ond mony will . . . . in woter. They conduct . . . . when molten or when in solution, but not when they ore . . . .

lithium, Li+ colcium, Co2n, iron(lll), Fe3+ Here ore 3 non-metol ions: fluoride, F- iodide, I-, sulfide, S2Drow o toble, like the one on poge 257, to show the formulos of the compounds between these metols ond non-metqls.

:

5" Exploin, using diogroms to help, how these otoms tronsfer electrons to form ions: o) Mognesium, Mg (which hos 12 electrons) ond fluorine, F (which hos 9 electrons). b)Mognesium, Mg (which hos 12 electrons) ond oxygen, O (which hos 8 electrons).

.

2. Which of these substonces ommonio, NH3 copper oxide, CuO leod bromide,PbBr2 methone, CH4 How did you decide

3

hove ionic bonds?

woter, H2O zinc chloride, ZnCl2 potossium fluoride, KF

?

Exploin, using diogroms to help, how the otoms in o) ond b) below, tronsfer electrons to form ions.

(Remember thot the 1st shellcon hold 2 electrons, the Znd shell 8 electrons, ond the 3rd shell olso holds 8 electrons.) o) Lithium, Li (which hos 3 electrons) ond fluorine, F (which hos 9 electrons). b) Potossium, K (which hos 19 electrons) ond chlorine, CI (which hos 17 electrons).

&

Look ot the Periodic Toble on poge 392 o) Whot is the link between the group o metal is in ond the chorge on its ions ? You con use sodium, mognesium ond oluminium os :

exomples.

b) Try to find o simpie mothemoticol equotion thot tells you the link between the chorge on o non-m etal ion ond its group number. Use oxygen ond fluorine os exomples. c) Corbon (which hos 6 electrons) never forms ions. Why not? d)Hydrogen (which hos 1 electron) con form both H+ ions ond H- ions. Exploin why ? e) Why do some people soy thot hydrogen should be obove lithium, Li, in the Periodic Toble, ond others orgue thot it should be obove fluorine, F?

Further questions on pqges 276 to 278. 255

nding

Goval In the lost chopter we sow how metols bond with non-metqls. Remember thot metol qtoms need to lose electrons, ond non-metols need to goin electrons. But think of oll those hydrocorbons in Chopter 11 ! Like mony compounds, they ore formed from just non-metals Which non-metols do they contoin ?

Both corbon ond hydrogen otoms need to goin electrons. So how do their otoms bond to eoch other ? How con they both goin electrons to get full outer shells ? It cqn t be like ionic bonding becouse there is no metol otom to give owoy electrons. Two non-metol otoms con both gain electrons by sharing ! If their outer shells overlop, they shore poirs of electrons. In this woy both otoms con goin elechons.

Methane is an important fuel. Its formula is CHo. The carbon and hydrogen atoms are joined to each other by covalent bonds

between non-metol qtoms. Let's look of the smollest hydrocorbon, methone It's formulq is CHa.

carbon atom

hydrogen atom

Corbon hos 4 electrons in its outer shell. It needs to goin 4 electrons to get o fullouter shell. (Remember thot the 2nd shell con hold 8 electrons.)

Hydrogen hos just 1 elechon. If it con goin 1 more electron, it will fill its shell. (The 1st shell is filled by just 2 electrons.)

1 corbon otom ond 4 hydrogen otoms overlop like this

Count the electrons in the outer shell of eoch corbon ond hydrogen otom in methone. o Is eoch shell complete ? Con you see thot the corbon now hos 8 electrons in its outer shell? How mony electrons does eoch hydrogen hove ? Is hydrogen stqble with this orrongement of electrons

?

It is electrostqtic ottroction between the poirs of electrons ond the C ond H nucleithot hold the qtoms together in the molecules. This ottroction (which is the covolent bond) only operotes between the poirs of nuclei.

In Chopter 11 we showed covolent bonds like this

O= ""'bon

metnane'

O = hydrogen

uH4

This'ball and stick'diagram shows the 4 single covalent bonds between C and H atoms. Each covalent bond is a pair of electrons.

Let's look of onother exomple of covolent bonding. Chlorine gos does not exist os single otoms. Remember thot o chlorine otom hos 7 electrons in its outer shell. It needs 1 more electron to fill it. How con it monoge to do this ?

Like mony goses, it is di-otomic. Two chlorine otoms bond together to mqke o Cl2 molecule. Look ot the diogroms below of the Cl2 molecule:

Citlorine aloms share a patr of e/eclrons in a covalenl bond covalent bond

ent bond

covalent bond

xx -14.

oj

a

aa

._

,.-.

*6',"

xx

'-*-*. Three ways to show the covalent bond in Cl2. The

:CI:CI:

righlhand one ls a 'dot and cross' diagram (showing the outer electrons only)

Count the electrons in the outer shell of eoch chlorine otom. Do they both hove 8 electrons? Are they both stoble compored to their otoms ?

Double bonds Do you recollthe molecule ethene from Chopter ll? Its formulo is C2Ha. We soid thot its corbon otoms ore joined by o'double bond'.

Con you remember how it forms poly(ethene)? (See poge 154.)

Corbon dioxide is onother molecule which contoins o double bond. Look ot the diogrom below:

o:

o

"eP

a double bond between the carbon and each oxygen atom

double bonds

o

Ethene has a double covalent bond betvveen its carbon atoms

How mony electrons ore in eoch oreo of overlop ? How mony electrons ore in the single covolent bonds in CHa ond Cl2 ? Eoch poir of electrons in the overlopping shells is o covolent bond. So o double bond is mode up of 4 electrons (2 poirs).

IO iC

iOI

double bonds (each double bond contains 2 pairs of electrons, i.e. 4 electrons)

'Dot and cross' diagram for CO2

257

)

Giont covolent structures

The greot voriety of life on Eorth depends on corbon's obility to form covolent bonds with itself As the element, corbon otoms con bond to millions of other corbon otoms in both diomond ond grophite.

Corbon in the form of diomond Do you know the hordest substonce on Eorth ? Look ot the photo opposite: Diomond's hordness mokes it o very useful mqteriol. You con reqd more obout its uses on poge 260.

Diqmond is mode from only corbon otoms. Think bock to the previous poge. How mony covolent bonds con eoch corbon otom form Look ot the diogrom below:

?

Some drll/s are tipped with diamonds. This one cuts through rock when drilling for oil.

covalent bonds between all the carbon atoms

The giant covalent structure of diamond

Eoch otom forms 4 strong covolent bonds with its neighbours. The otoms ore orronged in o giont covolent structure. Some people collthis o giont moleculor or mocromoleculor structure. o Does diomond hqve o high or o low melting point ? Exploin why.

Another substonce with o giont covolent structure is silico. Its chemicol nome is silicon dioxide (SiO2). It melts qt over 1500'C. Substonces with giont covolent structures

ore not soluble in wqter. Their porticles ore not chorged (unlike ionic compounds). So woter molecules ore not ottrocted to them. They don't conduct electricity in ony stote. There ore no free ions or electrons to corry the chorge. (Grophite is on exception; see the next poge.)

@tlr*i,ru11,''*uu,l'

Although diamond is very hard, it can be split in certain directions (cleaved) to make jewellery

Corbon in the form of grophite Another form of corbon is grophite. Diomond ond grophite ore ollotropes of corbon. Allotropes ore different forms of the some element (in the some stote). The corbon otoms in grophite ore olso held together in o giont covolent structure.

\ ,r

However, some of its properties ore very different from o typicol giont covolent substonce, such os diomond or silico.

,

Graphite (mixed with clay)is used ln

pencil'leads'

If you touch o lump of grophite, it feels smooth ond slippery. Your pencil contoins grophite. As you move it ocross your poper it flokes off, leoving o troil of corbon otoms. Look ot the diogrom below: strong covalent bonds between the carbon atoms in each layer I I

weaker forces hold the layers together

The giant covalent structure of graphite

The loyers con slide over eoch other eosily. o How does this exploin grophite's use in pencils

?

Do you know the only non-metol element thot conducts electricity well? Think of the electrodes we use in electrolysis. (See Chopter 7.) o How mony neighbouring corbon otoms ore bonded to eoch other by strong covolent bonds in grophite ? Why is this stronge ? The 4th electron from eoch corbon otom is found obove ond below the plone of the loyers. These electrons ore only held loosely to the corbon otoms. They con drift olong the loyers in grophite. We collthem 'delocolised' electrons. These electrons mqke grophite o good conductor of electricity. Look of the diogrom opposite: o Do you think thot grophite conducts better olong its loyers or ocross them ?

Grophite does not melt when you heot it. At over 3000'C it turns stroight into o gos. We soy it sublimes. This is colled sublimotion. o Why does it toke o lot of energy for grophite to sublime

+ 'delocalised' electrons can move along the layers in graphite

?

Chemistry of work Uses of diomond Jewellery We ollknow obout the use of diomonds in jewellery

If you hove ever looked in o jeweller's shop, you willknow how expensive they ore. Diomonds hove ideol properties for gemstones. A well-cut diomond reflects light better thon ony other gem (it hos'brillionce'). It olso disperses white light into the colours of the spectrum (it hos 'fire').

A diamond

brooch

Cutting tools Diomond is the hordest of oll substonces. It is used on the edges of drills on oilwells. (Look bock to the top photo on poge 258.) It olso lines circulor sows used to cut metol, stone ond other hord moteriols. A new process con now fuse together tiny diomonds. So insteod of metol cooted in diomonds, you con now use o solid diomond tool on o lothe. This con cut ond shope the hordest moteriols.

An engraver using a diamondlipped 'pen' to produce a design on g/ass

Diomond cooted surgicol instruments ore used for delicote operotions, like those on the eye.

Another use Which types of moteriols ore the best conductors of heot Most people would soy thot metols ore. However, diomond is o better thermol conductor ! On the other hond, it is o poor electricol conductor. This leods to its use in electronics to get rid of heot produced in circuits.

?

Diomond mines The diomond industry is very big business in South Africo. Diomonds ore often mined from some of the deepest mines in the world. The diomonds ore formed under huge pressure ond high temperotures woy beneoth the surfoce. The working conditions ore tough for the miners ond mony in South Africo live in poor townships. The dust from the mining woste is o constont problem. o Discuss the issues roised by the diomond industry.

Ihis surgeon is operating on an eye using diamond coated instruments

F Chemistry ot work : Corbon Uses of grophite Pencils We hove olreody tolked obout grophite's use in pencils on poge 259. lt is mixed with cloy to moke it horder. You know thot there ore different grodes of pencil. such os H. HB, or 28. Which grode of pencil mokes the dorkest lines on poper How do you think the omount of cloy vories in eoch

type of pencil? Which type do you think needs shorpening most often

2HHHB28

?

?

Lubricont Grophite feels very slippery. It con be used os o powder to lubricote metol ports on mochinery. When would you need to use solid grophite rother thon oil? Remember thot grophite only turns to o gos ot over 3000'C In some lubriconts. grophite is odded to improve its properties.

* !

oilto The layers of carbon aloms s/ide over each other eastly, makrng

graphite a good lubrlcant

Grophite into diomond

!

The diomonds used in cutting ond grinding tools ore colled industriol diomonds. They ore not mined from the ground, like gemstone diomonds. They ore mode in foctories from grophite.

Grophite is squeezed in o press ond heoted. A metol is used os o solvent ond o cotolyst. The temperoture is obout 1400'C in the press, ond the pressure is 60 000 times normol oir pressure I The diomonds ore mode in o few minutes. Under these conditions, onything contoining corbon, even wood, chonges into diomonds The diomonds mode ore smoll ond unottroctive. Monufocturers con vory the sizes to suit the use by chonging conditions. !

.

+;.

,i 7, .:

w dtn*,

lnclLtstrial dramonds are small and unattractive. However, sclenl/sls in the USA have developed a new technique They recently made a dianond over 25 crn longl

261

, Bucky-bolls ' In 1985, o new form of corbon wos discovered. Its molecules ore mode from 60 corbon crtoms joined together. The otoms fold oround ond moke o boll-shoped molecule. Look ot the photo opposite: The new molecule looks just like o footboll ! The corbon otoms form pentogons ond hexogons, like the ponels on o footboll. Its fuil nome is buckminster-fullerene. Scientists nomed it ofter on orchitect, Buckminster Fuller. ln 7967 , he designed o bucky-boll shoped building in Montreol. Buckminster-fullerene is o block solid thot dissolves in petrol to moke o deep red solution.

The new molecule hos excited o lot of interest. Other similor molecules hove been discovered. One is shoped like o rugby boll ond others ore shoped like tubes. A model of buckmrnster-fullerene

The fullerene fornily

-(,@ ot

Look of some of the fullerene fomilv below

-@

&

@

%"c

t-(J oo o u $o e

o.a

Elp I

A molecule of C,s. shaped like a rugby ball

"P, J6

b %

The oilginal bucky ball. C,;,,

#ffi We

$q$q

can also make larger cage-llke structures such as and Crrs

C2,,u

262

r)O a@ ^& @ .E'

O^GL

% ts o e h@ @ @ q@ ^c o @@

ec

Ort

@o@ oo €g

@? @6Do OGr

c55 @

"6"

s3a 6_

Chemi Uses of the fullerenes Chemists hove olso mode on exciting group of corbon ollotropes colled 'bucky-tubes'. Look ot the diogrom opposite: They moke these by joining together fullerenes. These tiny tubes ore sometimesreferred to os nonotubes.

The nonotubes ore used os:

o

r o

semi-conductors in minioture electricol circuits industriol cotolysts (the cotolyst is ottoched to the nonotube producing o lorge surfoce oreo) reinforcing tennis rockets (they ore very strong but light).

You con reod more obout nonotechnology on poge 336.

o Whot ore the odvontoges

ond potentiol drowbocks of developing new cotolysts with incredibly lorge surfoce oreos ?

Potentiol uses Bucky:TV

Sir Harry Kroto

Reseorchers in the USA hove found o woy of lining up 'bucky-tubes' on the surfoce of gloss. The 'bucky-tubes' stick out ot right ongles from the gloss which could be used os flot screens for TVs or computer monitors. The tubes could eoch fire electrons from the end

sticking out of the screen. This would reploce bulky cothode roy tubes used in most sets. It promises to give us brighter pictures thot you con view from o wider ronge of ongles.

Bucky-strength Isroeli ond Americon scientists hove shown thot bucky-tubes con withstond pressures olmost o million times otmospheric pressure. This mokes them obout 200 times stronger thon ony other fibre. They believe the bucky-tubes con be embedded in other moteriols like plostics to moke incredibly strong moteriols. These might be used, for exomple, in moking bullet-proof vests. Bucky-mules Bucky-bolls ond coges con trop otoms or groups of otoms inside their structures. Scientists ore developing woys of using these 'moleculor mules' to corry drugs or rodiooctive otoms, used to treot concer, to the sites in the body where they ore needed.

+ r,' l}--

'

t

t

-;

,

i_.

)'f ?'

i I

1*t}

t-t

.t

a

)

Simple moleculor structures

You olreody know thot covolent bonds ore strong. So hove you ever wondered why lots of substonces with covolent bonds ore eosy to melt or boil? Let's toke methone, CH4, os on exomple: It hos o very low boiling point. It boils ot - 161'C ! (Compore this with the volues given for the giont covolent strucfures in the toble opposite.) By the time you get to room temperoture (obout 20"C), methone is olreody o gos. And yet it hos strong covolent bonds holding its otoms together, just like diomond. So why is it so eosy to boil methone ?

With 2 non-metals, each atom wants more Both need electrons to make up the score. A deal is struck, "Our electrons we'll share." Covalent bonds formed by electron pairs.

moleculal structure Boiling pt.("C)

Substance

Boiling pt.("C)

diamond

4830

methane

-164

silicon sand (silica)

2355

water chlorine

100

Substance

2230

-35

j

weak forces between molecules

To onswer this question, you must reolise thot

^\

no covolent bonds ore broken when methone boils. When it boils, single CHa molecules move oport. They seporote from eoch other but they ore still CHa molecules.

(\^)

^hf

eob

Compore this with the giont covolent structures of diomond, silicon or sond. To boil these, we hove to breok oport the whole giont structure. Millions of covolent bonds do hove to breok in these exomples.

Substonces, with low melting points ond boiling points hove simple moleculor structures. Simple moleculor substonces hove strong covolent bonds joining their otoms within eoch molecule. However, they only hove weok forces between individuol molecules. Irlethane We soy thot they hove weok inter-moleculor forces.

ng covalent bonds

within each molecule has a simple molecular structure

Experiment 20.7 Heating iodine U:e lweezers to put o few iodine crystols in o flosk. Reploce the bung. Hold the bose in your honds for o few minutes, os shown: Look corefully through the flosk, ogoinst o white bockground.

o Whqt con you see ? /i\ o Do you think it is eosy or hord to seporote iodine molecules

o

from eoch other? Do you think it hos o giont structure ? Iodine turns stroight from o solid into o gos. Whqt is this type of chonge cqlled ? (See the bottom of poge 259.)

Iodine, 12, hos o simple moleculor structure. Weok forces hold its molecules in ploce in its crystols. It does not conduct electricity in ony stote. Thot's becouse its molecules corry no overoll chorge.

W

iooin"

\ / .3

:-

Experiment2A.2 Heating sulfur

loose plug

A

::llT"oi3l#:on* collect 2 spotulos of powdered sulfur in q test t u". Worm it slowly ond gently over o Bunsen flome in q fume-cupboord. o Whot hoppens ? Desoibe the chonges you see os it melts.

ol mineral wool

sullur , '

t

When it hqs melted, heot the sulfur more strongly. Keep the flome owoy from the mouth of the test tube. It could ignite ony sulfur vopour escoping. o How does the sulfur chonge ?

he4t

When the liquid is obout to boil, remove the minerol woolplug. Pour it quickly into o beoker of cold woter.

o

Whot hoppens

sullur

?

Get the solid formed out of the beqker. Pull ot it gently. o Whot hoppens ? Is the solid stretchy ?

1. Sulfur exists os Ss molecules ot room temperoture These crown-shoped molecules ore pocked neotly together to form crystols.

2. It melts of 115'C. This low melting point tells us thot sulfur hos o simple moleculor-stiucture. There ore relotively weok forces between its molecules.

plastic sulfur

II

strong covalent bon

weak inter-molecular

l;:lit"".

molecules)

I

3. As the molten sulfur is heoted more strongly, the rings of 8 sulfur otoms open up. They then join together to mqke long choins.

4. Neor its boiling point the long choins stort to breok up. They escope from the liquid os o gos

5. If you pour the molten sulfur into cold woter, plostic sulfur is mode. The sulfur does not hove time to chonge bock into its 56 molecules. It is 'frozen' in o long choin structure, like rubber Eventuolly the plostic sulfur goes hord. It chonges bock slowly into 56 molecules ogoin.

In generol the lorger the molecule, the stronger the intermoleculc forces.

cold

U heat

heat

I r

heat

U

u etc

heat

the chains start snapping and the liquid goes runny again

U

cold water

ffi. plastic sullur

265',

Summory o Non-metol otoms ore bonded to eoch other by covolent bonds. c A covolent bond is o shored pair oJ electrons.

c

r o

o

F

Covolent substonces con hove either: o ogiont covqlent structure, or

o o simplb"'moleculor structure.

Cl tlttritc Slorrs:h t(,1Dait c; Giont covolent structures ore huge 3-dimensionol networks of otoms. electrcns in a covalenl br:nd Millions of otoms qre oll joined by strong covolent bonds. This meons thot they hove high melting points ond boiling points. Simple moleculor substonces ore mqde of smoll molecules. The qtoms in eoch molecule ore joined together by strong covolent bonds. However, there ore only weak forces of ottroction between molecules. In generol, the lorger the molecule, the stronger the intermoleculor forces (so the higher the melting ond boiling points). Substonces with covolent bonding do nof conduct electricity (except for grophite).

S" Fluorine forms di-otomic molecules,

Questions

i " Copy ond complete: Non-metolotoms bond to eoch other by

...

.

electrons. These ore colled .... bonds. Covolently bonded substonces with high . . . .

points ond high boiling points, hove

...

;& .

structures. On the other hond, substonces with low melting points ond low boiling points hove . . . . moleculor sfuctures. These hove strong covolent bonds within eoch ... ., butweok forces .... molecules.

No covolently bonded substonces conduct electricity. except .. . .

F2.

(Fluorine otoms hove 9 electrons.) Drow o diogrom to show the bonding in on F2 molecule.

" Woter is o covolent compound. Its formulo is H2O. (Hydrogen otoms hove 1 electron.) (Oxygen otoms hove 8 electrons.) o) Drow o diogrom to show the bonding in on H2O molecule. b) How con you tell thot woter hos o simple moleculor structure ?

.

2, Look ot the toble below: Substonces A, B, C ond D oll hove covolent

l-r" Corbon exists os diomond ond grophite.

o) Whot do we coll different forms of the some element ?

bonds. Substance

Melting point ("C) Boiling point ('C)

A

-125

-90

B

5

C

2204

170 3900

D

55

325

o) Which substonce hos o giont covolent structure ?

b) Which type of structure do the other substonces hove ? c) Which substonce is o gos ot room temperoture (obout 20 "C) ? d)Which substonce is o liquid ot room temperoture ?

b) Diomond ond grophite hove very different properties ond uses. Use their structures to exploin these differences.

{:

Alon heoted some sulfur in o test-tube inside o fume-cupboord. He heoted it until it wos olmost boiling. o) Describe the chonges Alon would see in the test-tube. b) Exploin these chonges. c) Why did he do his experiment in o fumecupboord ?

7.

o) Motch eoch of these descriptions (A to E) to the correct substonce (1 to 5) :

8.

Descriptions: A. A block solid thot

dissolves in petrolto form o deep red solution. B. A gos thot turns limewoter milky. C. A tronsporent solid thot is the hordest substonce on Eorth. D. A dork grey solid thot is o non-metol but conducts electricip well. E. A gos thot we con use os the fuel in o cooker or o Bunsen burner. Substonces: 1. Corbon dioxide. 2. Grophite. 3. Methone. 4. Buckminster-fullerene. 5. Diomond.

b)Whot do we collo molecule thot is mode up of two otoms? c) Give the nome ond formulo of onother molecule with the formulo X2. d)Whv is the boiling point of oxygen - 183'C? e) Sulfur exists os rhombic ond monoclinic sulfur. Both ore crystolline solids. Whot nome describes these two forms of sulfur? f) Sulfur otoms hove 16 electrons. It does not oC, but os rings exist os 52 molecules of 20 of 8 otoms in Ss molecules:

b)Which substonces in the obove list ore compounds? c) Which of the substonces is mode up of molecules, eoch contoining 5 otoms? d) i) Divide the substonces into two groups:

'High boiling points' ond 'Low boiling points'. Discuss ony difficulties you hove clossifying the substonces. ii) How do the structures of the substonces exploin you onswer to port i)? e) Which of the substonces hove otoms joined to eoch other by strong covolent bonds? (Coreful!) f) Drow o diogrom to show the bonding in o corbon dioxide molecule. (You moy wish to use o 'dot ond cross' diogrom.) g) Which of the substonces is shown below?

o) Oxygen otoms hove 8 electrons. Exploin why we con represent on oxygen molecule os:

strong covalent bonds

weak inler-molecular forces (between molecules)

Exploin how eoch otom in on 56 molecule hos ochieved o complete outer shell of electrons. g) Whot is the missing word in this sentence?

Sulfur hos o higher melting point ond boiling point thon oxygen becouse its

moleculesore....

9.

This question is obout the fullerenes. Corry out some reseorch on the fullerenes.

Find out: o) how buckminster-fullerene wos discovered, b)why the discovery con be used os on orgument for funding 'pure' scientific reseorch,

c) the uses ond potentiol uses of the fullerenes.

Further questions on poges 278 to 28O.

25V

"

)

Metols

Think of some of the things oround your home thot ore mode of metol. Did you include oll the wiring, ony rodiotors, your hot-woter tonk, or your cutlery ond pons ? o Do you know which metols these things ore mode from o Which properties moke metols good for these uses ?

?

In the lost two chopters we hove looked ot ionic ond covolent bonding. But the otoms in o metol ore held together in o different woy.

) Metollic

bonding

Do you remember oll the properties of metols ? Any ideos we hove obout the bonding ond structure of metols must be oble to exploin their properties. Metols hove giont shuctures. Most: o hove high melting ond boiling points o conduct electricity ond heot . ore hord ond dense o con be hommered into shopes (they ore molleoble) . con be drown out into wires (they ore ductile). We believe thot metolqtoms (or positively chorged ions)

ore held together by o 'seo' of electrons. Look ot the diogrom of sodium metol below: sodium's outermost electron

llletals are very useful matenals

/l\

metallic bonding: t-)

sodium atoms

sodium ions bonded together by a sea of delocalised electrons

Eoch sodium otom gives up its electron from its outer shell into the 'seo' or 'cloud' of electrons. The electrons con drift obout in the metol. We coll them'delocolised' electrons. These free electrons exploin how electricity con poss through solid metols. o Whot hoppens when one end of the metol is mode positive ond the other end negotive ?

1.,,,

gGB.

o o

o

o

o

electrons can drift anywhere in the shaded area. There are strong electrostatic forces of attraction between the delocalised electrons and the positive metal ions. bonding the giant lattice together.

+

Electrons move towards the positive charge.These free electrons can also transfer heat through metals quickly

Chemistry of work: Imogine the energy sovings we could moke from o 'frictionless' troin; o troin thot could hover obove its trock, moking no contoct. Well thot is whot reseorchers hove developed using super-conductors. The MAGLEV (mognetic - levitotion) troin hos superconducting mognets on boord, which let it 'floot' obove the coils in its trock. A super-conductor is o substonce whose elechicol resistonce drops to zerobelow o certoin temperoture. This wos discovered in 1911, using mercury. The metol wos cooled by liquid helium to -269"C. You con't get much colder thon thot The resistonce thot every metol hos to electrons flowing through its sfuucfure just disoppeored.

!

Ihis lest train

has raced

along its track at

Since then, scientists hove been striving to invent moteriol thot f,2!,{rf"ir!i,!3!f[i""l3r[f'{u!f,3!'3, will super-conduct of higher temperotures. Now the record is large magnetic field around the train.

up to

_135.C.

*"

ie What do you think about developing the

high speed, low energy train?

This might sound cold but it is well obove the temperoture of o common coolont, liquid nitrogen. The higher this temperoture, the eosier it willbe to develop new opplicotions. The prize thot the reseorchers reolly wont is to tronsfer electricity olong the Notionol Grid with no energy losses. Normol copper wires heot up when electric current posses through it. If we could use new superconducting moteriols, there would be no resistonce of ol1. So we wouldn't hove to burn os much fossil fuel in power stotions, reducing oir pollution. Engineers hove now built electricity generotors thot ore 997o efficient. Tests olso show thot super-conducting wires would toke up 70OO% less room thon

A su pe r -con

ISIS

ucli ng cable

& E

!

conventionol cobles.

E E

t

In medicine, you hove seen the MRI body sconner on poge 58. Now there ore much smoller monitors thot don't subject the potient to such lorge mognetic fields. Reseorchers ore olso trying to develop new super-fost electronic circuits to use in computers. Look ot the projected growth of industries bosed on super-conductors: * Whot could offect the projections on the groph ? How might they grow even foster

d

o =

o)

o (g

o

tr

1995 2000 2010

2020

lSlS = lnternational Superconductivity lndustry Summit ?

Electronics Energy Transportation lndustrial Medical

F

Alloys

Hove you ever trovelled in on oeroplone ? Did you know thot the oeroplone wos mode moinly from oluminium ? c Why do you think oluminium is chosen for this job

?

Notice thot oeroplones ore mode mainly from oluminium If they were mode from pure oluminium, their wings would soon snop off Pure oluminium is not strong enough to cope with the greot stress put on wings during flight. !

Aeroplanes are made from aluminium alloys

So how con we combine the low density of oluminium with the strength on oeroplone needs ? Alloys give us the onswer.

An olloy is o mixture of metols. If smoll omounts of onother metol ore odded to oluminium, it becomes o lot stronger. The metols ore mixed together when they ore molten. (Notice thot metols never react with eoch other. They form o mixture, not o new compound.) You con see how olloying offects the structure of o metol in the next experiment:

Experiment

21.7

Bubble bath!

?

Now inject o lorger bubble into the middle of the dish This is like odding on otom of o different metol. In other words, you hove mode on olloy I

o

Con you see how this disturbs the regulor pottern

of bubbles

270

?

a bubble raft (a Petri dish containing a solution of washing-up liquid)

Exploining the properties of olloys Your observotions from the lost experiment will help you to understond olloys.

Look ot the diogrom below:

r> force

ts force

pure metal

layers slide over each other easily in a pure metal

In o pure metol, the otoms qre oll the some size. Loyers con slide over eoch other eosily. This hoppens when metols ore hit with o hommer, o Whot do we coll this property ? It olso hoppens when o metol is stretched. o Whot do we coll this property ? However, look whot hoppens when we odd otoms of o different size;

.

How do you think this copper blade was made? Why didn't it smash? a different sized atom disrupts the regular pattern

lorce the atoms can't slip past each other as easily in an alloy

+ialloy

The loyers of otoms con't slide over eoch other qs eosily now. They get 'jommed' in ploce. The olloy is o lot horder ond stronger thon the originolmetol. You con reod obout some uses of olloys on the next two poges

Aluminium olloys You know thot olloys ore mixtures of metols. The blend of metols hos different properties to the originolmetols. We sow how olloying oluminium greotly increoses its strength so it con be used to moke oeroplones. The olloy is colled durolumin. It hos obout 4"/" copper ond o little mognesium odded to the oluminium. Aluminium olloys ore expensive becouse we hove to extroct oluminium by electrolysis. (We con't use the cheoper reduction by corbon becouse oluminium is too reoctive to be disploced by corbon.) The process uses o lot of energy in melting the oluminium oxide ond then possing electricity through it

Titonium olloys Titonium olloys ore expensive. Although it is not o reoctive metol, we con't extroct it using cheop corbon. When we try to, titonium reocts with the corbon. This mokes the metol brittle. So we hove to use o more reoctive metol, such os sodium or mognesium, to disploce it. Also, of course, the reoctive metol hos hod to be extrocted by electrolysis ! The extroction of titonium tokes severol steps, which olso mokes it on expensive process.

Nlemory metals Some olloys ore smort ! They con 'remember' their originol shope. If they get deformed, ot o certoin temperoture they will return to this shope. The moin 'shope memory metol' is colled nitinol. It is on olloy of nickel ond titonium. Its uses include: o broces for teeth o ontennoe for mobile phones o under-wires for bros o fromes for spectocles ond sun-glosses c fire sprinklers o supports to open blocked orter]es.

\

hru,

This type of Nitinol has a transition temperature, which is below room temperature, so it reverls lo its original shape auto m ati c al ly. Ihese sungiasses are expensive at the moment.

Artificial joints The joints in our bodies toke o lot of weor ond teor.

The 'boll-ond-socket' type joints in the hip ond shoulder hove to work especiolly hord. Sometimes the joints ore ottocked by orthritis. This is o very poinful ond crippling diseose. Look ot the photo opposite Now people con be fitted with replocement joints. These ore mode of plostic ond titonium olloys. r Whot properties must on olloy used inside your body hove :

?

This hip joint is made from an alloy of tilanium. Like aluminium, titanium is protected by a tough oxide layer on its sulace.

Gold olloys Pure gold, os well os being very expensive, is o soft metol. Just think of the weor ond teor on o gold wedding ring.

The metol is mqde more hord-weoring by olloying it with copper. Hove you got onything mode from gold ? If you hove, do you know whot 'corot' gold it is ? This tells you how much copper is odded to the gold. The higher the corot, the less copper. Z4-corot gold is pure gold. On the other hond, 9-corot gold is obout two-thirds copper ond one-third gold.

Copper olloys Hove you ever heord o bross bond or o pop group with o bross section ? Bross is o mixture of copper ond zinc. Musicol instruments mode of bross moke o pleosing, sonorous sound. It con olso be stomped or pressed into the intricote shopes of the instruments Bross hos other useful properties os well. It is much stronger thon copper or zinc. Bross hos o lower melting point thon either metol. This mokes it eosier to cost into shopes. You've probobly heord of the 'bronze oge' . People hove been using the olloy of copper ond tin for thousonds of yeors. Bronze mode it possible to moke more complex ond effective tools ond weopons

Leod olloys Hove you ever used o soldering iron ? Solder is used to join up ports of electricol circuits. This olloy is mode from leod ond tin. It hos o low melting point for o metol Why is this importont ? The solder is mode into thick wire. It melts when held ogoinst o hot soldering iron. Other olloys melt ot even lower temperotures (obout 70"C). These ore used in outomotic fire sprinklers.

Mercury olloys Mercury is the only liquid metol ot 20'C.lt is useful for olloying becouse it con 'dissolve' other metols, without the need for melting os in other olloys. Its best known use is for fillings in teeth. The dentist con mix the mercury omolgom, which is gooey so it con be pressed into the tooth covip. It then sets hord quite quickly. People ore worried obout the toxicity of mercury in dentol core, ond new plostic olternotives ore now ovoiloble. The omolgom contoins obout 50% mercury plus silver, copper, tin ond zinc.

273

Summory r Metol otoms ore

these

most metols Mixhrres of metqls ore colled An olloy is stronger thon the

A/letal al.oms are usual

ionic Bonding

(between metals and non-metals)

covalent

metallic

(between non-metals)

(between metals)

,/\

I

v

I

ly'close-packed'

/

I

\

I

Structures

giant ionic

giant covalent

simple molecular

giant metallic

Melting point

high

high

low

high

Conduct electricity ?

not when solid, but they do when molten or dissolved in water (when ions are free)

no

no

yes (has free electrons)

Example

sodium chloride

diamond

water

ztnc

frc" F*g

F Questions

5. Anne hos been given somples of oluminium, copper ond on olloy of the two metols. She hos rods, wires ond blocks of the 3 metols. o) How ore olloys of oluminium ond copper mode ? b) Design o series of tests so thot Anne con find out which of the 3 metols: i) is hordest ii) is most difficult to snop (hos the

1" Copy ond complete : A '. . . .' or 'cloud' of electrons join metol otoms (or .... chorged ions) together in .... structures. Metols con . . . . electricity becouse these . . . . ore free to drift through the structure. Most metols hove . . . . melting points becquse it tokes o lot of energy to breok down their . . .

iii)

structures.

2. CopV ond complete

Soy how you mode eoch one oJair test ond how you would collect reliable dqta.

:

There ore 3 types of bonding

-

ionic,

greotest tensile strength) resists corrosion best.

ond

c) Whot results would you expect for the hordness ond tensile stength tests? Exploin why.

.. . . bonds form between metols ond non-metols. The ions ore orronged in . . . . structures, which hove high melting points. Sodium chloride is on exomple. It does not conduct electricity when . . . . , os its ions qre fixed in position. However, when molten or . .. . in woter, the .. .. become free to move. It is electrolysed os it conducts. Covqlent bonds form between non-. . . . otoms. These substonces cqn hove either o . . . . structure, like diomond (with o. . . . melting point), or be mode up of simple . . . . , like woter (with o. . . . melting point). Neither type of structure conducts electricity. The only

exceptionis..... Substonces with giont . . . . structures ore the only ones thot conduct electricity when solid.

3.

o) Moke o list of the generol properties of metols.

b)Write down ony metols you know thot don't hove the usuolmetollic properties. Nome o property thot all metols hove in c) common.

4.

Moke o summory toble obout olloys under these heodings:

Alto; .: ::.::::::i,'l

//\-

--4--

-

'^--A.^

6.

Look ot this toble:

A

1500

B

115

c

-0.5

D

660

x x x

x x

Exploin your onswers to eoch question below: o) Which substonce is mode up of ions orronged in o giont structure ?

b)Which is o metol? c) Which substonces ore mode up of relotively smoll individuol molecules ? d) Which is o non-metol solid ot 20'C with o simple moleculor structure ? e) Which substonce is broken down os it conducts electricity ?

7. Sodium, mognesium ond oluminium qre in Groups 7,2 ond 3 of the Periodic Toble. Sodium hqs 11 electrons, mognesium hos 12 ond oluminium hos 13 electrons. o) Drow eoch otom showing the orrongement of electrons. b)The metolelements hove metqllic bonding. How mony electrons do you think the otoms of eoch metol in o) donote into the 'seo' of electrons ? c) Aluminium is the best conductor of electricity. Sodium is the worst. Con you exploin this ?

Further questions on poges 281 to 283. aqts

zt3

Further questions on Structure ond Bonding

tr lonic compounds

3.

1. Look ot this informotion obout sodium ond

A B C D

chlorine:

o

o)

?lcr

i)

How mony protons does on otom of sodium hove ? t1l ii) How mony electrons does on otom of chlorine hove'? t1l iii) As well os electrons ond protons, most qtoms contoin o third kind of porticle. Whot is its nome? t1l b)When sodium forms compounds it usuolly does so os o positive ion with one unit of chorge. i) Whot chonge in electron structure occurs when o sodium otom becomes o sodium ion ? t1l ii) Whot chonge, if ony, occurs in the nucleus when the ion is formed ? t1l c) When chlorine forms on ionic compound it goins one electron. Whot symbol is used to represent the chloride ion formed in this

woy?

tll

d) Exploin why the formulo for the compound formed when sodium ond chlorine reoct is

NoClond not

NoCl2.

t2l

e) Whot does the informotion given below tell you obout the structure of eoch substonce ?

Chlorine melts ot -101'C. Sodium chloride melts ot 801"C.

Atoms con form ions with o single negotive chorge. To do this the otom muit

t4l

goin o proton goin on electron lose o proton lose on electron

tll

(A0A)

4.

The elements of Group 1 form ions with o single positive chorge e.g. No+. The elements from Group 2 form ions with o double positive chorge e.g. Coz+. Exploin this in terms of their electronic structures. t2l (OCR)

'5.

Use the Periodic Toble on poge392 to help you onswer this question. o) An otom of the element with otomic number t hos o moss number 19. i) Stote the number of neuhons ond protons in the nucleus of the otom. ii) Stote the number of electrons in on otom of the element. iii) Describe, with the oid of diogroms, the formqtion of ions in the reoction of the element with sodium. iv) Give the chemicol nome of the compound formed when the element reocts with sodium t7l b) Exploin why solid sodium chloride does not conduct electricity, but oqueous sodium chloride does. tsl (EDEXCEL)

6. The diogroms below show the electronic structure of qn otom of colcium ond on otom of oxygen.

(AOA)

2. When lithium

reqcts with fluorine, lithium fluoride, Lif, is formed. It is mode up of positive ond negotive ions. o) How ore the positive lithium ions formed from lithium otoms ? t1l b)How ore the negotive fluoride ions formed from fluorine otoms ? tll c) Exploin how the ions ore held together in lithium fluoride. t1l d)Nome this type of bonding. tll e) Exploin why the bonding in lithium fluoride, Lif, produces o high melting point

solid.

276

t2l

(WJEC)

o) Describe, os fully os you con, the ions thot ore formed when otoms of these elements

reoct.

b) Colcium oxide

t2l is on insoluble ionic compound.

Why do ionic compounds hove high melting points ?

Note: although a question may be markecl (AQA) etc., it will often be relevant to other examinations as well.

t2l

Further questions on Structure ond Bonding c) Whot must be done to the solid colcium oxide to moke it conduct electricity ? Suggest o reoson for your onswer. t2l

10" Mognesium oxide is o compound mode up of mognesium ions ond oxide ions.

(AOA)

7.

The Periodic Toble on pqge392 moy help you onswer ports o), i) ond ii) of this question. The diogrom below shows the structure of sodium chloride.

o) Whot is the chorge on eoch mognesium ion t1l b) Exploin how the mognesium ions get this

?

o I

sodium ion

)

)

__),.,

chorge.

t2l

(AOA)

11. The element mognesium (otomic number 12)

chloride ion

reocts with chlorine (otomic number 17) to form the compound mognesium chloride, MgClz.

o) Give the meoning of eoch of the following

words:

o)

i) element ii) compound t2l b)The diogroms below show the electron shells in o mognesium otom ond in o chlorine otom. Copy ond complete the diogroms to show the orrongement of electrons.

i)

How does the structure of o sodium ion differ from the structure of o sodium otom t1l ii) How does the structure of o chloride ion differ from the structure of o chlorine otom ? t1l iii) Whot ppe of chemicolbond is present in sodium chloride ? t1l b) Use the diogrom of sodium chloride to help you to exploin why: i) sodium chloride crystols con be cube

?

ii)

8.

shoped,

tll

iii)

solid sodium chloride hos o high melting point, t2l solid sodium chloride is on electricol

iv)

molten sodium chloride willundergo

insulotor,

electrolysis.

t2l

(AOA)

:

oxide.

t2l

(WJEC)

(Mg)

Chlorine atom

(Cl)

t2l

chloride, MgCl2? t4l d)The compound mognesium chloride hos ionic bonding. Exploin whot this meons.

t2l

Using the list of ions on poge 391 write the formulo of o) iron(ll) sulfote.

b)iron(lll)

Magnesium atom

c) Whot hoppens to these electron orrongements when mognesium reocts with chlorine to form mognesium

t2l

12.

(AOA)

The tqble shows the properties of two substonces.

Does it Melting Does it Substanee dissolve point ('c) smell? in water?

Whal colour is it?

Does it conduct

electricity when...

(No) ond chlorine (Clz) reoct together to form sodium chloride (NoCl). o) Write o symbol equotion for this reoction. lli b) Sodium chloride contoins sodium ions (No+). Write on equotion to show the formotion of o sodium ion from o sodium otom. Use the symbol e- to represent on electron.

o) Which of these substonces hos o giont ionic structure t1l b) Give two reosons for your choice [2]

(ocR)

(AOA)

9. Sodium

t1l

solid? A

yes

B

no

1

000

no

white

no

125

yes

yellow

no

?

melted?

no

?

277

Further questions on Structure ond Bonding 13. The diogroms below show the orrongements of electrons in the inner energy levels (shells) of potossium ond chlorine otoms.

chlorine

15. Use the Periodic Toble on poge392 to help you onswer this question. Exploin, with the oid of diogroms, how covqlent bonds ore formed between corbon ond hydrogen in methone, CH4. Indicote which noble gos electron configurotion is ochieved by the otoms.

t3l

(EDEXCEL)

16. Chlorine willcombine with the non-metol o) Use the Periodic Toble on poge 392 to help you onswer this port of the question. Copy ond complete both the diogroms by odding the correct number of electrons in the outer energy level of eqch otom. t2l b)Describe whot hoppens when potossium otoms ond chlorine otoms reoct to form potossium ions ond chloride ions. t2l c) Use the toble on poge 391 to help you onswer this port of the question.

i)

ii)

Write the symbols for the ions of potossium, mognesium ond chloride. /2J Use your onswers to write the formulos

of potossium chloride ond mognesium

chloride.

t2l

(AOA)

14. The diogrom represents the orrongement of electrons in o mognesium otom.

elernent, corbon, to form this moleculor

compound.

o) Whot is the type of bond in this molecule

b) Exploin how these bonds ore formed. (You moy use o diogrom.) t2l (AOA)

17. Which of the substonces A, B, C or D consists of smoll molecules Substance Melting Poinl high high low low

Number o,

neutrons electrons magnesium-24

.

tLl Electron arrangement

?

Electrical

conductivity ol solid

o) Copy ond complete the toble

?

tll

nil

good good nil

Electrical conductivity of solution in water good insoluble insoluble nil

t1l

(AOA)

18., The diogrom represents on otom of fluorine Only the outer electrons ore shown.

2,6,2

oxygen-1 6

b) Mognesium oxide contoins ionic bonding. Exploin fully, in terms of tronsfer of electrons ond the formotion of ions, the chonges which occur when mognesium oxide is formed from mognesium ond oxygen qtoms t4l (OCR) 278

The otoms in o fluorine molecule, F2, ore covolently bonded. Drow o diogrom to show the orrongement of electrons in q fluorine molecule. t2l (OCR)

Further questions on Structure ond Bonding o) Whot type of porticles ore represented by the crosses t1l

19. One oxygen otom willbond to two hydrogen otoms to form o woter molecule, H2O. One nitrogen otom will bond to three hydrogen otoms to form ommonio, NH3. Exploin, with the help of diogroms showing the orrongement of electrons, why oxygen ond nitrogen bond to different numbers of hydrogen otoms. t4l (OCR)

20. Hydrogen

reocts with chlorine occording to

the equotion: Hz(g) + Clz(g) -------> 2HC1(g) o) Nome the Ppe of bond present in hydrogen chloride. t1l b) How is this type of bond formed ? tll c) Stote two physicol properties of hydrogen chloride which result from this type of

bonding.

t2l

d) Drow o diogrom of the bonding in hydrogen chloride showing how ollthe electrons in eqch otom ore orronged.

t3l

(X)?

b)Whot type of chemicol bond holds the

together?

otoms in this molecule t1l c) Would you expect hydrogen chloride to be o gos, o liquid or o solid, of room temperoture ond pressure ? Exploin your

onswer.

the Periodic Toble. They form'the oxides, silicon dioxide (SiO2) ond cqrbon dioxide (COz). The properties of these two oxides ore shown in the toble below:

t2l

t\relting point

Boiling point Electrical conductivity

Silicon dioxide

sublimes at *78"C sublimes at -78"C poor

poor

Give the structures ond bonding of corbon dioxide ond silicon dioxide.

onswers.

Exploin your

[4]

b) Drow o diogrom to show the orrongement of outer electrons in o molecule of silicon chloride. (Atomic numbers: silicon 14, (EDEXCEL) chlorine :77

:

.)

t4l

woter

os fully os you con, why o molecule contoins two hydrogen otoms but o hydrogen chloride molecule,contoins only

24. Exploin, one.

H \_

(EDEXCEL)

'o

22, The hydrogen hqlides (hydrogen fluoride, hydrogen chloride, hydrogen bromide ond hydrogen iodide) ore importont chemicols. The diogrom below represents o molecule of hydrogen chloride.

H-cl

I

H. (You moy use o diogrom in your onswer

you

25. H

Carbon dioxide

Property

21, o) Drow o dot ond cross diogrom to show

point.

(AOA)

23. o) Silicon ond corbon ore both in Group 4 of

(EDEXCEL)

the electronic structure of o molecule of chlorine{l) oxide, Cl2O. Show only the electrons in the outermost shell (highest energy level), ond use DOTS for electrons from the oxygen otom ond CROSSES for electrons from the chlorine otoms. t2l b) Exploin, in terms of the forces present, why chlorine(l) oxide hqs o low melting

t3l

wish.)

tsl

if

(AoA)

Fluorine forms o goseous compound with oxygen, with the formulo F2O. o) Exploin how these two elements bond to form F2O ond nome the type of bonding

used. is o gos.

t3l

b) Exploin why the oxide of fluorine, F2O,

t2l

(WJEC)

27g

',,,,

'

,

Further questions on Structure ond Bonding

29.

We

o) Briefly describe two industrioluses of

nonotubes.

"ryap

part of giant structuie of

diamond

:',.'

Key o carbon atom molecule

o) Describe the bonding ond giont structure

of

diomond

t2l

b) i) Grophite is soft.

Exploin why. t2l ii) Grophite cqn conduct electricity. Expioin why t1l c) Consider the diogroms of port,of the giont structure of diomond ond the , buckminster-fullerene molecule. How would you expect the melting point of buckminster-fullerene to compore with thot of diomond ? Exploin your onswer. (EDEXCEL) ,1

,,,[3]

27. Thestructure of silicon

Fullerenes con be joined together to moke tube shopes colled nonotubes.

is similor to the

strucfure of diomond. Describe the structure of silicon ond exploin why it hos o high melting point. You moy drow o diogrom if this helps t4l (AAA)

t4l

b) Nonotubes con be used os coges to trop other molecules inside. In the future drugs used to keot concer moy be odminstered in this woy. Whot advontoges moy this use of nonotubes hove in the treotment of concer ? [S]

. :. 30. Both diomond ond grophite

A B C ,D

ore elechicol conductors ore lubriconts form the some products when burnt hove the some hordness t1l

(AOA)

31. You con use grophite to lubricote mochines becouse its structure

A B

ollows it to melt of low temperotures consists of loyers thot slide over one

C

consists of smoll, round otoms loosely

D

bonded to eoch other contqins otoms thot ore strongly bonded

onother

to four other corbon

otoms t1l

(AOA)

32. Corbon con exist in two forms, grophite ond diomond. Exploin why grophite con conduct electricity but diomond

connot.

t2l (EDEXCEL)

28. In 1985 buckminster-fullerene, o new ollotrope of corbon, wos discovered. The diogroms in question 26 obove show the orrongement of corbon otoms in diomond ond buckminster-fullerene. o) i) How ore the structures of buckminsterfullerene ond diomond similor t2l ii) How ore the structures of buckminsterfullerene ond diomond diffuient t2l b) The melting point of buckminsterfullerene is much lower thon thot of

? ?

diomondUse ideos qbout the structures of the two

ollotropes to exploin this

280

difference. t4l

33. Grophite

is mixed

with cloy to moke pencil

leods.

' o) i)

ii)

Nqme the element of which grophite is one form. t1l Nqme one other crystolline form of thig

element.

[t]

b)Sketch o diogrom to show the orrongement of otoms in grophite. t2l c) Suggest why this crystolstructure of grophite enobles it to leove o mork when o pencil is drown ocross o sheet of poper.

tll

(EDEXCEL)

Further questions on Structure ond Bonding

F

Metols ond structures

34" Reod the following occount, token from the

&

Star, ond onswer the questions which follow.

Express

traders selling from suitcases who have bcen operating in the town centre. Police offlcers caught "'traders" selling jewellery described as l8 carat gold. nickel

o) Whot is the nome given to o mixture of metols ? [1] b) Use poges 390 ond 391 to help you to

nickel

copper zinc

28 29 30

gold

iii)

t3l (g/cm3)

Melting point ("C)

Ni

8.9

'1450

Cu Zn Au

i)

Symbol

Density

1

084

1

064

7.1

19.3

ii)

ii)

plostic.

t1l

not prove thot the choin wos mode of

gold.

tll

35. Copper metol is used for moking electric wire, coins, pipes ond soucepons. For eoch of the obove uses give o difJerent reoson why copper is chosen. The first is done for you.

t2l

(AOA)

37. The toble

gives some doto obout metols ond metololloys. Use the doto throughout this question. 0ensity/

Electrical resistivity/Om

Tensile slrength/MPa

934

2.6

18 10

10

80 300 460

g per cm3

Melting poinU'C

aluminium iron

2.7 7.8

steel

7.8

1

700

15

aluminium alloy titanium

2.8 4.5

1

800

5

950

53

600 620

o) When on electric current posses through the metol filoment of o light bulb, light is given out os the filoment becomes 'white hot'. i) Suggest the best metol to use for o

filoment.

ii) Exploin your choice. b) i) The low electricolresistivity

gold. i) Describe

t1l on experiment to show thot foke gold conducts electricity. Stote whot opporotus you would need, whot you would do ond whot you would see. t3l ii) Why do metols conduct electricity? [2] e) Exploin why the experiment described in port d) would: i) prove thot the choin wos not mode of

(Nr)

t3l

electricity.

light bulb

c) Stote why the foke gold choin would feel 'lighter' thon o similor one mode of reol

d)

c)

metols.

Metal or alloy

toble.

a) b)

b) Exploin why metols such os nickel ond plotinum ore good conductors of

.

copper and zinc with no trace of gold.

Atomic number

Good conductor of electncity

36" o) Describe the structure ond bonding in

warned Christmas shoppers to beware of fake gold chains and jewellery. They advised people to uvoid unlicenced slrcet

Name

Electric wires Coins Pipes

t3l

Trading standards chiefs in Wolverhampton today

complete the

Reason for choosing copper

Saucepans

Warning on fake gold

The iake gold was a mixture of

Use of copper

ii)

t1l t1l

of oluminium meons thot oluminium is o very good electricol conductor. Exploin how the structure of oluminium enobles it to conduct electricity. t2l Discuss the properties thot should be considered by on engineer when choosing o moteriol for overheod power cobles. t5l (OCR)

38. Nitinol is on olloy of nickel ond titonium. It is o 'smort olloy'.

o) Exploin whot is meont by the terms:

i) olloy ii) smort olloy.

t1l t1l

b)Nitinol is used to moke spectocle fromes.

i)

ii)

Whot property of nitinol mokes it pcrrticulorly suitoble for this use ? t1l Whot odvontoge do spectocle fromes mode from nitinolgive to theweorer?[1]

281

Further questions on Structure ond Bonding

39.

o) The toble gives some informotion obout

three moteriols. Material

Carbon sleel

Reaction with

Beaction

Cost

lrelting

Density

Tensile

oxygen

with acidic

(e per

poirt

(dcm3)

strength

solution

lonne)

fc)

iorms porous oxide

dissolves

500

1

layer on surface,

slowly

539

(Mwm) 250-400

7.86

non"porous layer of

does nol

chromium oxide on

dissolve

2000

1440

7.8-8.0

500-1000

o1

aluniinium oxide,

re.torms

dissolves

compound

structure.

e) o giont covolent

1300

659

2.70

1

40-400

very slowly

+

+

+

+

+

+

+

moking cor bodies ond exhoust pipes. t6l b)An olloy con be mode from two metols. In very mony coses the otoms of the two metols differ in size. In these coses the olloy is horder thon the pure metols it contoins. Exploin why this is so. t3l (EDEXCEL)

A

o) By rcference to their strucfure, exploin how the porticles in o piece of metol ore held together ond how the shope of the metol con be chonged without it breoking. (You moy use o diogrom in your onswer.) t|l b) Exploin why metols ore good conductors of electricity ond suggest why this conductivity increoses ecross the Periodic Toble from sodium to mognesium to

oluminium.

t4l

(AOA)

shows the properties of

five substonces. Substance

A

Melling

Boiling

poinl {"C)

point ('C)

solid

800

1470

p00r

no reaclion

650

1

110

good

burns to

Etfect of heating in air

p00r

c

k

u^ l'{}{ - ar}./r

#

H

q\-a

DE

Choose, from A to E, the orrongement of porticles of room temperoture thot corresponds to: o) o substonce thot will conduct electricity when molten but not when solid t1l b)the element mercury t1l c) o substonce whose boiling point is below

room

temperoture

d) o solid metollic

element.

t1l

t1l (EDEXCEL)

43. During the formotion of o covolent bond the otoms ...

A B C D

goin or lose protons shore electrons goin or lose electrons shore

protons.

t1l

(AOA)

elements ore shown in the toble below. I

il

ilt

LiCI

BeCl2

BCls

NaCI

Mg

Atct3

V

VI

vil

C

NCl3

ocl2

FCi

sicl4

PCt3

sct2

w12

IV

o

lom a

white solid 19

%

44. The formuloe of the chlorides of some

Electrical conductivity when

liquid

%

B

i) ii)

41. The following toble

(EDEXCEL)

@qa

+

if scratched

Discuss the relotive merits of using corbon steel, stoinless steelond oluminium for

tl0.

t1l

the orrongement of the porticles in five different substonces.

scralched non-porous layer

t1l t1l t1l t1l

42. Questions o) to d) concern

surface, re{orms if

Aluminium

o) o metol b) o non-metollic element c) o moleculor covolent compound

d)on ionic

llakes off Slainless steel

Eoch substonce con be used once, more thon once or not of ollto onswer the following. Choose from A to E o substonce which is:

burns to form carbon

No chloride

formed

dioxide and water

0

114

p00r

burns to form an acidic gas only

E

282

1700

p00r

no reaction

o) Whot ore the formulos of the two missing

chlorides ? [2] b) Whot type of structure willeoch of the missing chlorides hove ? t2l

Further questions on Structure trnd Bonding b) Drow o diogrom to show the structure of sodium chloride ofter it hqs melted. t1l c) Exploin why sodium chloride hos q relotively high melting point. t2l d) Describe o test which you could do to show thot silver is o metql. Include o diogrom and stote the result of the test in

45. The diogroms below show different orrongements of porticles in five substonces o) to d)

o hY

your

q,

[4]

(EDEXCEL)

47. Here

is o list of compounds. colcium fluoride corbon dioxide potossium chloride sulfur dioxide nitrogen dioxide sodium oxide Choose from the list obove: o) 3 compounds which hove o moleculor

c

A

onswer.

structure,

b)3 compounds which hove on ionic structure. [1] ., 48. This question

D

fluoride b)ommonio c) copper

(oCR)

is obout mognesium ond its

o)The bonding in mognesium is metollic. i) Drow o diogrom to illustrote metollic bonding. t3l ii) Use your understonding of metollic to exploin why metols con be wlres t1l

tll

d)o mixture of ommonio ond hydrogen

l

compounds

Choose from A to E o substonce which is:

o)sodium

n

t1l t1l

tll

(EDEXCEL)

MgCl2 is o white similor to sodium chloride mqnufoctured by the mognesium chloride mognesium chloride hove to be molten ond not solid? t2l c) i) Drow o diogrom to show the orrongement of the electrons in mognesium oxide, ond show the chorges on the t3l

b)

46. The

represent four

ii)

A

ions.

Suggest o reoson why oxide is used to line the furnoces.

Questions 49-52

A B C D

simple moleculor

giont covolent giont ionic giont metollic Choose from the list A to D the type of structure which is found in

^v

temperqfure ond pressure

o) Which.diagrom represents:

i)

diomond

49. zinc. 50. substonces thot ore goses of room

D

ii)

sodium chloride

?

t2l

51. sodium chloride. 52. sulfur.

.

tll

tll tll

t1l (AOA)

283

chapter 22 Life on Eorth depends on woter. Without it, we wouldn't be here! The formulo of woter is H2O. The hydrogen ond oxygen otoms ore joined by coualenf bonds.

It hos o simple moleculor structure. The forces between its molecules ore not very strong. (Although the forces ore stronger thon you would expect for such o smoll molecule.) Woter freezes ot 0'C ond boils ot 100'C. Fortunotely for us, this meons thot woter is o liquid ot most temperotures on Eorth.

00

)mamoleculeof H20. Can you draw rny electrang

The uroter cycle

O has 8 electrons

The woter cycle shows us how the world's woter moves from ploce to ploce:

H has 1 electron

trom the powers the water cycle det

J-'-->

r

condensation of water to form clouds made from tiny water droplets

tt some water

evaporation of water from the sea

o How does woter vopour get into the otmosphere? o Exploin why it roins when clouds rise. o Why is it colled the woter 'cycle'? 2U

la

ohow my covalenl bonda?

)

Oceons

Oceons cover roughly 70% of the Eorth's surfoce. They moke up obout 97 % of the world's woter. We believe thot life on Eorth wos storted in the oceons,

obout 3 billion yeors ogo. Since then the chemicols in seo woter hove stoyed obout the some. These ore listed below. mass of saltin 1009 of 6ea.ti@tr(g)

salt

23

sodium chloride magnesium chloride

5

sodium sulfate

4

calcium chloride

1

potassium chloride

0.7

Water is the most abundant subsfance on the Earth's surface

These solts hqve entered the oceons following their weothering from rocks on lond. The dissolved solts ore corried to the seo by rivers.

So why don't the proportions of solts build up over time? This is exploined by chemicol precipitotion. As new solts enter the seo, other solts ore being deposited on the oceon floor os solids. Equilibrium hqs been reoched. The oceons olso contoin dissolved goses. These come from volconic octivity on the seo bed ond from the goses in the oir. The oceons ploy on importont port in the corbon cycle os reservoirs for corbon dioxide. (See poges 300 ond 304.)

Some people blame the Greenhouse effect for extreme weather conditions

The corbon dioxide con form hydrogencorbonotes which ore soluble in the seo woter: COz(g)

+H2O(l)

*

H+(oq) +HCOs-(oq) hydrogencorbonote ions

We olso get corbonote ions formed:

HCOs-(oq) =: H+(oq) + COs2-(oq)

These con form insoluble solts with colcium

or mognesium ions in the seo wqter: Co2+(oq) + CO32-(oq) --------* CoCOs(s)

Mg2*(oq) + CO32-(oq) --------- MgCO3(s) These ore colled precipitotion reoctions. (See poge 133.) We ore now producing so much CO2 thot the oceons con t get rid of it. We ore disturbing nofure's bolonce in the corbon cycle. Mony people

believe thot globolworming ond chonging weother potterns ore hoppening now becouse of the extro CO2. (See poge 149.)

The international conference on global warming was held in Kyoto, Japan, in 1 997. Politicians met again in 2000 to decide on each country's reduction in CO 2 emissions. However, the meeting broke down with no agreement reached. Then in llontreal (2005) there were finally signs of progress being made.

2f35

Chemistry ot work

of woter

Where do we get our woter from? We con use woter drown from:

o lokes o rivers o oquifers (woter held in underground rocks) o reservoirs (lorge lokes creoted for storing woter). These ore sources of fresh woter, but they still hove to be

purified to moke woter fit for drinking. (See pqge 288.) Unfortunotely, obout 97% of. the woter on Eorth is in the solty oceons. However, in hot countries they ore chonging seo woter into usoble woter. (See poge 294.)

Ihrs is a reseNoir at Howden Dam, Peak District National Park. lt serves Sheffle/d, Nottingham, Derby and Leicester.

Woter in the workploce A lot of woter gets used by industry or in energy production os : o A row moteriol - some monufqcturing processes involve woter, either in chemicolreoctions to moke o useful product or for steom to generote high pressures. (See the Hober process on poge 231.) o A coolont - power stotions use huge volumes of woter. You've probobly seen the mossive cooling towers belching out steom. (See thermol pollution onpoge 296.) o A solvent - woter con dissolve mony substqnces so it is used for cleoning, woshing owoy woste, ond for reqctions thqt toke ploce in solution e.g. brewing.

Woter of home The omount of woter we use of home is more

Use

The fermentation of sugar in a brewery takes place in aqueous so/utions

'i'

,Approxlmate volume ' of water-use (litres)

thon you might think. In the UK we use obout 150 lihes of woter per

shower

27

person eoch doy.

power shower

80

Look of how much woter different qctivities toke

bath

80

flushing toilet t,rtfr

lf,," *-**" j" -\), -")

-

iv'

,!,!

you wash a car, it takes about 7 litres of water per bucket lf

286

I

brushing teeth, washing hands

4

washing machine

80

dish-washer

30

washing dishes by hand

7.5

ln the garden, using a hosepipe uses about 15 litres/minute and a sprinkler use about 9 litres/minute.

)

Chemistry of work : Uses of woter World-wide usoge of woter Across the world, woter is used os shown below

tr tr

I

Farming lndustry and energy production Domestic

The octuolproportions differ from country to country. For exomple, some Africon notions con use olmost 90% of their wqter consumption in forming. Thot's becquse they need to irrigote

their crops. Whereos in Europeon countries, the proportion used in industry ond in producing energy is likely to be over 50%. The percentoge of woter used in industry con be used os q meosure of how developed o country is. The individuol usoge of woter (overoge per person) olso vories widely. A person in the USA is likely to use ot leost 20 times os much woter os o person in Africo eoch doy. o Why do people in developed countries use o lot more domestic woter thon people in developing notions? Discuss the issues

Water usage across the woild reflects differing life styles

involved.

Conserving our woter supplies You might wonder: 'why bother trying to sove woter when it oll gets recycled in the woter cycle?' However, once we hove used woter, there is olwoys o price to poy before putting it bock into the environment. We con't just dump dirty woter directly into rivers ond seos. Cleoning up our woste woter costs us money.

willbe more ond more people competing for the plonet's woter. So we need to conserve our wqter ond do even more to restore its quolity ofter use. By soving enerEg, we ore olso doing our bit to conserve woter. Thot's becouse power stotions use o high proportion of our woter. o Discuss how you could sove woter. Could governments help ? Whot do woter componies do when we hove o dry summer ? Does this offect your life ot oll?

As time posses there

What affects the reliability of our supply of water? Ihls person ls collecting water during a shortage.

287

)

Drinking woter

Did you know thot obout two-thirds of the moss of your body is mode up of woter ? So it's not surprising thot we should drink between 6 qnd 8 glosses of woter everydoy ! You don't wont to shrivel up like o dried prune ! We ore lucky thot we hove drinking woter bn top' Mony people oround the world hove to collect their own woter, often from contominoted sources We looked ot the importont job thot chlorine does in moking woter sofe to drink on poge 55. Now we con follow the journey of woter, from q reservoir to our tops of home.

Over 607o of your body mass ls made up from water

Look ot the diogrom below:

reservorr

clear water

tank

filtration

sedimentation

Addition of chlorine to kill bacteria

storage reservoir

mains supply

Let's look of the woys we treot wqter to mqke it sofe to drink

Aerotion The woter is stirred up to let oir (oxygen) mix with it. This con qlso be done by letting it foll down steps. This helps to remove iron(lll) ions in the wqter. They precipitote out os iron(lll) hydroxide. If this hoppens in your woter ot home,

iron(lll) hydroxide couses :

.

o o

vegetobles to turn brown teo to hqve on inky colour ond o bitter toste clothes to get rusty stoins ofter woshing.

288

Aeration prevents i ron (l I l) hydroxide precipitating out of your water at home. However, some areas still have old iron pipes which can cause problems.

Sedimentotion Lorger solid porticles ore ollowed to settle ot the bottom of the sedimentotion tonks. But dirty woter is o sol. There ore colloidolporticles of cloy dispersed in the woter. The tiny porticles ore electricolly chorged (negotive). They stoy spreod throughout the woter becouse they repel eoch other. So woter componies odd oluminium sulfote to coogulote the cloy. The porticles ore ottrocted to the highly chorged Al3+ ions. They form clumps which get heovy enough to settle on the bottom of the tonk.

Aluminium sulfate coagulates clay particles. Some people in Camelford (Cornwall) were badly affected when too much aluminium su/fafe was added to their water supply by accident.

The ocidity of the woter is controlled using lime slurry. This colcium hydroxide is olkoline so it roises the pH of the woter. The oluminium sulfote coogulont is good of removing olkoline substonces.

Filtrotion Then the woter is filtered through loyers of sond ond grovel to moke sure ollsolids ore removed. These filter beds con olso contoin corbon slurry to get rid of substonces thot would give the woter on odd smell or toste.

Chemicol purificotion Does your top woter ever smell of chlorine

SUMMARY OF WATER TREATMENT ?

Chlorine

Process

is odded to killbocterio in the woter This prevents diseoses.

The woter compony will odd enough chlorine to kill ollthe bocterio. But how would you like drinking woter thot tosted like it wos from o swimming pool? They remove ony excess chlorine by treoting the woter with sulfur dioxide. This reocts with the chlorine, getting rid of its smell ond toste. The chlorine is reduced to chloride ions, Cl-(oq).

to remove

Aeration Oxygen

N

Sedimentation aluminium sulfate

>
CqCOe(s) + COz(g) +

woter H2O(l)

(limescole)

The colcium corbonqte formed is the limescole you get inside kettles ond hot-woter pipes. Tempororily hord woter con be softened by boiling. Do you think this is o cheop woy to get rid of hordness Imogine your heoting bills if you hod to boil ollyour woter before you could use your woshing mochine

?

!

However, not oll hord woter con be softened by boiling Other colcium compounds, such os colcium sulfote from gypsum, ore not removed by boiling. These form

permonently hord woter.

This hot water pipe has been almost blocked by scale (or limescale). We can remove the scale by adding a weak acid. This reacts with the calcium carbonate: CaCOs(s) + 2H+(aq)

---> Ca2*(aq) + H2O(l) + COz@)

The weak acid is called a descaler.

292

Removing oll types of hordness We hove seen how we con soften tempororily hord woter by boiling. But permonent hordness con olso be removed. Permonent meons forever, but oll types of hordness con be removed from woter.

T.Washing soda (sodium carbonate) When you odd woshing sodo to hord woter, the colcium ions ore removed. They reoct with the corbonote ions from the woshing sodo. This forms insoluble colcium corbonote :

* corbonote ions --------> colcium corbonote Co2+(oq) + COg2-(oq) --------> CoCOs(s) (in hord woter) (from woshing precipitote (insoluble) sodo)

colcium ions

Washing soda removes hardness

This is colled on ionic equotion. It only shows the ions which ore offected in the reoction.

lf o solid forms when two solutions ore mixed, it is colled o preclpltdlon reoction. Most modern woshing powders hove their own woter softeners odded.

2.Ion-exchange column This method is more suitoble for lorge-scole treotment of hord woter. Look ot the diogrom opposite: The column is filled with o resin which holds plenty of sodium ions (No+ ions). Hord woter goes in ot the top. On the woy down, the colcium ions ore swopped for sodium ions. The colcium ions get stuck on the resin. Sodium ions, which don't couse hordness, come out in the woter of the bottom.

hard water ln calcium ions in hard water calcium ions (Ca2+) get stuck on the resin which contains sodium ions (Na*)

ion-exchange resin

- when

all the sodium ions (Na*) have been washed out, the column can be recharged by running salt water (sodium chloride)

Experiment 22.3 Remouinghardness Look bock to ExperimenlZ?.Z on poge'291. Use thqt method to test the hordness of'your woter somples before ond ofter heotment:

through it. Some resins contain hydrogen ions.

1. Test some tempororily hord woter. Now boil o fresh somple of the woter ond re-test it. soft water out

2.Tesl some permonently hqrd woter. Now odd o spotulo of woshing sodo to o fresh somple Moke sure it dissolves, then re-test. 3. Test your sornples of the hqrd woter ofter they hove possed through on ion-exchonge column.

Na+ ions replace Ca2* ions to soften the water

293

)

Desqlinotion

For mony hot countries, getting o relioble supply of fresh woter is difficult. With low roinfoll, rivers ond lokes run dry in hotter months. However, these countries sometimes hove lorge coostlines

They hove plenty of seq woter, but this is unsuitoble for most uses.

Thot is where desolinotion comes in. Speciol desolinotion plonts con toke most of the dissolved solts out of seo woter (or from brockish woter from morshes).

Eecrrlindton produces usqble woter from ees,woter by seporoting urotor froffi lhe dis*olved solts. You hove seen how distillotion works on poge 175. Woter is evoporoted, then cooled ond condensed to seporote it from dissolved solids. The process used in some desolinotion plonts is bosed on

You can drink the water from lhe sea water processed in this desalination

plant

distillotion.

Experiment 22.4 Distilling salt water Use the distillotion opporotus on poge 175 to collect pure woter from o solution of sodium chloride (common solt). You con use the glosswore or the micro-scole equipment shown. o How could you test thot the woter collected wos pure woter?

In o desolinotion plont, the pressure obove the woter is reduced. This lowers the boiling point of the seo woter. The process is colled

flosh distillotion.

o Why is it importont to lower the boiling point ? o Whot would be the moin costs in this type of plont?

Another process colled reverse osmosis is getting more populor. This uses o membrone to seporote the woter ond the solts. There is no heoting involved so it uses less energy thon distillotion. Howeveq energy is still needed to pressurise the woter. Look of the diogrom : High pressure

pump

Membrane assembly Freshwater

Sea water (or brackish water)

Stabilised Brine discharge

Todoy's membrqnes con remove 987o of dissolved solts from seo woter. However, corrosion of pumps ond pipes is o problem.

Desolinotion is used in Middle Eost countries thot con use money from their oilto poy the costs of desolinotion. In the Virgin Islonds, in the West Indies ,907" of woter used is desolinoted. 294

freshwater

)

Solubility curves

Soturoted solutions Only o certoin omount of solute con dissolve in o porticulor volume of solvent ot ony given temperoture. This omount vories from solute to solute.

A sdurated solutlon is o solution in which no more solute will dissolve of o given temperoture. We con describe how wello solute dissolves in woter by its solubility. The solubility of o substonce tells us how mony groms of it will dissolve in 100 g of

woter of o certoin temperoture. For exomple, the solubility of sodium chloride is 36 g per 100 g of woter ot25"C. Experiment 22.5 The solubility curue of potassium nitrate Meqsure out 10 g of potossium nitrote. Heot some woter to 70 "C in o smoll beoker. Tronsfer L0 cm3 of the hot woter to o boiling tube. Now odd the 109 of potossium nitrote to the boiling tube, ond stir with o gloss rod. This should form o solution thot is olmost soturoted. Let the tube cooldown. Note the temperoture when the first crystols oppeor. o At whot temperofure does the solution become sofurqted ? potassium nitrate Now odd onother 5 cm3 of woter to the boiling tube to moke the volume up to solution 15 cm3. Stir the solution so thqt the potossium nitrote re-dissolves. Worm the tube in o woter both if necessory. Agoin cool the tube down ond record the temperotureof whichthesolidoppeors. Repeotfortotolvolumes of 20,25ond30cm3of woter. o How will you convert your results into solubilities per 100 g of woter? Remember 100 cm3 of woter hos o moss of 100 g. (You could use o spreodsheet.) o Record your results ond solubilities, in 9/100 g of woter, in q toble. Think obout how to moke your results os relioble os possible. o Once you hove converted your results to solubilities per 100 g of woter, drow o solubility curve for potossium nitrote. o How does the solubility of potossium nitrqte vory with temperoture ? Solubility curves enoble you to: o reod the solubility ot temperotures you didn't investigote. o scole up or down to work out how much solid dissolves in ony volume of woter. o work out whot moss of solid is crystollised from o soturoted solution cooling between two given temperotures.

60

copper sulfate 50

a

2

3c

qo

63 5b

so

.90

!o

=O a=

og

20

6 10

0

20

30

40

50

60

70

80

Temperature ("C)

295

)

Woter pollution

Are you worried obout pollution of our rivers, lokes ond seos ? It is not possible to get obsolutely pure woter in noture becouse it is so good ot dissolving things. This is often useful to us, but olso mokes it eosy to pollute woter.

Eutrophicotion Do you remember the problem of eutrophicotion ? On poge 240 we sow how nitrate fertilisers pollute our rivers ond con get into woter supplies. Detergents oJten contain phosphafes which end up in rivers ond lokes. These olso contribute to excess growth of olgoe which covers the surfoce of the woter. Other life in the river connot survive the competition. As plonts, including olgoe, ond onimols die they ore decomposed by micro-orgonisms. These use up the dissolved oxygen in the river or loke.

f toke mchances uri tJ.r

at\

Thermql pollution Besides its use os o solvent, woter is olso used in industry os o coolont. It tronsfers energy owoy from o reoction. This roises the temperoture of the woter. An exomple is its use to tronsfer energy in power sfotions. The woter is not polluted when it is possed out into o neorby river. However, it is wormer thon the river woter.

This con offect the delicote bolonce of life in the river. Remember thot oquotic onimols rely on oxygen gos dissolved in the woter. We know thot:

Power stations can cause thermal pollution in rivers

The higher the temperoture, the less soluble o gos becomes in woter. So not os much oxygen dissolves in the wormer woter

ond onimols die. o How would you solve this problem

?

Other woste Chemicols dischorged from foctories con olso pollute our woter, olthough rules qre much stricter now. Pesticides in our drinking woter is onother problem which woter componies ore hoving to tockle. Pesticide residues con get into woterwoys from crop sproying in neorby fields. Our drinking woter is now checked for occeptoble levels of pesticides. o Whot ore your views on this issue ?

296

People in lilinamata Bay, Japan were poisoned by mercury which got into the food chain

Leod in woter Leod is o toxic metol. Like other heovy metols, it tends to occumulote in orgons once it gets inside your body. It is porticulorly dongerous for children under the oge of 6. This is becouse it hinders development of the broin. So no wonder leod woter pipes hove been bonned! Before we reolised just how poisonous leod is, plumbers used leod becouse it is so molleoble. It con be bent into shopes eosily so wos ideol for woter pipes.

Leod is not very soluble in woter but o little does dissolve, ond thot is enough to couse problems. You get more leod ions in your woter if the woter hos o low pH (ocidic) or if the woter is hot. In the toble on poge 290 it soys thot hqrd woter (which hos o higher pH) con prevent leod or copper getting into the woter. Leod pipes in old houses should hove been reploced by modern plostic pipes by now.

O/d houses had lead Plumbing

Even ofter it wos bonned, ond copper pipes were introduced, Ieod still monoged to get into drinking woter. Thot's becouse the plumbers joined up copper pipes using solder contoining leod. So houses built between 1930 ond 1980 still hove some risk of leod contominotion. However, there ore some simple things to do to ovoid the risk of leod o If you hoven't used o top for some time, run the woter for obout o minute before drinking from it. Thot's becouse woter thot hos been in old pipes for o few hours hos hod o chonce to dissolve more leod. o Never drink, or brush your teeth with, hot woter. o Never drink woter from the bothroom.

Woter filters More qnd more people ore using filters for their drinking woter. Even though our drinking woter meets high stondords, the filters ore seen os on extro sofety meosure. The filters contoin corbon, impregnoted with silver. The silver is on excellent boctericide. Although it is expensive, o filter will only contoin obout 0.077" silver. The filters con be joined to your cold woter top or you con pour your woter through o filter jug. Corbon obsorbs orgonic compounds. Some filters olso include on ion-exchonge resin thot gets rid of metol ions. However, some colcium ions in your woter willbring heolth benefits. (See poge 290.) The best filters will obsorb: o heovy metols, such os leod, copper, codmium, chromium, etc. o bod smells ond tostes o chlorine o most colcium ond mognesium ions (removing qbout 60%) o os well os killing 997o of. bocterio.

This water filter is fitted to your cold tap in the kitchen. You can buy taps with 'Cold', 'Hot' and 'Pure' handles to turn.

297

Investigation 22.6 Purifying water Your tqsk is to purifu o somple of muddy woter. You ore given o yoghurt pot, sond ond fine grovel. If you wont ony other mqteriols (except filter poper !) you con osk your teocher. See who con get the cleqnest somple of woter. o Why wouldn t you

No thank'S!

JH

hy drinking your 'cleon' woter?

o How do woter componies moke woter sofe to drink?

Summory

r

The 'woter cycle' shows how woter moves qround the Eorth.

o

Wcter is o good solvent. It forms solutions with mony solutes. This meons thot woter from noturol sources con hove o ronge of pollutonts dissolved in it.

r

00

Drinking woter is purified by physicol ond chemicol meons before it reoches our tops. Some people olso use woter filters of home.

o

Hord wcter contqins dissolved calcium or mqnesiumions. we con soften the wqter by precipitoting these ions out of solution or by possing it through on ion exchonge column.

o

We con plot the solubilip (in 9/100 g of woter) of o substonce

of different temperofures on o 'solubility curve'.

3.

some hot countries even though they hove lorge coostlines ? b) Exploin the process of desolinotion. c) Whot is the moin disodvontoge of desolinotion using distillotion ? d)Nome onother process thot con be used insteod of distillotion. Whot is its odvontoge over distillotion ?

1. Copy ond complete: Woter is good of . . . . mony solutes. The woter is the . . . . in the solution formed. Hordness in woter is coused by . . . . or . .. . ions. These con be removed by o . . . .

reoction orby using on

2.

298

.... ....

column.

o) Exploin why we sometimes describe oceons os 'reservoirs for corbon dioxide'. Use chemicol equotions in your onswer. b)WhV is it importont thot we reduce the omount of corbon dioxide in our otmosphere. c) Some countries orgue thot they should be ollowed to produce more corbon dioxide becouse they hove lots of forests. Exploin their reosoning. Whot ore your views ?

o) Why is shortoge of woter o problem for

4.

Limestone is insoluble in woter. However, woter flowing through limestone becomes hord. o) Exploin how colcium ions get into the woter. b) List the odvontoges ond disodvontoges of hord woter. c) Exploin how odding woshing sodo removes hordness from woter. d) How does on ion-exchonge resin soften woter?

5.

8. Write o newspoper orticle on woter pollution

Anno tested 3 somples of woter with soop solution. She recorded how much soop wos needed to get o permonent lother, before ond ofter boiling: before boiling

Water sample Sample A Sample B Sample C

I

ond how we con monitor woter quolity nowodoys. Poges 364 ond 365 con be the storting point of Your reseorch.

9. Look

atter boiling

8

7

1

1

7

2

ot the solubility curves below: copper sulfate sodium chloride

70

9oo o oo5u 96

63ao €E pP30

o)Whot con you deduce obout eoch somple of woter

?

OO

b) Exploin the chemicoldifference between

*q

permonent ond temporory hord woter.

3

c) Why is boiling not o good ideo to remove temporory hordness from woter on o lorge scole

10

0

.lo 20 30 40 50 60 70 80

90

TemPerature (C)

?

woter pipes or kettles

o) Whot do we meon by 'soturoted' solution

This question is obout purifying woter from o river so thot it is sofe to drink.

b) Exploin why oluminium sulfote is better ot this job thon sodium sulfote. c) Why is colcium hydroxide odded to woter ? d) How do we remove unpleosont tostes qnd odours from woter

?

e) Why is it desiroble to remove iron(lll) ions

from woter

c) Compore the effect of temperoture on the solubility of copper sulfote ond sodium chloride. d)At which temperoture do copper sulfote ond sodium chloride hove the some solubility ? e) You odd 100 g of sodium chloride to 100 g of woter ot 80 "C. Whot moss of sodium chloride remoins undissolved ?

f) Whot

?

ore diseoses thot ore corried in woter. Why don't we hove ony cqses of typhoid or cholero in this country

?

b) Whot moss of copper sulfote will dissolve in 100 g of woter to form o soturoted solution ot 55 "C ?

?

o)Whot is oluminium sulfote used for in the treotment of woter ?

is the moximum moss of copper

sulfote thot will dissolve in 25 cm3 of woter ot 40'C ?

f) Typhoid ond cholero

?

g) Whot is odded to woter to get rid of excess chlorine before the woter reoches our homes ?

7.

20

0

d)How con you remove limescole from hot

6.

.c

Imogine you ore teoching o group of 12 yeor olds obout how our drinking woter is treoted to moke it sofe. Drow o chort you could toke with you to help exploin.

g) You cool 50 cm3 of o soturoted solution of copper sulfote from 50'C lo 25 "C. Whot moss of copper sulfote crystollises out of

the solution

?

h)A student did on experiment to compore the solubility of 5 different solids ot 20'C. Whot type of groph would she use to disploy her results ? Exploin your onswer.

Further questions on poges 322 orlnd323.

299

chapter 23 We live in o mixture of goses, colled oir. The oir mokes up the Eorth's otmosphere, ond it is essentiol for life on our plonet.

Air is moinly o mixture of 2 goses - nitogen ond oxygen. But do you know which other goses ore oll oround us? Look ot the toble opposite:

Gases in air

o/o

nitrogen oxygen

78

carbon dioxide water vapour argon other noble gases

There ore olso smoll omounts of pollutont goses. Pollution vories from ploce to ploce.

ol air

21

0.04 varies 0.93

1

The composition of the air has been much the same for the last 200 mittion years

Solubility of goses We sow in the lost chopter (on poge 296) how life in woter

depends on dissolved oxygen gos. The-omount of oxygen dissolved depends on the temperoture. Look ot the grophs below: Solubility of oxygen gas

o 3 0.01 o

oo)

(U

3 o

0.01

o

:

.C

o E

0

0.2

.c 0.15 N

0.005

o a (!

0.3

o) 0.25

o) N

Solubility of carbon dioxide gas o 0.35

(s

o

10

20

temperature ('C)

O

0.1

a o (U

0.05

E

0 0

10

20

temperature ('C)

You con see thot:

Gqses get less soluble (Is

woter rises.

Look ot the first groph: Con you remember obout the thermol pollution of woter? Why is this o problem to oquotic life?

o

Look ot the second groph: We olso sow on poge 285 how the oceons ore importont in dissolving corbon dioxide gos (o 'greenhouse' gos). o Whot will hoppen to the omount of corbon dioxide obsorbed by the oceons os their temperoture rises due to globolworming? Why is this o problem ? 300

30

)

Chemistry of work : Uses of nitrogen

Nitrogen is seporoted from tiquefied oir by froctionol distillotion. The qir is turned into liquid by repeotedly compressing, cooling ond letting the goses expond. Corbon dioxide ond woter vopour'ore seporoted off os oC most of the solids first of ol1, Once the temperoture is ot obout *200 goses hove condilnsed into liquids. (Look ot the toble opposite.) These gqses ore then qllowed to worm up in o froctionoting column. The ni*ogen boils off first crt = 196 "C. It is collected from the top of the column ond liquid oxygen comes out qt the bottom.

Gas

Boilirrg poinUG

nitrogen argon

-196 -186 -183

oxygen

Nitrogen for freezing Liquid nitrogen is very cold. It's olmost -200 "C Therefore, it con be used to freeze things quickly. Food con be frozen on o conveyor belt os it is produced. Hospitols con use it to store tissues

!

for mony yeors. It con olso be used to mend leoking pipes You con pour liquid nitrogen on the pipe. Itfreezes the liquid inside the pipe while you repoir the leok. This soves money becouse you don't hove to droin the whole pipe.

Liquid nitrogen cqn olso freeze morshy ground thot is too wet for mechonicol diggers.

Sperm can be frozen and stored in liquid nitrogen

Nitrogen is not reoctive As well os freezing food, nitrogen helps to stop

food 'going off in onother woy. Nitrogen is on un-reoctive gos. So when we pock foods, nitrogen is used inside the seoled pockoging. This keeps the reoctive oxygen gos in the oir owoy from the food. Bocterio connot multiply, ond the food stoys fresh longer. There is o risk of fire on the giont ships thot corry crude oil. The vopour from the oil is dense, ond con form on explosive mixture with the oir.

Packing peanuts on a production line

It is especiolly dongerous when oil is pumped oshore, or when the ship's tonks ore cleoned out. Nitrogen gos is pumped into the tonks to remove ony oxygen Then on occidentol spork will not result in disoster.

Do you know which is the reoctive gos in the oir Think of some reoctions we hove seen, such os combustion or oxidotion. Which gos is needed for these reoctions to toke ploce ?

?

Bemember the test for oxygen: o glowing splint re-lights.

Oxygen is used up when things burn or

during respirotion in our cells. Look ot the reqctions below:

Experiment23.T Oxygen and burning

beaker

Try the experiment shown with the night-light.

o Whot hoppens to the flome ? o Whot hoppens to the levelof the woter in

trough

the beoker?

o Exploin why this hoppens. o Wox is o hydrocorbon. Whot is formed

qs it burns ? (See pqge 147.) o why can'twe use this experiment

Experiment

23.2

to find out the proportion of oxygen in oir?

Oxygen and rusting

iron wool inside

Set up the opporotus os shown:

a wet test-tube

Leove it for o week.

r

o

after a week

Whot hoppens to the level of wqter in the test-fube Exploin why this hoppens. (See poge 76.)

?

water

Experiment23.3 How much oxygen? Set up the opporofus os shown: oooooo o@N@rrt

o

rNoAoro{o@o oooooooooo heat

Heot the copper. At the some time, poss oir over it, from syringe to syringe. after Corry on heoting untilthe volume does not go down ony further. Let the opporotus cool, then reod the finqlvolume of oir left. o How much oir is left qt the end? o Exploin whot hos hoppened (include the word equotion copper + oxygen -------> copper oxide). o Why should you let your opporotus cool down before toking the finol reoding on the syringe ? o Whqt ore the sources of error in this experiment?

302

the experiment

)

Chemistry of work: Uses of oxygen About 20% of the oir is mode up of oxygen Do you know the moin difference between oxygen ond nitrogen ? Let's look of some uses of the reoctive gos oxygen:

Oxygen for breothing We ollneed oxygen to breothe. Con you think of ony ploces where you need to toke

your own supply of oxygen to survive Look ot these photos:

?

Premature bables somelimes need oxygen to help them breathe

The air gets thinner as you go higher

This welder is burning a mixture of ethyne gas (a hydrocarbon) and pure oxygen

Oxygen from liquid oir We con seporote the goses in oir by the

froctionol distillotion

of liquid oir. After removing woter vopour ond cqrbon dioxide, the oir is cooled ond compressed. The cold, compressed oir is ollowed to expond into o lorger spoce. This cools the goses down even more. By repeoting the process severoltimes the temperoture drops to -200 'C. The oxygen ond nitrogen in the oir liquefy ot this temperoture. When this mixture is wormed, nitrogen boils off first os it hqs o lower boiling point thon oxygen. This tokes ploce in o froctionoting column.

Gas

Boiling point ("C)

nitrogen

-

196

argon

-

186

oxygen

-

183

303

CO,

You con see from the toble on poge 300 thot oir contoins obout 0.04% corbon dioxide. This doesn't seem o lot ! However, 250 yeors ogo there wos only 0.028%. As you know from poge 749, corbon dioxide is o 'greenhouse' gos. It helps to keep the Eorth worm But con you remember why people ore worried obout the increosing omount of corbon dioxide ?

.

is colourless

o

is slightly soluble in water (forming a weakly acidic solution)

.

is denser lhan air

.

puts out fires

r lums limervater

millqy

Corbon cycle Corbon dioxide is o vitol port of the corbon cycle The corbon cycle shows how corbon is moved from ploce to ploce oround the Eorth. Look ot the cycle below:

carbon dioxide

I

burning lossil fuels

I

in the atmosphere

heating (in industry and deep underground)

chemical reactions

dissolves in oceans

chalk and limestone

photosynthesis

(and other carbonate rocks)

coal, oil and natural gas

decay and respiration

\

concentrated in

f**,* carbon nts

tn

decay and pressure

shell creatures shells form rock

\

\.

carbon in animals The carbon cycle

Most of the corbon on Eorth is in rocks. The corbon tropped in fossilfuels is releosed when we burn the fuels. The oceons obsorb o lot of the CO2 produced.

304

Insoluble corbonotes ond soluble hydrogencorbonotes ore formed. (See poge 285.) However, the oceons connot remove oll the extro CO2we ore now producing.

)

Chemistry of urork:

corbon dioxide

Fizzy drinks Corbon dioxide gos is slightly soluble in woter. It forms o weokly ocidic solution. Look qt the photos: Carbon dioxide puts the 'fizz' in drinks. lt is dissolved under pressure into the drink to form 'carbonated' water.

The hlgher the pressure

the morc soluble a gas becomes. Champagne and sparkling wine is bottled before fermentation has finished. (See page 166.) The carbon dioxide builds up pressure in the bottle.

What happens when you

release the pressure by opening a can or bottle?

'Dry ice' If you cool down corbon dioxide gos, it turns into o solid. It doesn't form o liquid. The solid corbon dioxide is known os 'dry ice'. It is much colder thon ice. At room temperoture, it sublimes (turns from the solid into o gos). Look of these uses of 'dry ice' :

Lumps of 'dry ice' sublime. Ihis cools down the water in the air to give smoky eflects on slage.

lce cream samp/es can be kept cold with 'dry ice'

Fire extinguishers Most things won't burn in corbon dioxide gos. For exomple, it puts out o lighted splint. However, this is nof the test for corbon dioxide. Other gqses, such os nitrogen, do the some thing. Do you know the test for corbon dioxide ? Con you remember why the limewoter goes milky (See poge 111.)

Corbon dioxide is denser thon oir. It forms o 'blonket' over o fire. This cuts off the oxygen supply for the combustion reoction.

?

Carbon dioxide puts out most fires

Ozone molecules ore mode up from 3 oxygen otoms, 03. They ore found moinly in our upper otmosphere. Ozone molecules obsorb hormful ultroviolet light from the Sun. They protect us ond without it life on Eorth would not hove developed os it hos. (See the next poge.)

.r'

o Ozone shields us against harmful u.v. light

Hove you heord obout the hole in the ozone loyer? On poge 55 we sow how CFCs (chloro-fluoro-corbons) ore domoging the ozone loyer oround our plonet. CFCs ore unreoctive orgonic compounds contoining chlorine, fluorine ond cqrbon otoms e.g. CCI3E They were used in oerosolsproys ond in fridges untilscientists discovered their effect on the ozone loyer in the 1980s.

The ozone layer is under attack. Ihis shows the hole over Antarctica.

In the upper otmosphere the CFCs ore broken down by energy from sunlight. A chlorine otom forms when its covolent bond, to corbon, breoks: energy from sunlight

CCI3F-CCI2F'+

Cl'

Remember thot o covolent bond is o poir of electrons. The covqlent bond between corbon ond chlorine breoks 'evenly'. Corbon tokes one electron, ond chlorine tokes the other:

!+., l!,

...---...*

-J' + (ocl'chlorine otom or free rodicol) I

FR,CE

oo Free radicals are very reactive!

Atoms or molecules with o free (spore) electron ore colled ftee rqdicqls. Free rodicols ore oery reactive. The chlorine free rodicols ottock ozone molecules in ropid choin reoctions, destroying our protection. As more ultroviolet light reoches us on the surfoce, we willsee more heolth problems, such os:

o increqsed risk of sunburn o foster ogeing of our skin o skin concer o domoge to our eyes, such os cotorocts. Fortunotely mony countries hove now bonned the use of CFCs. Chemists hove found other compounds to use insteod. Do you protect your skin dangerous u.v.light? HFCs (hydro-fluoro-corbons) ond olkones do not domoge the ozone loyer. However, other developing countries ore still producing CFCs. o Why do you think they still use them ? o How could notions help eoch other to solve this problem for us oll?

306

from

)

Where on Eorth did our otmosphere come from

?

It is hord for us to imogine how old the Eorth reolly is. It might help you to think of the Eorth's history os q 24-hour clock. On this scole, humons orrived on Eorth of one second to midnight ! When the Eorth wqs formed (obout 4600 million yeors ogo) its otmosphere wos probobly mode from hydrogen ond helium for o short time, just like 99 T" of the universe. The Eorth itself wos o mixture of molten moteriol including iron. As the Eqrth cooled down, o solid crust formed on the

outside. The molten rock underneoth often burst through the thin crust. Volconoes were erupting oll over the Eorth's new surfoce. These volconoes gove out goses, just like volconoes do todoy. Some theories suggest thot the moin gos wos corbon dioxide, just like the otmospheres of Mors ond Venus todoy. There wos olso some woter vopour ond nitrogen plus smoll qmounts of methone ond ommonio in this eorly otmosphere.

€p

..r:flp

rdh-

qb

As the Eorth cooled down even more, the steom condensed ond fell os roin. It filled up hollows in the solid crust,

ond the oceons were formed. The first living things ore thought to hove developed in the oceons. One theory is thot life storted neor volconoes on the oceon floor. All the elements needed for simple cells to evolve were there. The first orgonisms evolved into simple plonts, like olgoe. These used up corbon dioxide during photosynthesis ond mode the first molecules of oxygen gos (Oz). The omount of oxygen in the otmosphere built up slowly over millions of yeors. The oxygen wos importont becouse some of it turned into ozone (Og). Ozone stops hormfulroys from the Sun reoching the Eorth's surfoce. (See poge 306.) So it become possible to live out of the woter. Some of the oxygen reocted with ommonio, giving off nitrogen. More nikogen wos formed by bocterio Iiving in the soil. The levels of methone begon to foll os it too reocted with oxygen. Eventuolly, obout 200 million yeors ogo, the otmosphere reoched the mixture we hove todoy of roughly 20o/" oxygen ond 80 7" nitrogen. Much of the corbon from CO2 in the originol otmosphere is now tropped in fossilfuels ond corbonote rocks. (See the next poge.)

307

Summory

Early Volcanic A

mgthang

dioxide ammonia

reacted with

CHo

NHu

This process happened relatively quickly and the Ievels of CO2 dropped

4Sr CO, dissolved in oceans, then concentrated into the shells of sea creatures as

calcium carbonate

condensed as the Earth cooled down

JL

reacted with oxygen

Plants

+

denitrifying bacteria in the soil

+ Sedimentary Rocks ilke limestone or chalk

oxygen Oz (21%) Our A

308

I

oxygen built up very slowly

Oceans

nitrogen N2

(78%)

No w

)

3.

Questions

o) Why does the omount of woter vopour in

the oir vory

1. Copy ond complete:

b) Drow o flow diogrom of the woter cycle. Include these words:

The Eorth's otmosphere contoins obout

four-fifths .... ond one-fifth .... . However, its eorly otmosphere wos mode up of goses from . . . . These included corbon dioxide, ...., .... ondsteqm. The first oceons formed when the steom . . . . os the Eorth cooled down. The first . . . . gos wos formed by photosynthesis in plonts.

clouds, seo, rivers, roin evoporotes, condenses

c) How do the i) soil, ii) plonts ond iii) onimols, odd to the woter vopour in the oir ? d)Where does the energy for the woter cycle come from ?

2. Somi did on experiment to find out how much oxygen is in the oir.

?

4. Look ot the corbon cycle on poge 304. o) Why does the omount of corbon dioxide in the oir vory from ploce to ploce ?

+

b) The word equotion for photosynthesis is:

corbon * woter --------> glucose dioxide

heat

She storted with 100 cm3 of oir. She possed the oir bock ond forth over the hot copper by pushing eoch syringe in turn. She sow the copper turning to block copper oxide.

expect to be left

?

c) Which gos would moke up most of the somple left ot the end of her experiment

?

d)Why should Somi let the gos cool down before toking her finol volume reoding ? e) Whot would hoppen if Somi storted with too little copper in the heoted tube ?

f)

One of the syringes hod o plunger thot did not move smoothly in ond out. Exploin how this might offect the results of the experiment.

g) Woyne soid thot it would be better to use o

condle stonding in woter, covered by o beoker to find out how much oxygen is in the oir. List os mony points os you con to persuode Woyne thot he is wrong !

oxygen

Exploin how the corbon in corbon dioxide gets into plonts. c) Exploin 4 woys in which the corbon in plonts con get bock into the otmosphere.

o) Use o word equotion to show how Somi hos removed the oxygen from the oir.

b)Somi corried on with her experiment until there wos no further chonge in the volume of gos left. Not ollthe copper hod turned block. Whot volume of oir would you

*

d)Whot hoppens to the corbon dioxide obsorbed in the oceons ? (Also see poge 285.)

5.

o) Which volconic goses mode up the Eorth's

eorly otmosphere ? b)Which plonets todoy hove otmospheres similor to Eorth's eorly otmosphere? c) Describe the processes thot removed the originol goses from the otmosphere. How did this increose the proportions of oxygen ond nitrogen in the qir ? d)Why wos ozone importont to the development of life on Eorth ? e) i) How hos pollution domoged the ozone loyer? ii) Whot ore we doing to tockle the problem ?

6. Drow spider

diogroms showing some uses of nitrogen, oxygen ond corbon dioxide.

Further questions on poges 324-325. 309

chapter 24

)

Journey to the centre of the Eorth

\

,

crusl

As you know, the Eorth is surrounded by o thin loyer of goses. But hove you ever wondered whot is inside our plonet ?

If you storted digging o hole stroight down, obout 13 000 kilometres loter you would come out in Austrolio ! But whot would you find on the woy ?

outer core rnner

core

First of ollyou would go through the Eorth's thin crust. All of our resources for row moteriols come from the crust, the oceons ond the otmosphere.

It con be os thin os 5 km under the oceons, going up to obout 70 km under the continents. The thin crust is the leost dense of the Eorth's loyers Under the crust you find the montle. This loyer goes down olmost holf woy to the centre of the Eorth. The montle is olmost entirely solid. However, there is o smoll omount of molten moteriol under the lithosphere (crust ond uppermost port of the montle). This zone, under the lithosphere, is colled the

atmosphere

The crust and upper paft of the mantle are called the lithosphere. The overall density of the Earth is greater than the average density of lts crusl. Ihis shows that the materials inside the Earth must be different to, and more dense than, the rocks in the crust.

osthenosphere. Next, you reoch the outer core. This is o dense liquid, mode of molten iron ond nickel. Both of these metols ore mognetic. They moke the Eorth behove like o giont mognet itself.

J, o o

SCOTLAND

o5

r

3F

t

Finolly there is the inner core. This is the densest port of the Eorth. Unlike the outer core it is solid becouse of the very high pressure. It is olso mqde of iron ond nickel

There was a young man from Perth, Who tunnelled for all he was worth.

The outer ond inner core moke up just over one-holf of the Eorth's rodius.

He became a real bore As he shof through the core And came out t'other side of the Earth

310

!

When molten rock cools down, it usuolly forms crystols. These moke up igneous rock. The word igneous comes from the Lotin

"This 'hard case' has grains I see well, A rock that has risen from the fires of hell. The rock set in crystals as fhe magma rose higher, Forming igneous rock - from the Latin for 'fire'."

word for 'fire' (ignis). The molten rock comes from deep underground. It tends to rise to the surfoce through crocks in the Eorth's crust If the molten rock, or mogmtr, reoches the surfoce, it forms o volcono.

Sherlock irspecls granite roc:k

Some igneous rocks ore mode from smoll crystols, like the rock bosolt. Others hove lorger crystols, like gronite So whot offects the size of the crystols in on igneous rock ?

Experiment 24.7 Crystal sizes You connot melt rocks with o Bunsen burner. In this experiment you willuse o solid cqlled 'sqlo['to model the behqviour of rock. If you look corefully you con see how the rote of cooling qffects crystol size. Wqtch the crystols form on the two slides. You moy need to stort off the crystols on the worm slide with o smqll 'seed' crystol of sqlol. You con use o hond lens to observe the size of the crystols.

o

50'c warm water molten salol

t

slide

from

warm

lreezer

heat

Whot do you conclude from this experiment?

Molten rock thot erupts from o volcono is colled lovo. It cools down quickly. This forms rocks with smoll crystols, colled 'fine groined' rock. Basalt is the moin exomple. It is o dense rock, rich in iron minerols. Most oceon floors ore mode from bosolt. It is on extrusive igneous rock. Rhyolife is onother extrusive igneous rock. This is rich in silico ond is less dense thon bosolt. Other molten rock rises towords the surfoce but never reoches it. It cools down slowly. Bosolt: quick coollng surrounded by rocks under the ground. The solid rock formed hos lorge crystols, like granite It is soid to be 'course groined'. It is on intrusive igneous rock. Gobbro is onother course groined rock. But whereos gronite is rich in silico, gobbro is rich in iron. The gronite formed beneoth the surfoce con loter be exposed by Eorth movements or by weothering ond erosion of the softer surrounding rock. You con find out more obout igneous rocks on poge 318.

--->

lorge cryetole

3i1

)

Our chonging plonet

We con use the noturolrodiooctivity in rocks

to find out how old the Eorth is. It is thought to be obout 4 600 000 000 yeors old ! This vost time-scole is hord for us to imogine. There hos been plenty of time for chonges coused by: o weothering o erosion o volconoes, o movements of the Eorth's lithosphere. These hove re-modelled the surfoce of the Eorth. New mountoin ronges hove formed to reploce older mountoins worn owoy by weothering.

ancient rocks (over 2000 million years area where fossils of Mesosaurus (a reptile) are found

Drifting continents In 1915, o Germqn scientist colled Alfred Wegener put forword his ideos obout the history of the Eorth It hod olreody been noticed thot Africo ond South Americo looked like two pieces in o jig-sow. Alfred thought thot the two continents were once joined together. Over millions of yeors they become seporoted ond then drifted oport. He found thot the ppes of rock motch ocross Africo ond South Americo. So did the fossils. But he could not exploin how the continents hod moved.

Ihe shapes of South America and Africa stot together as in jig-saw. Ihis glves us evidence that the continents were once joined and must have drifted apart.

a

o

What other evidence is there ?

Key

:

.r.-rr:: earthQUdke zones

'.'.'

volcanoes

i.

:. --..!.'

"3;.

tl:rt.

I :t

I i

'i: ..i..

..

:....

.a I

l. ':'J:j'"' 'A

'.!'

.i'

..:'

312

'":..,:'

...::

t.

..f

t.

l' 'it

i:, '':....:.'r,.......,..

ir:.,

)

Plote tectonics

Perhops it wos not surprising thot other scientists

didn't think much of the 'drifting continents' theory. People believed thot feotures like mountoins, were formed when the Eorth's eorly crust shronk ond wrinkled os it cooled down. (See poge 307.) They olso thought thot the continents were once joined by 'bridges' of lond thot hod since sunk below the oceons. However, ofter Alfred Wegener's deoth, scientists storted to notice things thot supported his theory. The some rock ond fossil feotures were found between other poirs of continents. Then explorers of the oceons discovered evidence thot the seo-bed wos spreoding. In other words, continents urere octuolly moving oport. All the continents were once At lost, people hod to toke the ideos of Alfred Wegener seriously. joined together. The huge land mass was called Pangaea. The theory of plote tectonics wos formed. This soys thot the Eorth's crust ond upper montle is mode up from huge slobs of rock, colled tectonic plotes. It olso exploins how these mossive chunks of lithosphere move. The plotes ore still moving todoy, olthough only o few centimetres o yeor. This smollmovement is enough to couse eorthquokes ond volconoes. Lorge eorthquokes hoppen where plotes slip o few metres post eoch other. Volconoes oppeor where molten rock from beneoth the crust rises to the surfoce through joints between the plotes. Key Look ot the mop on the lost poge: f mountain ranges It shows oreqs offected by eorthquokes ond volconoes. plate boundaries You con use these to find the shope of the plotes below *- direction plates are moving :

\ Plale

\

\

\

\_ Pacific Plate

Pacilic Plate

\

Nazca Plate

South American Plate

lndoAustralian Plate

Antarctic Plate

,:.:::::,:,,'

1f

\_

313

)

Moving plotes

Nowodoys, we hove developed theories to exploin how the plotes move Do you remember whot lies underneoth the lithosphere? The osthenosphere contoins up to 10% molten moteriolwhich forms o film oround the edges of crystols. This ollows solid moteriol to flow very slowly under the lithosphere. But even the solid montle beneoth the osthenosphere con flow too. The plotes move becouse of the huge forces coused by convection currents. These ore set up in the slowly flowing montle under the tectonic plotes. Experiment

24.2

Conuection currents

Set up the opporotus os shown: Use tv'teezers to ploce q crvstql

potossiumrnongonot"(\rlD ot the bottom of the beoker.

r

o

--of

convection currents

7\

lAPotassiummanganate(vll)

potassium

manganate(Vll) crystal

Y

\

Drow o diogrom to show whot hoppens. Exploin how two of the Eorth's plotes might move oport.

t

t

I

heat

We know it gets hotter the deeper into the Eorth we go. But where does the heot come from ?

Noturol rodiooctive otoms ore decoying inside the Eorth ollthe time. These nucleor reoctions give out lots of energy. One theory suggests thot they give out enough energy to set up the convection currents thot move the Eorth's plotes. Look ot the mop on poge 313: It shows the plotes ond the direction they ore moving. The plotes in different ports of the world con be: o slipping pasf eoch other, o mooing towards eoch other, or o moving away from eoch other.

)

Plotes slipping post eoch other

Some plotes ore trying to slip post eoch other. The most fqmous exomple of this is the Son Andreos foult. It runs down the west coost of the USA. It morks the boundory between the Pocific plote qnd the North Americon plote. When the plotes slip, there is on eorthquoke. As yet, we connot predict exoctly when the plotes

willslip. So people in Colifornio hove to live with the threot of on eorthquoke of ony time. (See poge 320.)

314

This is the San Andreas fault. You can see where the two plates meet.

San Los Angeles

Pacific plate Pacific Ocean

The red arrows show the movement of the plates on either side of the fault

Eorthquokes Hove you seen the TV pictures on the news ofter on eorthquoke ? Look ot the photos of the domoge they con couse: As you con see, the shock woves from on eorthquoke con be very strong. Friction stops two plotes from sliding post eoch other smoothly. During on eorthquoke, the two plotes overcome the friction. They slip suddenly. This hoppens of the eorthquoke's focus. The focus moy be deep underground. Then the shock woves spreod out in olldirections. The ploce directly obove the focus on the surfoce is colled the epicentre. The woves get weoker os they trovelfurther from the epicenhe, but they con still be detected on the other side of the world !

On Boxing Day, 2004, an earthquake under the lndian Ocean caused a huge tidal wave. The 'tsunami' killed over a quarter of a million people. An early warning syslem is now being put in place However, scientists cannot predict when an earthquake will take place accurately yet. (See

page 319.)

Scientists use o finely bolonced instrument colled o seismogroph to record these vibrotions.

Jopon lies on the boundory of two plotes. Tollbuildings in Joponese cities ore now built on giont shock obsorbers. Speciolcomputers con odjust the shock obsorbers to reduce the movement of the building.

Around 100000 people died in this earthquake in Pakistan

Some buildings in Japan are designed to withstand an earthquake

In 2005, on eorthquoke in Pqkiston killed oround 100 000 people Most people were crushed os buildings collopsed. o Why do you think so mony buildings foiled to stond up to the shock woves ? You con reod obout predicting eorthquokes on poge 320.

Jlc

)

Plotes moving towords eoch other

There ore 2 types of moteriol forming the plotes. In some ploces the plotes ore thin ond dense. These ore found under the oceons (bosoltic crust). Other plotes qre thicker ond

crust

oceanic crust

edge the Andes in

oceanic

as America)

trench continental crust

less dense. These moke up the continents (gronitic crust).

In some ploces 2 plotes ore moving towords eoch other. Where they meet, the denser oceonic crust slips under the continentol crust. This is colled subduction. The friction between the plotes con couse eorthquokes. The rock con even get so hot thot it melts ond rises to the surfoce to form volconoes.

Look ot the mop on poge 313: Con you see where this is hoppening

Oceanic crust slipping under conti n e ntal c ru st (su bd u ction)

eventually ?

Eventuolly, the whole oceonic port of the plote slips under the continentol crust. Then two oreos of continentql crust collide. The crust folds upwords, forming mountoins. Metomorphic rocks con form under this greot pressure. The Himoloyos ond the Alps were formed like this.

r, :lf::lirrritrtr

i

.:iiri.

:::

..:.:

w

-1.

rnountain chain where continents haye collided (such as the Himalayas)

Folds ond foults The greot forces involved when plotes move con couse loyers of rock to snop. This forms o fqult. Sometimes the loyers bend, forming o fold. Loyers con even be turned upside down! Experiment

24.3

st col I i di ng folding layers of rock

Smoshing plates !

Use coloured strips of modelling cloy to show the loyers of rock. Move 2 blocks of wood together to show how the loyers con fold. Use q knife to cUt the loyers, then move them slightly to form o foult.

o

Co nti nental c ru

an anti-cline

a syncline

Cqn you think of o reoson why rocks sometimes form o fold and sometimes o foult? a fault

316

)

Plotes moving owoy from eoch other

Where plotes move oport, mogmo rises to the surfoce This usuolly hoppens under the oceons. As the molten rock sets, o ridge forms. An exomple is the mid-Atlontic Ridge.

Look ot the mop on poge 313. Con you see where the mid-Atlontic Ridge

mid-oceanic

r'On\

oceanlc crust

.a

is ?

Look ot the photo of Icelond: Icelond is port of the mid-Atlontic Ridge. Islonds ore mode when the new rock builds up obove the level of the seo.

Seo floor spreoding You hove olreody seen how the continents were once joined together. Studies of the oceon floor hove given us more evidence thot some plotes ore moving oport. The rocks qt the ridge contoin o lot of iron compounds. As you know, iron is mognetic. Its otoms line up when the molten rock sets on the seo bed. They point towords the North Pole. However, every few hundred thousond yeors, the Eorth's mognetic field is reversed. The South Pole becomes mognetic north. The rocks on the seo floor show when these chonges hoppened.

Look ot the bonds of rock in the diogroms

lceland is part of the mid-Atlantic ridge

A

ridge

ocean floor

:

They give us evidence thot the seq floor is spreoding In foct, eoch yeor you hove to trovel qbout on extro 2 cm to get to Americo !

normal

IR TARES

GO UP

A.Yreci Cq,

thrs

$ea'r.

Earth's polarity is reversed

Strpes of rock with reversed magnetism have built up on the sea floor. (See page 321 , Q7.)

317

)

Volconoes

You hove seen how molten rock, colled mogmo, rises through foults in the Eorth's crust. If the mogmo breoks through to the surfoce, it is colled lovo. Volcqnoes form where the lovo sets into rock. Do you think thot the rock formed will be igneous (See poge 311.)

Atlount St Helens in the USA. lt

Lovq vories in different ploces. Some lovq is runny, some is thick. This is becouse mogma con hove different mixtures of minerols in it. It con olso orrive of the surfoce qt different temperotures, or with different omounts of goses dissolved in it. All of these offect the thickness (viscosity) of the lovq. You con ky this investigotion: Investigation 24,4,

?

erupted in 1980, killing more than 60 people.

This lava has cooled down and has almost stopped flowing.

aff ect the fhickn

esg.

o/

I au,a,,,?

You con use teocie

:! a a How will you ",! Cheek your,plon with your

The shope of o volcono depends on the thickness of its lovq. Iron-rich bosolt lovo forms this type of 'sofe' volcqno shown opposite: Do you think thot runny lqvo willset neorer to o volcono's vent (outlet) ? Thin, runny lovo forms o volcono which is very wide, with shollow sides. We don't usuolly get violent eruptions in this type of volcono.

stsft

!

,,:,

runny lava flow vent

200 km Mauna Loa, Hawaii (a shallow-sided volcano)

Look ot the bottom diogrom: Thicker lovo sticks neorer the vent. Silico-rich rhyolite forms like this. It forms o steep sided volcono. This type of volcqno is more dongerous. The vent con get blocked up by the thick lovo. The pressure builds up inside. Suddenly, we get q violent eruption os the lovo bursts through. The eruption throws out 'bombs' of molten lovo ond osh rises high in the oir. We olso get pumice (o light rock full of gos bubbles) formed os the lovo cools down. When the osh settles, we cctn get sedimentory rock forming over time os loyers build up.

,,'1.1,,t18

thick lava steep-sided cone 1.5 km

8km lvlount Pel6e, West lndies (a steep-srded volcano)

)

Chemistry of work: Predicting volconoes Volconoes Volconologists hove o ronge of doto they use to try ond predict eruptions. They con give us the probability of on eruption, but they ore still vogue. It's o bit like weother forecosters soying you hove o 30% chonce of roin. We find thot people live neor volconoes becouse the lond is fertile. So giving o worning of on eruption con sove thousonds of lives.

F, (_

,Nl-

The scientists corefully monitor o volcono, looking for signs of obnormol octivity. Here ore some techniques volconologists use to predict os best

t,'

they con: o They use tiltmeters - these qre o bit like spirit levels. They con detect slight chonges on the sides of the volcono. As mogmo builds up before on eruption, the sides stort bulging. tittmeter measures angle of the slope

o

o

Lookotthediogromsopposite: lti';ffiX]ilT[;ffTffi1'3.i"J*'

They con meosure the distonce ocross the top of the volcono occurotely using loser beoms or surveying instruments. If the cone gets wider, thot is o sign of mogmo building up. The lotest GPS (globol positioning sqtellite systems) ore olso now used to monitor movement. Volconologists hove found thot os mogmo rises neorer the surfoce, the mixture of goses normolly given off chonges. For exomple, there moy be o sudden increose in the percentoge of sulfur dioxide

angle ol slope increases as

sides bulge out

ft

.,- { \l \t \ti

e:'

Volcanologists still collect data first-hand, desplte the use of sate//ites nowadays

I

distance across cone increases

releosed.

o

They con monitor the vibrotions ot the surfoce, looking for signs of increosed octivity. Before on eruption, seismometers pick up hundreds of hemors per hour. Every volcono is different. But by studying q volcono over o long period of time, you con get to know its own signs of on eruption. Even then we con't be sure of the exoct size.

the volcano changes belore an eruption

..i

We can monitor tiny earth tremors using seismometers

i'319

I

)

Chemistry ot

cting eorth quokes

Eorthquokes As we know from poge 315, eorthquokes con be devostoting.

But ogoin, moking occurote predictions of when they willtoke ploce is difficult The some technology is used os volcono forecqsts. Morkers ploced ocross o plote boundory con be monitored for movement. The lotest sotellite imoges con detect movement of plotes down to 1 mm per yeor. It hos olso been found thot rocks heot up before eorthquokes os q result of exfueme compression. So sotellites with infro-red comeros con monitor the Eorth's surfoce for unexpected rises in temperofure.

An earthquake in Haiti

The use of new ond improved techniques is groduolly improving our obility to predict the unpredictoble !

nohrrol rock

lhe thin oceanic crust is lorced under the thicker continental c.ust

triction heat and eadhquakes deep und€r ground

start he16

the rock metts again and is

)

5.

Questions

prone to eorthquokes

1. Copy ond complete: The Eorth is mode from o thin outer the. ., otr. . . . liquidcoreondqninner core which is . . . . . The Eorth's crust is mode from mossive slobs of slowly moving rock colled tectonic . . . . . They move becouse of . . . . currents in the . . . . . Where they meet you get. . . . ond volconoes.

2.

crust ?

the Eorth's core. d)Give one woy in which the egg's yolk is different from the Eorth's core. e) How could you represent the Eorth's plotes on the egg ?

?

c) Whot is the epicentre of on eorthquoke ? d)Whot precoutions could you toke ogoinst eorthquokes if you lived in Los Angeles ?

6.

o) Whot is 'subduction'?

b) How were choins of mountoins, like the Alps ond Himoloyos formed ? c) Whot 'powers' the movements of the Eorth's plotes ?

7.

o) Exploin whot we meon by 'seo-floor spreoding'. b)Which type of rock willform on the seo-

floor of o mid-oceon ridge ? c) Look ot the diogrom below:

o) Whot evidence did Alfred Wegener put forword for his theory of 'drifting

continents'? b)At one time ollthe continents were thought to be joined together in o huge lond moss colled Pongoeo. Whot evidence is there in this diogrom to support this theory ?

i f

4.

?

b) Whot is the focus of on eorthquoke

Imogine thot the Eorth is like on egg ! q) Which port of the egg is like the Eorth's b) Which port of the Eorth is represented by the white of the egg ? c) Give one wqy in which the egg's yolk is like

3.

o) Why ore Son Froncisco ond Los Angeles

areascovered by

t( ;

r

8. Lovo from different

volconoes hos different thicknesses. The temperoture, dissolved goses, ond chemicol composition of the lovo offect the flow. Look ot these two volconoes

mtrh

volcano A

volcano B

sam_e^

gtacra soils (Iormeo z5u million years ago)

o) Troce or get your own printed mop of the

world ond mork on the plote boundories. b) Whqt evidence is there thot these boundories ore the ploces where plotes meel?

Exploin the pottern of stripes in the rocks on either side of the ridge.

o) Exploin the different shopes of the two volconoes. b) How do volconologists try to predict when volconoes will erupt ? List the techniques ovoiloble. c) Why is predicting eruptions on 'inexoct science'?

Further questions on poges 326 ond327. 321

Further questions on Eorth Chemistry

) 1.

In qddition to filtrotion, two other processes ore now corried out to moke woter suitoble for domestic use. These processes ore sedimentotion ond chlorinotion. Exploin whot is meont by sedimentotion.

Woter o) The solubility of o solid chonges os the temperoture chonges. Whot do you

understond by the term 'solubility'

?

t4l

b) A student investigoted the solubility of two

different solids at vorious temperotures. The tqble shows the results obtoined. Temperature

t2l 3. A bottle of minerolwoter

Solubility of solid (g/1009 water) Sodium chloride

Potassium chlorate

0 20 40 60 80

33,0 33.5 34.0 34.5 3s.o

3.5 7.5 14.0

lon

v) vi)

2.

73 8

24.O

magnesium potassium

37.5

sodium

18

chloride hydrogencarbonate sulfate

28

some?

ii)

t1l

Whot is the solubility of the two solids ot the temperoture in port (iii)? tll If o sqturoted solution of potossium chlorote contoining 50 g of'woter is cooled from 70'C to 30"C, whot moss of the solid would crystollise? [4J If o solution is mode by dissolving 15 g of eoch solid in the some 100 g of woter qt 70 "C qnd the solution is cooled to 20'C, crystols ore observed. Which solid crystollises ? Exploin your onswer with reference to both solids. t4l (Nl)

5

388

tll

Nome the chemicol compound which would moke up most of the solid left

behind. t2l b)This minerolwoter is hord woter. Whot is meont by hord woter? tll c) Exploin why hord woter should not be used in hot woter systems. t2l d) Give one qdvontoge of hqrd woter. tll 4.

(AoA)

The tqble qt the top of the next poge gives some informqtion obout the wqters of the Old Sulphur Well in the North Yorkshire spo town of Horrogote. These minerol woters qre from the strongest sulphur spring in Englond. o) i) Suggest how this woter cqme to contoin

ii)

minerols.

t2l

Use poge 391 to help you onswer this

question. Write the formulo of the borium compound present in this

Until 1909, the wqter wos simply stored

piped to customers but comploints qbout toste ond odour led to the instollotion of filter beds. A quote of the time reod 'the qppeoronce of the public woter supply wcs such thot the poor used it os soup, the middle closs for woshing their clothes qnd the weolthy for wotering their gordens'.

1

o) A somple of this woter wos evoporoted ond o solid left behind. i) Whot is evoporotion ?

At which temperoture ore the solubilities of the two solids the

The following extrqct is tqken from on informqtion sign neor o reservoir.

322

Concenlration in mg/l

calcium

i) Plot the results for the two different solids on o piece of groph poper. t?l ii) Compore the effects of increosing the temperoture on the solubility of eoch solid. t2l

iv)

hos this informotion

on the lobel.

("c)

iii)

(EDEXCEL)

b) i) Corbonqted drinks

ii)

woter. tll

ore fizzy.

How could this minerolwoter be mqde [2] Worm fizzy drinks 'go flot' foster thon coldfizzy drinks. Exploin why. t2l

fizzy?

Note: although a question may be marked (AQA) etc,, it will otten be relevant to other examinations as well

Further questions on Eorth Chemistry b)The following informotion is from the website of Wessex Woter, o supplier of top

Old Sulphur Well (Chemical analysis by Thorpe in 1875)

minerals

woter.

milligrams per litre

Water naturally contains a range of trace substances at levels suitable for drinking: many of these substances are essential to our

12,738.63 93.59

sodium chloride barium chloride strontium chloride calcium chloride magnesium chloride potassium chloride lithium chloride ammonium chloride magnesium bromide magnesium iodide calcium carbonate magnesium carbonate silicon sodium sulphydrate

a trace

621.98 602.68

health. The content of water is complex and varies from area to area, usually because of the different rocks and soils through which the water filters. The quality of drinking

136.72 10.73 14.69 32.54

water in the Wessex Water region is extremely high and is among the best in Europe. We carry out 300 000 tests 0n drinking water every year. Our drinking water completely meets the European Union

1.61

424.32

84.85 9.99 74.34

and UK standards.

(Data: HanogateMuseums and Arts)

www.wessexwqter. co.$k

c) i) Describe o simple test thot you could do to show thot this minerol woter is hqrd. Give the result of the test. t2l ii) Give one exomple which shows thot hord woter is good for heolth. tll lul) Desoibe one problem coused by hord

woter.

tll

iv) Use the toble to ncrme one minerql which mokes this woter t1l v) Ion exchonge columns remove hordness (AOA) from woter. Exploin how.

hord. t2l

5.

The following lobelis found on qbottle of woter. lon

mg dm-3

hydrcgercilbonate

450

calcium

160

phloride

75

sodium

62

magnesium

28

sulphate

25

potssium

5

oitrate

0.3

fluoride

o.2

Bottled at source

.lrtGLAlp -$ArEa N{ffiral MlmeraltVffi SINCLAIR Natural Mineral Water f€ll s rain or snow b€fore the age of polhtion. Every drop of SINCLAIR Natural Mineral Water hro naturaly filtered thmugh white wdstone for at le6t 3000

ym.

could you test, in the loborotory, whether o somple of wqter is hord or

soft?

minerol woter.

t2l

c) Another extroct from Wessex Woter's website olso gives the following

informotion. A number of different processes can be used to purify water to the high quality required by law. The water arriving at a treatment works flows through fine filters to remove algae, insects and any other objects. The steps are: 1. Sedimentation A small amount of chemical coagulant is added to help bind together any impurities so that they will be trapped in the sand filters. 2. Sand filtration The water flows into fine sand filters which trap particles of impurity. 3. Chlorination Filtered water is treated with lime and chlorine.

q) i) How

ii)

Use evidence from the possoge to give two reosons why it is os sofe to drink woter from Wessex Woter os to drink bottled

t4l

Whot would you see if you corried out the test on Sinclqir wqter ? Use evidence from the lobel to exploin your onswel.' [2]

i) ii)

Whqt would hoppen if chemicol coogulont wos not odded to the

woter? nl Suggest why the sqnd used in the filters is fine (smollgroined). ttl

iii) Why is chlorine odded to the woter?

t1l i (EDEXCEL) 323

Further questions on Eqrth Chemistry

)

The otmosphere

6. The chemicolindushy

uses row moteriols.

These mqy come from the oir or the ground.

Air is o mixture of goses which con be seporoted by froctionol distillotion. o) The pie chort shows the composition of dry oir.

o) Which gos, present in oir, provides the plonts with the corbon they need t1l b)Nome the process thot plonts use to chonge this gos into cqrbon t1l c) How do onimols get the corbon compounds they need (AOA)

? compounds. ? tll

8. The toble

below gives informotion obout the Eorth's otnosphere of vorious times in its history.

Copy ond complete the lobelling of the pie chort. noble gases carbon dioxide 0.04%

Time

Atmosphere

4500 million years ago

Hydrogen and helium.

3800 million years ago

Mainly carbon dioxide, steam and hydrogen, with small amounts of methane, ammonia and hydrogen sulfide.

2600 million years ago

Carbon dioxide begins to decrease.

1800 million years ago

Oxygen begins to build up

Yo

nitrogen

{

b) Combustion of fossil fuels increoses the 'qmount of corbon dioxide in the otmosphere. Describe two noturol processes thot

t3l

otmosphere.

NHe.

Nome the other

element.

t3l

tll (EDEXCEL)

7. The diogrom below is of the corbon cycle. DIOXIDE

.9 I

respiralion and GAS

photo-

decay respiration

CHALK and decay and pressure

p16ssure

of shells and sea ANI feeding

324

ii)

f i Ic

in the ATMOSPHERE

decay and

otmosphere 3800 million yeqrs ogo. t1l b) Suggest whot coused: the decreose in cqrbon dioxide concentrqtion in the otmosphere 2600 million yeors ogo the build up of oxygen in the oknosphere 1800 million yeors ogo. [2J c) Use the toble obove to exploin how the oceons formed, ond suggest on opproximote dqte for their formotion. tsl d)The toble below shows the concentrotion of corbon dioxide in the oir ot the Mouno Loq observotory in Howoii over o period of 30 yeors from 1958.

i)

remove corbon dioxide from the c) Nitrogen is exhqcted from the oir ond, in the Hqber process, is reocted with onother element to produce ommonio,

o) Stote the origin of the goses present in the

Io

co o ot o

ass eso s+s 340

sgs seo 325 320

gts 310

58 60 62 64 66 68 70 72 74 76 78 S0 82 84 86

88

year

Give, ond exploin, two reqsons why the corbon dioxide concentrqtion hos been (rorxcrl; increosing since 1958. t4l

Further questions on Eorth Chemistry

9. For mony yeors

scientists hove meosured the omount of cqrbon dioxide in the otmosphere. They hove shown thot the omount of corbon dioxide is increosing.

b)The otmosphere on Eorth todoy is very different from the eorly otmosphere, The pie chort shows the omounts of different goses in the oir todoy. Choose goses from the box to lobelthe pie chort.

350 carbon dioxide 340

orgon hydrogen

concentration 3go

'"

lii!'l:x"'

dioxide nitrogen

320 310

't960 1965 1970 197s 1980 1985 year

o) An increose in the Eorth's temperofure cquses corbon dioxide to be given off from oceqns. Suggest why corbon dioxide is releosed from oceons when they become wormer.

b) Suggest why some scientists do not occept thqt this exploins the reoson for the increose of corbon dioxide in the

otmosphere.

c) Corbon dioxide con be formed by burning corbon. Write the bqlonced equotion for this

reoction.

t2l

trl

tll

(Eorxcrl)

10. o) During the first billion yeors of the Eorth's existence, thercwere mony octive volcqnoes. The volconoes releosed the goses thot formed the eorly otmosphere.

(AoA)

11. About 200 yeors ogo Joseph Priesfley corried out experiments on different goses. He colled one gqs thst he investigoted 'fixed sir'. We now coll this gos corbon dioxide. o) How do we know thot Priestley used the words 'fixed oir'? trl b) When Priestley put o mouse in 'fixed sir' (corbon dioxide) it hod difficulty breothing. The mouse would hove died if he hod not removed it. Priestley then put o green plont into 'fixed oir' expecting it to die.

plant

carbon dioxide large sealed jar

i)

ii)

i) ii)

Describe how volconoes coused the oceons to be t2l Most of the eorly otmosphere wos

formed.

corbon dioxide. Give one woy in which corbon dioxide is removed from the otmosphere. tll

c) fu o result of his experiments,

Priestley

suggested thot everyone should plont bees by their houses to 'keep the oir good to breothe'.

Whot gos do the trles produce'to keep the tfil (nOnl oir good to breothe'? 325

''

Further questiont on Eorth Chemistry

)

The Eorth

12. Thetheory of plote tectonics

16. liony wos sfudying rocks in o quorry. He is believed

to

'

mode this sketch of the side of the quorry.

exploin why:mountqins qre formed. o) Whot ore tectonic plotes ? t2l b) Exploin, os fully os you con, one woy in *hich tectonic plotes couse mountoins to be formed. t3l (AOA)

13. o) Give three feotures thot moy be

boundory. Exploin your qnswer. t4l

observed ot o plote tsl b) Whot cquses the Eorth's plotes to move ?

c

A

(AOA)

14. The diogrom shows how o line of underwoter mountoins is forrning in the middle of the Atlontic Oceon. This is colled o mid-ocesn ridge.

o) The rock ot C is very hord rock contoining lorge crystols.

Describe how this rock wos formed. t2l b) Rock A ond rock B hove the some chemicol composition but qre different types of rock. Describe how rock B wos formed.

t3l

ocean

(rorxcrl;

17. Complete the following sentences by filling in the missing words. The Eorth's crust ond upper montle ore split into q number of lorge pieces colled . . . . plotes.

igneous, metornorphic

Heot produced by nqturol . . . . processes cquses . . . . currents in the Eorth's montle which in turn mokes the plotes move. This movement con cquse sudden ond disoshous events of the plote boundories

or

such

o) Solid rock forms when the liquid from the montle loyer reoches the woter.

i)

Which type of rock willform:

sedimentory? tll ii) Exploin why the crystols formed,in this rock arevery smqll. t2l

b) Europe ond North Americo ore ot opposite sides of the Atlontic Oceqn. Exploin why Fuleps ond North Americo move q little further,,oport eoch yeer.

t2l

(ocR)

15. At one time it wqs believed thot mountoin ronges on the Eorth's surfoce were the result of shrinking of the crust os the Eqrth cooled down.

i

tectonic plotes move. Give two other pieces of evidence which suggest thot tectonic plotes move. (AOA)

[2]

326

os.... or....

.

t\l

18. Eorthquqkes often strike without ony worning ond con couse the destruction of mony buildings. Eorthquokes ore cqused by the movement of tectonic plotes. q) Whqt ore tectonic plotes ? [2] b) Exploin, os fully os you con, whot couses the movement of tectonic plotes. tsl c) How does the movement of tectonic plotes couse on earthquake? t1l d)Exploin why scientish cqnnot occurotely predict when on eorthquoke will toke ploce. t2l

Further questions on Eorth Chemistry 19. Scientists once though thot mountoins qnd

21. In some

volleys were formed becouse the Eorth hod shrunk in size. Scientists todoy think thot mountoins ore formed becouse of the movement of tectonic

plotes. o) Why did scientists think thot the Eqrth

hod shrunk in size

?

?

b) Whot ore tectonic Plotes c) Suggest why mony scientists did not ot

t1l t1l

first occept the ideq of 'continentol

drift'.

t2l

is o lorge wove which con couse the flooding of coostol regions. Tsunomis con be coused by on eorthquoke toking ploce under the seq. The diogrom shows how qn eorthquoke con couse o tsunomi.

20. Atsunomi

ploces on the Eorth's surfqce mogmo from the montle rises up through the crust ond erupts os lovo from volconoes. o) Use ideos qbout the density of mogmo to describe how it rises up through the crust.

t2l b) Mqgmo con hqve different compositions thot result in differences in the lovq from volconoes ond the rocks thot form when the lqvo cools. These differences ore summorised in the toble below Complete the toble using words from the list below.

gronite runny lmro composition

Type of eruption

Material ejected

i)

flowing

iii)

explosive

ash and pumice

Magma

ii)

gabbro

t4l c) Some geologists study volconoes. Suggest why this study is importont. t2l d)Mqny people live neor to volconoes, despite the donger of on eruPtion. Suggest odvontoges of living neqr to o volcono. t2l

Plate A Plate B

o) Whot is on eorthquoke ? b) Exploin, os fully os you con, whY

t2l

eorthquokes toke ploce. t3l c) Exploin, with the help of the diogrom, why this eorthquoke coused o lorge tsunqmi wove to form. t2l

327

)

Chemicol industry

From your troiners to your toothposte, you con thonk the chemicol industry for providing the moteriols we oll toke for gronted. We con think of the chemicols they moke in two ports:

o o

troditionol bulk chemicols speciolist (fine) chemicols.

Troditionolbulk chemicols would include the monufocture of:

o ommonio

r

o o

sulfuric ocid iron ond steel

nitric

ocid

o fertilisers o products from oil o products from solt - sodium o products from limestone.

chloride

These operote on o lorge scole in huge plonts. The industries tend to run their processes continuously. They con moke their product 24 hours o doy, 7 doys o week. These continuous processes ore economicol. Thot's becouse

they con keep conditions ideolfor the reoctions, soving energy, ond moke o constont supply of product. These products hove been in demond for o long time so componies

Road tankers deliver many products for the chemical industry

hove long-estoblished customers. However, developing countiies ore now competing. Their prices con be lower becouse of reduced lobour costs. Thot's why steelproduction hos decreosed shorply in the UK.

We olso hove componies who moke speciolist (fine) chemicols. These include some phormoceuticolcomponies. They moke drugs

on demond for their customers in botch processes. They use just the right omounts of reoctonts to moke the order.

Others componies, like brewers, will olso operote botch processes becouse they need to leove the reoctonts o while to reoct. In o brewery the fermentotion is cqrried out in lorge vots. when the

reoction to moke the olcohol (ethonol) is finished the vot is emptied. Its contents go on for further processing ond the vots ore re-filled with fresh reqctonts.

A botch process is not os efficient os o continuous process in generol. Botch processes toke more workers to operote them, which odds to costs. The troditionol chemicqls do not need o lot of money spending on reseorch ond development. Their processes hove been refinedover mony yeors. However, speciolist drugs componies spend much more on developing new products.

Fermenting sugar rs a batch process

Developing o new drug In the cose of o developing o new drug, the reseorch storts with experiments to moke o compound thqt works. In the post o reseqrch chemist might moke one or two hundred new compounds in o yeor. However, now they con moke thousonds. Thot's becouse, since the 1990s, more ond more chemists ore using mochines to help. The mochines con moke thousonds, or even millions, of compounds o yeor. They con outomoticolly mix ollpossible combinotions of promising reoctonts. This is colled

'combinotoriol chemistry'. These con then be screened to see if they ore effective drugs.

So this cqn sqve time ond lobour costs, but then the long process of testing the new drug hos to stort. It usuolly tokes between 7 to 10 yeors from discovery to generol use. It is estimoted thot this costs obout f400 million pounds for o new drug. This con include onimoltests ond severolrounds of clinicoltriols on humon volunteers.

Developing and testing new drugs takes years and cosls millions of pounds

Those people ogoinst testing on onimols orgue thot effects on onimols do not predict effects on humons onywoy. Mony drugs thot poss onimoltests then go on to foiltheir clinicoltriols. The clinicoltriols will involve the use of o plocebo test group. These people believe they ore toking the new drug. In foct their dose contoins no drug of oll. These oct os o control group ond their results ore compqred to the group toking the drug. Reseorchers will see if ony differences ore significont. Here is o simplified flow chort to show whot hoppens: Preclinical research

Discovery of possible drugs from many thousands of options generated

cultures and whole organs in lab tests

Phase ll clinical trials

-

Short term animal testing

- effect of drug on tissue

Phase lll clinical trials

large no. of patients with the disease more safety checks and dosage efiectiveness

- more trials on large nos. - cumulative toxicity

-

(many drugs fail at this stage) doses needed any side effects

Phase I clinical trials

- small no. ol healthy volunteers and toxicity

- salety

Submit application to be licensed by law

Developing a new drug

So o drugs compony needs to get bock oll its development costs before it storts moking o profit. However, o successful new drug con moke billions of pounds !

ero

s-,

:

)

Drugs

Whot do you think of when you heor the word 'drugs'? Drugs ore substonces which offect the body in some woy. Thot effect might be good or bod. Drugs con help us or might horm us if obused. o Con you nqme ony drugs thot ore oddictive ? Let's look ot the development of o clqss of drugs colled onolgesics. These ore drugs thot relieve poin. We con stqrt the story ot the time of the oncient Egyptions ond the oncient Greeks. The Epyptions used o bush colled myrtle to moke o treotment for muscle poins.

Then Hippocrotes, the fother of modern medicine, used the leoves ond bork of willow trees to eose poin. He mode it into o teo ond gove it to mothers to help with childbirth The next time thot willow wos recorded os o drug wos in 1763 - o gop of obout 2000 yeors ! The Reverend Edword Stone wrote to the RoyolSociety telling them of the effects of chewing o willow twig. This led to the seorch for the octive ingredient.

Hippocrates - the ancient Greeks used willow to relieve pain

In 1835 onother plont, o flower from the riverbonk, wos olso discovered to hove these onolgesic effects. Both plonts were used to moke solicylic ocid. It wos nomed ofter the Lqtin word for willow, sa1ix. Look of its structure below:

o*a'o"

I

OH where

\ C r' c...C ./ is a benzene ring I C. ,,C\ C,/ \ I

However, there wos o problem with solicylic ocid. It coused poinful ulcers in the mouth ond ottocked the lining of the stomoch. Chemists tried the sodium solt of solicylic ocid too. This wos soluble in wqter becouse of its ionic structure It wos not so bod for your mouth ond stomoch, but tosted just owful !

A French chemist colled Chorles Frederic Gerhqrdt mode o sofer drug in 1853. Look of its structure opposite:

I

o

\,2

OH

C

o- co aspirin

cH3

But the drug wos tricky to moke ond it wos forgotten until 1899. It wos then thot Felix Hofmonn rediscovered Gerhordt's method. He wos seorching journols for poinkillers for his fother who hod orthritis. This one worked o treot, without the side effects. Felix worked for o lorge Germon chemicol compony

colled Boyer. He told them of the drug's success ond convinced them to monufocture it. It wos given the trode nome Aspirin. At first it wos produced os o powder, but in 1915 the first toblets were sold.

Aspirin is an analgesic

Germony hod to give up the rights to the nome Aspirin ot the end of the First World Wor. This wos port of the Treoty of Versoilles. In foct, Boyer bought bock the rights in 1996 for mony millions of pounds. Aspirin is used for heodoches, fevers, ond in lorger doses for orthritis. It is now olso used in smolldoses to reduce the risk of heort diseose. However, the long term use of the toblets every doy hos brought with it the old problems. People ore worried obout the side effects, such os internolbleeding. About 6"h of ospirin users suffer from bleeding intestines. The seorch for new onolgesics did not stop ot ospirin. In the 1950s o new drug colled porocetomol wos introduced. This did not couse internolbleeding. Howeveq it did not reduce the swelling from orthritis like ospirin.

Then in the lote 1980s phormocists could sell ibuprofen bver the counter'. This wos much better of reducing the swelling, os well os the poin, from orthritis ond rheumotism.

lbuprofen was developed by chemists at Bools

Other reloted drugs were developed in the 1980s. An exomple wos benoxoprofen. This wos sold to obout holf o million potients in the USA in its first six weeks. But then the reports of bleeding, ond liver ond kidney domoge storted. It wos bonned in 7982 ond wos implicoted in 80 deoths in the UK ond 30 deoths in the USA. This roises questions obout how we test new drugs.

Loborotory onimols ore tested with lorger doses thon humons would toke to look for side effects. Then field triqls ore corried out with volunteer potients before o drug is possed os sofe for the public. (See poge 329.)

.

What are your views on testing drugs on animals?

i

r:&t

iitiltiffi:il{:.,..::,

)

Points ond pigments

Hove you ever pointed o room ? Why do people point their homes Point protects moteriols, but whot else is importont when you

?

choose which point to use ? Thot's where pigments come in. They ore the finely ground solids thot give points their colour.

Whot's in o point? In generol points contoin:

o A pigment (to provide colour). o A binder (to help the point ottoch itself to on object ond to form o protective film when dry).

o A solvent

(to help the pigment ond binder spreod well during pointing by thinning them out).

Do you remember looking ot emulsions on poge 176 ? They were mode of two liquids - oil ond woter - mixed thoroughly

together.

An emulsion is on exomple of o colloid.

of two or more in eoch other. You've probobly heord of emulsion points. These qre woter-bosed, but the binder is oily so when stirred up with the woter, we get on emulsion.

Emulsion paint is an oil-in-water

emulsion

The pigment is sometimes soluble in the solvent but is often insoluble. It is mode of tiny specks of solid. They ore so smoll you con't see them individuolly. They ore suspended in the point. They ore so tiny thot they don't settle out eosily. We coll this type of colloid o sol or o suspension. You con tell o sol from q solution becouse light will poss eosily through o solution. It looks cleor. Howeveq light is scottered by the bits of solid in o sol. It looks tronslucent. So o point con be on emulsion ond o sol.

Experiment25.7,, La,okingof sols

and solutions

We will try dissolving different powders in woter, Shoke o little of the solid in hqlf o test tube of wqter. Line the tubes up in q test tube holder. Ploce o lomp on the other side or put the holder on o window sill.

o

Which mixtures ore sols qnd which ore solutions?

ffi i$iitlriiili,[rii*$msffi .,,i'

solutions

I

\

1

t

\

Gloss paints ore the oil-bosed points thot give o hord, shiny finish. The pigment is dispersed through on oil (such os linseed oil), which con be thinned with o solvent (such os turpentine).

Point drying Hove you ever touched wet point by mistoke ? Point tokes o while to dry. Some points dry os the solvent evoporotes. The binder ond pigment ore left behind to coqt the surfoce. There is no chemicol reoction involved here. (Remember evoporotion is o physicol chonge - see poge 25.) The binder is likely to be mode of long molecules thot get tongled up together once the solvent hos evoporoted. Other points dry by meons of o chemicolreoction. Some points contoin plont oils. We hove mentioned the linseed oil in gloss point. It is extrocted from the flox plont Another common oilis tung oil. This is extrocted from the nuts of o tung tree. We hove looked ot plont oils in Chopter 14. Remember thot they

contoin unsoturoted hydrocorbon choins within their molecules. It is the corbon-corbon double bonds thot reoct with oxygen when the point is exposed to oir. Hove you ever opened o tin of point ond found it hod o skin ocross the top? This is the hordening process, storted becouse some oir hos got into the tin ond reocted with the point. The oxidotion of the oils forms cross-links between oil molecules. Groduolly we get o polymer built up. (See poge 153.) It is this polymer thot forms the tough shiny cooting on the surfoce This is how vornishes horden ond protect wood.

oil molecule cross-links between oil molecules

Tung oil hordens foster thon linseed oilbecouse it hos on extro double bond in eoch choin.

Varnish forms a hard shell to protect wood

!

.rilss:r .l'':;r{;ii;liii,1

)

Smort pigments

Hove you ever used o 'strip thermometer'? They give o visuol disploy of the temperoture os numbers 'mogicolly' light up. Some substonces respond to temperoture chonges by chonging colour They obsorb heot (infro-red rodiotion) ond give out light. We con use these

o o o o

thermochromic pigments to colour:

points plostics

poper fobrics.

Thermochromic pigments can be used on a thin plastic film to make a thermometer

They ore useful wherever you need o visuol worning of o chonge in temperoture. For exomple: o cups for hot drinks o electric kettles I ong surfoces thot might get hot o storing food (e.g. frozen food thot gets too worm

octive ond intelligent pockoging on poge 159).

-

blue thermochromic paint

see

green paint at 20'C

**"'

You con olso use the thermochromic pigments to test fuses or botteries. This will work by o current heoting o wire in the test circuit, which produces o chonge in colour. The pigments ore soluble in ocrylic, so we con use them in points to produce interesting effects. Look of the diogrom opposite:

low ordinary paint

lo 27"C

/'

blue turns colourless at 27'C green paint turns yellow at 27"C

So a green paint wiil turn yellow as rl gets warm. Can you think of a use for this?

Experiment,z1.2 Thermochromicpaints Mix o very smoll omount of'thermochromie pigment into ocrylic ond wqter down to moke your point. Apply this to q thin plostic cup. Allow to d4r'Then pour in some hot woter. o Whot hoppens ? Pour the hot woter out. o Whqt hoppens ?

f

(doc C(i 'm thecmochfornaicl

We olso hove pigments thot

willglow in the dork. These ore colled phosphorescent pigments (used in photochromic points).

They obsorb energy from light ond then releose it os glowing light. They hove token the ploce of moteriols like zinc sulfide. The new pigments will glow ten times os long. So hoving been exposed to light olldoy, the pigments willreleose light ond glow ollnight. They hove reploced hozordous rodiooctive moteriols used on old wotch ond clock honds. In the 1920s, Americon women were employed to point luminous numbers on wotches. This wos delicote work ond the women would use their lips to moke o fine point on their brushes. They didn t reolise the dongers. The point contoined rodiooctive rodium ! Unfortunotely mony developed concer of the jow, ond other concers Ioter in life.

))

>)>

We now see phosphorescent pigments on road and emergency

signs

)

Dyes ond dyeing

The pigments we hove looked of con olso be used on fobrics. The smort pigments con moke dyes thot will chonge colour when you weor them. But there ore lots of noturol dyes thot we hove been using for thousonds of yeors. We con extroct these from plonts, eorth or even insects. The problem with noturol dyes is thot they fode quickly. They ore eosily woshed out of fobrics. Thot's where mordqnts con help. A mordont helps o dye ottoch itself more firmly onto the molecules in o fobric. It improves o dye's colour-fostness.

Roman emperors wore special purple togas. /t took 10 000 sma// sea mol/uscs to make enough dye for one toga.

Experiment 25.3 Make your own dye Boil up some shongly coloured plont moteriol for obout 15 minutes Add more woter if necessory to stop it boiling dry. You wont o deeply coloured liquid to test on your white fqbrics. You con test: a. The efuct of different mordants Sook seporote somples of your fobric into o beqker contoining different mordonts. Try: i 125cm3 of vinegor ii 125cm3 of woter with o teospoon of creom of tortor qdded iii 125cm3 of soturoted sodium chloride solution. Then wring out your fobric somples ond sook them in your dye. There is a wide variety of synthetic dyes Rinse with cold woter ond leove to dry. now available to manufacturers Also dye o somple with no mordont odded to oct os q control. Test them next lesson - ore they colour-fqst? o Which mordont is most eff.ective? b. The colour-fastness on differenttabrics c. Different plant material Moke your tests os fqir ond os sofe os possible. Let your teocher check your plon before storting. o Which foctor willyou vory ond'which willyou control in eoch investigotion ? o Try to think of o woy to generote quontitotive doto. o 'Evoluote your investigotion. l

Synthetic dyes In 1856, o young chemist colled Williom Perkins mode o surprise discovery. He wos trying to moke quinine - o drug to fight molorio. However, he mode o purple dye by mistoke. It wos the first synthetic dye. His row moteriol come from cool tor, ond this signolled the stort of the chemicol industry. He tried his purple dye on silk ond found it for better thon existing dyes. At this time, o lot of triol ond error wos involved in looking for new moteriols. Perkins' discovery led to o roce for more dyes. Germon chemists were successful in developing mony new dyes.

William Henry Perkins (1 838-1 907) discovered the first really synthetic dye

iff$ffiffiffiffi

Nonotechnology is the design ond creotion of mochines thot ore so smoll we meosure them in nonometres. It is difficult for us to imogine o nonometre (nm). The tiny sizes involved in nonotechnology ore mind-boggling. The nonometre is the unit of meosurement used on on otomic level:

lnm=10-9m

Nonoscientists study porticles thot ore between 1 ond 100 nm in size.

In other words, o nonometre is o billionth of o metre. You could get obout o million nonometres ocross o pinheod

;l

rt !r

r,Llt Nonotechnologists ore now moking mochines thot ore less thon 100nm in size. They hove the techniques to move individuolotoms or molecules. Then they con ploce them where they wont them. At the moment, reseorch is in its eorly stoges. There ore two opprooches to moking the moleculor mochines.

l\ t* lL l\

,l

lr ,\ ,r {\ r\

,f,

lr

ll

/\

t. I' l.

Jr

e\

Scientlsls at lBlll placed 1 10 molecules of carbon monoxide on the surface of copper. They used the latest atomic force mlcroscopes to position the molecules.

You con:

o Sculpt

or 'chisel owoy' of moteriols until you ore left with the molecules or otoms thot you wont on the surfoce. This method is used in microelectronics.

o Build

your mochine up from individuol otoms or molecules. You con do this by physicolly moving the molecules using otomic force microscopes, os in the photos, or by chemicol reoctions in solution.

The chemicol technique seems to offer the best woy forword. Physicolly moving molecules oround tokes too long, so ony products mode would cost too much money.

This atomic force microscope can move and reposition atoms or molecules

:, r.:336

t. d, {.

Sun-screens You con now find nonotechnology improving sun-screens. Scientists con coot individuol specks of titonium oxide powder with o complete cooting of silico. The thickness of the silico cooting con be odjusted of on otomic level. These 'nonoporticles' seem to be more effective of blocking the Sun's roys thon conventionolu.v. obsorbers. So nonotechnology willsove mony people from domoged skin ond concers cqused by too much ultroviolet light.

t

Future opplicotions? Some soy thot nonotechnology willgive us heolth-core thot con treot individuol cells. Perhops we'llbe oble to monitor our heolth on o cellulor levelwith highly selective sensors. This should increose our life spons. Nono-bucky-tubes (see poge 263) ore now being developed thot will one doy seorch for concerous cells.

q"

looks like

o,.,otachno rs

.q"

toking oFt ,G\ T''9

Or imogine tiny mochines potrolling your blood vessels, cleoning off ony fot deposits from their wolls. This would help those ot risk from strokes. Imogine computers with memory copocities ond speeds thot we con only dreom obout now. The tiny mochines built so for include 'moleculor model kit' rotors, 'robots', motors ond circuits And just imogine the surfoce oreo possible using nonoporticles os cotolysts !

-/

Will nonotechnology horm us? Cosmetic componies ore developing onti-wrinkle creoms with nonoporticles thot con poss through skin to its lower loyers. There, the octive ingredients con stimulote the production of new cells. However, people soy thot there hos been little reseorch into the effects of nonoporticles thot could penetrote into the bloodstreom They soy thot these cosmetics should hove the some testing ond licensing process os phormoceuticol drugs. (See poge 329.) uuu

,

l

f

F K. Eric Drexler wrote a book called 'Engines of Creation'. ln the book he specu/ates that one day we might invent a nanomachine that can reproduce itself . Then the world could be overrun by 'grey goo', as he calls it. Some people are so worried that they have called for a halt in nanotechnology research.

*

Whot ore your views on these issues ?

)

)

Detergents

Detergents ore cleoning ogents. See poge 178 for the emulsifying effects of detergents They help to remove greose ond oily stoins. They olso help woter sook into fobrics. The experiment below shows how o detergent offects the forces between molecules of the surfoce of woter.

ff: : Ii f;il i,lfr] :; ;::: ff l 3!,!:,#i: Experiment 25.4 Detergents and surface tension Corefully floot q needle on the surfqce of o beoker of woter. Stort with the needle on o smoll piece of pqper towel, which will sink os it soqks up woter. Now gently qdd o drop of detergent to the woter in the beqker.

o

Whot hoppens to the needle ? Try to exploin why.

The needle floots becouse of woter's surfoce tension. There ore relotively strong forces between the molecules of woter of its surfoce. If we con weoken these forces, woter will sook into fobrics more effectively. Experiment 25.5 Hard water Add o few drops of soop solution to holf o test tube of hqrd woter. Put o bung ot the top ond shoke the tube.

o

Whot hoppens

lather

?

Now repeot the experiment but use o soopless detergent. . Whot difference do you notice ?

+

hard water hard water + soap solution soapless detergent

Woshing-up liquids generolly contoin : o A surfoctont (the octuol detergent thot removes the greose). o Wqter (to thin out the mixture so it con squirt more eosily from the bottle).

o o

Colouring ond frogronce odditives (to improve the oppeol of the product to potentiol customers). Rinse ogent (to help woter droin off crockery).

25.6

Comparing detergents Design on investigotion to compore the effectiveness of either: lnuestigation

r

Woshing-up liquids

o Woshing

powders

-

eco-friendly ogoinst conventionol brond.

- biologicol

i,
NoCl(oq) + H2O(l) + NHe(s)

ommonium

Ammonia gas turns damP red litmus paper blue

ommonio

chloride

3ffi11, ,':ii:r

We hove looked of vorious chemicol tests for different ions But if you ore on environmentol scientist checking woter or oir for pollution the omounts present moy be tiny. This is where the use of instruments to onolyse somples hos become very importont. As we get to know more obout electronics ond computers, the instruments we now hove ore incredibly sensitive. They con detect omounts of pollutonts thot would be for too smollto onolyse by chemicol tests in o lob.

Let's look of one inskument thot identifies elements ond one thot identifies compounds:

Atomic obsorption spectrometers These mochines ore good ot identifying elements present.

The somple is usuolly heated in a flame. This breoks down the somple into otoms which ore then excited. Some electrons in the otoms jump into higher energy levels (or orbitols). They obsorb energy from the flome. When they foll bock to lower energy levels the energy is given out os ligl-rt energy. This exploins the flome tests we did to identify metols on poge 362.

Sensltlve instruments can detect small amounts of substance. They can be used Io test lor drugs in athletes and mineral ions in blood. They analyse samples in forensic labs and hosplta/s, as well as monitortng pollutants.

In o spectrometer we con onolyse the wovelength of the light. Eoch ppe of otom obsorbs ond gives out its own porticulor

pottern of rodiotion.

This is colled its spechum. We con use this to identify elements. We just compore peoks ond troughs from the unknown somple with elements we do know.

The flame alomises the sample and excites electrons in an

Computers hold records on eoch element ond motch up the

ato m

i

c absorpti

o

n s pectro mete r

spectro for us. You con olso see how much of the element is present in the somple.

This, ond similor methods, give us occurote woys to monitor woter for metols. On poge 296 we sow how dongerous mercury cqn be. We con now troce mercury down to os little os 0.000 000 001 g. Other pollutonts, such os zinc, leod ond codmium, con olso be detected. Woter componies con meosure the concentrotion of colcium, mognesium, oluminium ond iron in their woter.

Atomic obsorption spectrometers ore olso used in the steel industry Remember thot steel is o mixture of elements with iron. Steel mokers need to control corefully the omounts of troce metols present. The quolity of steel depends on this.

Ihrs rs the characteristic spectrum of cadmium

Visible-ultroviolet spectroscopy We hove olso seen how people ore worried qbout the pesticides thot we now find in woter. (See poge 296.) r Why con't we use on otomic obsorption spectrometer to identify o pesticide in o woter somple ? o Whot would hoppen to o pesticide molecule in the flome inside the spectrometer ? Visible-ultroviolet spectroscopy is o gentler method. It doesn't use o flome to breok up the molecule into otoms. We simply shine light of different wovelengths through the solution to be onolysed. So the somple is not destroyed in the onolysis. A detector then tells us which wovelengths hove been obsorbed. These ore usuolly broad bands of wovelengths. They ore not shorp peoks like the emission spectro on the lost poge.

Look ot the visible-ultroviolet spectrum of o compound below:

Light source and equipment to vary its wavelength

Sample

Detector

spectrum of a red organic compound

L*

0)

c(6

Simpilfied diagram of vrsible spectrophotometer

-o

o a (6

400

450

500

550

600

wavelength (nm)

This mokes it horder to motch one spectro to onother, but it con stillbe done. We con olso onolyse omounts of compound present by comporing ogoinst known omounts. This method will only work if the substonce we onolyse obsorbs light in the visible or ultroviolet ronge. Most of the pollutonts in woter ore colourless. They don t obsorb in the visible ronge of wovelengths (or in the ultroviolet ronge). But we con reoct them with o compound thot chonges them into o coloured molecule. We con test for nitrote ions (from fertilisers) ond for phosphote ions (from detergents) using this method. This helps us to guord ogoinst eutrophicotion. (See poge 240.)

-

u.v

)

Anolysing spectro

You hove seen two methods of instrumentol onolysis on the previous two poges. There ore olso mony other instruments ovoiloble to chemists in helping to solve crimes, diognose illness ond identify pollutonts. Most instruments produce print-outs or screen-shots of o spectrum These moinly show wovelengths of rodiotion given out or obsorbed. Samp/es can be passed through a machine that separates the eomponents in a mixture before they are analysed. Gas-liquid chromatography is often used. The vaporised sample is sent through a resin. The different substances take different times to pass through.

For exomple, we use infro-red rodiotion. The different types of bonds in orgonic molecules obsorb chorocteristic frequencies. So o spectrum con tell us whot groups ore in on unknown

molecule. Computers con now motch the spectrum of on unknown compound to o huge dotobose of stored spectro. This is colled

fingerprinting.

lnfra-red spectrum of ethanol

Here is the infro-red spectrum of ethonol, C2H5OH

00

o

c 80 G

Another technique is colled moss spectrometry This breoks molecules oport by bombording them with electrons. Then the frogments ore onolysed in the moss spectrum. We con use this to identify elements or compounds.

=E o c 6

60 This shows that an OH group is present

40

o\

4000

2500 2000 1500 1000

3500

Wavenumber

Mass spectrum of ethanol

Here is the moss spectrum of ethonol

3'l

=o

The peaks show the mass of fragments produced. The peak for the heaviest ion tells us lhe relative formula mass.

60

tr

o 40

s

45

20

Another common technique is nucleqr mognetic resononce (n.m.r. ). This onolyses smoll chonges in the energy of nuclei in o mognetic field.

15

46 20

40

60

The peaks tell us about the hydrogen atoms in ethanol

12

10

864 Chemical shift(d) (p.p.m.)

1,..',',

100

n.m.r. spectrum of ethanol

It is used o lot to identify orgonic compounds.

..'

80

Mass-to-charge ratio

Here is the n.m.r. spectrum of ethonol:

S

500

(cm t)

2

0

F Quontitotive onolysis

?

o-- C ---9

The police send blood somples to forensic scientists. They onolyse the concentrotion of ethonol in the blood of suspected drink drivers They con find this from the size oI one of the peoks in the infro-red spectrum of the somple (see previous poge). This gives numericol doto (quontitotive doto) thot con be used in court.

I

ffi l

Whot's the formulo? We con olso onolyse on unknown orgonic compound chemicolly to find out its formulo. We burn the compound in oxygen. Then the goses mode ore possed through tubes thot obsorb woter vopour ond corbon dioxide formed. The goses ore onoiysed by mochines before ond ofter they enter the obsorption tubes. They tell us the moss of wqter

CIF$ r'r'ir;ir.t';: / l;jli I a. i ,fri'iai iif1l.'L:l:; lrrir.Lr iiil' ill.ri-i/.r i', r,'rr l, {.i rlIii ]r i-ili.rira-ri ll r ilra:li i)ioo(1

ond corbon dioxide produced. Let's look of how we con process the doto: Example

A somple of o compound wos found to contoin corbon, hydrogen ond oxygen. Its relotive formulo moss wqs found to be 46. On complete combustion of 9.2gof the compound in oxygen, 77.6gof corbon of woter vopour were obsorbed in tubes. Whot is the chemicolformulo of the compound? (A, volues: C = !2,H : 1, O : 16) This is like working out the empiricol formulo on poge 349. But first we hove to find the moss of corbon ond hydrogen from the doto provided obout CO2 ond H2O. So how much corbon is there in L7 .69 of corbon dioxide ? The relotive formulo moss of CO2 is 12 + (16 x2) M (of which 12 is mode up of corbon)' So we hove (12 + 441 x 17 .6gof corbon in the unknown compound 4.8 g of corbon.

:

:

So the empiricolformulo is C2H6O. This is olso the octuol moleculor formulo becouse we ore told its relqtive formulo mqss is 46,

i.e. (2x12) + (6 x 1) + (1

x 16):46

367

Summory

F

Anions

Anion

Formula

Test

Results of test

Carbonate

Corz-

Add hydrochloric acid and test gas produced by bubbling through limewater.

Rapid effervescence and carbon dioxide produced gives white precipitate with limewater

Add dilute nitric acid to solution of ion and then barium chloride solution.

Dense white precipitate of barium sulfate is produced.

Sulfate(vr)

SOoe-

CO32-(s) + 2H+(aq)---r. H2O(l) + COz(g)

Ba2+(aq)

+ SO42- (aq)----> BaSOa(s)

Sulfate(rv) (or sulfite)

So.z-

Add dilute hydrochloric acid

Effervescence as acidic sulfur dioxide gas is produced. The SO2 gas decolourises acidified manganate(vrr) solution.

Chloride

cr-

Add dilute nitric acid followed by silver nitrate solution.

White precipitate formed.

(as above)

Pale cream precipitate formed, i.e. AgBr(s)

(as above)

Pale yellow precipitate formed, i.e. Agl(s).

Nog-

Add NaOH solution to compound and aluminium powder. Heat.

Pungent smell of ammonia gas which turns damp red litmus blue.

Cation

Formula

Test

Results of test

Ammonium

NHr*

Add NaOH solution and heat.

Gas turns damp red litmus blue

Magnesium

M92+

Copper

Cu2*

lron (ll)

Fe2+

lron (lll)

Fe3+

Rusty brown precipitate formed.

Aluminium

Al3+

White precipitate formed which dissolves in excess alkali.

Sodium

Na+

Yellow flame,

Potassium

K+

Lilac flame

Bromide

Br-

lodide Nitrate(v)

F

Ag*(aq)

+ Cl-(aq)---> Agcl(s)

Cotions

White precipitate formed Pale blue precipitate lormed. Sodium hydroxide (NaOH) solution

Dirty green precipitate formed.

Lithium

Li+

Calcium

Ca2+

Barium

Ba2+

Pale green (apple green) flame.

Copper

Cu2+

Blue/green flame

Name of gas

Formula Test

Results of test

Carbon dioxide Ammonia

CO,

Pass gas through limewater

NH"

White precipitate formed in suspension (milky) Fled litmus turns blue

Sulfur dioxide

Soz

Damp red litmus paper Acidified potassium manganate(vrr).

F

368

Flame test

Red (scarlet)flame

Brick red flame.

Goses

Colour changes from purple to colourless

5.

sodium hydroxide solution ond worming with powdered oluminium. A gos is given off thqt turns red litmus blue.

1. We con test for some onions ( . . . . chorged ions using . . . . reoctions in which osolid forms in the solution. Other qnions reoct to give off . . . . which we con identify e.g. red litmus turns . . . . with ommoniq. We con use . . . . tests to identifu some cotions e.g. No+ ions. Reoctions with sodium . . . . solution identify others. For exomple, iron(lll) ions form o. . . . precipitote.

o) Nome the gos given off.

b) Drow o toble to record the flqme colours for i) sodium, ii) potossium, iii) copper,

iv) colcium, v)borium. c) i) Whot do you see when you odd sodium hydroxide solution to both colcium chloride ond mognesium chloride ? ii) Write q bqlqnced symbol equotion for eoch reoction. iii) Whot do we coll this type of reoction ? iv) Write on ionic equotion to describe eoch reoction. v) How could you distinguish between colcium ond mognesium in the chlorides tested ? d)A compound gives o liloc flome test. When dissolved in nihic ocid ond silver nitrote is odded, you get o creom precipitote. i) Nome the compound. ii) Write on ionic equotion for the reoction of the compound with silver nitrote solution.

2. How con we positively identify zinc corbonote ond copper corbonote

?

3. An unknown white compound gives off on ocidic gos thot decolourises potossium mongonote(VII) solution. The compound forms o white precipitote with dilute sodium hydroxide solution which dissolves in excess

olkoli. Whot is the unknown compound?

4.

We con test for the nitrote ion by odding

Alex hos 3 unknown solts - A, B ond C. He does o flome test on eoch solt. These ore his results:

6.

o) Nome on instrument thot is usefulfor detecting unknown elements.

b)Why is the instrument in o) not usefulfor

o) Nome the metolin eoch solt. b)Alex dissolved eoch solt in dilute nitric

ocid.

When he odded silver nitrote solution to A, o pole yellow precipitote wos formed. He did the some to B, but the precipitote wos white. C formed o white precipitote with bqrium nitrote solution. D gove off o gos with the ocid, which Alex bubbled into limewoter. The limewoter turned milky. Nome solts A, B, C ond D. c) Give the test ond positive result for the Fe2* ion.

detecting compounds ? c) Nome on instrument thot is good ot detecting molecules of compounds. d) Give some uses of these types of sensitive instrument.

e)Why ore they usefulin industry?

7. An unknown hydrocorbon somple

is burned in oxygen. It releoses 17.72g of corbon dioxide ond 10.86 g of woter. o) How mony moles of cqrbon ore there in 17 .72g of corbon dioxide ? b) How mony moles of hydrogen ore there in 10.869 of woter? c) Whot is the empiricolformulo of the hydrocorbon? (Answer on page 375.) Further questions on poge 373.

369

Further questions on Synthesis qnd Anolysis

b) i) 1. The chemicols mode in industry con be described os bulk chemicols or fine chemicols. o) Exploin the difference between bulk chemicols ond fine chemicols. t2l b) Phormoceuticol drugs ore fine chemicols. Moking ond developing o new phormoceuticoldrug is usuolly much more expensive thon o bulk chemicol such os sulfuric ocid. Describe three foctors thqt moke the drug -t3l so much more expensive.

2.

Some phormoceuticol chemicols ore extrocted from plonts, others ore synthesised. o) Describe the processes used in the extroction of chemicols from plonts. tsl b) Exploin whot is meont by the term

synthesised.

t1l

c) Suggest why chemicols extrocted from plonts moy be more expensive thon those thot ore synthesised. t2l

S" The development of o new phormoceuticol drug is very expensive. o) List three foctors thot contribute to the high cost of this development. t3l b) Briefly describe how ony new phormoceuticol drug hos to be tested. t3l c) A compony intending to morket o new drug corries out extensive morket reseorch. Exploin why. t2l

4.

ii)

Describe two uses of point contoining thermochromic pigments. t2l For eoch use, exploin whot odvontoge this point hos over conventionolpoint.

t2l

6. Mony new drugs ore developed from noturol sources.

Mony noturol substonces hove some drug octivip but they often hove hormfulside effects. Scientists try to develop new drugs from these

nqturol substonces. The scientists follow o stondord procedure for reseorching ond developing o new medicine. stage

thousands of compounds are synthesised

1

stage 2

tested in test tubes

stage 3

one in 500 compounds look promising

stage 4

several are tested on animal cells

stage 5

only two or three compounds are effective

stage 6

safety testing in animals

stage 7

safety and effectiveness in humans: first sludies in human volunteers, then studies in patients

Point is o colloid. o) Exploin whot is meont by the term colloid.

t2l

b) Oil-bosed points contoin o solvent thot evoporotes os the point dries. i) Describe the chemicol chonge thot olso tokes ploce when point dries. t2l ii) How does this improve the quolities of the point? t1l c) How do emulsion points differ from oilbosed points ? [2]

5. Thermochromic pigments con be odded to ocrylic points. o) Whot is meont by the term

thermochromic?

370

o) Exploin why the chemicols ore not tested on humons before stoge 7. t2l b) Exploin why studies ore corried out on humon volunteers, before the potients in

stoge

7.

t2l

c) Different people hove different views obout using onimols in medicolreseorch. Suggest why some people disogree with using onimols in medicol reseorch. One mork is for o cleor, ordered onswer.

t1l

Note; although a question may be marked (AQA) etc., it will oflen be relevant to other examinations as wel

[2

+1]

(ocR)

Further questions on Synthesis ond Anolysis 14. Anolysis of o somple

7. Which one of the following moss ?

(Relotive otomic mosses:

of the compound sodium oxide, showed thot it contoined 2.3g of sodium ond 0.8g of oxygen. Use this informotion to workoutthe formuloof the compound sodium oxide in questions o) to e).

hos the greotest

H: 1, O :

16,

No:23,S=32,Cl:35.5)

A B C D

o) Whot is the moss of eoch element in the

1 mole No

0.5 mole NoCl 0.6 mole NoOH 0.2 mole No2SOa

t1l

(AOA)

8. Which of the following

hove o concentrotion of 0.1 mole/dm3 ? (Relotive otomic mosses: H: 1, N: 14, 32) O: 16, No - 23, (1) HNOs(oq) contoining 6.3 g/litre (2) NoOH(qq) contoining 2 g in 500 cm3 (3) H2SO4(oq) contoining 0.98g in 100cm3

S:

t1l

Questions

(AoA)

sodium oxide ? b)Whot is the moss of 1 mole of eoch element? c) How mony moles of eoch element combine? d) Whot is the simplest rotio ? e) Whot is the formulo of sodiumoxtd"

looo,

15. Joseph Priestley discovered oxygen gos in \774bv heoting mercury oxide. A teocher repeoted the experiment ond found thot2.77 g of mercury oxide decomposed on heoting to produce 0.169 of oxygen. Colculote the formulo of mercury oxide. (Show oll your working.) (Relotive otomic mosses :

9-1" 1

Use poges 390 qnd 391 to help you. From the list A to D,

A3 B6 C9 D18

Hg (mercur7):207,

O: 16) t3l

(AOA)

choose the number which is the:

9.

Moss in groms of woter produced when 1 g

of hydrogen is burned completely. 2H2 +

02

--------> 2H2O

t1l

10. Moss in groms of mognesium in 10 g of mognesium oxide,

MgO.

t1l

11. Number of otoms of beryllium, Be, which hove the some totolrnoss os one otom of

qluminium,

Al.

t1l

(AOA)

H: 1, O:16) [1) (AOA)

13. 0.5 mole of metol X combine with 1.0 mole of non-metolY. Whot is the formulo of this compound of X NH4NO3 o) Colculote the relotive formulq mosses for nitric ocid (HNO3) ond ommonium nitrote (NH4NO3). (H: 1, N: 14, O: t2l b) Colculote the moss of nitric ocid needed to moke 400 tonnes of ommonium

16).

nitrote.

L2. Colculote the number of moles of woter molecules, H2O, present in 90g of ice. (Relotive otomic mosses:

16. Most of the nitric ocid thot

(AOA)

t2l

(oCR)

L7. Whot moss of chlorine would be needed to moke 73 tonnes of hydrogen chloride ? Hr+ Cl2 --------> 2HCl The relotive otomic moss (A,) of chlorine (Cl) is 35.5. The relotive otomic moss (A.) of hydrogen (ocR) (H) is

1.0.

tsl

37t

Further questions on Synthesis ond Anolysis 18. Aluminium oxide is electrolysed to extroct oluminium. Oxygen gos is produced ot the corbon onode which is then burned owoy os described in the following equotion:

C+O2

-

COz

Given the following relotive otomic mosses:

Al:27 C:12 O:

16.

For eoch 32 tonnes of oxygen used colculote: o) the moss of corbon burned ond b) the moss of corbon dioxide produced. Show your working. (1 tonne : 1000kg)

t2l

c) Colculote the moss of oluminium produced from 204 tonnes of oluminium oxide given the equotion, 2Al2O3 --------> 4Al+ 3O2 Show your working. t2l (WJEC)

f 9. A student heoted strongly o known moss of powdered titonium so thot qll the titonium combined with oxygen from the oir. The following results were obtoined. Moss of contoiner * titonium : 35.9 g :31.1g Moss of empty contoiner Moss of contoiner * contents ofter

heoting:39'1g o) Whot would be o suitoble contoiner for

the student to use ? b) Colculote the moss of titonium ond of oxygen combining in the experiment. c) Use the toble on poges 390 ond 391 to write down the relotive otomic moss of titonium ond of oxygen. d) Use your onswers to ports b) ond c) obove to colculote the (empiricol) formulo of the titonium-oxygen compound. You must show your working.

t?l

(EDEXCEL)

24. The symbol equotion below shows the reduction of iron(lll) oxide by corbon Fe2Os +

3CO --------> 2Fe + 3COz o) Colculote the formulo moss of iron(lll)

Silver tornishes becouse it reocts with hydrogen sulfide in the oir to form silver sulfide. A somple of silver sulfide contoins 10.8 g of silver ond 1.6 g of sulfur. Colculote the formulo of silver sulfide. You must show ollyour working to goin full morks. (Relotive otomic mosses:

S:32; Ag:

t4l 22. o) Colculote the relotive formulo

108) (AOA)

moss (M,)

of potossium chlorote, KCIO.3. (Relotive otomic mosses: O: 16;

Cl:35.5;

K:39)

t2l

b) Colculote the percentoge of oxygen in potossium chlorote. t2l (AOA)

23. The equotion for the reoction of mognesium with hydrochloric ocid is: Mg(s) + 2HCl(qq) --------> MgCl2(oq) + Hz(g) Use poges 390 ond 391 to colculote the relotive formulo mosses (Mr) of

MgCl2 b) Hz

:

tll

o)

t1l

c) Colculote the volume of hydrogen (ot 1 otmosphere ond 25 "C) which could be obtoined from 1g of mognesium reocting with excess hydrochloric ocid. [The relotive formulo moss of hydrogen meosured in groms occupies o volume of 24litres (24 dm3) ot the obove

conditions.l

t2l

(wiEC)

burning 72g of mognesium metol in excess

oxide. (Use the toble on poges 390 ond 391) [2] b) Colculote the moss of iron thot could be obtoined from 32 000 tonnes of iron(lll)

t3l

silver.

24. Whot moss of MgO would be produced by

monoxide.

oxide.

21 . This question is obout two compounds of

(AOA)

oxygen?

t2l

Equotion for reqction: 2Mg+ 02 -------> 2MgO (Relotive otomic mosses:O: 16, Mg: 24) (wJEC)

Answers to Further questions on 'lvloles' are on page 375. JIZ

Further questions on Synthesis ond Anolysis

:a:/ A student wos osked to perform f ie. Column A gives the nomes of some onions (negotive ions) ond some cotions (positive ions). Column B gives the tests for these ions - but they ore not in the correct order. Motch the tests to the ions: t7l

A Sodium ion Column

Column B 1. Add dilute hydrochloric

- test for corbon dioxide with limewoter 2. Add dilute sodium hydroxide ond worm test for ommonio with domp red litmus poper 3. Corry out o flome test - look for o bright yellow flome 4. Add borium chloride solution - look for o white precipitote 5. Corry out o flome test - look for o blue/green flome 6. Add silver nitrote solution - look for o white precipitote 7. Carry out o flome test - look for o red flome ocid

ion

Colcium

Copper

ion ion

Ammonium

Chloride

Sulfote

ion

ion

Corbonote

ion

some tests

on o substonce lobelled A. The results of these tests ore given below.

. . .

o

Substonce A is o white solid which gives o liloc flome test. Substonce A reocts with dilute ocid B to produce gos C ond o colourless solution D. Gos C turns limewoter cloudy. Dilute nitric ocid followed by silver nitrote solution wos odded to solution D. A white precipitote E wos produced.

o) Identify:

i) gos C ii) compound A iii) the negotive ion present in

t1l t2l

D

solution

iv) ocid B

t1l t1l t1l

E

v) precipitote b) Briefly describe how you could perform o (AOA) flome test on substonce

A. t3l

XS. A student corries out the iollowing reoctions to identify o green solid A. green solid A I

add dilute sulfuric acid

gas C

light biue solution B I

i*S. Chemicoltests con be used to identify compounds. The toble below shows the results of some tests corried out on three solutions, A, B ond C. Use the informotion in the toble to identify solutions A, B ond C. Give the nome of: o) solution A t2l b)solution B t2l c) the metolion in solution C. t1l Solution

Flame test

Hydrochloric

Yellow

Carbon dioxide gas produced

acid is added A

Brick-red

c

add a few drops oi dilute sodium hydroxide

+l

liqht blue

add to

limewater

precipitate

turns milky

o) Nome solid A, solution B ond gos b) Write o bolonced equotion for the reoction of solution B with sodium

hydroxide.

C.

tsl

t3l

(oCR)

Sodium hydroxide solution is added

Silver nitrate solution is added

Whlte precipitate insoluble in excess sodium hydroxide solution

White precipitate

Dark green precipitate

J/J

19 300 C

is

70