Class 7 Physics - BeTOPPERS IIT / NEET Foundation Series - 2022 Edition

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IIT FOUNDATION Class VII

CHEMISTRY

© USN Edutech Private Limited The moral rights of the author’s have been asserted. This Workbook is for personal and non-commercial use only and must not be sold, lent, hired or given to anyone else.

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USN Eductech Private Limited Hyderabad, India.

PREFACE Our sincere endeavour in preparing this Book is to enable students effectively grasp & understand the Concepts of Chemistry and help them build a strong foundation in this Subject. From among hundreds of questions being made available in this Book, the Student would be able to extensively practice in each concept exclusively, throughout that Chapter. At the end of each Chapter, two or three Worksheets are provided with questions which shall cover the entire Chapter, helping each Student consolidate his / her learning. This Book help students prepare for their respective Examinations including but not limited to i.e. CBSE, ICSE, various State Boards and Competitive Examinations like IIT, NEET, NTSE, Science Olympiads etc. It is compiled by our inhouse team of experts who have a collective experience of more than 40 years in their respective subject matter / academic backgrounds. This books help students understand concepts and their retention through constant practice. It enables them solve question which are ‘fundamental / foundational’ as well questions which needs ‘higher order thinking’. Students gain the ability to concentrate, to be self-reliant, and hopefully become confident in the subject matter as they traverse through this Book. The important features of this books are: 1.

Lucidly presented Concepts: For ease of understanding, the ‘Concepts’ are briefly presented in simple, easy and comprehensible language.

2.

Learning Outcomes: Each chapter starts with ‘Learning Outcomes’ grid conveying what the student is going to learn / gain from this chapter.

3.

Bold-faced Key Terms: The key words, concepts, definitions, formulae, statements, etc., are presented in ‘bold face’, indicating their importance.

4.

Tables and Charts: Numerous strategically placed tables & charts, list out etc. summarizes the important information, making it readily accessible for effective study.

5.

Box Items: Are ‘highlighted special topics’ that helps students explore / investigate the subject matter thoroughly.

6.

Photographs, Illustrations: A wide array of visually appealing and informative photographs are used to help the students understand various phenomena and inculcate interest, enhance learning in the subject matter.

7.

Flow Diagrams: To help students understand the steps in problem-solving, flow diagrams have been included as needed for various important concepts. These diagrams allow the students visualize the workflow to solve such problems.

8.

Summary Charts: At the end of few important concepts or the chapter, a summary / blueprint is presented which includes a complete overview of that concept / chapter. It shall help students review the learning in a snapshot.

9.

Formative Worksheets: After every concept / few concepts, a ‘Formative Worksheet’ / ‘Classroom Worksheet’ with appropriate questions are provided from such concept/s. The solutions for these problems shall ideally be discussed by the Teacher in the classroom.

10. Conceptive Worksheets: These questions are in addition the above questions and are from that respective concept/s. They are advised to be solved beyond classroom as a ‘Homework’. This rigor, shall help students consolidate their learning as they are exposed to new type of questions related to those concept/s.

11. Summative Worksheets: At the end of each chapter, this worksheet is presented and shall contain questions based on all the concepts of that chapter. Unlike Formative Worksheet and Conceptive Worksheet questions, the questions in this worksheet encourage the students to apply their learnings acquired from that entire chapter and solve the problems analytically. 12. HOTS Worksheets: Most of the times, Summative Worksheet is followed by an HOTS (Higher Order Thinking Skills) worksheet containing advanced type of questions. The concepts can be from the same chapter or as many chapters from the Book. By solving these problems, the students are prepared to face challenging questions that appear in actual competitive entrance examinations. However, strengthening the foundation of students in academics is the main objective of this worksheet. 13. IIT JEE / NEET Worksheets: Finally, every chapters end with a IIT JEE / NEET worksheet. This worksheet contains the questions which have appeared in various competitive examinations like IIT, NEET, AIEEE, EAMCET, KCET, TCET, JIMPER, BHU, AIIMS, CBSE, ICSE, State Boards, CET etc. related to this chapter. This gives realtime experience to students and helps them face various competitive examinations. 14. Different Types of Questions: These type of questions do appear in various competitive examinations. They include:

• Objective Type with Single Answer Correct

• Non-Objective Type

• Objective Type with > one Answer Correct

• True or False Type

• Statement Type - I (Two Statements)

• Statement Type - II (Two Statements)

• MatchingType - I (Two Columns)

• MatchingType - II (Three Columns)

• Assertion and Reasoning Type

• Statement and Explanation Type

• Roadmap Type

• FigurativeType

• Comprehension Type

• And many more...

We would like to thank all members of different departments at BeTOPPERS who played a key role in bringing out this student-friendly Book. We sincerely hope that this Book will prove useful to the students who wish to build a strong Foundation in Chemistry and aim to achieve success in various boards / competitive examinations. Further, we believe that as there is always scope for improvement, we value constructive criticism of the subject matter, as well as suggestions for improving this Book. All suggestions hopefully, shall be duly incorporated in the next edition. Wish you all the best!!!

Team BeTOPPERS

CONTENTS 1.

Language of Chemistry

..........

01 - 22

2.

Acids, Bases and Salts

..........

23 - 36

3.

Air and Its Components

..........

37 - 62

4.

Hydrogen

..........

63 - 76

5.

Coal and Petroleum

..........

77 - 84

6.

Types of Changes

..........

85 - 102

7.

Key and Answers

..........

103 - 138

Language of Chemistry Chapter -1

Learning Outcomes

By th e e n d o f th i s c h ap te r , yo u w i l l u n de r stan d • • • • • • •

Elements Compounds Atoms Molecules Ions Structure of Atom Atomic mass

• • • • • •

Isotopes Valency Formation of compounds Writing Chemical Formulae of Compounds The Laws of Chemical Combination Writing and balancing chemical equations

1. Elements The term element was first used by Robert Boyle in 1661. Later, a French chemist. Lavoisier, defined elements as ‘the basic form of matter that cannot be broken down into simpler substances by chemical reactions’. The smallest particle of an element is an atom. An element consists of the same kind of atoms. Iron (Fe), carbon (C), sulphur (S), mercury (Hg), oxygen (O), etc. are examples of elements. There about 114 elements known so far. Among them, 92 elements occur naturally and the other 22 elements have been prepared artificially by the scientists in the laboratories.

2. Compounds Compounds are formed when two or more elements combine chemically in a fixed proportion. The smallest particle of a compound having existence on its own is known as a molecule. The properties (physical and chemical) of compounds may or may not be similar to their constituents. For example, hydrogen is a combustible substance and oxygen supports combustion. However, water, which is a compound of hydrogen and oxygen, neither burns nor supports combustion. On the other hand, it is used as a fire extinguisher.

3. Atoms The building blocks of an ant hill are small sand particles. Also, bricks are the building blocks of a building. Similarly, atoms are the building blocks of matter. Atoms are indivisible particles that cannot be destroyed or created by any chemical means.  According to Dalton’s atomic theory, all matter is made up of tiny particles called atoms. This would mean that a rod of iron is made up of millions of atoms of iron. Size of an atom Atoms are very small in size. They are not visible even under a powerful optical microscope. The size of an atom is indicated by the radius of the atom called the atomic radius. It is often expressed in nanometres. Therefore, 1nm 

1  109 m 109

Hydrogen atom is the smallest of all atoms. Representation of atoms Dalton was the first scientist to use symbols to represent different elements. Every symbol he proposed also represented a definite quantity of the respective element. The symbols of some common elements as proposed by Dalton are shown in given figure.

7th Class Chemistry

2

Symbolic representation is rather convenient and meaningful. Symbols are significant as:

Symbols used by Dalton G Gold

S Silver

L Lead

Mercury

1.

They represent a particular element.

2.

They represent one atom of that element.

4. Molecules Phosphorus

Sulphur

Carbon

Water

Oxygen

Hydrogen

However, these symbols of elements as proposed by Dalton were difficult to draw and remember. Therefore, an alternative method of representing elements was proposed by J.J. Berzelius. He suggested that alphabets can be used as symbols to represent the elements. Further, these symbols can be made from one or two letters of the name of the element. The modern symbols of elements made use of this idea. IUPAC (International Union of Pure and Applied Chemistry) approves the names of the elements. Also, it approves the symbol of the element made from one or two letters of the English or Latin name of that element. As a rule, the first letter of a symbol is always written as a capital letter and the second letter as small letter. The modern symbols of some common elements are given in the following table. Element Aluminium

Symbol Al

Argon

Ar

Calcium Carbon Chlorine Copper (Latin -Cuprum) Fluorine Gold (Latin -Aurum) Hydrogen

Ca C Cl Cu F Au

Iodine

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H I

Element Iron (Latin-Ferrum) Lead (Latin-Plumbum) Magnesium Nitrogen Oxygen Potassium (Latin-Kalium) Silicon Silver (Latin-Argentum) Sodium (Latin-Natrium) Zinc

Symbol Fe Pb Mg N O K Si Ag Na Zn

We know that the smallest particle of a substance is called an atom. An atom is very small in size and it cannot be divided further. Although atoms are the smallest particles of a substance, atoms of most elements are not stable and cannot exist independently. Therefore, two or more atoms of the same or different elements combine to form a stable entity called molecules. Hence, a molecule can be defined as the smallest entity of a substance, capable of independent existence. The constituting atoms of a molecule are held together by a strong attractive force. For example, (H2) is a molecule in which two hydrogen atoms are chemically bonded. Similarly, hydrogen atoms can also combine with oxygen atoms to form water molecules. A molecule is the smallest particle of an element or a compound that can exist independently and possess all the properties of the substance to which it belongs. Molecules of Elements: The molecules of an element are composed of identical atoms. For example, an oxygen molecule (O2) consists of two oxygen atoms; and a nitrogen molecule (N2 ) consists of two nitrogen atoms. N 2  and  O 2  are  called diatomic molecules. Thus, the  atomicity  of  nitrogen  and  oxygen  is two. When  three  atoms  of  oxygen  combine,  a molecule of ozone (O 3 ) is formed. Here, the atomicity of oxygen  is three. The number of atoms constituting a molecule is known as its atomicity. The atomicity of some common elements is given below.

Language of Chemistry Non-metal Helium

3 particle’. It was coined by a French philosopher Rene Descartes in 1620s. Although the existence of molecules was accepted by many chemists since the early 19th century (as a result of Dalton’s laws of Definite and Multiple Proportions), the work of Perrin on Brownian motion (1911) of particles of liquids and gases is considered to be the final proof of the existence of molecules.

Atomicity Monoatomic

Neon Argon Oxygen

Diatomic

Hydrogen

Formative Worksheet

Nitrogen

1.

Ratio by mass of atoms

Ratio by number of atoms

1:8

2:1

14:3

1:3

3:8

1:2

Compounds are formed when two or more elements combine chemically in fixed proportion. (A) compound (B) a molecule (C) an atom (D) an element The smallest particle of a compound having existence on its own is known as a molecule. (A) a molecule (B) compound (C) an element (D) an atom Statement I: The proportion of compound are similar to the properties of constituent elements. Statement II: Water is a compound. (A) Statement I is correct, statement II is incorrect (B) Statement I is incorrect, statement II is correct (C) Both statements, I and II are correct (D) Both statements, I and II are incorrect Statement I: Carbon is an element. Statement II: Carbon dioxide is a compound. (A) Statement I is correct, statement II is incorrect (B) Statement I is incorrect, statement II is correct (C) Both statements, I and II are correct (D) Both statements, I and II are incorrect Match the following A) Nitrogen (p) compound B) Helium (q) metalloid C) Sodium chloride (r) element D) Sulphuric acid (s) mixture 1 nm = ____________m. (A) 10–7 (B) 10–8 –9 (C) 10 (D) 10–10 Match the following Element Ancient symbol

3:4

1:1

A) Hydrogen

p)

1:16

1:1

B) Phosphorus

q)

C) Sulphur

r)

D) Oxygen

s)

Chlorine Fluorine Phosphorus Sulphur

2.

Tetra-atomic Polyatomic (8 atoms per molecule) Molecules of Compounds The molecules of a compound are formed when atoms of different elements combine chemically in definite proportions.For example, the molecules of carbon dioxide (CO2) consist of one carbon (C) atom and two oxygen (O) atoms. Therefore, the ratio by number of atoms present in the molecule of carbon dioxide is C : O = 1 : 2. This means that the ratio by mass of atoms present in the molecule of carbon dioxide (C: O) is 3:8 (12 × 1: 16 × 2 = 12:32, where 12 u and 16 u are the atomic masses of carbon and oxygen atoms respectively). The given table illustrates some examples of molecules of compounds. Compound

Water Ammonia Carbon dioxide Carbon monoxide Hydrogen peroxide

Combining Elements Hydrogen, Oxygen Nitrogen, Hydrogen Carbon, Oxygen Carbon, Oxygen Hydrogen, Oxygen

3.

4.

5.

6.

7.

Curiosity Corner The term ‘molecule’ is  derived  from  the  French word ‘molécule’, which means ‘extremely minute

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7th Class Chemistry

4 8.

9.

10. 11. 12. 13.

14. 15.

16.

Match the following Element Latin name A) Iron p) plumbum B) Lead q) Ferrum C) Potassium r) Argentom D) Silver s) Kalium The smallest particle of matter that exist independently is called (A) an atom (B) An ion (C) a molecule (D) compound Which of the following is a molecule (A) H2 (B) He (C) Ne (D) All Which of these elementary molecules? (A) Cl2 (B) O3 (C) O2 (D) All Which of the following are compound molecules? (A) Cl2 (B) O3 (C) N2 (D) H2 O Match the following Molecule Atomicity A) Sulphur p) 1 B) Fluorine q) 2 C) Ozone r) 3 D) Helium s) 4 t) 6 u) 8 The element with highest atomicity (A) Hydrogen (B) Helium (C) Sulphur (D) Carbon Which of the following are diatomic? (A) Hydrogen (B) Chlorine (C) Fluorine (D) All x is atomicity of ozone. ‘y’ is the atomicity nitrogen. If xy represents the atomic number of an element, then the element is (A) phosphorus (B) Sulphur (C) Carbon (D) Aluminium

Conceptive Worksheet 1.

2.

3.

4.

The baric form of matter that cannot be broken down into simpler substances is called (A) an element (B) an atom (C) a molecule (D) compound The smallest particle of matter that takes part in a chemical reaction is called (A) an element (B) an atom (C) a molecule (D) compound Which of the following is smallest of all atoms? (A) Hydrogen (B) Nitrogen (C) Oxygen (D) Neon Which of the following scientists introduced the symbols for the first time? (A) Aristotle (B) Bohr (C) Jaques Charles’ (D) Dalton

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5. 6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

The symbol for sodium (A) S (B) So (C) Sd (D) Na The latin name of gold is (A) Kalium (B) Natrium (C) Aurum (D) Cuprum The latin name of Tungsten is (A) Aurum (B) Cuprum (C) Natrium (D) Wolfram Which of the following is true for symbols? (A) short hand form of an element (B) represent one atom of that element (C) Both (D) None of these F2 is ______________. (A) an elementary molecule (B) a compound molecule (C) a mixture (D) all the above The number of atoms constituting a molecule is known as its (A) valency (B) atomicity (C) atomic number (D) mass number Ozone is (A) mono atomic (B) diatomic (C) triatomic (D) tetratomic Which of the following is monoatomic (A) Helium (B) Neon (C) Argon (D) All The ratio of mass of atoms in water: (A) 1 : 8 (B) 1 : 4 (C) 1 : 2 (D) 1 : 1 The ratio of number of atoms in Ammonia is (A) 1 : 6 (B) 1 : 5 (C) 1 : 4 (D) 1 : 3 The ratio of number of atoms in carbon monoxide is (A) 1 : 1 (B) 1 : 2 (C) 1 : 3 (D) 1: 4

5. Ions An ion is a charged species in which an atom or a group of atoms possess a net electric charge. The net electric charge of an ion can either be positive or negative. Positively charged ions are called cations and  negatively  charged  ions  are called anions. Molecules that are composed of metals and nonmetals contain charged species. For example, potassium chloride (KCl) consists of K+ ion (cation) and Cl” ion (anion).  Similar to  molecules, an  ion can be monoatomic, diatomic, tetra-atomic, etc. Ions

Language of Chemistry

5

may consist of a single charged atom or a group of atoms that have a net charge over them. A group of atoms carrying a charge are known as polyatomic ions. The name of some common ions with their symbols is given below. Cation Symbol Atomicity Aluminium Al3+ Monoatomic

Anion Symbol Atomicity Bromide Br - Monoatomic

Ammonium NH4 + Polyatomic

Carbonate CO3 2-

2+

Calcium Ca Monoatomic +

Now, let us recap the whole topic quickly with the help of the following animation. The tablegiven belowillustrates some examples of ionic compounds.

Tetra-atomi c -

Cuprous ion Cu Monoatomic

Chloride Cl Monoatomic

Cupric ion Cu2+ Monoatomic

Fluoride F- Monoatomic

Hydrogen H+ Monoatomic

Hydride H- Monoatomic

Ferric ion Fe 3+ Monoatomic

Hydroxide OH- Diatomic

Magnesium Mg 2+ Monoatomic

Iodide I - Monoatomic

Nickel Ni

Monoatomic

Nitrate NO3

2-

2.  +

Potassium K Monoatomic

Tetra-atomi c

Silver Ag + Monoatomic

Nitride N3- Monoatomic

Sodium Na + Monoatomic

Nitrite NO3 2-

Zinc Zn2+ Monoatomic

Tetra-atomi c

Hydrogen

Oxide O2- Monoatomic

carbonate HCO32- Polyatomic

Phosphate PO4 3- Polyatomic

Combining Elements

Calcium oxide Magnesium chloride Aluminium su lphide

Calcium, oxygen Magnesium, chlorine Aluminiu m, sulphur

Ratio by mass

Ratio by number of ions

5:2

1:1

24:71

1:2

27:32

2:3

6. Structure of Atom

1  2+

Ionic Compound

3. 

4.

An atom consists of three types of particles. These are: · Protons(positively charged) · Electrons(negatively charged) · Neutrons (neutral) The major features of the model are: All protons and neutrons are present inside the nucleus, which is situated at the centre of the atom. Electrons reside outside the nucleus and revolve around the nucleus in well-defined orbits. The size of the nucleus is very small in comparison to the size of an atom. As per Rutherford’s calculations, the size of the nucleus is 105 times smaller than an atom. As the mass of the electron is negligible in comparison to the mass of the proton, almost all the mass of the atom is concentrated in the nucleus.

Sulphate SO4 2- Polyatomic Sulphite SO3

2-

Tetra-atomi c

Ionic compounds Compounds in which molecules are formed by the combination of cations (positively charged ions) and anions (negatively charged ions) are known as ionic compounds. An example is zinc oxide (ZnO). This is formed on the combination of zinc ion (Zn2+) and oxide ion (O2"). Other examples of ionic compounds are magnesium chloride (MgCl2), potassium bromide (KBr), sodium chloride (NaCl), etc.

The number of protons in the atom of an element is known as the atomic number of  the  element. That is, Atomic number = Number of protons The total number of protons and neutrons inside the nucleus of an atom of an element is known as the mass number of  the  element. That is, Mass number = Number of protons + Number of neutrons www.betoppers.com

7th Class Chemistry

6 For example, for magnesium, Atomic number = Number of protons = 12 Mass number = Number of protons + Number of neutrons = 12 +12 = 24 In a neutral atom, the number of protons and neutrons are equal so that their opposite electrical charges cancel each other, making the atom electrically neutral.

Formative Worksheet 17. Match the following Column-I Column-II A) Carbonate ion p) Monoatomic B) Aluminium ion q) Diatomic C) Cuprous ion r) Triatomic D) Sodium ion s) Tetra atomic 18. Which of the following are poly atomic ions. (p) Sulphate ion (q) Hydrogen (r) Hydride ion (s) Nitrite ion (A) only P, Q (B) only Q, R (C) only R, S (D) All 19. Which of the following ions are cations (A) Aluminium (B) Hydride (C) Nitrite (D) Nitrate 20. Which of the following ions are anions (A) Nitride (B) Sulphide (C) Oxide (D) All 21. Which of the following is a diatomic anion? (A) Oxide (B) Nitride (C) Carbide (D) Chloride 22. Which of the following is a triatomic cation? (A) Calcium (B) Magnesium (C) Both (D) None 23. Which of atomic numbers represent that of a non metal? (A) 1 (B) 7 (C) 8 (D) all 24. The atomic number of calcium is (A) 5 (B) 10 (C) 15 (D) 20 25. The number of protons in phosophorus is (A) 5 (B) 10 (C) 15 (D) 20 26. The number of protons in sulphur (A) 12 (B) 14 (C) 16 (D) 18

Conceptive Worksheet 16. The charged species in which an atom or group of atoms posses a net electric charge is known as (A) Isotope (B) An atom (C) A compound (D) An ion www.betoppers.com

17. The ion that has positive charge is called (A) Cation (B) Anion (C) Mixture (D) Compound 18. Carbonate ion is (A) Mono atomic (B) Dia atomic (C) Tri atomic (D) Tetra atomic + 19. Silver ion (Ag ) is (A) Mono atomic (B) Dia atomic (C) Tri atomic (D) Tetra atomic 20. Which of the following is an ionic compound? (A) NaCl (B) MgCl2 (C) CaO (D) All 21. Atom possess (A) Electron (B) Proton (C) Neutron (D) All 22. Which of the following are present inside the nucleus? (A) Electrons + protons (B) Protons + Neutrons (C) Electrons + Neutrons (D) All 23. The number of protons inside the atom of an element is known as (A) Atomic number (B) Mass number (C) Isotopic number (D) None 24. The sum of protons and Neutrons inside the nucleus of an atom is called (A) Atomic number (B) Mass number (C) Isotopic number (D) None 25. The number of neutrons is Carbon (C–12) (A) 3 (B) 6 (C) 8 (D) 14

7. Atomic mass Mass is a characteristic property of matter. Hence, the atoms present in matter also possess mass. The mass of an atom is known as the atomic mass. Atoms of a given element are identical in shape, size, mass, chemical properties, etc. Atoms of different elements have different masses and chemical properties. Determination of the atomic mass It is difficult to determine the mass of an individual atom. However, relative atomic mass can be determined by comparing the mass of a particular atom with that of an atom of standard reference. The  unit  of  the  mass  of  an  atom  is atomic mass unit (amu). Initially,John Dalton suggested that the mass of a hydrogen atom should be taken as a standard reference of atomic mass

Language of Chemistry

7

unit. Later, one-sixteenth of the mass of an oxygen atom was taken as the standard. In 1961, IUPAC (International  Union  of  Pure  and th

1  Applied Chemistry) adopted one-twelfth  12  of   the mass of a carbon-12 isotope as the standard unit to measure relative atomic masses. IUPAC named  this  unit  as  theunified atomic mass unit (u). Thus, Atomic mass unit 

1 × Mass of a C-12 12

atom

1 Mass of a C-12 atom 12 Hence, the relative atomic mass of the atom of an element is defined as the average mass of the atom 1u 

 1th  as compared to one-twelfth  12  the mass of one   carbon-12 unit. For example, the atomic mass of oxygen is 16 u. The atomic mass of some common elements is given in the following table. Element

Atomic mass (u) Hydrogen 1 Helium 4 Carbon 12 Nitrogen 14 Oxygen 16 Fluorine 19 Neon 20 Sodium 23 Magnesium 24 Chlorine 35.5

Element Potassium Calcium Argon Iron Copper Zinc Bromine Silver Gold Sulphur

Atomic mass (u) 39 40 40 56 63.5 65 80 108 197 32

8. Isotopes Unlike the mass number, the atomic number is unique for an element. In nature, a number of atoms of some elements have been identified having the same atomic number, but different mass numbers. Such atoms are known as isotopes. Isotopes are defined as atoms having the same atomic number, but different mass numbers. These atoms contain an equal number of protons and electrons, but a different number of neutrons.

For example, in nature, hydrogen is found in three forms with different mass numbers, namely, protium

 H 1 1

deuterium

 H 2 1

and tritium,

 H 3 1

These

are the three naturally occurring isotopesof hydrogen. The atomic number of each isotope is 1, but the mass number varies i.e., it is 1, 2, and 3 respectively. Some other examples of isotopes include C- 12 and C-14, which are isotopes of carbon, and Cl-35 and Cl-37, which are isotopes of chlorine. Applications In nature, an element is found as a mixture of its isotopes. The chemical properties of all isotopes of an element are the same, but physical properties are different. Therefore, the isotopes of some elements have specific properties that make them very useful. For example, an isotope of uranium exhibits nuclear fission properties. It is used in nuclear reactions as a fuel. An isotope of cobalt is used to treat cancer while an isotope of iodine is used to treat goitre.

Formative Worksheet 27. The species having same atomic number and different mass number are called (A) isotopes (B) isobars (C) isotones (D) isoelectronic species 28. Isotopes have (A) same number of electrons (B) same number of protons (C) same chemical properties (D) all the above 29. Isotopes differ in (A) number of electrons (B) number of protons (C) number of neutrons (D) chemical properties 30. The mass of one atom potassium is ______ times the mass one hydrogen atom (A) 10 (B) 15 (C) 20 (D) 39 31. Atomic weight of an element is ‘x’. The weight of one atom of that element is: (A) ‘x’ amu (B) x × 1.66 × 10–24g –27 (C) 1.66x × 10 kg (D) All 32. The ratio of weight of one atom of an element to its atomic weight is equal to: (A) 1 amu (B) mass of (C) 12 amu (D) None

1 th of C – 12 isotopic atom 12 www.betoppers.com

7th Class Chemistry

8 33. The mass of one atom of an element is 40 × 1.66 × 10–24g. The number of protons in its nucleus is: (A) 40 (B) 20 (C) 10 (D) 5 34. The weight of Helium atom in grams is: (A) 2 (B) 4 (C) 6.64 × 10–24 (D) 1.66 × 10–24 35. The mass of an atom of an element ‘x’ is 39. The number of atoms of it present in Gram atomic weight is: (A) 1 (B) 1.66 × 1024 (C) 6.023 × 1023 (D) 96500 36. The total mass of 100 atoms of silicon is (A) 2800 (B) 2800 amu –22 (C) 28 × 1.66 × 10 g (D) 280 kg

Conceptive Worksheet 26. Which of the following has atomic mass 35.5? (A) Sulphur (B) Chlorine (C) Phosphorus (D) Magnesium 27. The mass of one twelfth of mass of C-12 atom is equal to (A) 1u (B) 2u (C) 3u (D) 12u 28. The atomc mass of calcium is (A) 10 (B) 20 (C) 30 (D) 40 29. The atomic mass of calcium is _______ the times of neon. (A) 1 (B) 2 (C) 3 (D) 4 30. The ratio of atomic mass carbon to that of magnesium is (A) 1 : 1 (B) 1 : 2 (C) 1 : 3 (D) 1 : 4 31. Atomic mass of sulphur = z × atomic mass of oxygen. The value of z is ________. (A) 1 (B) 2 (C) 3 (D) 4 Name of cation Aluminium Ammonium Calcium

3+

Al

NH

Valency 3

 4

2+

Ca

2+

1 2

1 1 th of C-12 (B) th of O-16 12 14 (C) 1g of H2 (D) 1.66 × 10–23 kg 35. 1 atomic mass unit = (A) 1/12 th mass of a carbon – 12 atom (B) 1.66 × 10–24g (C) 6.023 × 10–23g (D) 6.023 × 1023g (A)

9. Valency The combining power or the combining capacity of an atom or an element is called its valency. The number of atoms of other elements with which one atom of an element combines is decided by the valency of that element. For example, both hydrogen and chlorine have a valency of 1. Therefore, one atom of hydrogen reacts with one atom of chlorine to form one molecule of hydrogen chloride. Valency of ions (cations and anions) The valency of an ion is equal to the charge on it. The valencies of some common ions are given in the following table. Name of anion Sulphite Bromide Carbonate

Symbol Valency 2

SO3 Br

-

CO -

Cu H+ 2+ Fe

2 1 2

Iron(III) Magnesium

Fe Mg2+

3+

3 2

Chloride Cl Hydride H Hydrogen HCO 3 Carbonate Hydroxide OH Nitrate NO3

Nickel

Ni

2+

2

Nitrite

+

2 1

2 3

Copper(II) Hydrogen Iron(II)

2 1 1 1 1

NO2

1

2-

Potassium Silver

K Ag+

1 1

Oxide Phosphate

O PO34

2 3

Sodium

Na

+

1

Sulphate

SO4

2

2

Sulphide

2-

2

Zinc

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Symbol

32. X is an element whose atomic mass is half that of oxygen. Y is an element whose atomic mass is double that of oxygen. Z is an element whose atomic mass is 32 times that of hydrogen. Ratio of atomic masses of X, Y and Z is (A) 1 : 4 : 8 (B) 1 : 8 : 4 (C) 1 : 2 : 8 (D) 1 : 8 : 2 33. The modern atomic weight scale is based on: (A) C12 (B) O16 (C) H1 (D) C13 34. 1 amu is equal to:

2+

Zn

2

S

Language of Chemistry Can an element exhibit more than one valency? Variable Valency Some elements have changeable combining capacities i.e., they exhibit more than one valency. Some elements with their variable valencies are listed in the following table. Element Iron (Fe) Copper (Cu) Silver (Ag) Nitrogen (N) Phosphorus (P) Sulphur (S) Tin (Sn) Lead (Pb)

9 Thus, the formula of aluminium sulphate is Al2(SO4)3. Brackets are used when we have two or more of the same ions in a formula. Here, the bracket with a subscript 3 indicates that three sulphate groups are joined to two aluminium atoms. Formation of some more elements is shown below:

Valencies 2, 3 1, 2 1, 2 3, 5 3, 5 2, 4, 6 2, 4 2, 4

10. Formation of compounds A chlorine atom (Cl) has a tendency to gain 1 electron and form a chloride ion (Cl-). This chloride ion will readily combine with any cation carrying one positive charge such as sodium on (Na+) to form a molecule of sodium chloride

11. Writing Chemical Formulae of Compounds

Some more examples are given below to demonstrate the method of writing chemical formulae of compounds. (a) Formula of calcium oxide Symbol Al SO4

Charge

3+

2-

We know that each element can be represented by a unique symbol given to it such as hydrogen by H, sodium by Na, phosphorus by P, carbon by C, etc. Can you list what symbols are given to hydrogen, oxygen, nitrogen, iron, and sodium? Now, can you represent water, which is made up of hydrogen and oxygen, using these symbols? Compounds are formed when two or more elements combine chemically. Hence, compounds can also be represented using symbols. Water is a compound and is formed when hydrogen combines with oxygen in a fixed ratio. Hence, it can be www.betoppers.com

7th Class Chemistry

10 represented symbolically, based on the symbols of its constituents. Here, we will learn how to write the chemical formulae of various compounds utilising the symbols of their constituting elements.

Some more examples are given below to demonstrate the method of writing chemical formulae of compounds. (a) Formula of Calcium Oxide

Writing the Chemical Formula of a Compound Chemical formula of a compound is the symbolic representation of its atomic constituents. In other words, a chemical formula represents the composition of a molecule in terms of the symbols of the elements present in that molecule. To write the chemical formula of a compound, one should have prior knowledge of two things: 1.

The symbols of the constituent elements

2.

The combining capacity (valency) of each atom or ion constituting the compound

The valencies or charges on the ions must be balanced.

ii.

In case of a compound consisting of a metal and a non-metal, the symbol of the metal is written first. For example, in calcium chloride (CaCl2) and zinc sulphide (ZnS), calcium and zinc are metals, hence they are written first, whereas chlorine and sulphur are non-metals.

iii.

In case of compounds consisting of polyatomic ions, the polyatomic ions are enclosed in a bracket before writing the number to indicate the ratio. For example, in aluminium sulphate [Al2 (SO4)3], the polyatomic sulphate ion SO24  is enclosed in a

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Charge

2-

2+

(b) Formula of Aluminium Sulphate Symbol Al SO 4

Charge

3+

2-

Thus, the formula of aluminium sulphate is Al2(SO4)3. Brackets are used when we have two or more of the same ions in a formula. Here, the bracket with a subscript 3 indicates that three sulphate groups are joined to two aluminium atoms. The chemical formula can give us a lot of information about the compound. Let us discuss what all information a chemical formula can give us, taking the example of carbon dioxide. The chemical formula of carbon dioxide is CO2. Using this formula, we obtain the following information about carbon dioxide: 1. 

Two elements are present in CO 2 . They are carbon(C) and oxygen (O).

2. 

CO2 represents one molecule  of carbon dioxide.

3. 

The valency of carbon is twice than that of oxygen.

4. 

CO2 is a neutral molecule. It has no charge.

5. 

The ratio by mass between carbon and oxygen C: O is 12:32 i.e., 3:8.

bracket before writing the subscript 3. Now, let us try to write the chemical formulae of some binary compounds. Compounds composed of two different elements are calledbinary compounds. These  are  the  simplest  compounds. While writing the chemical formulae for compounds, we first write the constituent elements and their valencies and then cross over the valencies of the combining atoms.

O

Thus, the chemical formula of calcium oxide is CaO.

While writing the chemical formula, certain rules have to be kept in mind. These rules are given below: i.

Symbol Ca

Language of Chemistry

Formative Worksheet 37. Match the following Element Valency A) Lithium p) 1 B) Barium q) 2 C) Aluminium r) 3 D) Zinc s) 4 38. Which of the following ions are divalent (P) Nitride (Q) Nitrate (R) Nitrite (S) Sulphate 39. x, y and z are the valencies of sulphide, carbonate and sulphite ions respectively. If ‘K’ is valency of phosphate, then find

40.

41.

42.

43.

44.

x yz k (A) 1 (B) 2 (C) 3 (D) 4 Which of the following has same valency (P) Oxide (Q) Nitride (R) Aluminium (S) Magnesium (A) P, Q and R, S (B) Q, R and P, S (C) P, R and Q, S (D) None Statement-I: The valency of iron are 2, 3 Statement-II: The valencies of silver are 1, 2 (A) Statement I is correct, statement II is incorrect (B) Statement I is incorrect, statement II is correct (C) Both statements, I and II are correct (D) Both statements, I and II are incorrect Statement-I: The valency of phosphate and nitrate is same. Statement-II: The valency of potassium and hydroxide is same (A) Statement I is correct, statement II is incorrect (B) Statement I is incorrect, statement II is correct (C) Both statements, I and II are correct (D) Both statements, I and II are incorrect Which of the following exhibit variable valency? (P) Iron (Q) Silver (R) Copper (S) Gold (A) only P, Q (B) only R, S (C) only P, Q, R (D) P, Q, R, S x, y and z are learnt valencies exhibited by Iron, Silver and lead. What is value of x + z – y? (A) 1 (B) 2 (C) 3 (D) 4

11 45. i)

Cations are called __________

ii)

Anions are called __________ (i)

(ii)

(A) acidic radicals p) basic radicals (B) basic radicals

q) acidic radicals

(C) acidic

r) acidic

(D) basic

s) basic

46. Iron and chlorine combine to form FeCl2, FeCl3. The valency of iron in these compounds are : (A) 2, 3 (B) 3, 4

(C) 2, 4

(D) 3, 4

47. i) The name of the element with lower valency in a compound ends with suffix ______. ii) The name of the element with higher valency ends with suffix ________. (i)

(ii)

(A) ous

p) ous

(B) ic

q) ous

(C) ous

r) ic

(D) ic

s) ic

48. Statement A : Copper combines with chlorine to form Cu2Cl2 and CuCl2. Statement B : The valency of copper in these compounds is 1 and 2. (A) ‘A’ is true, ‘B’ is false. (B) ‘A’ is false, ‘B’ is true. (C) Both ‘A’ and ‘B’ are true. (D) Both ‘A’ and ‘B’ are false. 49. Correct formula of a trivalent metal nitride is: (A) M3N2

(B) MN2

(C) MN

(D) M2N3

50. Chemical formula for calcium sulphate is CaSO4. The formula for ferric sulphate is: (A) Fe2 (P 2O7 )3

(B) Fe4 P 3O14

(C) Fe2(SO4)3

(D) Fe3PO4

51. Write the formula of the compound formed by each of the following pairs of ions. a) Ca2+ and PO3-4

b) Na+ and S2 O2-3

c) Mg2+ and N3–

d) Mn2+ and O2–

e) Ba2+ and S2–

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7th Class Chemistry

12

Conceptive Worksheet 36. The combining capacity of an element is called? (A) Atomic number (B) Mass number (C) Valency (D) Atomic mass 37. The valency of Aluminium is (A) 1 (B) 2 (C) 3 (D) 4 38. The valency of sulphate ion is (A) 1 (B) 2 (C) 3 (D) 4 39. Which of the following ions valency is (A) Nitrite ion (B) Nitrate ion (C) Magnesium ion (D) Sodium ion 40. The valency of hydroxide ion is (A) 1 (B) 2 (C) 3 (D) 4 41. The valency of Sulphur is (A) 2 (B) 4 (C) 6 (D) All 42. The formula of Calcium oxide is (A) CaO (B) Ca2O (C) CaO2 (D) Ca3O 43. The number of electrons, lost, gained or shared with one atom of the element in order to acquine stable configuration of nearest noble gas element is called _______. (A) Valency (B) Atomicity (C) Molecularity () None of these 44. An atom (or) a group of atoms which can exist independently with charge(s) is called : (A) Ion (B) Molecule (C) Compound (D) Substance 45. Radicals are formed by the loss of electron (or) electrons. Such radicals are called ________. (A) Anions (B) Cations (C) Compounds (D) Molecules 46. Radicals are formed by the gain of electrons. Such radicals are called _______. (A) Anions (B) Cations (C) Compounds (D) Molecules 47. The phosphate of a metal has the formula MPO4. The formula of its nitrate will be: (A) MNO3 (B) M2 (NO3)2 (C) M(NO3)2 (D) M(NO3)3 48. Sodium phosphate has the chemical formula: (A) Na 2 P 2 O7 (B) Na 3PO4 (C) Na 4 P2 O7 (D) Na 3PO3 49. Which of the following is not the correct formula? (A) H2S (B) NaHSO4 (C) SiO2 (D) NaCl2

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12. The Laws Combination

of

Chemical

At the end of the nineteenth century, scientists were able to differentiate between elements and compounds. Antoine Laurent Lavoisier and Joseph Louis Proust gave two laws, explaining the chemical combinations of elements. These laws are called the Law of conservation of mass and the Law of constant proportion. Law of conservation of mass The law of conservation of mass states that the mass of a closed system will remain constant in a chemical reaction. In other words, mass can neither be created nor destroyed in a chemical reaction. This law was first formulated by Antoine Laurent Lavoisier in 1789. This law can be demonstrated by performing the following activity. Law of Constant Proportion As we know, compounds are composed of two or more elements. The proportion in which elements are present in a compound remains the same, irrespective of its method of preparation. For example, pure water obtained from any source (well, river, lake, or sea) and from any country (India, Russia, America, etc.) will always contain two hydrogen atoms and one oxygen atom. Hydrogen and oxygen combine together in the ratio of 1:8 by mass respectively to form water, and the ratio by the number of atoms for water will always be H : O = 2 : 1. Thus, 18 g of water contains 2 g of hydrogen and 16 g of oxygen.Similarly, in ammonia, nitrogen makes up 14/17 of the mass of ammonia while hydrogen makes up the remaining 3/17 of the mass. Irrespective of the source from which ammonia is obtained, it will always contain nitrogen and hydrogen in the ratio of 14: 3 by mass. Thus, 17 g of ammonia contains 14 g of nitrogen and 3 g of hydrogen; and 34 g of ammonia contains 28 g of nitrogen and 6 g of hydrogen. This led to the law of constant proportion. Thus, according to the law of constant proportion, a chemical substance always contains the same elements in a fixed proportion by mass, irrespective of its source. The law of constant proportion is also known as the law of definite proportion. This law was introduced by Proust, which stated that ‘in a compound, the elements are always present in definite proportions by mass’.

Language of Chemistry

13

13. Writing and balancing Chemical Equations When zinc is dipped in a solution of hydrochloric acid, zinc chloride and hydrogen gas are produced. This is an example of a chemical reaction. Representing a reaction in a sentence form can be quite complex and laborious at times. Can  the same chemical reaction be explained in a manner that is more concise and simple to write and understand? To describe a chemical reaction more concisely, equations of the reactions are written. These equations can be written in different ways such as word equations and chemical equations. Word equations The above chemical reaction between zinc and mineral acid can be represented as:  Zinc chloride + Zinc + Hydrogen chloride  Hydrogen In a word equation, the reactants are written on the left hand side of a forward arrow. The products are written on the right hand side of this arrow. The arrow signifies that the reaction proceeds from the reactants towards the products. Chemical equations A word equation can be further written in a concise form by using symbols and formulae of the chemical compounds, molecules, or elements involved in the reaction. The chemical equation of the above reaction can be written as:

Zn 

 Zinc

2HCl

 Hydrochloric 

  ZnCl2  Zinc

chloride 



H2

 Hydrogen 

A chemical equation also indicates the number of atoms of each element involved in a reaction. Let us take the example of photosynthesis. In the process of photosynthesis, carbon dioxide and water act as reactants and glucose and oxygen are obtained as products. Thus, the reaction for the process will be written as: 6CO2 + 6H2O   C6H12O6 + 6O2 Balanced Chemical Equations Now, we know how to write chemical equations. We also know that the law of conservation of mass states that mass can neither be created nor destroyed. Thus, in a chemical reaction, the total mass of the reactants should be equal to the total mass of the products. This means that

the total number of atoms of each element should be equal on both sides of a chemical equation. Such an equation is called abalanced chemical equation and the method by which it is obtained is called balancing of chemical equations. Therefore, we have to balance every chemical equation we write. An equation having an equal number of atoms of each element on both the sides is called a balanced chemical equation. We will now learn how to balance a chemical equation. Zn  HCl   ZnCl2  H 2  Reac tan ts   L.H.S 

 Pr oducts   R.H.S

If you observe the above equation carefully, then you will notice that the number of hydrogen and chlorine atoms present on the right hand side and the left hand side are not equal. On the left hand side, there is one atom of both hydrogen and chlorine, but on the right hand side, there are two atoms each of hydrogen and chlorine. The balanced equation of the given equation can be written as: Zn + 2HCl   ZnCl2 + H2 This equation has an equal number of atoms of Zn, H, and Cl on both sides of the equation. Let us now learn the step-by-step process of balancing a chemical equation. In the reaction of barium chloride and aluminium sulphate, barium sulphate and aluminium chloride are produced. Step I: Write the unbalanced chemical equation for the given reaction. BaCl2 + Al2 (SO4)3   BaSO4 + AlCl3 Step II: List the number of atoms of the various elements present in the unbalanced equation in the form of a table. Element

Ba

Number of atoms on the reactant side (L.H.S) 1

Number of atoms on the product side (R.H.S) 1

Cl Al

2 2

3 1

S

3

1

O

12 (4×3)

4

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7th Class Chemistry

14 Here, we can see that only barium has an equal number of atoms on both sides of the equation. Step III: In the next step, select a compound, which contains the maximum number of atoms. In this case, the compound will be aluminium sulphate (it has 2 atoms of Al, 3 atoms of S, and 12 atoms of O). From this compound, select the element, which has the maximum number of atoms and which is present in only one compound on both sides i.e., oxygen in this case. To balance the number of oxygen atoms, we can multiply barium sulphate present on the right hand side by 3 (as shown below). It should be kept in mind that coefficient ‘3’ will be written as 3BaSO4 and  not as  (BaSO4)3. Oxygen atoms

Before balancing To balance

Number of Number of atoms atoms on on L.H.S R.H.S 12 in Al2(SO 4)3 4 in BaSO4 12

3×4

Now, the equation becomes: BaCl2 + Al2 (SO4)3   3BaSO4 + AlCl3 Again, compare the number of atoms of the various elements present in the chemical equation (as shown in the table below). Element Number of atoms on L.H.S Ba Cl Al S O

1 2 2 3 12

Number of atoms on R.H.S 3 3 1 3 12

Step IV: As the atoms of both oxygen and sulphur are balanced, we will now balance the atoms of aluminium.

Aluminium atoms Before balancing To balance

Number of Number of atoms on atoms on L.H.S R.H.S 2 in Al2(SO4)3 1 in AlCl3 2 2 ×1

Now, the equation becomes: BaCl2 + Al2 (SO4)3   3BaSO4 + 2AlCl3 Make the table again to compare the number of atoms of the elements on both sides of the equation. Element Number of atoms on L.H.S Ba 1 Cl 2 Al 2 S 3 O 12

Number of atoms on R.H.S 3 6 2 3 12

We can see that the atoms of aluminium, sulphur, and oxygen are balanced. Step V: Now, only the atoms of barium and chlorine are unbalanced. We will first balance the atoms of barium. Barium atoms Before balancing To balance

Number of Number of atoms on atoms on L.H.S R.H.S 1 in BaCl2 3 in (3 BaSO4) 3 ×1

3

Now, the equation becomes: 3BaCl2 + Al2 (SO4)3   3BaSO4 + 2AlCl3 Let us again prepare a table to compare the number of atoms of the elements on both sides of the equation. Element Number of atoms on L.H.S Ba 3 Cl 6 Al 2 S 3 O 12

Number of atoms on R.H.S 3 6 2 3 12

It can be observed that the chemical equation is balanced now. www.betoppers.com

Language of Chemistry

15

3BaCl2 + Al2 (SO4)3   3BaSO4 + 2AlCl3 This method of balancing a chemical equation is called the hit-and-trial method. To make a chemical equation more informative, the physical state of the reactants and the products is mentioned along with their chemical formulae. They are written in common brackets. Solids are  denoted  by  writing (s). Liquids are  denoted  by writing (l). Gases are  denoted  by  writing (g). Solutions in water are  denoted  by  writing (aq). For example, the reaction of limewater with carbon dioxide that results in the formation of a precipitate of calcium carbonate and water is represented as: Ca  OH  2  aq   CO 2  g    CaCO 3  s   H 2 O  l  Calcium hydroxide

Carbon dioxide

Calcium carbonate

Water

In this reaction, calcium hydroxide is present in the form of a solution in water, carbon dioxide is present as gas, calcium carbonate is produced as a precipitate i.e., in the solid state, and water is formed in the liquid state. The energy changes involved in a reaction are denoted by writing the changes involved in the equation itself. If energy is used in the reaction, then it will be written on the left hand side. If it is released in the process, then it is written on the right hand side. For example, combustion of butane is accompanied by the evolution of heat and light energy. Therefore, the equation for the same will be written as:

2C4 H10  13O2  10H2 O  8CO2  Heat  Light The reaction conditions (such as temperature, pressure, catalyst, etc.) for a reaction are indicated above or below the forward arrow in a reaction. Below are some balanced chemical equations: 300atm.300 C  CH3 OH  aq  1 CO  g   2H 2  g   ZnO  CrO

Carbon monoxide

Hydrogen 

  2  2KClO3s  MnO Carbon monoxide

3

2

2KCl

s  Potassium chloride

Methyl alcohol

 3O 2 g  Oxygen

Write the balanced equations for the following chemical reactions. 1. Barium chloride + Sodium sulphate ’! Barium sulphate + Sodium chloride. 2. Sodium + Water ’! Sodium hydroxide + Hydrogen

Formative Worksheet Balance the following skeleton equations. 52. C2 H 4

+

O2

 CO 2 + H2O

53. C2 H 2

+

O2

 CO 2 + H2O

54. CH 4

+

O2

 CO 2 + H2O

55. NH 3

+

Na  NaNH2 + H 2

56. Mn(OH)2 + Na2O2  Na2MnO4 + NaOH 57. Al2(SO4) 3 + NaOH  Al(OH)3 + Na2SO4 58. KI + H2SO4  KHSO4 + H2O + SO2 + I2 59. CuFeS2 + O2  Cu2S + FeS + SO2 60. FeS + O2  FeO + SO2

Conceptive Worksheet 50. Cu2S + CuSO4

 Cu +

SO2

51. Cu2O + Cu2S

 Cu +

SO2

52. CuSO4 + KI

 CuI + I2 + K2SO4

53. Fe + N2O  N2 + Fe3O4 54. CuCl CuCl2

+ +

SO2 + HCl H2O + S



55. NaAg(CN)2 NaCN

+ +

 Zn Zn(CN)2 + Ag

56. FeCl3 Fe(CNS)3

+ +

NH4CNS  NH4Cl

57. Ca 3(PO 4 ) 2 Ca(H2 PO 4 ) 2

+ +

H2 SO 4 CaSO4



58. CaCN2 +

+

H2 O



+ +

 HNO 3 NH4NO3 + H2 O

CaCO3

NH 3

59. Mg Mg(NO3) 2

60. Cu2S + O2  Cu2O + SO2

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7th Class Chemistry

16

Summative Worksheet 1.

2.

Which of the following statements represents the law of conservation of mass? (A) Atoms of a given element are identical in mass. (B) Atoms of different elements have different masses. (C) Mass can neither be created nor destroyed in a chemical reaction. (D) In a chemical substance, elements are always present in definite proportions by mass. In a chemical reaction, x g of silver nitrate (AgNO3) reacts with 7.3 g of hydrochloric acid (HCl) to produce 28.7 g of silver chloride (AgCl) and 12.6 g of nitric acid (HNO3) [Atomic mass of Ag = 108 u, Cl = 35.5 u, N = 14 u, O = 16 u]. AgNO3  HCl   AgCl  HNO3 xg

7.3g

28.7g

12.6g

What is the value of x? (A) 17 g (B) 17.5 g (C) 34 g (D) 34.5 g 3. The ratio by mass of carbon and oxygen in carbon dioxide is 3:8. The respective masses of carbon and oxygen required to react completely to form 33 g of carbon dioxide are (A) 9 g and 24 g (B) 12 g and 21 g (C) 21 g and 12 g (D) 24 g and 9 g 4. Which of the following symbols is approved by the IUPAC for copper? (A) Ca (B) Co (C) Cu (D) Cl 5. Which of the following elements has atomicity 2? (A) Helium (B) Nitrogen (C) Aluminium (D) Phosphorus 6. The ratio by mass of atoms for sodium oxide is (A) Na:O = 8:23 (B) Na:O = 16:23 (C) O:Na = 16:23 (D) O:Na = 8:23 7. The ratio by the number of atoms for aluminium oxide is (A) Al:O = 1:2 (B) Al:O = 1:3 (C) Al:O = 2:3 (D) Al:O = 3:2 8. Which of the following ions is mono-atomic? (A) Nitrate (B) Sulphite (C) Sulphide (D) Hydroxide 9. What is the chemical formula of sodium carbonate? (A) NaCO3 (B) Na2 CO3 (C) Na(CO3)2 (D) Na 3 (CO3)2 10. The molecular mass of calcium hydroxide is (A) 57 u (B) 58 u (C) 74 u (D) 97 u www.betoppers.com

11. Which of the following compounds has a molecular mass equal to 95 u? (A) Sodium nitrate (B) Carbon disulphide (C) Calcium hydroxide (D) Magnesium chloride 12. The formula unit mass of potassium chloride is (A) 74.5 u (B) 59.0 u (C) 113.5 u (D) 110.0 u 13. Protons are i , whereas neutrons are ii . The information inwhich alternative completes the given statement? (A)

i ii positively charged neutral

(B)

i ii neutral negatively charged

i ii (C) negatively positively charged charged i (D) positively charged

ii negatively charged

14. In which of the following situations, an atom would have a positive charge? (A) Number of protons = 1, number of electrons = 1 (B) Number of protons = 1, number of electrons = 2 (C) Number of protons = 2, number of electrons = 1 (D) Number of protons = 2, number of electrons = 2 15. An atom of an element ‘X’ has 7 protons and has a mass number of 14 u. How many neutrons are present in the atom of ‘X’? (A) 21 (B) 10 (C) 7 (D) 0 16. The given figure shows a schematic atomic structure of a neutral atom.

Which of the following elements is represented by the given structure? (A) Boron (B) Nitrogen (C) Aluminium (D) Phosphorus

Language of Chemistry

17

17. Which of the following species is not an isotope of hydrogen? (A) 11 H

(B) 12 H

(C) 13 H

5.

(D) 14 H

18. The fuel used in nuclear reactions is an isotope of (A) hydrogen

(B) uranium

(C) cobalt

(D) iodine

19. An atom is positively charged if it has (A) number of protons = 7, number of electrons = 8, number of neutrons = 8 (B) number of protons = 9, number of electrons = 9, number of neutrons = 10 (C) number of protons = 8, number of electrons = 7, number of neutrons = 9 (D) number of protons = 6, number of electrons = 8, number of neutrons = 6

6.

7.

20. A neutral element X has 10 electrons and 12 neutrons in its atom. The atomic number of element X is (A) 10

(B) 12

(C) 20

8.

(D) 22

21. Neutron is absent from the nucleus of an atom of (A) boron

(B) lithium

(C) hydrogen

(D) phosphorus

9.

HOTS Worksheet 1.

2.

Each compound can be represented by: (A) Formula

(B) Definition

(C) Atom

(D) Symbol

Which one of the following statement is correct regarding the formula of a compound?

11.

12.

(A) It tells which elements are present in a compound. (B) It tells the number of atoms of each element present in a compound. (C) Both 1 and 2 (D) None of the above 3.

4.

What is the formula of common salt? (A) NaCl

(B) NaOH

(C) Na2CO3

(D) NaHCO3

Which of the following are oxides of metals? (A) Calcium oxide

(B) Copper oxide

(C) Mercury oxide

(D) Nitrogen dioxide

13.

14.

Statement I : The symbolic representation one molecule of a compound representing the number of atoms of various elements present in it is called formula of the compound. Statement II : Formula of sulphur dioxide is SO3. (A) Statement-I, Statement-II both are true and Statement-II is the correct explanation of Statement-I. (B) Statement-I, Statement-II both are true but Statement-II is not the correct explanation of Statement-I. (C) Statement-I is true, Statement-II is false. (D) Statement-I is false, Statement-II is true. Total number of atoms present in methane molecule is: (A) 2 (B) 3 (C) 4 (D) 5 How many oxygen atoms are present in 3 moles of potassium nitrate? (A) 3 (B) 5 (C) 6 (D) 9 The formula of steam is: (A) CH4 (B) H2 O (C) CO (D) CO2 Column I Column II Molecule name Formula a) Hydrogen chloride (A) FeS b) Lead oxide (B) PbO c) Washing soda (C) HCl d) Iron sulphide (D) Na2 CO3 What is the formula of baking soda? (A) NaHCO3 (B) NaCl (C) Na2SO4 (D) Na2 CO3 Statement I : The symbols in a formula can be prefixed (or) suffixed by a numeral. Statement II : Gaseous form of water is called steam. (A) Statement-I, Statement-II both are true and Statement-II is the correct explanation of Statement-I. (B) Statement-I, Statement-II both are true but Statement-II is not the correct explanation of Statement-I. (C) Statement-I is true, Statement-II is false. (D) Statement-I is false, Statement-II is true. How many atoms of sulphur are present in S 8 molecule? (A) 6 (B) 4 (C) 8 (D) 3 Which of the following contains more than six oxygen atoms? (A) Al2(SO(D)3 (B) 3KNO3 (C) 2H2O (D) 4ZnO www.betoppers.com

7th Class Chemistry

18 15. How many zinc atoms are present in 4 molecules of zinc oxide? (A) 2 (B) 3 (C) 4 (D) 5 16. Column-I Column-II a) A gas with two oxygen atoms (A) Methane b) A gas with one chlorine atom (B) Carbon dioxide c) A gas with one oxygen atom (C) Carbon monoxide d) A gas with four hydrogen atoms (D) Steam 5) Hydrogen chloride 17. Choose the correct statements: i) Common name of sodium carbonate is washing soda. ii) Common name of sodium chloride is common salt. iii) Common name of copper sulphate is blue vitriol. iv) Common name for calcium carbonate is lime stone. (A) i, ii (B) ii, iii (C) iii, iv (D) All of these 18. Which of the following information is conveyed from the given formula C6H12O6? (A) It represents one molecule of glucose. (B) It has 6 atoms of carbon. (C) It has 12 atoms of hydrogen. (D) It has 6 atoms of oxygen. 19. A compound ‘X’ has two atoms of aluminium three atoms of Sulphur and twelve atoms of Oxygen. The chemical formula of the compound ‘X’ is: (A) Al2(SO D)2 (B) Al2(SO D) (C) Al2(SO D)3 (D) Al(SO D) 20. NaClO4 is the chemical formula of : (A) Sodium chlorate (B) Sodium chlorite (C) Sodium hypochlorite (D) Sodium perchlorate 21. Molecular formula of sulphur is _________. (A) S4 (B) S5 (C) S6 (D) S8 22. An ion (or) a radical formed by the acceptance of one electron is called: (A) Monovalent electro negative ion (B) Valency (C) Both 1 and 2 (D) None of these www.betoppers.com

23. What is the formula of bisulphite? (A) HCO3-

(B) HS-

(C) HSO3-

(D) HSO-4

24. An ion (or) radical formed by the acceptance of two electrons is called: (A) Bivalent electro negative ion (B) Radical (C) Both 1 and 2 (D) None of the above 25. Which of the following ions are trivalent ? (A) Nitride

(B) Phosphide

(C) Phosphite

(D) Carbonate

26. Statement I : The valency of iodide ion is -1 . Statement II : The valency of silicate ion is -2 . (A) Statement-I, Statement-II both are true and Statement-II is the correct explanation of Statement-I. (B) Statement-I, Statement-II both are true but Statement-II is not the correct explanation of Statement-I. (C) Statement-I is true, Statement-II is false. (D) Statement-I is false, Statement-II is true. 27. What is the formula of peroxide ion? (A) O2– (B) O-2

(C) O2-2

(D) O-3

28. What is the formula of hydroxide ion? (A) OH– (B) H–

(C) HS– (D) HSO3-

29. Which of the following is an electronegative radicals? (A) CO23 (B) NO3 (C) S2 30. Column I

(D) All of these

Column II

Ion/ radical

Formula

(A) Hydride

p) H

(B) Nitrite

q) ZnO22

(C) Nitrate

c) NO-2

(D) Zincate

d) NO-3

31. Which of the following are trivalent electro negative ion ? (A) Phosphate

(B) Zincate

(C) Sulphide

(D) Acetate

Language of Chemistry 32. Statement I : sulphite.

33.

34.

35. 36.

37.

38.

39.

40.

19

The formula of HSO3 is hydrogen

Statement II : The formula of HSO3 is hydrogen sulphate. (A) Statement-I, Statement-II both are true and Statement-II is the correct explanation of Statement-I. (B) Statement-I, Statement-II both are true but Statement-II is not the correct explanation of Statement-I. (C) Statement-I is true, Statement-II is false. (D) Statement-I is false, Statement-II is true. The valency of chloride ion is -1 and calcium is +2. What is the formula obtained by these two ions? (A) CaCl (B) Ca2Cl (C) CaCl2 (D) CaCl3 Which of the following ions are bivalent ? (A) Silicate (B) Peroxide (C) Zincate (D) Nitrate What is the valency of oxide ion? (A) +1 (B) +2 (C) -2 (D) -3 Column I Column II (A) Cyanide p) O2 (B) Super oxide q) CN– (C) Hydroxide r) OH (D) Fluoride s) F– t) I2 Identify the right chemical formula for the following compounds. i) Calcium sulphate ii) Magnesium oxide iii) Potassium nitrite i ii iii (A) Ca(HSOD)2 MgO KNO 3 (B) CaSO4 MgO KNO 2 (C) CaS Mg2O 2 KNO 3 (D) None of the above. A metal M forms a compound M2HPO4. What will be the formula of the metal sulphate? (A) M2SO4 (B) M2(SO D)3 (C) MSO4 (D) M(SO D)3 Chemical formula for calcium sulphate is CaSO4. The formula for ferric sulphate will be: (A) Fe2 (P 2O7 )3 (B) Fe4 P 3O14 (C) Fe2(SO D)3 (D) Fe3PO4 The phosphate of a metal has the formula MPO4. The formula of its nitrate will be: (A) MNO3 (B) M2(NO C)2 (C) M(NO C)2 (D) M(NO C)3

IIT JEE Worksheet I.

Single Correct Answer Type

1.

Which of the following is present in the nucleus of hydrogen? (A) Single proton (B) Two protons (C) Zero protons (D) Three protons 2. The protons and neutrons collectively present with in the nucleus are called: (A) Protons (B) Nucleons (C) Mesons (D) Nutrinos 3. What is the mass of one proton? (A) 1 a.m.u (B) 1 gram (C) 2 kg (D) 0.1 kg 4. What is the charge of neutron? (A) +1 (B) -1 (C) Zero (D) All of these 5. The number of electrons donated by an atom is equal to: (A) Electro negative valency (B) Electro positive valency (C) Variable valency (D) All the above 6. The valency of hydrogen is: (A) +1 (B) +2 (C) +3 (D) +4 7. Latin name of iron is : (A) Cuprum (B) Ferrum (C) Natrium (D) Argentum 8. What is the lower valency of silver? (A) +4 (B) +3 (C) +2 (D) +1 9. Variable valency is represented by ________ numbers. (A) Italic (B) Numerical (C) Roman (D) All of these 10. Choose the correct statements. (A) Sulphate is a bivalent electronegative ion (B) Bicarbonate is a monovalent electro negative ion. (C) Nitride is a monovalent electro negative ion. (D) All the above.

II. Multiple Correct Answer Type 11. Which of the following are the examples of noble gases? (A) Helium (B) Neon (C) Krypton (D) Xenon www.betoppers.com

7th Class Chemistry

20 12. 1 a.m.u = (A) Mass of one proton (B) Mass of one neutron (C) Mass of an electron (D) None of the above 13. Which of the following are bivalent electropositive ions ? (A) Mg (B) Ca (C) Na (D) Pb 14. Which of the following are trivalent electro positive ions? (A) Al3+ (B) Cr3+ (C) Fe3+ (D) N H4 15. What is the suffix we attach at the end of the name of metal for lower valency? (A) - oic (B) - ous (C) - ic (D) - um 16. Which of the following atoms can exhibit variable valency? (A) Fe (B) Copper (C) Silver (D) Mercury

IV. Paragraph Type Paragraph-I

III.

21.

Reasoning Type

17. Statement I : The nucleus of an atom is positively charged. Statement II : The protons and neutrons present within the nucleus are called nucleons. (A) Statement-I, Statement-II both are true and Statement-II is the correct explanation of Statement-I. (B) Statement-I, Statement-II both are true but Statement-II is not the correct explanation of Statement-I. (C) Statement-I is true, Statement-II is false. (D) Statement-I is false, Statement-II is true. 18. Statement I : The number of electrons donated (or) accepted by an atom of an element so as to have 8 electrons in its outermost orbit is called valency. Statement II : The metallic ions formed by the donating 3 electrons from their outermost orbit are called trivalent electropositive ions. (A) Statement-I, Statement-II both are true and Statement-II is the correct explanation of Statement-I. (B) Statement-I, Statement-II both are true but Statement-II is not the correct explanation of Statement-I. (C) Statement-I is true, Statement-II is false. (D) Statement-I is false, Statement-II is true.

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19. 20.

22.

23. 24. 25.

i) The number of electrons donated or accepted by an atom of an element so as to have 8 electrons in its outermost orbit, is called valency. ii) Metals have one to three electrons in their outermost shell (valence shell) which they tend to donate to the other elements. iii)In donating electrons, the number of protons in the nucleus increases as compared to number of electrons. With the result, the residual metallic ions gets positively charged. iv)he number of electrons donated by an atom is equal to its electropositive valency. How many electrons can be lost by Fe+2 ion? (A) One (B) Two (C) Three(D) Four What is the symbol of ferric ion? (A) Fe2+ (B) Fe+ (C) Fe3+ (D) Fe4+ Aluminium is: (A) Monovalent (B) Bivalent (C) Trivalent (D) Tetravalent Paragraph-II The total number of protons and neutrons present in the atom of an element is known as its mass number. It is represented by ‘A’.  Mass number (A) = Number of protons + Number of neutrons (n)  Mass number (A) = Atomic number (Z) + Number of neutrons (n)  A= Z + n Number of Neutrons in Nucleus: We know, A = Z + n  n = A – Z. Based on this information answer the questions given below. In an element, A = Z. Identify the element. (A) Hydrogen (B) Lithium (C) Beryllium (D) Boron The ratio of of A to Z in oxygen is (A) 1 : 1 (B) 2 : 1 (C) 3 : 1 (D) 4 : 1 The total number of nucleons in phosphorus is (A) 28 (B) 29 (C) 30 (D) 31 The ratio of number of neutrons in helium to that beryllium is (A) 1 : 1 (B) 2 : 5 (C) 3 : 7 (D) 5 : 9

Language of Chemistry

21

26. A, B and C are the number of neutrons in hydrogen, helium and lithium. A+B+C= (A) 5 (B) 6 (C) 7 (D) 7

IV. Integer Type 27. The diameter of nucleus of an atom is 10x times smaller than the diameter of an atom.The value of x is ______. 28. The valency of carbonate ion is __________.

V. Matrix Matching (Match the following) 29. Column-I Atom/ion (A) Na (B) Na+ (C) Cl (D) Cl¯ 30. Column-I (A) Carbonate (B) Dichromate (C) Chromate (D) Chloride

Column-II Number of electrons present in the atom/ion p) 17 q) 18 r) 11 s) 10 t) 13 Column-II p) CrO24 q) Cl– r) CO32s) Cr2 O72t) Cr2 O7-



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22

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7th Class Chemistry

By the end of this chapter, you will understand • • •

Acids Acid rains Bases

• •

Indicators Salts

Chapter -32

Acids, Bases and Salts

Learning Outcomes

Properties of Acids

1. Introduction We have learnt in the previous class that it is possible to classify substances into groups based on their physical properties. Substances can also be grouped simply on the basis of whether they are sweet, salty, sour, or bitter to taste. Have you ever squeezed a lemon and tasted the juice without adding water or sugar? Yes! It’s extremely sour. So, why are substances sour or bitter to taste? Substances like lemon juice taste sour because of the presence of a chemical called acid in them. In Latin acere meaning sour. Materials containing an acid are called acidic substances. Have you ever accidentally tasted soapy water while taking bath? Well! It tastes bitter. It is also slippery. Your soap is slippery and bitter because of the presence of a chemical called base in it. Washing soda, baking soda, etc., contain bases. Substances containing bases are called basic substances.

2. Acids

Some of the characteristic properties of acids are: • Acids have a sour taste. • Acids also have the ability to corrode metals such as iron and aluminium. For this reason, acids are generally stored in glassware. • Mineral acids such as nitric acid and sulphuric acid can destroy human tissues, clothes, paper, etc. Thus, one should handle acids with care as they can cause burns upon contact with the skin. • Acids are soluble in water. Most acids dissolve in water either at room temperature or on heating to form a clear solution. For example, vinegar is a 3-5% solution of acetic acid in water. • Depending on the amount of water, acids can be either dilute or concentrated. • If the amount of water is more in an acid, it is called dilute acid and if the amount of water is less, it is called concentrated acid.

Strong Acids and Weak Acids

As we have seen, acidic substances contain acids. Acids are of two types: 1. Mineral or laboratory acids 2. Organic acids Hydrochloric acid (HCl), sulphuric acid (H2SO4), nitric acid (HNO3), etc. are some examples of mineral acids that are used in the laboratory.

Acids can be strong or weak. A strong acid is highly corrosive and can cause severe burns. Nitric acid and sulphuric acids are a few examples of strong acids. Weak acids, on the other hand, are not as destructive as strong acids. Organic acids are generally weak acids.

Organic Acids

Uses of Acids

Organic acids occur naturally in animal and plant materials.

Hydrochloric Acid (HCl) • Dilute hydrochloric acid is used in various industries for removing deposits from inside boilers. This process is known as de-scaling. • Hydrochloric acid is also used for cleaning sinks and sanitary ware. • It helps in the purification of common salt. Sulphuric Acid (H2SO4) Sulphuric acid is such an important industrial chemical that it is called the King of chemicals.

Mineral Acids

Examples Tartaric acid Acetic acid Formic acid Malic acid Citric acid Lactic acid Oxalic acid

Source Grapes Vinegar and tomato Stings of ants and bees Apples Lemon and oranges Milk Spinach

7th Class Chemistry

24 Due to its oily appearance, it was earlier called oil of vitriol. Some of its major uses are as follows: • Sulphuric acid is used in car batteries • It is used in the manufacture of paints, drugs, dyes, and artificial silk. • It is also used to produce fertilizers such as ammonium sulphate and super phosphate. Nitric Acid (HNO3) • Nitric acid is used in the manufacture of explosives such as TNT (trinitrotoluene) and nitroglycerine. • It is used by goldsmiths for cleaning gold and silver ornaments. • It is also used for the production of fertilizers such as ammoniumnitrate. Acetic Acid (CH3COOH) • Acetic acid is used directly to enhance the flavour of food. In fact, we commonly know acetic acid as vinegar. • It is also used as a cleansing agent in products meant for cleaning windows, floors, utensils, etc. It also helps to remove stains on woodwork and carpets. • Acetic acid is used as a preservative in pickles, etc. Most micro-orgnasims cannot live in an acidic environment. An acidic environment either slows down their activities or can also kill them. This is why you will find vinegar in many common packaged food items such as pickles, sauces, ketchups, etc.

3. Acid rains Pollutants such as sulphur dioxide gas and oxides of nitrogen present in the air react in the atmosphere with water and oxygen to form sulphuric acid and nitric acid respectively. These acids come down as rain. Acid rains cause great damage to plants and animal life, it also damage buildings and monuments.

Formative Worksheet 1.

2.

3.

4.

5.

6.

7.

8.

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Which of the following is an acid? (A) Sea water (B) Tap water (C) Lime juice (D) Human saliva Which of the following substances is an acid? (A) Alcohol (B) Sea water (C) Ammonia (D) Soap solution An acid will convert the colour of litmus paper to which colour? (A) Red (B) Blue (C) Green (D) Yellow When a litmus paper is dipped in soap solution, its colour changes to blue. However, when the litmus paper is dipped in vinegar, its colour changes to red. It can be concluded from the given observations that (A) soap solution is acidic, whereas vinegar is basic (B) soap solution is basic, whereas vinegar is acidic (C) soap solution as well as vinegar is acidic (D) soap solution as well as vinegar is basic When a litmus paper is dipped in alcohol, its colour changes to red. However, when the litmus paper is dipped in water, its colour does not change. What can be concluded from this observation? (A) Alcohol is acidic in nature (B) Alcohol is basic in nature (C) Water is acidic in nature (D) Water is basic in nature Joanne prepares a list of chemicals that change the colour of litmus paper to blue. I. Baking  soda II. Sea  water III. Citrus juice IV. Ammonia Which substance is listed incorrectly by Joanne? (A) I (B) II (C) III (D) IV Oranges, lemons, grapefruits, all taste sour because they all have a high amount of vitamin C. When few drops of blue litmus solution are added to lime juice, the colour of the solution becomes (A) Yellow (B) red (C) orange (D) blue Which of the following acids is not present in acid rain? (A) Carbonic acid (B) Sulphuric acid (C) Ascorbic acid (D) Nitric acid

Acids, Bases and Salts 9.

25

Lime water is i , soda water is ii , and distilled water is in iii nature. The information in which alternative completes the given statement? (A)

(B)

(C)

(D)

i

ii

iii

acidic

acidic

neutral

i

ii

iii

acidic

basic

neutral

i

ii

iii

acidic

neutral

basic

i

ii

iii

basic

acidic

neutral

10. Which of the following acids is present in curd? A ) Sulphuric acid (B) Acetic acid (C) Lactic acid (D) Citric acid 11. Litmus solution is a natural indicator used to distinguish between acids and bases by showing a colour change. Litmus is naturally obtained from A ) lichen (B) turmeric (C) beetroot (D) tamarind

Conceptive Worksheet 1.

2.

3.

4.

5.

6.

Acids are ________ to taste. (A) sweet (B) sour (C) Bitter (D) none HCl is a (A) mineral acid (B) organic acid (C) weak acid (D) All Which of the following is an acid. (A) HCl (B) HNO3 (C) H2SO4 (D) All Tartaric aicd is a . (A) mineral acid (B) organic acid (C) weak acid (D) All Which of the following is an organic acid? (A) Acetic acid (B) Malic acid (C) Formic acid (D) All Match the following organic acid Source (A) Oxalic acid p) lemon (B) Acetic acid q) milk (C) Lactic acid r) vinegar and tomato (D) Citiric acid s) spinach

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

Which of the following is true for acids? (A) Acids are sour to taste (B) Acids are soluble in water (C) Both (D) None Addition of water (A) Dilutes an acid (B) concentrates an acid (C) Both (D) None Nitric acid is (A) a strong aicd (B) a weak acid (C) a neutral acid (D) None Acetic acid is (A) a strong aicd (B) a weak acid (C) a neutral acid (D) None Which of the following acid used for purification of common salt? (A) HNO3 (B) HCl (C) H2SO4 (D) CH3COOH Which of the following acids is called king of chemicals? (A) Hydrochloric acid (B) Suphuric acid (C) Nitric acid (D) Formic acid Which of the following acids is used in batteries? (A) Hydrochloric acid (B) Suphuric acid (C) Nitric acid (D) Formic acid Which of the following acids is used in TNT (tri nitro toluene)? (A) Hydrochloric acid (B) Suphuric acid (C) Nitric acid (D) Formic acid Vinegar is (A) Formic aicd (B) Tartaric acid (C) Acetic acid (D) Oxalic acid Which of the following acid is used as a presrvative? (A) Formic aicd (B) Tartaric acid (C) Acetic acid (D) Oxalic acid Which of the following are responsible for acid rain (A) SO2 (B) NO2 (C) Both (D) None

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7th Class Chemistry

26

4. Bases Basic Substances Basic substances are those which contain bases. Examples: Sodium hydroxide (NaOH) Calcium hydroxide [Ca(OH)2] Bases also occur in plant and animal bodies such as corn starch, fresh egg white, etc. Many bases are found in household cleaners. Bases may have a strong irritating odour and should be used with caution as it can harm the skin and eyes.

Properties of Bases Some of the characteristic properties of bases are: • Bases are bitter in taste • Solutions of bases are soapy to touch. If you rub a drop or two of a very dilute solution of sodium hydroxide or potassium hydroxide between your fingers, they will feel slippery. • Bases may or may not be soluble in water. Bases that can dissolve in water are called alkalis. Some examples of soluble bases or alkalis are sodium hydroxide, potassium hydroxide, and calcium hydroxide. An Interesting Fact There are acids and bases in our body, HCl is present in the stomach. The saliva in your mouth is basic in nature. Blood when healthy is also basic.

Uses of Bases Calcium Hydroxide (Slaked lime) [Ca(OH)2] • It is used to neutralize the acidity in soils. • It is an ingredient in whitewash and mortar. • It is a component of the Bordeaux mixture used for protecting agricultural crops from pests. • It is used in the preparation of dry mixes for painting and decorating. Magnesium Hydroxide [Mg(OH)2] • It is also called of Milk of Magnesia. • It is used as an antacid or a laxative. It helps to correct excess acidity in the stomach. Sodium Hydroxide [NaOH] • It is also called of Caustic Soda • It is used in the manufacture of paper, textiles, and detergents. • In homes it is occasionally used to unblock drains. Ammonium Hydroxide and Other Weak Bases • It is also called of Caustic Soda • It is used in the manufacture of paper, textiles, and detergents. • In homes it is occasionally used to unblock drains.

5. Indicators To overcome this, certain chemicals called indicators have been developed. Indicators are substances which show a change in colour when brought in contact with acids and bases.

Litmus

Strong and Weak Base Like acids, bases can also be strong or weak. Strong bases are very corrosive and can burn the skin. Caustic soda or sodium hydroxide (NaOH) and caustic potash or potassium hydroxide (KOH) are strong and corrosive bases. On the other hand, copper hydroxide [Cu(OH)2], zinc hydroxide [Zn(OH) 2 ], and ammonium hydroxide (NH4OH) are weak bases.

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The most common indicator used in the laboratory is the litmus. It is extracted from lichens and is available either in the form of solutions or in the form of strips of paper known as litmus paper. Litmus paper is either red or blue in colour. It changes colour depending upon whether the compound is an acid or a base. Blue litmus paper turns red under acidic conditions. Red litmus paper turns blue under basic conditions.

Phenolphthalein Phenolphthalein is another indicator. Acids turn colourless and bases turn pink in Phenolphthalein.

Acids, Bases and Salts

Methyl orange Methyl orange is another indicator. Acids turn pink and bases turn yellow in methyl orange.

Neutral Substances The solutions that do not effect a change in colour in any of the indicators are neither acidic nor basic. These substances, as you already know, are called neutral substances. Examples: Sodium chloride, sugar, etc.

Universal Indicators We also know that acids or bases can be either strong or weak. So, if we have two solutions that are acidic, how do we find out which one is more acidic? Similarly we would have situation where we would have to know which one of the two solutions is more basic in nature. Scientists have made it very easy to know the strength of an acid or a base. Different strengths have been given what is known as a pH number which ranges from 1 to 14. 1 is considered as strongly acidic and 14 strongly basic. 7 is neutral. You can measure pH of a solution using universal indicator. A universal indicator is a mixture of indicators so chosen that it gives a different colour for different pH values. The indicator can be used as a liquid or can be soaked into paper. This paper is called pH paper. When a pH paper is dipped in an acid or a base, the colour obtained can be matched with the chart given below

27 For example, red cabbage juice will change to deep red with acids, to purple with neutrals, and to green and yellow with bases.

6. Salts Salts is a general term used for the substances that are formed when an acid and a base react with each other. This reaction is called a neutralization reaction. The reaction between vinegar and baking soda is also a neutralization reaction. Vinegar, as we already know contains an acid and baking soda contains base. In common usage, salt refers to table salt. In chemistry, salt refers to the product of the reaction between an acid and a base. So, when vinegar reacts with baking soda, salt is formed. Water and carbon dioxide gas are also the products of this reaction. Similarly, the common table salt is formed by the reaction of hydrochloric acid (HCl) with sodium hydroxide (NaOH). Hydrochloric acid + Sodium hydroxide 

Acid

Base

Sodium chloride + Water Salt Salts can be acidic, basic, or neutral. Types of Salts Acidic salts are formed when a strong acid reacts with a weak base. Basic salts are formed when a strong base reacts with a weak acid. When a strong acid reacts with a strong base, neutral salts are formed. Neutralization reactions are quite common in everyday life.

Neutralization in everyday life: Indigestion

Natural Indicators Indicators can be prepared very easily from brightly coloured parts of plants such as flowers (china rose, rose), roots (beet root), stems (turmeric), and leaves (red cabbage). Indicator solution can be prepared by boiling coloured parts of the plant e.g., petals in water for sometime and straining out the petals. This solution gives different colour in acidic and basic solutions.

To digest food properly the liquid in the stomach must be acidic. But too much acidity leads to indigestion. One takes antacids, which usually contains baking soda or magnesium hydroxide to neutralize the excess acid.

Insect Stings When a bee stings, it injects an acidic liquid into the skin. The sting is neutralized by rubbing calamine lotion which contains zinc carbonate.

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7th Class Chemistry

28

Formative Worksheet 12. Substances that are bitter in taste contain some kind of (A) Salt (B) base (C) acid (D) oxide 13. A base will convert the colour of litmus paper to

19.

A substance X is bitter to taste and soapy to touch. Hence, substance X is _____i____ in nature, and it will turn the colour of China rose indicator to ____ii____. The information in which alternative completes the given statement? (A)

(A) Red (B) blue (C) green (D) yellow 14. All bases are bitter in taste. Which of the following substances is a base? (A) Milk

(B) Vinegar

(C) Lemon juice

(D) Baking soda

15. A list of some substances is given below. I. Vinegar

(B)

(C)

II. Lemon juice

III. Distilled water IV. Baking soda V. Limewater

VI. Curd

Which of the following pair of substances is basic in nature? (A) I and II

(B) IV and V

(C) II and III

(D) IV and VI

16. Sodium burns in air forming a white powdery substance called sodium oxide, Na2O. This oxide, when dissolved in cold water, has a soapy touch and turns red litmus paper blue. The nature of the solution formed by dissolving Na2O in water is (A) Acidic

(B) alkaline

(C) neutral

(D) amphoteric

(D)

ii

acidic

magenta

I

ii

acidic

green

i

ii

basic

green

i

ii

basic

magenta

20. Shashank takes 10 mL of liquids I and II. He observes that liquid I turns blue litmus red and liquid II turns red litmus blue. He also observes that when the two liquids are mixed, the resulting solution becomes warm. He then boils the solution to dryness. Consequently, a substance III is left in the beaker. Using his observations, Shashank can conclude that Liquid I is  i and B is ii in nature. The substance III obtained in the beaker is a salt. The salt produced in the reaction can be iii  in nature. The information in which alternative completes the given statements?

17. Which base is commonly known as slaked lime? (A) Sodium hydroxide

i

(A)

(B) Calcium hydroxide

i

ii

iii

acidic

basic

acidic, basic, or neutral

i

ii

iii

basic

acidic

acidic or basic

i

ii

iii

neutral

basic

neutral or basic

i

ii

iii

acidic

neutral

acidic or neutral

(C) Potassium hydroxide (D) Ammonium hydroxide

(B)

18. Excessive use of chemical fertilisers and pesticides makes the soil acidic. Plants do not grow very well in acidic soil. Which of the following substances should be added to such a soil?

(C)

(A) Sodium chloride (B) Acetic acid (C) Limewater www.betoppers.com

(D) Water

(D)

Acids, Bases and Salts

Conceptive Worksheet 18. Bases are ___________ in taste. (A) Sour (B) Bitter (C) Sweet (D) none 19. Bases that are soluble in water are called. (A) Salts (B) Crystallized Bases (C) Alkalis (D) none 20. Which of the following acid is present in stomach?. (A) HNO3 (B) HCl (C) H2SO4 (D) CH3COOH 21. Blood is ________ in nature. (A) Acidic (B) Basic (C) Neutral (D) None 22. Which of the following is a strong base? (A) NaOH (B) KOH (C) Both (D) None 23. Which of the following is a weak base? (A) NaOH (B) KOH (C) Ca(OH)2 (D) None 24. Which of the following in an ingredient of white wash? (A) Milk of magnesic (B) Slaked slime (C) Caustic soda (D) Caustic potash 25. Bordeaux mixture contain __i__ and milk of magnesia is ___ii__. (A) i – Mg(OH)2; ii – Ca(OH)2 (B) ii – NaOH; ii – Mg(OH)2 (C) i – Ca(OH)2; ii – Mg(OH)2 (D) i – Ca(OH)2; ii – Mg(OH)2 26. __________ are the substances that show a change in colour when brought in contact with acids and bases. (A) Salts (B) Indicators (C) Alcohols (D) ehers 27. Which of the following is an indicator? (A) Litmus (B) Phenolphthalein (C) Methyl orange (D) All 28. Blue litmus paper turns red under _____ conditions. (A) Acidic (B) Basic (C) Neutral (D) None 29. Acids turn __i___ and bases turn __ii__in phenolphthalein. (A) i – yellow; ii – pink (B) ii – colourless; ii – pink (C) i – pink; ii – colourless (D) i – pink; ii – yellow

29 30. Blue litmus paper turns red under _____ conditions. (A) Acidic (B) Basic (C) Neutral (D) None 31. If PH of a solution is 1, then it is (A) Acidic (B) Stongly aicd (C) Weak acidic (D) None 32. The pH of basic solution is (A) 1 (B) 3 (C) 7 (D) 9 33. Acids change red cabbage juice to (A) green (B) yellow (C) purple (D) deep red

Uses of Salts Soil Treatment Most plants grow best in neutral soil. If the soil is too acidic, or too alkaline, the plants do not grow properly or do not grow at all. Usually, it is too acidic so a base such as quicklime (calcium oxide), slaked lime (calcium hydroxide), or chalk (calcium carbonate) is added.

Factory Waste Liquid waste from factories often contains acid. If it reaches a river, the acid will kill aquatic life. This is usually prevented by neutralizing the waste by adding a base such as slaked lime.

Properties of salts Some of the characteristic properties of salts are: • Salts are mostly solids which melt as well as boil at high temperatures. • Salts are generally soluble in water. For example, sodium chloride, potassium sulphate, aluminium nitrate, ammonium carbonate etc., are soluble salts while silver chloride, lead chloride, copper carbonate, etc., are insoluble in water.

Water of Crystallization Generally, salts are found as crystals with water molecules present in them. This water is called water of crystallization and such salts are called hydrated salts. For example, copper sulphate has five molecules of water for each copper sulphate molecule. This is written as CuSO4.5H2O. It also gives colour to some crystals. On heating, hydrated salts lose their water of crystallization and as a result, the crystals lose their shape and colour and change to a powdery substance. The hydrated salts that have lost their water of crystallization are called anhydrous salts. www.betoppers.com

7th Class Chemistry

30

When hydrated copper sulphate is heated, it gives out water molecules to form white powdery anhydrous copper sulphate, which on addition of water again converts to hydrated copper sulphate. Examples MgSO4 .7H2 O [Magnesium Sulphate], FeSO4.7H2O [Ferrous Sulphate] S. No.

Name of the salt

Chemical formula

Parent acid

Uses Flooring in the form of marble, making lime (CaO), cement and for extraction of iron In cleaning, detergents, water softening and manufacture of glass

1

Calcium carbonate (marble, limestone, chalk)

CaCO3

Carbonic acid

2

Sodium carbonate (washing soda)

Na 2CO3.10H2O

Carbonic acid

3

Sodium bicarbonate (baking soda)

NaHCO3

Carbonic acid

In bakery and medicines

4

Silver nitrate

AgNO3

Nitric acid

5

Ammonium nitrate

NH4NO 3

Nitric acid

In photography for developing films Fertilizers and explosives

6

Potash alum (phitkari)

K2SO4 . Al 2(SO 4)3 – 24H2O

Sulphuric acid

In purification of water

7

Sodium chloride (Common salt)

Hydrochloric acid

As seasoning for food, in manufacture of chlorine and sodium carbonate

NaCl

Formative Worksheet

(D)

21. Which of the following substances is used to relieve indigestion? (A) Curd (B) Vinegar (C) Acetic acid (D) Magnesium hydroxide 22. The reaction between  i and ii is called neutralization reaction. In this reaction, iii and iv are produced along with the evolution of heat. The information in which alternative completes the given statements? (A)

i

ii

iii

iv

a base

a salt

an acid

water

i

(B)

an acid

(C)

i an acid

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ii

iii

a base ii a salt

iii a base

water

(A)

(B)

(C)

iv hydrogen

ii

iii

iv

an acid

a base

a salt

hydrogen

23. In a neutralisation reaction, an acid reacts with a base to produce i and ii . During the process, the reaction mixture generally becomes iii . The information in which alternative completes the given statements?

iv

a salt

i

(D)

i

ii

iii

hydrogen

oxide

hot

i

ii

iii

hydrogen

oxide

cold

i

ii

iii

salt

water

cold

i

ii

iii

salt

water

hot

Acids, Bases and Salts

31

24. Stephen puts a red litmus paper on a soap bar. The paper turns blue in colour. Then, he puts the paper in orange juice and the paper turns red in colour. This test indicates that the soap bar i is in nature and the orange juice is ii in nature. Which of the following alternative correctly completes the sentence? 25. If dilute hydrochloric acid is added to sodium hydroxide, then the reaction mixture will become i and the products obtained will be ii and   iii . The information in which alternative completes the given statement? (A)

(B)

(C)

(D)

i

ii

iii

hot

sodium chloride

water

i

ii

iii

hot

sodium chloride

hydrogen

i

ii

iii

cold

sodium

water

i

ii

iii

cold

sodium

hydrogen

26. Indicators are substances that give different colours and are commonly used in detecting acids and bases. Methyl orange and phenolphthalein are the common indicators. The use of indicators depends upon the strength of the acid and the alkali solutions which are being neutralized. Solution X turns the colour of methyl orange to pinkish red. Solution X is (A) amphoteric in nature (B) basic in nature (C) acidic in nature (D) neutral in nature 27. Katherine performs the following chemical reaction in her laboratory. HCl + NaOH + X  NaCl What is the composition of X? (A) H2O2 (B) H2O (C) HCN (D) Na 2O2 28. Which of the following chemical equations is an example of a neutralisation reaction? (A) 2Na + 2HCl  2NaCl + H2 (B) CH4 +  2O2   CO2 + 2 H2O (C) NaCl + AgNO3   NaNO3 + AgCl (D) H2SO4 + 2  NH4OH  (NH4)2SO4 + 2 HOH

29. Which of the following colour changes is observed when phenolphthalein is added to a base? (A) Colourless to red (B) Red to colourless (C) Colourless to pink (D) Pink to colourless 30. Which of the following substances will not turn China rose indicator green? (A) Antacid (B) Shampoo (C) Lime water (D) Distilled water 31. Which of the following substances would show a colour change with turmeric paste? (A) Vinegar (B) Lemon (C) Soap (D) Curd 32. A substance X is sour to taste. Another substance Y was  added  to  X.  On  doing  so,  the temperature of reaction mixture increased. Also, two new substances were formed, both of which were neutral in nature. One of the substances formed is used as common salt. The information in which alternative correctly represents X and Y?

X

Y

Hydrochloric acid

Sodium hydroxide

(A)

(B)

X

Y

Sulphuric acid

Magnesium hydroxide

X

Y

Acetic acid

Sodium hydroxide

(C)

(D)

X

Y

Lactic acid

Magnesium hydroxide

Conceptive Worksheet 34. Acid + Base   Salt + Water. This is a (A) Combination reaction (B) Decomposition reaction (C) Neutralisation reaction (D) None 35. Strong acid + weak base   (A) Basic salt (B) Acid salt (C) Neutral salt (D) None 36. Weak acid + Strong base   (A) Basic salt (B) Acid salt (C) Neutral salt (D) None

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7th Class Chemistry

32 37. Strong acid + strong base   (A) Basic salt (B) Acid salt (C) Neutral salt (D) None 38. Antacid contain (A) Baking soda (B) Magnesium hydroxide (C) Both (D) None 39. The acidity in the soil is neutralized by adding (A) CaO (B) Ca(OH)2 (C) CaCO3 (D) All 40. The salts that contain water of crystallization are called (A) hydrated salts (B) Acidic salts (C) Neutral salts (D) Basic salts 41. Match the following: A) Marble p) NaHCO3 B) Washing soda q) NaCl C) Baking soda r) CaCO3 D) Common salt s) Na2CO3 . 10H2O 42. Match the following: Salt Acid A) Marble p) Hydrochloric acid B) Silver nitrate q) Sulphuric acid C) Potash atom r) nitric acid D) Common salt s) Carbonic acid

(C)

(D)

3.

4.

2.

Which of the following indicators produces green colour when added to a base? (A) Turmeric (B) China rose (C) Phenolphthalein (D) Litmus solution Raju wants to test the acidic, basic, or neutral nature of two different solutions (I and II) with the help of a red and blue litmus paper. He observed that the colour of red litmus paper turns blue with solution I,whereas blue litmus paper remains unaffected with it. On the other hand, both red and blue litmus papers remain unaffected with solution II. Which table correctly concludes the natures of solutions I and II? (A)

(B)

Solution

Nature

I

Basic

II

Neutral

Solution

Nature

I

Acidic

II

Neutral

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5.

6.

Nature

I

Neutral

II

Acidic

Solution

Nature

I

Neutral

II

Basic

Which of the following acids causes acidity in stomach? (A) Sulphuric acid (B) Acetic acid (C) Hydrochloric acid (D) Nitric acid __i___turns __ii___ litmus paper ___iii___. The information in which alternative completes the given statement? (A)

i Distilled water

ii red

iii blue

(B)

i Lemon juice

ii red

iii blue

(C)

i Sodium hydroxide

ii blue

iii red

(D)

i Nitric acid

ii blue

iii red

Summative Worksheet 1.

Solution

Which of the following word equations correctly represents the neutralization reaction? (A) Acid + Base  Salt + Water + Heat (B) Acid + Salt  Base + Water + Heat (C) Acid + Water  Base + Salt + Heat (D) Acid + Heat  Base + Salt + Water Distilled water is in nature, but lime water is in nature. The information in which alternative completes the given statement? (A) i ii (B)

(C) (D)

acidic

neutral

i

ii

neutral

basic

i

ii

neutral

acidic

i

ii

basic

acidic

Acids, Bases and Salts

33

7.

When a drop of phenolphthalein is added to a solution of baking soda, the colour of the solution changes to (A) red (B) pink (C) purple (D) magenta 8. Which of the following substances would give a red colour with blue litmus paper? (A) Window cleaner(B) Milk of magnesia (C) Vinegar (D) Soap 9. Which of the following terms does not represent an indicator? (A) Rose (B) Litmus (C) Turmeric (D) Phenolphthalein 10. The wastes produced from factories contain many chemicals. These chemicals change the colour of blue litmus solution to red while the red litmus solution remains unaffected. When these chemicals are discharged in the water bodies, it harms the aquatic life. This is because these chemicals are __i__ in nature. Thus, __ii__substances should be added to these chemicals before discharging them. The information in which alternative completes the given statements? (A)

(B)

(C)

(D)

i

ii

acidic

neutral

i

ii

acidic

basic

i

ii

basic

acidic

i

ii

basic

neutral

2.

3.

Which of the following substances can X be?

4.

On mixing lemon juice and limewater, a colourless solution is obtained. This reaction is known as neutralisation reaction. Which of the following statements is correct about the given activity? (A) The resulting solution has no effect on litmus solution. (B) The resulting solution can be used to treat acidic soil. (C) Heat is absorbed during the reaction. (D) No new substances are formed.

(A) Solid baking soda

(B) Sugar solution

(C) Soap solution

(D) Vinegar

Seema took some petals of China rose and kept them in hot water. After some time, she added a little shampoo to it. Which alternative represents the colour of the solution obtained by Seema after the addition of shampoo?

5.

(A) Magenta

(B) Green

(C) Yellow

(D) Blue

Prashant made a list of some acids and their respective sources. Name of acid Source 1 Citric acid Lemon 2 Lactic acid Milk 3 Oxalic acid Orange 4 Tartaric acid Tamarind Which of the sources of acid is incorrectly matched in Prashant's list?

HOTS Worksheet 1.

Few drops of tamarind juice were added to turmeric paper, China rose, and red litmus paper. The colour changes will be (A) yellow, magenta, and red respectively (B) yellow, magenta, and blue respectively (C) red, magenta, and blue respectively (D) red, magenta, and red respectively

(A) Lemon 6.

(B) Milk

(C) Orange (D) Tamarind When an ant bites, it causes pain and irritation. A certain substance, which is a common household substance, when applied to the affected area gives relief. The substance turns red litmus paper blue, and blue litmus paper remains unaffected with it. Hence, the mentioned substance is ____i____ in nature, and the sting of an ant contains _____ii____ substance. www.betoppers.com

7th Class Chemistry

34 The information in which alternative completes the given statement? (A)

(B)

(C)

(D)

7.

ii

neutral

a basic

i

ii

basic

an acidic

i

ii

acidic

a basic

i

ii

neutral

an acidic

Raju took some vinegar and limewater in two separate beakers I and II. Then, he tested the colour change of blue and red litmus papers with these solutions. He observed that red litmus paper turns blue and blue litmus paper remains unaffected with limewater, whereas blue litmus paper turns red and red litmus paper remains unaffected with vinegar. He then mixed suitable amounts of vinegar and limewater in beaker III and tested the colour change of litmus paper with this solution. He observed that both litmus papers remained unaffected with this solution. He also observed that the reaction mixture becomes hot. On the basis of this experiment, he concluded that beaker III contains a ____i_____ solution and heat is ____ii______ during the process. The information in which alternative completes the given statement? (A)

(B)

(C)

(D)

8.

i

i

ii

neutral

produced

i

ii

neutral

absorbed

i

ii

acidic

produced

i

ii

basic

absorbed

A substance 'X' is sour to taste. Hence, substance 'X' is ____i____ in nature, and it turns the colour of ____ii____ litmus paper _____iii____. The information in which alternative completes the given statement?

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(A)

(B)

(C)

(D)

9.

i

ii

iii

basic

red

blue

i

ii

iii

acidic

blue

red

i

ii

iii

acidic

red

blue

i

ii

iii

basic

red

blue

Sumit collected two substances X and Y from his laboratory. He tested them to find out whether they are acidic, basic, or neutral in nature. He prepared a solution of X and Y in water. Then, he tested for colour change in red and blue litmus papers with these solutions. The given table shows the effects of solution X and Y on red and blue litmus papers.

X

Effe ct on red litmus paper Blue

Effe ct on blue litmus pape r No change

Y

No change

Red

Solution

From the experiment, he concluded that X is ____i___ in nature, while Y is ___ii___ nature. (A) i ii (B)

(C) (D)

basic

neutral

i

ii

basic

acidic

i

ii

acidic

basic

i

ii

acidic

neutral

10. Ravi mixed sodium hydroxide and hydrochloric acid in a beaker. By touching the beaker, he observed that the resulting solution is hot. He then tested the acidic, basic, or neutral nature of the reaction mixture with the help of a litmus paper. He observed that both red and blue litmus papers remain unaffected with the solution. What can be concluded from Ravi's experiment? (A) The resulting solution is acidic in nature and heat is absorbed during the reaction (B) The resulting solution is basic in nature and heat is evolved during the reaction (C) The resulting solution is neutral in nature and heat is evolved during the reaction (D) The resulting solution is neutral in nature and heat is absorbed during the reaction

Acids, Bases and Salts

35

11. Rohan collected four different solutions: lemon juice, water, cola, and household lye. He then tested the acidic, basic, or neutral nature of each solution with the help of red and blue litmus paper. The given table lists the results of his experiment. Test Effect on red Effect on blue solution litmus paper litmus paper Lemon juice No change Red

Water

No change

No change

Cola Household lye

No change

Red

Blue

No change

Which of the following statements cannot be concluded by Rohan? (A) Cola is basic in nature (B) Water is a neutral solution (C) Lemon juice is acidic in nature (D) Household lye is basic in nature

IIT JEE Worksheet I.

Single Correct Answer Type

1.

NH3 (Ammonia) is ? (A) Acidic (B) Basic (C) Amphoteric (D) Neutral The formula of Table salt is ? (A) NaCl (B) KCl (C) MgCl2 (D) CuCl2 Identify the basic salt among the following ? (A) Pb(OH)NO3 (B) NaNO3 (C) KOH (D) Pb(OH)NO3 Name of the double salt is ? (A) Mohr’s salt FeSO4(NH4)2SO4.6H2O (B) Potassium Ferrocyaride K4Fe(CN)6 (C) Sodium potassium carbonate NaKCO3 (D) Barium sulphate BaSO4 NaOH + HCl  NaCl + H2O ; in this reaction NaCl is formed by the process of ? (A) Decomposition reaction (B) Double decomposition (C) Netralization reaction (D) Precipitation reaction Among the following which is soluble in hot water ? (A) PbSO4 (B) AgCl (C) KHCO3 (D) PbCl2

2.

3.

4.

5.

6.

7.

Among the following which is an indicator? (A) Drisehman stain (B) Benedict Reagent (C) Phenolphthalein (D) Methelene blue 8. Name of the factory indicator among the following is ? (A) Methyl orange (B) Phenolphthalein (C) Vanilla essence (D) KMnO4 solution 9. In Lime water, strips of Litmus paper shows the colour of ? (A) Red (B) Pink (C) Green(D) Blue 10. Name the acid which gives brown fumes in normal condition ? (A) Carbonic acid H2CO3 (B) Sulphuric acid H2SO4 (C) Nitric acid HNO3 (D) Hydrocyanic acid HCN 11. The mild base that can be use as an antacid is ? (A) Magnesium hydroxide Mg(OH)2 (B) Zinc hydroxide Zn(OH)2 (C) Calcium hydroxide Ca(OH)2 (D) Ammonium hydroxide NH4OH 12. Among the following which one is responsible for the acidity in our stomach ? (A) Hydrogen chloride HCl (B) Hydrogen bromide HBr (C) Hydrogen floride HF (D) Hydrogen iodide HI

II. Multiple Correct Answer Type 13. HNO3 is a (A) mineral acid (B) organic acid (C) weak acid (D) strong acid 14. Which of the following is an acid? (A) HCl (B) HNO3 (C) H2SO4 (D) NaOH 15. Which of the following is an organic acid? (A) Acetic acid (B) Malic acid (C) Formic acid (D) HCl 16. Which of the following is true for acids? (A) Acids are sour to taste (B) Acids are soluble in water (C) Acids have ability to corrode (D) Acids change red litmus to blue 17. Which of the following are responsible for acid rain? (A) SO2 (B) NO2 (C) O2 (D) O3 www.betoppers.com

7th Class Chemistry

36 18. Which of the following is a strong base? (A) NaOH (B) KOH (C) Ca(OH)2 (D) NH4OH 19. Which of the following is a weak base? (A) NaOH (B) KOH (C) Ca(OH)2 (D) Zn(OH)2

III. Integer Type 20. The pH of strong acid is ___________. 21. The pH of neutral solution is ___________. 22. The number of water molecules in hydrated copper sulphate is ___________. 23. The number of water molecules in hydrated magnesium sulphate is ___________. 24. The number of water molecules in hydrated ferrous sulphate is ___________.

IV. Matrix Matching 25. Match the following organic acid Source (A) Oxalic acid p) lemon (B) Acetic acid q) milk (C) Lactic acid r) vinegar and tomato (D) Citiric acid s) spinach 26. Match the following: Salt Formula A) Marble p) NaHCO3 B) Washing soda q) NaCl C) Baking soda r) CaCO3 D) Common salt s) Na2CO3 . 10H2O 27. Match the following: Salt Acid A) Marble p) Hydrochloric acid B) Silver nitrate q) Sulphuric acid C) Potash atom r) nitric acid D) Common salt s) Carbonic acid



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B y t h e en d o f t h i s ch a p t e r, y o u w i l l u n d er s t a n d       

Properties of air Activities to prove the properties of air Activities to show different components in air Application of air pressure Atmospheric Pressure Importance of air in daily life Air is necessary for combustion – Activity

      

Uses of different constituents of air Fuel and Combustion Importance of oxygen for all forms of living beings Air Pollution Respiration In Plants Photosynthesis Oxygen and Carbon dioxide cycle

1. Introduction Air is found every where on the earth. Living things cannot survive without air. Air is necessary for breathing and combustion. The earth is surrounded by an envelope of air, is commonly called ‘atmosphere’. The air not only contains oxygen and nitrogen, but also variety of other gases in small amounts. The chief amongst the other gases are carbon dioxide, water vapour, ozone and noble gases (Helium, Neon, Argon, Krypton and Xenon are collectively called noble gases). In addition to these, there are impurities like dust particles, carbon particles, carbon monoxide, nitrogen dioxide and sulphur dioxide. The composition of the air changes from place to place. In cities, where there are more vehicles, factories, etc., the percentage of carbon dioxide is more than that in the villages. The percentage of nitrogen in air, by volume, varies from 77.9% to 78.03%. Constituent of air Percentage 1. Nitrogen

78.03%

2. Oxygen

20.9%

3. Noble gases

0.94%

4. Carbon dioxide

0.03%

5. Water vapour

Variable

6. Impurities

Variable

2. Properties of Air i) ii) iii)

Air is a colourless gas It occupies space Air has weight and exerts pressure in all directions

Chapter - 43

Air and its Components

Learning Outcomes

Components of Air i) Air is not a single substance ii) It consists of many gases like nitrogen, oxygen, carbon dioxide and water vapour iii) Air is a mixture

3. Activities to prove the Properties of Air I. i) ii)

Air occupy Space: Take a balloon and blow air by the mouth. Twist the mouth of the balloon and tie with a thread and press the balloon. iii) We feel the experience that air which cannot be seen by the eye occupied a space in the balloon. This experiment shows that air occupies space. II. Air has Weight: i) Make a hole in the middle of a twig of broom. ii) From the middle point of the twig make two holes at an equal distance. iii) Introduce a thread from the middle hole of the twig and suspend it freely. iv) Tie balloons blown with air with equal volume. v) The twig must be horizontal. vi) Make a tiny hole to the balloon on one side. vii) The air goes out and the twig with the punctured balloon comes down showing that the balloon which has air in it has more weight. III. Air exerts Downward Pressure: i) A glass vessel is taken and is half filled with water. ii) A small piece of cork dropped on the water floats on it. iii) A glass is inverted on the floating cork and is pushed over the floating piece of cork. iv) The air in the glass exerts pressure and pushes down the cork. v) This shows that air exerts downward pressure.

7th Class Chemistry

38 IV. Air exerts Upward Pressure: i) Air exerts pressure to all sides. ii) A glass tumbler is filled with water up to the brim. iii) A thick paper is placed over the mouth of the glass and the glass is inverted with the paper. iv) The paper does not fall down. v) It is because the air from below is exerting pressure and is supporting the paper. vi) It means that air has upward pressure. V. Air exerts Sideward Pressure: i) A tin made of thin metal sheet is taken. ii) The tin is heated with a spirit lamp and after that air in it is pushed out. It is closed with a lid. iii) After some time you observe that the sides of the tin are pressed and the tin is twisted. iv) It means that the air pressure on the sides of the tin made it to be twisted. v) Thus we prove that air exerts sideward pressure.

4. Activities to show different Components in Air I. Oxygen: Invert a glass on a burning candle flame. After few seconds the flame of the covered candle goes off. This happens because the oxygen inside the glass is used up in burning. II. Carbon dioxide: Activity-1 i) Take some lime water in a china dish and place it in the air for sometime. ii) A white layer is formed on the lime water. iii) The carbon dioxide present in the air is absorbed by the lime water and calcium carbonate is formed as a white layer. This proves the presence of carbon dioxide in air. Activity-2 i) Take lime water in a china dish. ii) Place it in air. A white layer is formed on the lime water. iii) So the carbon dioxide in the air is absorbed by the lime water and calcium carbonate layer is formed. iv) This demonstrates that air contains carbon dioxide. III. Water vapour: Activity-1: We will observe the outer sides of the glass containing ice pieces will turn pale due to the www.betoppers.com

condensation of water vapour showing the presence of water vapour in the air. Activity-2: i) Take a crystal of anhydrous copper sulphate and place it in a watch glass in the air. ii) The copper sulphate becomes blue. iii) The anhydrous copper sulphate has absorbed water vapour in the air and turned hydrous blue copper sulphate. IV. The proportion of Nitrogen in Air: i) The proportion of nitrogen in air is found to be less where the leguminous plants are in abundance. These plants have nodules in their root system. Some kind of bacteria is found in these nodules. ii) These bacteria change the Nitrogen in the air into nitrate and supply it to the plants. iii) Human and animal excreta and dead bodies on earth surface are putrefied by a kind of bacteria. As a result of these reactions, the Nitrogen present in those compounds gets released and reaches air in the atmosphere. V. Composition of Air (contains Oxygen and Nitrogen 1: 4) by Volume: i) Light a candle and fix it in a tub. ii) Pour water until a half of the candle is drowned. iii) Place an inverted glass on the burning candle. Divide the upper portion above the level of water into five equal parts. iv) Water level rises by one part after the flame of the candle goes off. v) In the air the supporter of combustion, oxygen, and the non supporter of combustion nitrogen are present. vi) The experiment shows that air contains 1/5 volume of active oxygen useful in burning, in addition with 4/5 by volume of inactive gas nitrogen which does not support combustion. vii) It shows that air contains oxygen and nitrogen in the ratio 1:4. VI. Variation of Water vapour: i) The volume of water vapour is high in the sea coastal area ii) It is low in the plateau regions. iii) The temperature shows its effect on water vapour in air. iv) When the temperature is high, the volume of water vapour increases in air.

Air and its Components

39

v)

In winter season, mist and fog are formed due to the presence of water vapour in air in excess. VII. Variation of Carbon dioxide: i)

ii)

iii) iv)

v)

8. When fuel is ignited carbon dioxide is evolved. A large quantity of carbon dioxide is found in the atmosphere where more industries are established. Carbon dioxide also evolves from the surface of the earth like the death valley in Java and 9. Grotodel Cave in Naples. Dense forests contribute even distribution of carbon dioxide in atmosphere, Plants prepare food by photosynthesis using carbon dioxide and water in the presence of sunlight. That is why the amount of carbon dioxide is less in dense forests.

Formative Worksheet 1.

2.

3.

4.

5.

6.

7.

Air exerts ______ pressure. (A) Upward (B) Downward (C) Sideward (D) All The atmosphere consists mainly ___________ (A) Oxygen and Nitrogen (B) Nitrogen and Hydrogen (C) Hydrogen and Oxygen (D) None of the above What is the ratio of oxygen and Nitrogen in the atmosphere, respectively (A) 2 : 4 (B) 4 : 2 (C) 4 : 1 (D) 1 : 4 The volume of water vapour high in the regions of: (A) Coastal areas (B) Plateau regions (C) Industrial areas (D) All the above The air that is present on the earth is called; (A) Atmosphere (B) Photosphere (C) Hydrosphere (D) Electrosphere Carbon dioxide evolved from the surface of the earth on: (A) Death valley in Java (B) Grotodel cave in Naples (C) Dense forest of Mexico (D) Dense forest of Africa Statement I : Leguminous plants have nodule on their roots. Statement II : The bacteria present on nodules takes nitrates from the plants. (A) Both Statements are true, Statement II is the correct explanation of Statement I.

1.

2.

3.

4.

(B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true. Identify the true statement from the following: (A) When fuel is ignited carbon dioxide is evolved. (B) Dense forests contribute even distribution of carbon dioxide in atmosphere. (C) Plants prepare food by photolysis. (D) In industrial area large quantity of carbon dioxide is found in the atmosphere. Column-I Column-II a) Nitrogen and oxygen 1) Grotodel cave b) Water vapour 2) Nodules as their roots. c) Leguminosae 3) 4 : 1 d) Naples 4) Mist 5) Death valley

Conceptive Worksheet Air is: (A) Element (B) Mixture (C) Compound (D) Gas Gas evolved, when fuel is ignited: (A) Oxygen (B) Nitrogen (C) Water vapour (D) Carbon dioxide Air contains in a little quantity: (A) Neon (B) Chlorine (C) Hydrogen (D) Fluorine __________ is turned lime water milky. (A) Nitrogen (B) Oxygen (C) Chlorine

5.

6.

7.

(D) Carbon dioxide

Plants prepare food by ________. (A) Respiration (B) Photolysis (C) Photosynthesis (D) Electrolysis The bacteria which changes the ________ in the air in to nitrate. (A) Hydrogen (B) Nitrogen (C) Oxygen (D) None of these Which plants are having nodules in their root system? (A) Pamacae (B) Leguminous (C) Fabacae (D) None of these

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7th Class Chemistry

40

5. Application of Air Pressure Air possesses weight and air exerts pressure. We are using this air pressure for different purposes. I. Ink Filler: i) We use ink filler for filling ink in our fountain pens. ii) Dip the stem of the ink filler in ink. Press the rubber bulb with your fingers and release it slowly. iii) Air is released in the form of air bubbles in the ink. iv) When the air inside the filler is blown and vacuum is created in it, the air pressure inside it is reduced. v) Atmospheric pressure acts on the surface of the ink contained in the ink bottle and the air pressure inside the filler is less than that of the atmospheric pressure. vi) Hence ink enters inside the filler. vii) Place the stem of the ink filler in the barrel of the pen and press the rubber bulb. viii) The ink inside the filler gets released and falls into the barrel of the pen. ix) The ink is filled up into the pen through the ink filler as a result of the air pressure. II. Air Pump:

2 A

1 B

3

4

Parts : 1) Valve B, 2) Valve A, 3) Leather cap, 4) Barrel

Air Pump working system: 1. Air pumps are used for filling air in cycle tubes, football bladders. These pumps can also be used for exhausting air from any vessel and there by creating lower pressure. 2. The construction of the air pump is shown in figure. It consists of a barrel, where in a piston moves. It has two leather caps attached to its inner stem. 3. This piston can be moved to and fro inside the barrel. 4. The second side of the barrel consists of valves A and B with two nozzles. 5. Valve ‘A’ allows the air to get inside the barrel where as air gets released through the valve ‘B.’ 6. When the piston is pulled out, the volume of air inside the barrel increases. There by, the air pressure inside it decreases. www.betoppers.com

7.

At this juncture, valve ‘A’ opens itself and the air outside it enters into the barrel with great pressure. 8. When the piston is pushed inside, the volume of air inside the barrel decreases and the pressure increases. 9. Hence the air is released through the valve ‘B1 ’. 10. The air contained in any vessel can be exhausted by attaching it to valve ‘A’ and operating the piston to and fro. It can be filled up into the foot ball bladder by connecting it to valve ‘B’. III. Kerosene Pump:

3

Parts : 1. Valve 2. Piston 3. Barrel 4. Side tube

4 2

1 Kerosene Pump

Construction: i) The Kerosene Pump consists of a long metallic cylindrical tube. The upper portion is wider and is closed with a lid. ii) Very nearer to the upper portion, there is a bent side tube soldered to the pump. iii) There will be a thin iron rod in the cylindrical tube which can be moved up and down. iv) At the bottom of the rod a circular metal disc is soldered. This type of iron rod is called piston. v) The bottom of the cylindrical tube is closed leaving a small hole. A small thin iron sheet is fixed at the bottom. This works as a valve. Working: i) The Kerosene Pump is immersed in the kerosene tin and the piston is pushed inside and is then pulled up. ii) The atmospheric pressure acting on the surface of kerosene makes the kerosene to enter the tube through the valve. iii) When the piston is pushed down, the valve at the bottom is closed. Then kerosene comes up to the tube above the disc attached to the piston.

Air and its Components iv)

41

Now the piston is pulled up, kerosene flows ormative orksheet out from the side bent tube. v) Kerosene comes down to the iron disc 10. Which of the following is / are working as air attached to the bottom of the piston. pressure? vi) By moving the piston quickly in either direction (A) Ink filler (B) Kerosene pump kerosene flows out through the bent tube (C) Air pump (D) All attached to the cylindrical tube. 11. Statement I : The air pressure inside the filler is vii) By moving the piston up and down the required less than that of the atmospheric pressure. quantity of kerosene can be drawn from the Statement II : Because of this, ink enters inside the tin. filler IV. Lift Pump: (A) Both Statements are true, Statement II is the correct explanation of Statement I. The pumps used for lifting water from wells are (B) Both Statements are true, Statement II is not known as lift pumps or common pumps. correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true. 12. ___________ is used for drawing kerosene from a tin? (A) Air pump (B) Kerosene pump (C) Lift pump (D) Ink filler 13. _________ pump used for lifting water from wells.

V.

Modern applications of atmospheric pressure: i) Air is filled with high pressure inside the tyres of vehicles like cycles, scooters, cars, trucks, aeroplanes. These vehicles run smoothly by utilising these tyres. ii) Compressed air is used in the brake system for stopping a moving train. iii) Compressed air is also used for digging purpose in the mines and in the machines used for crushing the stones. iv) Air is also used for drying wet clothes, agriculture products like food grains and dry fruits. v) Wind mills also work through the wind flow. The wind mills are used for drawing water from the tube wells, for running flour mills and for production of electricity. vi) For separating grain from husk through winnowing. vii) Air helps for the movement of boats, gliders, parachutes and helicopters. Birds, insects etc., fly in air using the difference in air pressure.

F

14.

15.

16.

17.

18.

W

(A) Kerosene pump (B) Air pump (C) Lift pump (D) Ink filler ___________ are fly in air using the difference in air pressure. (A) Insects (B) Aeroplanes (C) Scooters (D) Wind mills Statement I: The air pumps are used for filling air. Statement II: In air pumps, when the piston is pushed inside, the volume of air inside the barrel increases. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true. Important part in a pump : (A) Valve (B) Barrel (C) Piston (D) Liquid Identify the correct statement: (A) Wind mills work through the wind flow. (B) Air is used for drying agricultural products. (C) Air helps for the movement of boats gliders and parachutes. (D) Wind mills are used for drawing water from the tube wells. These fly in air using the difference in air pressure: (A) Parachutes (B) Sail boats (C) Helicopters (D) All the above www.betoppers.com

7th Class Chemistry

42 19. The pumps used for lifting water from walls __________ (A) Air pumps (B) Lift pumps (C) Kerosene pumps (D) Common pumps 20. These are useful both for filling and exhausting air: (A) Kerosene Pump (B) Lift Pump (C) Air Pump (D) Syphon

Conceptive Worksheet 8.

9.

10.

11.

12.

13.

14.

What is used for filling ink in fountain pens? (A) Air pump (B) Ink filler (C) Kerosene pump (D) None ________ is used for filling air in cycle tubes, foot ball bladders (A) Air pump (B) Ink filler (C) Kerosene pump (D) None A valve is a device which works in: (A) One direction (B) Two directions (C) Multi directions (D) None of the above This is helpful for the working of kerosene pump: (A) Liquid pressure (B) Vapour pressure (C) Solid pressure (D) Atmospheric pressure When the volume of air inside the barrel increases then the air pressure inside it is________. (A) Increases (B) Decreases (C) Constant (D) None When we heat the tin we observe the side of the tin are pressed, because: (A) Air exerts downward pressure (B) Air exerts upward pressure (C) Air exerts side ward pressure (D) All the above Number of valves in a kerosene pump: (A) 1 (B) 2 (C) 3 (D) 4

6. Atmospheric Pressure Air has weight, so it exerts pressure on earth’s surface. This pressure is called ‘Atmospheric Pressure’. Torricelli designed the Cistern Barometer. It is mainly used to measure the atmospheric pressure. Cistern barometer:

Cistern barometer www.betoppers.com

The construction of a Cistern barometer: i) Take a thick walled glass tube of length one meter and diameter 1 cm which is closed at one end. ii) Mercury is poured into this tube without any air bubbles. iii) Close the open end of the tube with your thumb and invert it. Place the open end of the tube in a trough of mercury and remove the thumb. iv) A portion of mercury in the tube falls down into the trough. Mercury in the tube stands still at a certain height of centimeters. This is called Mercury column. v) Vacuum is developed above the surface of mercury column. This is called Torricellian vacuum. vi) The height of the level of mercury column in the tube from the level of mercury in the trough is measured. This is nearly 76 cms. vii) Usually this will be 76 cms near the sea level. This is called normal atmospheric pressure. viii) The pressure exerted by the atmosphere at a point on the surface of the mercury in the trough is equal to the pressure exerted at any point in the tube which is in the same horizontal line. ix) It means, the weight of 76 cm height of mercury column exerts the same pressure in the tube as exerted by the atmosphere outside the tube. x) This is the reason that height of mercury is used in measuring the atmospheric pressure. The information we can get by using a barometer: i) At any place, atmospheric pressure is known with a barometer. ii) The height of any place from the sea level can be found with a barometer. iii) Forecast of storms, rains can be made with the help of barometer. iv) For every height of 272.7 meters from the sea level, a decrease of 2.54 cms of pressure takes place. v) For every depth of 272.7 meters from the sea level, an increase of 2.54 cms of pressure occurs. vi) Gradual decrease in the height of the mercury column in the barometer indicates the rainfall.

Air and its Components

43

vii) Sudden fall in the height of the mercury column 28. Vacuum in the barometer is called: in the barometer forecasts occurrence of (A) Volt vacuum (B) Torricellian vacuum storms. (C) Ampere vacuum (D) Edison’s vacuum

Formative Worksheet 21.

22.

23.

24.

25.

29. Statement I: Gradual decrease in the height of the mercury column forecasts the cyclones. Statement I: Barometer is used to measure Statement II: Sudden fall in the height of atmospheric pressure. mercury column forecasts occurrence of storms. Statement II: The height of mercury column near (A) Both Statements are true, Statement II is the the sea level will be 76cms. correct explanation of Statement I. (A) Both Statements are true, Statement II is the (B) Both Statements are true, Statement II is not correct explanation of Statement I. correct explanation of Statement I. (B) Both Statements are true, Statement II is not (C) Statement I is true, Statement II is false. correct explanation of Statement I. (D) Statement I is false, Statement II is true. (C) Statement I is true, Statement II is false. 30. The liquid used in the barometer is : (D) Statement I is false, Statement II is true. (A) KOH solution (B) Hydrochloric acid Cistern barometer is designed by: (C) Mercury (D) All the above (A) Boyle (B) Torricelli 31. Statement I: The height of mercury column (C) Charles (D) Graham shows the volume of atmosphere at a particular Normal atmospheric pressure is ___________ of place. mercury column. Statement II : It also denotes the mean sea level (A) 76 cm (B) 76 km of a particular place. (C) 76 mm (D) 76 m (A) Both Statements are true, Statement II is the correct explanation of Statement I. Sudden fall in mercury barometer forecasts: (B) Both Statements are true, Statement II is not (A) Wind blow (B) Rain correct explanation of Statement I. (C) Storm (D) Cool weather (C) Statement I is true, Statement II is false. This is used to find the atmospheric pressure: (D) Statement I is false, Statement II is true. (A) Barometer (B) Spherometer (C) Speedometer (D) Gravitometer onceptive orksheet Gradual decrease in mercury column in the 15. _______ is formed above the surface of the Barometer forecasts: mercury column (A) Storm (B) Rainfall (A) Volume (B) Pressure (C) Cool weather (D) Dry weather (C) Vacuum (D) All the above Statement I: With the help of barometer we can 16. The height of mercury column will be high below know the height of a particular place form the sea the _______ areas. level. (A) Sea-level (B) Moon level Statement II: For every 272.7 meters of height (C) Sun level (D) None form the sea level 2.54 centimeters of pressure 17. Air has weight so it exerts pressure on earth’s decreases. surface, the pressure is called_______. (A) Both Statements are true, Statement II is the (A) Atmospheric volume correct explanation of Statement I. (B) Atmospheric pressure (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Atmospheric energy (C) Statement I is true, Statement II is false. (D) None of the above (D) Statement I is false, Statement II is true.

C

26.

27.

W

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7th Class Chemistry

44 18. The mercury column is used to measured: (A) Atmospheric pressure (B) Atmospheric volume (C) Atmospheric energy (D) Atmospheric weight 19. This is needed for respiration: (A) Carbon dioxide (B) Hydrogen (C) Nitrogen (D) Oxygen 20. Absence of oxygen leads to: (A) Life (B) Death (C) Dullness

(D) Activity

7. Importance of Air in Daily Life We cannot live without air. We need air for breathing. Plants and animals also need air for breathing. So air is necessary for living beings. We use fire for different purposes. Air is necessary for burning or combustion of objects. I. Firewood Oven: i) When fire wood is placed in the oven, the air present in between them is used for burning. ii) For facilitating burning in the fire wood oven we use a hand fan or blow air through a wooden tube. II. Kumpati: i) In the kumpati (Sigri), the grate (metal bars fixed to an angular frame) prevents the coal pieces from falling down. ii) There are gaps in between the metallic rods of the grate which allow the passage of air. III. Kerosene Stove: i) In a Kerosene Wick Stove there is a cylindrical sheet with holes drilled. ii) These holes allow the passage of air. iii) For a continuous combustion process there should be supply of air without interruption.

8. Air is necessary for Combustion – Activity Candle burns in air

Glass tumbler Water

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Candle does not burns in the absence of air

i)

Take a glass trough and fill 1/3 of its volume with water. ii) Add a spoonful of caustic soda (Sodium hydroxide) and few drops of coloured ink to the contents of the trough. iii) Place a wooden slab or stone in the trough and place a lighted candle on it as shown in the figure. iv) Invert a wide mouthed glass jar over the burning candle. The candle is put off within few seconds. At the same time the coloured water in the glass jar raises. v) The supporter of combustion i.e., oxygen in the air, contained in the glass jar was exhausted and carbon dioxide is released in its place. Hence oxygen in the air is useful for combustion. vi) The carbon dioxide so formed is absorbed by caustic soda solution. The nitrogen which is still available in air does not give support for burning. vii) As vacuum is created in the glass jar, the coloured water raises in the trough. viii) However if the glass jar is not placed in an inverted position over the burning candle, the candle goes on burning forever, as air is available continuously. ix) Hence, we can say that oxygen in air is necessary for burning.

9. Uses of different Constituents of Air I. Nitrogen: The percentage of nitrogen in air, by volume, varies from 77.9% to 78.03%. Significance of Nitrogen in Atmosphere It dilutes the activity of oxygen. Thus, the combustion of fuel during burning takes place at a moderate rate. The compounds of nitrogen are of vital importance to plants as they help the plants to manufacture proteins. However, free nitrogen cannot be absorbed by plants. The free nitrogen is converted into its compounds by the following natural methods. During lightening, an electric spark passes through air. Due to this spark, nitrogen combines with oxygen to form nitric oxide gas.

Air and its Components

45 III. Carbon dioxide:

electric N 2  O 2    2NO spark

Nitrogen

Nitric oxide gas

Oxygen

The nitric oxide gas, further reacts with oxygen and water vapour present in air to form nitric acid vapour. NO

Nitric oxide gas

4NO2

Nitric dioxide gas

 O2

Oxygen

electric    spark 

2NO 2

The percentage of carbon dioxide in air, by volume, varies from 0.03% tn 0.04%. The areas where a lot of fuel burns have more percentage of carbon dioxide. Significance of Carbon dioxide in Atmosphere:

•

Nitric dioxide gas

 O 2  2H 2 O   4HNO3 Oxygen

Water

Nitric acid

When it rains, the nitric acid in very dilute form is washed down to earth, where it reacts with soil carbonates to form soil nitrates. CaCO3 Calcium carbonate

6CO 2

Carbon dioxide

Water

C6 H12 O6  6O 2 Glucose

Nitric acid

Calcium nitrate

CO2

Carbon dioxide

 H 2O

•

Water

The soil nitrates, so formed, act as excellent food for the growth of plants. Symbiotic Bacteria are present in nodules of pod bearing plants such as peas, grams, sweet peas, etc. The bacteria absorb nitrogen directly from air and convert it into compounds of nitrogen. These compounds are absorbed by the plants for the manufacture of proteins.

•

Nitrogen being inert gas is used in the preservation of foods. The containers containing food are flushed with nitrogen to drive out oxygen and then sealed. Because, of the absence of oxygen, the bacteria do not grow and hence food remains fresh. II. Oxygen: The percentage of oxygen in air by volume, varies from 20.8% to 20.9%. Significance of Oxygen in Atmosphere:

•

It supports all animals and plant life on the earth, as it is essential for respiration.

•

It is essential for the combustion of fuels. Man burns an enormous amount of fuels for his energy needs. Oxygen helps in the combustion of fuels to form carbon dioxide and water vapour as principal products.

•

Sunlight  6H 2 O   Photosynthesis

 2HNO3  

Ca  NO3  2 

•

It acts as food for plants. During photosynthesis, plants absorb carbon dioxide and water vapour. These are converted into carbohydrates and oxygen in the presence of chlorophyll and sunlight.

In nature, it dissolves in water. This, in turn, helps to keep the water fresh and is a source of respiration for water animals.

Oxygen

Carbon dioxide, dissolved in water, can dissolve rocks containing calcium carbonate (chalk) or magnesium carbonate. The salts, so formed, are calcium bicarbonate and magnesium bicarbonate. These dissolved salts give taste to natural water. Furthermore, they satisfy the needs of plants for growth, as calcium and magnesium ions are needed by the plants.

MgCO3  H 2 O  CO2   Mg  HCO 3 2 Magnesium Water Carbon Magnesium dioxide carbonate bicarbonate

CaCO3  H 2 O  CO 2   Ca  HCO3 2

Calcium Water Carbon carbonate dioxide

•

Calcium bicarbonate

It does not allow the earth to radiate heat energy rapidly at night. It is because the carbon dioxide molecules present in air reflect back heat radiations.

Note: The temperature in big cities is higher than in the countryside because the heat radiations are reflected back in the cities due to the presence of excessive carbon dioxide. IV. Water vapour: The percentage composition of water vapour in air, by volume, varies from 0.4% to 4%.

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7th Class Chemistry

46 Significance of water vapour in atmosphere:

•

The presence of water vapour in air determines climatic conditions. Excessive water vapour causes rain. The amount of rain produced depends upon the geographical location and the surroundings. Depending upon the temperature, the water vapour produce snow, fog, mist, hails and other phenomenon.

•

The presence of water vapour controls the rate of evaporation from the plants and animals.

•

The presence of water vapour is very essential for the growth of plants.

•

The presence of water vapour is very essential for health and comfort of animals. Excess or deficiency of water vapours in air can lead to a number of problems related to good health.

V.

Noble Gases:

A group of gases which do not react chemically with any substance are called noble gases. They are Helium, Neon, Argon, Krypton and Xenon. Their percentage composition in air by volume is 0.94%. Significance of Noble Gases in Air: Apparently, they do not have any use for the animals or plants. They can be separated from air and put to a number of industrial uses.

•

Helium gas is very light and is used for filling weather observation balloons.

•

Argon gas is used for filling electric bulbs at low pressure.

•

Neon gas is used for making advertising glow tubes, which you see at night on big Shops, Hotels, etc. VI. Impurities: The percentage of impurities in air is variable, depending upon the location of place. In general, the air contains a large amount of impurities in industrial areas. Following are the impurities present in air: i) Dust Particles: Small amount of dust particles do no harm. As a matter of fact, they help in the precipitation of water vapour and, hence in the formation of clouds and rain. However, an excessive amount of these can cause serious respiratory problems.

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Smok e Par t i cl es: Smoke particles are present in a large amount where coal is used as fuel. They also act as nucleus for the precipitation of water vapour. However, an excessive amount of these can lead to serious respiratory problems. iii) Sulphur dioxide, Nitrogen dioxide, Carbon monoxide and Hydrogen sulphide: These gases are present in variable amounts in big cities, industrial districts, etc. They can cause the following problems.: a) They can cause serious respiratory problems. b) They can destroy ozone layer, which protects us from ultra-violet radiations. c) They can cause acid rain, which ruins crops and forests.

ii)

10. Fuel and Combustion I. Fuel: Any cheap material Which burns in air or oxygen with the release of large amount of heat energy and light energy is called fuel. Following are the commonly used fuels for heating or lighting : 1. Wood: Wood is the most commonly used fuel in rural India. In addition to it biomass (stems left after harvesting crops and leaves shed by the trees) is also used as fuel. Dried cow-dung cakes are also used as fuel. 2. Coal: Coal is generally used as an industrial fuel in big factories such as cement factories, steel mills and glass factories. In addition to it, vast quantities of coal are used in thermoelectric power stations for raising steam. 3. Kerosene Oil: It is used as a household fuel in wick stoves and pressure stoves. It is also used for illumination in wick lamps and petromax lamps. 4. LPG: It is liquefied petroleum gas. It is used as a household fuel in urban India. 5. CNG: It is compressed natural gas. It mostly consists of methane gas. It is used as a fuel in CNG buses and big-factories. It is also directly piped to the homes and is used as fuel. II. Combustion: The process of burning of fuel in the air, with the release of large amount of heat energy and’ light energy is called combustion.

Air and its Components

47

During the process of combustion, the oxygen of the air reacts with the carbon and hydrogen present in the fuels (in the form of compounds) to form carbon dioxide gas and water vapour. Fuel + Oxygen (from air)  Carbon dioxide + Water vapour + Heat The carbon dioxide gas and water vapour so formed are released in air. The heat energy released is put to various domestic or industrial uses. III. Air is necessary for Combustion - An activity: Take a candle about 8 cm long, and fix it in a plastic trough. Pour water into the trough as shown Light the candle.

White anhydrous copper sulphate turns bule

Suction with mouth

Funnel

Burning candle

Cold water

Lime water turns milky

Products formed due to the burning of candle

Burning candle Plastic trough Water (a)

Glass tumbler

IV. Carbon dioxide and water vapour are the products of combustion- An activity

The candle goes off

Water

Now invert a glass tumbler over the burning candle. You will see that the candle flame burns for a few seconds. The flame then starts flickering and finally goes off. The reason is that the burning candle does not receive any fresh supply of air on account of water seal. Thus, the activity proves that air is necessary for burning. Similarly, we know from our everyday experience that, if wood fire gets dull, it flares up on blowing air through it. Conversely, if sand is poured over the burning wood, it gets extinguished. It is because, we cut off the supply of air.

Fix a funnel in an inverted position as shown. To the stem of the funnel connect a plastic tube, which is connected on the other end to an absolutely dry U-tube containing small amount of anhydrous copper sulphate (white in colour). To the other end of Utube, connect another plastic tube, whose other end goes into a test tube containing fresh limewater. In the mouth of test tube fix a suction tube. Light a candle under the funnel and start suction from the suction tube. In few minutes following observations are made : The anhydrous copper sulphate (white) in the U-tube changes to blue colour: Reason: It is because, the anhydrous copper sulphate reacts with the water vapour to form blue coloured hydrated copper sulphate. Obviously, water vapours must be the product of combustion of candle. These water vapours must have condensed in the U-tube to form liquid water. Thus, we can say that one of the products of combustion of wax is water vapour. The limewater turns milky: Reason: It is because, limewater reacts with carbon dioxide to form milky colour. Obviously, carbon dioxide must be one of the products of combustion of wax.

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7th Class Chemistry

48

11. Important of Oxygen for all forms of Living Beings

1.

Set up the apparatus as shown. Open the pinch cock A and keep the pinch cock B closed. Put your mouth on the tube M and suck in air, so that fresh air enters flask F1 and after bubbling through lime-water, enters into your mouth and then lungs.

2. Respiration The process of respiration is similar to the process of burning, except that heat energy is released in controlled amount.

Now close the pinch cock A and open the pinch cock B. Exhale out the air from your lungs, such that it bubbles through the limewater in flask F2 and finally passes out of it. Repeat the inhaling and exhaling for 10 times,

The air is absolutely essential for respiration for all forms of life. Before we discuss anything else, let us try to understand respiration in human beings. I.

Our food mainly consists of compounds of carbon, hydrogen and oxygen, such as 3. starches, sugars, fats, etc. These food materials break down in our digestive system to form simpler compounds. These simpler compounds mix in the blood stream and are carried to individual cells. At the same time oxygen (from inhaled air) dissolves in the blood stream in the lungs during the action of breathing. This 32. dissolved oxygen in the blood is also carried to the individual cells. In the cells, the simpler compounds formed from the food materials react with oxygen to form carbon dioxide and water with the release of heat energy. The heat energy is utilised for performing various body functions and in maintaining the body temperature at 37°C. The carbon dioxide and water are exhaled. 33. Definition: The collective process of absorption of oxygen (from air) into the blood stream and then oxidation of food materials in the cells with the release of heat energy, carbon dioxide and water in 34. the exhaled air is called respiration.

You will observe that limewater in flask F1 very slightly turns milky, whereas limewater in flask F2 rapidly turns milky. Thus, the experiment clearly proves that exhaled air contains more carbon dioxide than the inhaled air.

Formative Worksheet

Experiments to show that exhaled contain CO 2 : The exhaled air contains more carbon dioxide and water vapour as compared to inhaled air. This can be proved by the following experiments : M outh Fresh air

Pinch cock A

Pinch cock

Exhaled air

Lime water turns milky rapidly F1

Column-II

a) LPG

1) White in colour

b) CNG

2) Compressed natural gas

c) Anhydrous copper sulphate

3) Wood, coal, kerosene oil

d) Fuel

4) Flux colour 5) Liquid petroleum gas

Our food mainly consists of compounds of: (A) Carbon

(B) Hydrogen

(C) Oxygen

(D) Nitrogen

Statement I: When a glass tumbler inverted over a burning candle the flame burns for a few seconds then it goes off. Statement II: The burning candle does not receive any fresh supply of air on account of water deal. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false.

B

Lime water turns milky slowly

Column-I

F2

(D) Statement I is false, Statement II is true. 35. Which of the following is correct statement? A) We can live with out air. B)

Exhaled air contains more carbon dioxide than inhaled air

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Air is necessary for burning or combustion of objects.

Air and its Components

49

23. Which gas is necessary for burning? (A) Nitrogen (B) Carbon dioxide (B) (B) only correct (C) Hydrogen (D) Oxygen (C) (A) only correct 24. In addition to wood. Which is used as fuel? (D) Both (A and (B) are incorrect (A) Coal (B) Bio mass Statement I: The anhydrous copper sulphate in (C) Kerosene (D) All the above the U-tube change its colour to blue colour. Statement II: The anhydrous copper sulphate 25. Which one of the following is fuel? (A) Wood reacts with the water vapour to form blue coloured hydrated copper sulphate. (B) Bio mass (A) Both Statements are true, Statement II is the (C) Dried cow-dung cakes correct explanation of Statement I. (D) All the above (B) Both Statements are true, Statement II is not 26. ___________ is necessary for burning/combustion correct explanation of Statement I. of objects: (C) Statement I is true, Statement II is false. (A) Air (B) Water (D) Statement I is false, Statement II is true. (C) Both 1 & 2 (D) None The limewater turns milky because: 27. Which gas is used as compressed natural gas? (A) It reacts with carbon monoxide (A) Carbon dioxide (B) Ethane (B) It reacts with oxygen (C) It reacts with carbon dioxide (C) Methane (D) Hydrogen (D) All the above Which is used as a house hold fuel in urban India? 12. Air Pollution When the air contains harmful or undesirable (A) LPG (B) Kerosene oil substances, generated by the activities of man or (C) CNG (D) Coal nature, such that their concentration interferes with Identify the correct statement/s: human health or is injurious to plants or animals, it (A) Wood is the most commonly used fuel in rural is said to be polluted air, and the undesirable substances are called pollutants. India. (B) Coal is generally used as a industrial fuel. I. Role of nature in Air Pollution (C) Kerosene oil is used as a household fuel in 1. When wind blows hard, it carries dust particles urban India. and sand particles in large amount from one (D) LPG is used as a fuel in buses. place to another place. When the forest fires The anhydrous copper sulphate turns to blue coloured take place, large amount of carbon particles hydrated salt because: (smoke) and carbon monoxide enters the air as pollutants. (A) It reacts with carbon dioxide 2. When volcanoes erupt, huge amount of ash (B) It reacts with water vapour and sulphur dioxide is added in the air as (C) Both (A) & (B) pollutants. (D) None 3. During the pollination of crops and trees, a significant amount of pollens enter in the onceptive orksheet atmosphere. The air polluted with pollens causes allergy in some persons and creates What is used for making carbohydrates in the problems like sneezing and asthma. presence of sunlight and water. (A) Oxygen (B) Carbon dioxide (A) Both (A) and (B) are correct

36.

37.

38.

39.

40.

C 21.

(C) Hydrogen

W

(D) Nitrogen

22. What is need to living organisms for respiration? (A) Nitrogen (B) Carbon dioxide (C) Oxygen (D) Hydrogen www.betoppers.com

7th Class Chemistry

50 II. Role of Human in Air Pollution Most of the pollution is caused by the activities of human beings : 1. Large amount of coal is burnt in thermal plants for the generation of electricity. These plants throw out huge amount of smoke and ash in the atmosphere, which can be detected in the radius of 20 km or more from the location of power plant. 2. Vehicles using petrol or diesel produce large amount of smoke and carbon monoxide. In the big cities, such as Delhi, Mumbai, etc., vehicular pollution is causing lot of problems. The vehicles emit hydrocarbons, carbon monoxide, lead, nitrogen oxides and particulate matter. 3. Burning of wood or coal or kerosene oil in not properly designed ‘Chulha’ or stoves produce large amount of smoke, ash, carbon monoxide, sulphur dioxide and nitrogen oxide. 4. Burning of refuse in big cities, especially the plastic bags, etc., causes lot of pollution due to the formation of carbon monoxide, sulphur dioxide and nitrogen dioxide. 5. Pesticides spread in the fields also cause air pollution. III. Factors causing Air Pollution : 1. Combustion of Fuels: Air is polluted by the combustion of charcoal, kerosene, diesel, petrol. It is also polluted by gases produced during burning of fire wood in the houses. 2. Deforestation: Decrease in the area of forests causes decrease in the volume of oxygen. 3. Emission of Gases by Vehicles: When fuel is ignited in vehicles it emits carbon monoxide, nitric oxide, sulphur dioxide and compounds of lead. Unignited carbon particles reach and make air polluted. 4. Industrialisation: Factories release harmful gases dust, smoke, soot etc., and these substances mix with air and make it a polluted air. 5. Methods of Cultivation: We use pesticides as a preventive against pest. Synthetic fertilizers are used excessively for more yield of crops. When we use these fertilisers and pesticides in large quantities pollution occurs. 6. Atomic Explosion and its malady: For rapid development in various fields most of the countries conduct atomic explosions, thereby www.betoppers.com

causing damage to the people and plants. Accidents which occur in space by various aeroplanes and spacecrafts can also pollute air. 7. Sound Pollution: The sounds above the audible range are also factors for atmospheric pollution. IV. Role of Carbon dioxide in Air Pollution Greenhouse Effect: The trapping of solar heat energy in earth’s atmosphere is called ‘Greenhouse effect’. It has been found that wavelength of infra-red rays (heat rays) is inversely proportional to the temperature of the object emitting these rays. It means, lower the temperature of a hot object, the longer is wavelength of infra-red rays emitted by it. The solar heat radiations consist of infrared radiations of very short wavelength, as the Sun is at extremely high temperature. These radiations easily pass through atmosphere. On reaching the surface of the Earth, these radiations are absorbed. With the result, the temperature of the Earth rises during the day time. However, at night the Earth radiates out the heat radiations at a temperature far below the temperature of the Sun. Thus, heat radiations are of very long wavelength. The long wavelength heat radiations cannot easily penetrate through atmosphere, because carbon dioxide molecules and clouds act as excelled reflectors. The gases such as carbon dioxide, water vapour and methane are called greenhouse gases. Thus, heat radiations are trapped in the atmosphere which keep the Earth reasonably warm during night. Example: It has been found that if a car with its doors and windows closed is parked in the sun, the interiors of the car become very hot as compared to temperature outside. It is on account of the Greenhouse effect. The smaller wavelengths of the heat radiation pass through the glass windows of car and are absorbed by its interior. However, the heat radiations given out by the interior are of longer wavelength and hence do not pass out of the glass windows. Thus, heat is trapped within the interior of car and hence its temperature rises. Harmful results of Greenhouse Effect: As a matter of fact, the greenhouse effect helps in keeping the Earth reasonably warm and hence is creating better conditions for the survival of life

Air and its Components However, it has been noticed that for the last 100 years the consumption of fossil fuels has increased manifold. This, in turn, has increased amount of carbon dioxide in the atmosphere, with the result 1. Greenhouse effect has increased. The average temperature of Earth has gone up by 2°C. It is feared that, if temperature further rises, it might result in ‘global warming’. This, in turn, will melt 2. ice on the polar caps, thereby raising the level of sea water by a few metres. This, in turn, will result in submerging of coastal regions and islands, causing extensive damage. Useful applications of Greenhouse effect:

•

•

Growing vegetables and flowers in snow bound regions: In cold countries, the land gets covered with snow in winter. Thus, 3. nothing could be grown. The farmers in cold countries erect huge sheds having glass walls. The glass allows the smaller wavelength of solar heat radiation to pass into the shed, but does not allow longer wavelength of heat 4. radiation to pass out during night. Thus, a Greenhouse effect takes place within the shed which keeps it reasonably warm. Flowers and vegetables are grown in the specially designed sheds. In fact, the name “Greenhouse effect” by itself is derived from the green plants grown in the glass sheds. Use of glass in keeping homes warm: In cold countries, windows and doors are double panelled with thick plane glass. The glass allows the smaller wavelength of heat radiations of solar energy to pass into the rooms, but does not allow longer wavelength of heat radiations to pass out. Thus,

51 Greenhouse effect takes place and hence rooms keep reasonably warm. V. Controlling air pollution due to human activities: In the houses, we must use improved ‘chulha’, if we use wood or coal as fuel. In case kerosene oil is used as fuel, we must use improved stoves, so that the production of smoke and carbon monoxide is minimised. In the thermal power plants; cement plants; steel plants, etc., we must provide electric precipitators, so that smoke and ash entering the atmosphere are minimised. The sulphur dioxide gas; nitrogen dioxide gas formed in above plants should be removed. This can be done by passing the gases through water, before letting them into atmosphere. The sulphur dioxide and nitrogen dioxide dissolve in water. We must use efficient internal combustion engines in our vehicles, so that petrol or diesel burns completely without emitting any smoke. The harmful gases present in the exhaust should be removed by using catalytic converter. We must grow more trees as they are capable of removing harmful gases. VI. Controlling methods for Air Pollution: i) ii) iii) iv) v)

By checking the emission of smoke from motor vehicles. By checking or controlling the emission of smoke from factories. By using the devises which can filter the agents causing the pollution. Reforestation methods. Controlling the usage of fertilisers, spreading of dust particles and educating the people about the pollution of air and its preventive methods.

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7th Class Chemistry

52 Table showing the effects of air pollution S.No

Source

Pollute d s ubs tances

Effect

1

H omes

Carbon dioxide

Carbon dioxide cuases: 1. D if ficulty in breathing 2. Increase in the termerature of ear th. 3. Certain changes in atmosphere

2.

Combust ion of f uels

Carbon dioxide, Sulphur dioxide

Since it is poisonous it causes headache, mental dis or der, lethargy and also leads to death.

Transport

Carbon monoxide Sulphur dioxide

Sulphur dioxide causes breathlessness in human be ings and animals. It also destroys plants , chlor ophyll in plant leave s, it checks the gr ow th of plants.

4.

Indus tr ies

Sulphur dioxide, N itric oxide, Carbon Monoxide, Zinc, Chromium, N ickel, Lead, Soot partic les.

Smoke containing the par ticles of zinc, chromium , lead cause diseases of skin, lungs, asthma and other allergies.

5.

A tomic explosions

Str ontium 90

Cancer: harmful to plants and anima ls.

6.

Aer oplane, Jet plane

Carbon compounds Florocarbons

Destroys the Ozone layer. It causes diseases related to lungs, eyes, skin, digestive system.

3.

7.

Sound above audible Sound pollut ion range

Formative Worksheet 41. Air is polluted by combustion of: (A) Charcoal (B) kerosene (C) Diesel (D) Petrol 42. When fuel is ignited in vehicles it emits: (A) Carbon monoxide (B) Sulphur dioxide (C) Both (A) & (B) (D) Carbon dioxide 43. Which pollution causes deafness and affects central nervous system? (A) Air pollution (B) Sound pollution (C) Water pollution (D) None 44. ___________ causes breathlessness in human beings and animals (A) Carbon dioxide (B) Carbon monoxide (C) Sulphur dioxide (D) All the above 45. When fuel is ignited in vehicles it emits: (A) Carbon monoxide (B) Nitrogen oxides (C) Sulphur dioxide (D) Compounds of lead.

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Causes deafness and affects central nervous system leading to mental disability.

46. Atomic explosions causes: (A) Cancer (B) Headache (C) Disease related to lungs (D) Deafness 47. The gases released by factories are: (A) Dust (B) Smoke (C) Soot (D) All the above 48. What are the factors causing air pollution: (A) Air is polluted by the combustion of fuels. (B) Air is polluted by emission of gases by vehicles. (C) Air is polluted by industrialisation. (D) Using fertilizers and pesticides in large quantities causes pollution. 49. Statement I : Air is polluted by gases produced during of fire wood in the houses Statement II : Decreases in the area of forests causes decreases in the volume of oxygen. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true.

Air and its Components 50. CaCO3 + H2O + _____ 51.

52.

53.

54.

55.

56.

 Ca(HCO(C)2 (A) CO (B)CO2 (C) C (D) O2 The trapping of solar heat energy in earth’s atmosphere is called: (A) John Thomson effect (B) Green house effect (C) Zeeman effect (D) All the above Which of the following is the correct statement/s: (A) During photosynthesis, plants absorb carbon dioxide and water vapour. (B) Dissolved salts give taste to natural water. (C) The trapping of solar heat energy on earth atmosphere is called greenhouse effect. (D) Carbon dioxide can dissolve rocks containing calcium carbonate (Chalk) or Magnesium carbonate. Identify the controlling methods of air pollution. (A) By checking the emission of smoke from motor vehicles. (B) By checking or controlling the emission of smoke from factories. (C) Deforestation methods. (D) By using the devises which can filter the agents causing the pollution. __________ particles are cause diseases of skin, lungs, asthma and other allergies. (A) Zinc (B) Chromium (C) Lead (D) CO2 How to reduce pollution of air. (A) By using electric precipitators in power plants, cement plants and steel plants (B) By passing gases (SO2 and NO2 ) through water (C) By using catalytic converters in vehicles (D) By growing more trees. Statement I: Combustion of fuels, deforestation, emission of gases by vehicles, industrialization are the main factors for air pollution. Statement II: The harmful gases present in the exhaust should be removed by using catalytic converter. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true.

53

Conceptive Worksheet 28. Atmosphere is polluted by: (A) Nitrogen dioxide (B) Sulphur dioxide (C) Carbon dioxide (D) All the above 29. Solid liquid and gaseous substances are present in higher volumes in air it is called. (A) water pollution (B) Air pollution (C) Sound pollution (D) None 30. Decrease in the area of forests causes decrease in: (A) Volume of O2 (B) Volume of CO2 (C) Volume of O2 & CO2 (D) None 31. What is / are the green house gases: (A) Carbon dioxide (B) Water vapour (C) Methane (D) All the above 32. _________ will result in submerging of coastal regions and islands. (A) Thermal power station (B) Steel plants (C) Wind mills (D) Global warming 33. ___________ is/are act as reflectors, during greenhouse effect. (A) CO2 molecules (B) Clouds (C) Both (A) and (B) (D) None 34. Burning of plastic bags causes air pollution due to the formation of: (A) Carbon monoxide (B) Sulphur dioxide (C) Nitrogen dioxide (D) All the above 35. In houses if we use wood or coal as fuel, we must use: (A) kerosene oil (B) Chulha (C) Both (A) & (B) (D) None 36. We must provide electric precipitators in: (A) Thermal power plants (B) Cement plants (C) Steel plants (D) All the above 37. Sulphur dioxide and nitrogen dioxide gas should be removed in power plants by: (A) Passing through alcohol (B) Passing through water (C) Passing through petrol (D) None 38. What are the products emitted by vehicles? (A) Sulphur dioxide (B) Carbon monoxide (C) Nitric Oxide (D) None of the above

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7th Class Chemistry

54

13. Respiration in Plants Guard Cells

4. Stomatal Aperture Outer wall

Inner Wall

the rim of the funnel, so as to prevent the entry of air. Leave the apparatus undisturbed for overnight. You will find that limewater turns milky. It is because the germinating seeds give off carbon dioxide during respiration.

Epidermal Cells

14. Photosynthesis Chloroplasts Stomata

Structure of Stomata Much like animals, the plants also respire day and night. However, the rate of respiration in plants is far slower than animals for the simple reasons that plants do not perform as many activities as do the animals. During respiration the plants breath through stomata, the minute openings on the surface of leaves. An opening (stoma or pore) of a stomata is surrounded by two kidney shaped cells called guard cells containing chloroplasts for photosynthesis. During respiration, the stoma opens and the air diffuses in the cells. After the oxidation the carbon dioxide diffuses out. The activity given below shows that plants breathe out carbon dioixde during respiration. To show that plants produce carbon dioxide during respiration:

The chemical process taking place in the green leaves is called photosynthesis. Definition: The process due to which the plant leaves absorb carbon dioxide gas from atmosphere and then in the presence of water, chlorophyll and sunlight, convert it to glucose (sugar) and oxygen is called ‘photosynthesis’. Photosynthesis Carbon dioxide + Water

Light  

Sugar + Oxygen

Chlorophyll

It is interesting to note that photosynthesis is the reverse chemical process of respiration. During respiration, it is the glucose and oxygen which react chemically to form carbon dioxide, water and release heat energy. However, during photosynthesis, the carbon dioxide and water react chemically by the absorption of light energy to form glucose and oxygen.

15. Oxygen and Carbon dioxide Cycle

Cotton wool plug Glass funnel Germinating seeds Grease seal

Small dish containing clear limewater Grease seal Glass plate

To prove plants breath out carbon dioxide

For doing this activity you need germinating seeds. The seeds can be germinated by placing the Germinating seeds (seeds of barley, wheat, beans, etc.) in thick moist cloth for 48 hours. 1. Take a clean glass plate and over it place about 25 g germinating seeds. Sprinkle some water over the seeds. 2. Along with seeds place a small dish containing clear limewater. 3. Place an inverted funnel over the germinating seeds and limewater as shown in Fig. 5.10. Plug the stem of funnel with cotton wool. Apply grease all along www.betoppers.com

Vast amount of oxygen present in the air is consumed during the respiration of billions of plants and animals, which in turn release the vast amount of carbon dioxide and water vapour. Furthermore,

Air and its Components

55

large amount of oxygen is consumed during the process of combustion of fuels. In spite of the fact that oxygen is being continuously consumed, its amount in air remains same. During the day time, the carbon dioxide diffuses into the pores of green leaves. Here, it reacts with water, in the presence of chlorophyll to form oxygen and glucose. The oxygen is released in the air. The glucose is converted into sugar and then starch by a very complex process. As the volume of oxygen released is equal to the volume of carbon dioxide absorbed.

Formative Worksheet 57. Which of the following is correct statement: (A) Like animals, the plants also respire day and night. (B) During respiration, the stoma opens and the air diffuses in the cells. (C) Plants breath out carbon dioxide during respiration. (D) Plants breath out oxygen during respiration. 58. Statement I : The rate of respiration in plants is for slower than animals. Statement II : The plants do not perform as many activities as do the animals (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true. 59. Column-I Column-II a) Stomata 1) Stoma b) Guard cells 2) Kidney shaped cells c) Chlorophyll 3) Photosynthesis d) Glucose 4) Minute opening on the surface of leaves 5) C 6H12 O6

60. Statement I: Stoma is the minute opening of stomata Statement II: Stomata is surrounded by two kidney shaped cells called guard cells. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true. 61. Statement I: During the respiration, the glucose and oxygen react chemically to form CO2, water and release heat energy. Statement II: Photosynthesis is the reverse chemical process of respiration. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true. 62. Statement I: Living organisms need carbon dioxide for respiration. Statement II: Absence of oxygen leads to occurrence of death in living organisms. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true.

Conceptive Worksheet 39. The plants breath (during respiration) through: (A) Stomata (B) chloroplast (C) Metaplast (D) Both (A) and (C) 40. An opening of a somata is: (A) Stoma (B) Pore (C) Both (A) and (B) (D) None 41. The plants breath out ________ during respiration (A) CO2 (B) O2 (C) H2O (D) None 42. The day time, the carbon dioxide reacts with water in the presence of chlorophyll to form: (A) Oxygen and Glucose (B) Glucose and Carbon dioxide (C) Water and Glucose (D) Oxygen and water www.betoppers.com

7th Class Chemistry

56 43. The process of photosynthesis, which gas is evolved: 5. (A) CO2 (B) O2 (C) Water vapour (D) None 44. The chemical process taking place in the green leaves is called: 6. (A) Photolysis (B) Photosynthesis (C) Catalysis (D) Electrolysis 45. The carbon dioxide react with water in the presence of chlorophyll to form: (A) Oxygen & Glucose (B) Sugar and Starch (C) Oxygen & Starch (D) None

Summative Worksheet 1.

2.

3.

4.

Windmill is a device that uses energy of (A) Blowing air to generate electricity (B) Blowing air to propel sailing yachts (C) Flowing water to generate electricity (D) Flowing water to propel sailing yachts Plants also consume oxygen for respiration similar to animals. It is said that trees should not be cut down in order to maintain the balance of oxygen in the atmosphere because (A) Animals take more oxygen than plants (B) Plants release more oxygen than what they take (C) Animals release more oxygen than what they take (D) Plants recharge the soil with oxygen dissolved in soil Which two components of air comprise 99% of total volume? (A) Nitrogen and dust (B) Nitrogen and oxygen (C) Carbon dioxide and oxygen (D) Nitrogen and carbon dioxide Consider the following statements about air. I. Atmosphere is a thin layer around earth that is composed of air. II. Nitrogen is essential for burning. Air occupies space. Among the given statements: (A) Only I is incorrect (B) Only II is incorrect (C) I & III are incorrect (D) II & III are incorrect

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Which of the following components of air is primarily used by the green plants to make their food? (A) Oxygen (B) Nitrogen (C) Dust particles (D) Carbon dioxide Air is used by the living organisms for respiration. It contributes ii percent to the total composition of air. The information in which alternative completes the given statements? (A)

(C)

i

ii

Oxygen

78

i

ii

Nitrogen 78 7.

(B)

i

ii

Nitrogen 21 (D)

i

ii

Oxygen

21

The energy stored in blowing wind is (A) Responsible for the formation of clouds (B) Used by plants during photosynthesis (C) Used to produce electricity (D) Required to burn objects 8. Which of the following statements about air is incorrect? (A) It cannot be seen. (B) It contains dust particles (C) Moving air is called wind. (D) Water does not contain air. 9. In the absence of air, I. Windmills do not produce electricity II. Birds and insects cannot fly III. Sailing yachts do not move IV. Aeroplanes do not move Among the given statements, (A) Statements I and II are true, while III and IV are false (B) Statements I and II are false, while III and IV are true (C) Statements I, II, III and IV are false (D) Statements I, II, III and IV are true 10. Shakeel observed bubbles when he immerses a cotton ball into a bowl of water. Bubbles appear from cotton because (A) Cotton produces bubbles (B) Cotton cannot dissolve in water (C) Water produces air in the presence of cotton (D) Water occupies the spaces in cotton, thereby releasing air

Air and its Components

57

11. Oxygen and carbon dioxide is cycled in the atmosphere between (A) Animals and mountains (B) Mountains and oceans

16. Plants produce i by the process of ii The information in which alternative completes the given statement? (A) i ii

food combustion

(C) Plants and animals (D) Plants and oceans

(B)

12. It is one of the components of air. It is used by living organisms during the process of respiration and is essential for burning.

(B) Volcanoes

(C) Green plants

(D) Human beings

ii

nitrogen combustion (C)

This component of air is returned to the environment by (A) Rain

i

i

ii

Oxygen photosynthesis (D)

i

ii

dust photosynthesis

13. Carbon dioxide and oxygen is cycled through the 17. There is fine hair and mucus inside the nostrils to prevent i from getting into the ii . environment by the processes of burning or The information in which alternative completes combustion, respiration and photosynthesis. the given statement? I

III

(A)

i

ii

nitrogen respiratory system Burning

II

IV

Respiration

(B)

(A) I and II

(B) II and III

(C) III and IV

(D) IV and I

ii

dust particles respiratory system

Photosynthesis

Carbon dioxide is released during the processes labelled

i

(C)

i

ii

water vapour digestive system (D)

i

ii

14. Which of the following components of air is filtered oxygen digestive system by the fine hair and mucus present in the nostrils 18. Humans release i gas during ii process. during breathing? The information in which alternative completes (A) Dust (B) Nitrogen the given statement? (C) Water vapour

(D) Carbon dioxide

15. Which of the following constituents of air can be seen floating in the air when a beam of sunlight enters a dark room?

(A)

ii

nitrogen respiration (B)

i

ii

carbon dioxide respiration

(A) Nitrogen, oxygen, carbon dioxide (B) Smoke, oxygen, water vapour

i

(C)

(C) Nitrogen, dust, carbon dioxide

i

ii

oxygen

transpiration

i

ii

(D) Smoke, dust, water vapour (D)

water vapour transpiration

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7th Class Chemistry

58 19. Which of the following alternatives contains the names of gases that are incorrectly matched with the processes associated with them? (A)

Gas

Process

Oxygen Respiration (B)

Gas

4.

Process

Among the given statements, (A) Only statement I is incorrect (B) Only statement III is incorrect (C) Both statements I and II are incorrect (D) Both statements II and III are incorrect The given figure shows a pie chart of the constituent gases in the atmosphere. IV III

Carbon dioxide Photosynthesis (C)

II

Gas

Process

Nitrogen Burning I

(D)

Gas

Process

Water vapour Water cycle 20. Which of the following means of transportation uses wind as a source of energy? (A) Bicycle (B) Rickshaw (C) Bullock cart (D) Yacht

5.

HOTS Worksheet 1.

In which alternative are a process and the component of air involved in it correctly matched? (A) Component of the air Process

Oxygen

Water cycle

6.

The portion of the pie chart representing oxygen is labelled (A) I (B) II (C) III (D) IV Which of the following activities cannot be performed in the presence of strong winds? (A) Burning of wood (B) Generation of electricity (C) Movement of sailing yatch (D) Dispersal of seeds and pollens Arunima fixes two small candles of the same size in the middle of two shallow containers labelled I and II. She fills the containers with equal amount of water. She then covers the candle with two inverted glasses of different sizes as shown in the given figure.

(B)

Component of the air

Process

Nitrogen

Photosynthesis

(C) Component of the air

Water vapour

Process Respiration

(D) Component of the air Process

Carbon dioxide 2.

Burning

This atmospheric gas is used by green plants to make food. It is produced by living organisms during respiration. It is also produced when an object is burned. The gas described is (A) Oxygen (B) Nitrogen (C) Water vapour (D) Carbon dioxide 3. Consider following statements regarding nitrogen I. About 3/4th of the atmosphere is made up of nitrogen II. Living organisms use nitrogen for respiration. III. Nitrogen is a part of the photosynthesis process www.betoppers.com

Which of the following observations is Arunima expected to make? (A) Both the candles extinguish at the same time (B) The rise of water level in each container is the same (C) The candle in container II extinguishes before the one in container I. (D) The rise of water level in container II is greater than that in container I.

Air and its Components 7.

59

The given figure shows a pie-chart representing the volume percentages of the main constituent gases in the atmosphere. III II

I

Why do traffic policemen wear masks? (A) To avoid inhaling oxygen through respiration (B) To inhale nitrogen through respiration (C) To avoid inhaling dust and smoke through respiration (D) To inhale carbon dioxide through respiration 12. Energy of i is used in ii to produce electricity directly. The statement is completed by the information in alternative

Which constituent gas is represented by portion II i ii (A) in the pie-chart? (A) Oxygen (B) Nitrogen the Sun sawmills (C) Water vapour (D) Carbon dioxide i ii (B) 8. Radha wakes up in the morning and observes a beam of sunlight entering her room from a tiny hole the Sun windmills in the window. She sees some tiny shining particles, i ii (C) which appear to dance merrily around in air. These particles show that air contains blowing air sawmills (A) Dust (B) Oxygen i ii (D) (C) Water vapour (D) Carbon dioxide blowing air windmills 9. Consider the following statements regarding carbon dioxide. 13. Carbon dioxide is a component of air. It is used by I. It is produced when an object is burnt. (A) Bees to produce honey II. It is consumed by living organisms during (B) Fishes during swimming respiration. (C) Animals to make their food III. It is released by green plants during (D) Green plants to make their food photosynthesis. 14. The gases released by a tree during photosynthesis Among the given statements, and by an animal during respiration, are indicated (A) Only I is incorrect by the arrows in the figure. (B) Only III is incorrect (C) Both I and II are incorrect (D) Both II and III are incorrect 10. On a hot evening, Mutum sits under a big tree. After sometime, he feels fresh and cool. Mutum feels fresh because the tree releases The gases marked as I and II are (A) Nitrogen (B) Oxygen (A) Both oxygen (C) Glucose (D) Smoke (B) Both carbon dioxide 11. Traffic policemen manning busy intersections wear masks while controlling the traffic. (C) Oxygen and carbon dioxide respectively (D) Carbon dioxide and oxygen respectively 15. This component of air is released by animals during respiration and is consumed by plants through the process of photosynthesis. This component of air is (A) Dust (B) Smoke (C) Carbon dioxide (D) Water vapour

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7th Class Chemistry

60 16. We can see water vapour that is present in the air, when it condenses on a (A) Hot surface (B) Cold surface (C) Rough surface (D) Smooth surface 17. Which of the following statements about nitrogen is correct? (A) It forms a small portion in the composition of air. (B) It forms the maximum portion in the composition of air. (C) It is used by living organisms during respiration. (D) It is used by the gr een plants during photosynthesis. 18. Oxygen in the air is used by living organisms during (A) Respiration (B) Decomposition (C) Collection of water (D) Production of food 19. When sunlight is allowed to enter through a small hole in a dark room, a certain component of air, X, can be seen floating in the air in the form of particles. This component X of air is (A) Dust or smoke (B) Oxygen or nitrogen (C) Dust or oxygen (D) Nitrogen or smoke 20. When wood is burnt, it produces a certain gas X that is a component of air. This gas when inhaled in large amounts causes suffocation. The gas X is identified to be (A) Carbon dioxide (B) Water vapour (C) Oxygen (D) Nitrogen

IIT JEE Worksheet I. 1.

Single Correct Answer Type

The component of air that is necessary for burning a candle is (A) Dust (B) Smoke (C) Vapour (D) Oxygen 2. Which of the following components of air is primarily used by the green plants to make their food? (A) Oxygen (B) Nitrogen (C) Dust particles (D) Carbon dioxide 3. Shakeel observed bubbles when he immerses a cotton ball into a bowl of water. Bubbles appear from cotton because (A) Cotton produces bubbles (B) Cotton cannot dissolve in water (C) Water produces air in the presence of cotton (D) Water occupies the spaces in cotton, thereby releasing air www.betoppers.com

4.

We can see water vapour that is present in the air, when it condenses on a (A) Hot surface (B) Cold surface (C) Rough surface (D) Smooth surface 5. Carbon dioxide is a component of air. It is used by (A) Bees to produce honey (B) Fishes during swimming (C) Animals to make their food (D) Green plants to make their food 6. This component of air is released by animals during respiration and is consumed by plants through the process of photosynthesis. This component of air is (A) Dust (B) Smoke (C) Carbon dioxide (D) Water vapour 7. When wood is burnt, it produces a certain gas X that is a component of air. This gas when inhaled in large amounts causes suffocation. The gas X is identified to be (A) Carbon dioxide (B) Water vapour (C) Oxygen (D) Nitrogen 8. Oxygen in the air is used by living organisms during (A) Respiration (B) Decomposition (C) Collection of water (D) Production of food 9. Plants also consume oxygen for respiration similar to animals. It is said that trees should not be cut down in order to maintain the balance of oxygen in the atmosphere because (A) animals take more oxygen than plants (B) plants release more oxygen than what they take (C) animals release more oxygen than what they take (D) plants recharge the soil with oxygen dissolved in soil 10. Which of the following means of transportation uses wind as a source of energy? (A) Bicycle (B) Rickshaw (C) Bullock cart (D) Yacht

II. Multiple Correct Answer Type 11. Identify the true statement from the following: (A) The composition of air changes from place to place. (B) Air occupies space and has weight. (C) The percentage of nitrogen in air, by volume 28.03% (D) The temperature is high, the volume to water vapour increases in air.

Air and its Components

61

18. Statement I: Air has weight, it exerts pressure 12. Identify the true statement from the following: on earth surface. (A) Compressed air is used in the brake system Statement II: Air pressure is called atmospheric for stopping a moving train. pressure. (B) Compressed air is used for digging. (A) Both Statements are true, Statement II is the (C) The wind mills are working through wind flow. correct explanation of Statement I. (D) Air helps for the movement of boats, gliders (B) Both Statements are true, Statement II is not and parachutes. correct explanation of Statement I. 13. Identify the correct statement: from the following: (A) Air has weight (B) Air exerts pressure as earth surface (C) Torricelli a scientist designed cistern barometer. (D) Barometer is used to measure the weight of air. 14. Which are the commonly used fuels for heating. (A) Wood (B) Coal (C) LPG (D) Kerosene oil 15. The green house gases are: (A) Carbon dioxide (B) Water vapour (C) Methane (D) None

(C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true. 19. Statement I: Mountaineers take oxygen cylinders with them. Statement II: In high attitudes the density of air decreases it becomes difficult to live there. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true. III. Reasoning Type 20. Statement I : The temperature in big cities is higher than in the country side. 16. Statement I : Air is a colourless gaseous substance Statement II : The heat radiations are reflected back in the cities due to the presence of CO2. Statement II : Air has weight and exerts pressure in all directions. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (B) Both Statements are true, Statement II is not (C) Statement I is true, Statement II is false. correct explanation of Statement I. (D) Statement I is false, Statement II is true. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true. IV. Paragraph Type 17. Statement I: The carbon monoxide turns lime Any cheap material which burns in air or oxygen water milky. with the release amount of heat energy and high Statement II: Carbon dioxide evolves from the energy is called fuel. The process of burning of fuel surface of the earth like the death valley in Java. in the air, with the release of large amount of heat energy and light energy is called combustion. (A) Both Statements are true, Statement II is the correct explanation of Statement I. 21. ________ is used in thermoelectric power stations for raising steam. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (A) Wood (B) Coal (C) Statement I is true, Statement II is false. (C) LPG (D) CNG (D) Statement I is false, Statement II is true. 22. _________ fuel is used for illumination in petromax lamps. (A) Kerosene oil (B) Coal (C) CNG (D) LPG

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7th Class Chemistry

62 23. ________ is contain methane gas and used as a fuel in buses. (A) Coal (B) kerosene oil (C) CNG (D) LNG 24. The food materials break down in our digestive system to form: (A) Simple compounds (B) Complex compounds (C) Both (A) and (B) (D) Similar compounds 25. Our food mainly consists compounds of. (A) Starches (B) Sugars (C) Fats (D) All the above 26. The exhaled air contains more as compared to inhaled air. (A) Carbon dioxide (B) Water vapour (C) Oxygen (D) Both (A) & (B) 27. __________ is use for preventive against pest. (A) Pesticides (B) Fungisides (C) Herbisides (D) None 28. ____________ are used for more yield of crops. (A) Synthetic fertilizer (B) Manure (C) Biomass (D) None 29. The sounds above the audible range are called: (A) Green house effect (B) Water pollution (C) Radiation (D) Sound pollution

V. Integer Type 30. Height of mercury column near the sea-level is usually ______cms. 31. The percentage of carbon dioxide in air is:

VI. Matrix Matching 32. Column-I Composition of air a) Nitrogen b) Oxygen c) Carbon dioxide d) Noble gases

Column-II Percentage 1) 20.9% 2) 0.03% 3) 0.94% 4) 28.9% 5) 78.03% 33. Column-I Column-II a) Ink filler 1) To lifting water from walls b) Air pump 2 To draw kerosene from tin c) Kerosene pump 3) To fill air in bladders d) Lift pump 4) To draw ink form bottle 5) drying wet clothes www.betoppers.com

34. Column-I a) Barometer

Column-II 1) Vacuum is developed above the surface of mercury b) Torricellian vacuum 2) Pressure increases of 2.54 cms c) Height of 272.7 mts 3)Pressure decrease of from the sea level 2.54 cms. d) Depth of 272.7 mts 4) Atmospheric fromsea level pressure 5) Mercury column 35. Column-I Column-II Cause Effect a) Wind blows hard 1) High amount of ash and sulphur dioxide b) The forest fire takes 2) Large amount of dust place and sand particles carried out. c) Pollination 3) Large amount of smoke and carbon monoxide d) Volcanoes erupt 4) Causes allergy 5) Carbon monoxide, sulphur dioxide and nitrogen oxide. 36. Column-I Column-II a) Catalytic converters 1) Capable of removing harmful gases b) Growing more trees 2) To minimise the smoke and ash entering the atmosphere. c) Electric precipitators 3) Causes air pollution d) Pesticides 4) Remove harmful gases present in the exhaust. 5) Chulha 

By the end of this chapter, you will be understand

   

Dual nature of hydrogen Discovery of hydrogen Occurrence of hydrogen Preparation of hydrogen

   

Physical Properties of hydrogen Chemical Properties of hydrogen Test for hydrogen Uses of hydrogen

1. Introduction Hydrogen was the first element to be formed, after the universe was formed millions of years ago. It is the lightest and simplest atom known to man. It is a colourless, odourless and tasteless gas that weighs about one-fourteenth as much as an equal volume of air. Hydrogen is the element that makes the sun shine. A huge amount of energy is given out when the nuclei of atoms of hydrogen join up or fuse together in the Sun’s interior. This process of nuclear fusion accounts for the light and heat given out by the sun. Symbol

H

Atomic weight

1.008

Atomic number

1

Electronic Configuration Valency

K 1

1

Dual Nature of Hydrogen Hydrogen has the simplest electronic configuration of ‘one’ and hence it: a) Either loses one electron, behaving like

b)

electropositive alkali metals. Eg: H – 1 e–  H+, Li – 1 e–  Li+, Na – 1 e–  Na+ Gains one electron, behaving electronegative halogens. Eg: H + 1e–  H–, F + 1 e–  F–, Cl + 1 e–  Cl–.

Robert Boyle prepared hydrogen in 1672, by treating iron with sulphuric acid, but was unable to establish its elementary character. The credit of discovery of hydrogen goes to Henry Cavendish, who prepared it by the action of dilute hydrochloric acid, with zinc in 1766. He not only established its elementary character, but also proved that, when hydrogen is burnt in air it forms water. Because of its property of water formation, it was named hydrogen by Lavoisier in 1783, as hydrogen means water former in Greek language.

In Volcanic gases

Found in minute traces in the earth’s crust (0.98%)

Free State

Occurrence of Hydrogen on earth

It is present in acids and alkalis (NaOH, HNO3, etc)

Plants and animal tissues are made up of compounds of hydrogen along with carbon, oxygen and nitrogen

like

Discovery of Hydrogen

2. Occurrence Found in minute traces in the earth’s atmosphere (0.01%)

Chapter – 47

Hydrogen

Learning Outcomes

Combined State

It is also found in petroleum products, natural gas, coal, etc.

One-ninth of the mass of water is hydrogen

It is present in proteins, hydrocarbons, alcohols, amines, vitamins & carbohydrates

7th Class Chemistry

64

3. Preparation General Methods of Preparation i) From Cold Water:

ii)

Metal

Cold water

Metal hydroxide

1) 2K +

2H2O

2KOH +

Hyd Reason why method is not preferred rogen H2 • The reaction is violent and exothermic. • The liberated heat ignites the hydrogen.

2) 2Na + 2H2O

2NaOH +

H2

• The reaction is violent but comparatively less than potassium. • Hydrogen is difficult to collect.

3) Ca+

Ca(OH) 2 +

H2

• The reaction is slightly vigorous but calcium is comparatively more expensive.

2H2O

From Boiling Water / Steam:

Metal (heated)

Boiling water / steam

Metal oxide

Hydrogen

H 2O 

MgO +

H2

1) Mg +

2) 2Al +

3H2O 

Al 2O3 +

3H2

3) Zn +

H 2O 

ZnO +

H2

4) 3Fe +

4H2O

Fe 3O4 +

4H2

Acid [dil.]

Salt

Hydrogen

1) Mg +

2HC l 

MgCl 2 +

H2

2) 2Al +

3H2SO4 

Al 2(SO4)3+

3H2

3) Zn +

H2SO4 

ZnSO4 +

H2

4) Fe +

2HC l 

FeCl2 +

H2

Observations •

Mg, Al, Zn, Fe do not react with cold water to liberate hydrogen.

•

Magnesium reacts with boiling water liberating hydrogen but the reaction is slow.

•

When steam is passed over heating Mg, Al, Zn and Fe they form the corresponding oxide and hydrogen.

•

Reaction of iron with steam is reversible

iii) From Acids: Metal

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Observations K, Na and Ca react with dil. H2SO4 or dil. HCl but the reaction is highly explosive and practically not feasible. Mg, Al, Zn and Fe react with dil. HCl liberating hydrogen and forming respective salt.

Hydrogen

65

Note: 1)

Nitric acid in the dilute form is not used in the preparation of hydrogen from metals. HNO3 is a powerful oxidising agent and the nascent oxygen formed on its decomposition oxidises the hydrogen to water. Magnesium and Manganese how ever, react with very dilute HNO3 at the low temperatures liberating hydrogen. Since, the oxidising action of the acid is much reduced due to dilution. Lead cannot be used in the preparation of hydrogen using dilute acids. Lead reacts with dil. HCl and dil. H2SO4 forming an insoluble coating of lead chloride (PbCl2) and lead sulphate (PbSO4) respectively and hence further reaction comes to a stop.

2)

iv) From Alkalis: Metal (Powdered)

Alkali (conc. sol.)

1) Zn

+

2NaOH

  

Na 2ZnO2

+ H2

2) Zn

+

2KOH

  

K2ZnO2

+ H2

3) Pb

+

2NaOH

  

Na 2PbO2

+ H2

2NaAlO2

+ 3H2

2KAlO2

+ 3H2

Salt

 4) 2Al + 2NaOH + 2H2O  

5) 2Al + 2KOH

 + 2H2O  

Principle of Preparation: Hydrogen is prepared in the laboratory by the action of dilute a c i d s like dil HCl or dil H2SO4 on zinc. Reactants: Granulated zinc and dil. Hydrochloric acid. Procedure: Granulated zinc is placed at bottom of the Woulfe’s bottle and hydrochloric acid [or sulphuric acid] is added slowly from the thistle or dropping funnel. Hydrogen gas evolves with brisk effervescence. Equation: Zni + 2HCl(dil.)  ZnCl2 + H2(g)  Collection: The hydrogen gas is collected by the downward displacement of water. dil.HCl

H2

Observations Zn, Pb and Al on boiling with conc. alkali solutions, i.e., NaOH or KOH react to form their soluble salts and liberate H 2.

Precautions: Hydrogen forms explosive mixture with air. Following precautions should be taken to avoid its leakage. i) The complete apparatus should be made air tight. ii) The lower end of the thistle funnel should be below the level of the dilute acid in the flask. Purification: The hydrogen evolved contains impurities such as NO2 , SO2, CO2 , H2 S, etc. It is passed through apparatus like three washer bottles and a u-tube, which will absorb the impurities. Pure and dry hydrogen

Impure hydrogen

Thistle funnel

Pb(NO3) 2sol.

AgNO3 sol.

Woulfe’s bottle

KOH sol.

Anhydrous CaCl2

Hydrogen gas Beehive shelf

Acid layer Granulated Zinc

Water

(1)

(2)

(3)

The constituents in each apparatus and the impurity removed by each apparatus is shown in the following chart.

Laboratory preparation of hydrogen by the action by dil.HCl on granulated zinc

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7th Class Chemistry

66 Apparatus

Composition

Impurities absorbed

Washer bottle (1)

AgNO 3 solution

As H 3(Arsene) and PH 3 (Phosphine)

Washer bottle (2)

Pb(NO3)2 solution

H 2S (Hydrogen Sulphide)

Washer bottle (3)

KOH solution

NO2, SO 2 and CO3

U – tube

Anhydrous CaCl2

Moisture (H2O)

Metals which are not preferred for the preparation of Hydrogen from Acids: Metal

Reason

Metal

K

It is expensive and reacts violently.

Na

It is expensive and reacts violently.

Ca

It is expensive and the rate of production of hydrogen is so fast that it is difficult to collect ti.

Fe

Mg

It is expensive and the rate of production hydrogen is so fast that it is difficult to collect it.

Pb

Reason Al is covered with a layer of Al2O 3 which does not allow the acids to r eact.

Al

Reacts slowly, hence heat is required. Due to the impurities in iron, large amount of H2S and SO 2 are also f ormed. Reacts slowly with acids to form insoluble salts PbCl2 and PbSO4 which slows down the reaction of lead with the acid.

Metals which are not preferred for the preparation of Hydrogen from Acids:

Industrial Method I.

Bosch Process

Reaction

Step-1

Step - II

Production of water gas

Reduction of steam to hydrogen by carbon monoxide: 0

0

1000 C C  H2 O    CO  H2  

C oke 

st ea m 

450 C  CO2  2H2  CO  H2  H2O  Fe O Wa ter g as

Water g as

st ea m 

2

3



Reactants

Hot coke and steam.

Water gas and excess steam.

Temp

Around 10000C.

Around 450 0C.

Catalysts

--

Fe2O 3 and promoter Cr2O 3 ( Chromic oxide ).

Nature of reaction

Endothermic.

Exothermic.

Process

Passage of steam over hot coke.

Excess steam is mixed with water gas and passed over a catalyst and at elevated temperatures.

Step-3

Separation of CO2 and unreacted CO from the above mixture. (a) Removal of CO 2: By dissolving mixture in water under pressure ( 30 atm) and KOH

 2KOH + CO

2

 K 2CO3 + H2 O

(b) Removal of CO: By dissolving mixture in ammonical cuprous chloride solution.

 CuCl + CO + 2H O  CuCl.CO.2H O  2

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2

Hydrogen

67

II. By Electrolysis i)

By Electrolysis of Water: When electric current is passed through acidulated water (water containing sulphuric acid), it splits into hydrogen and oxygen as shown in the reaction.   2H + O 2H 2 O   2 2

ii)

The process of electrolysis is carried out in an apparatus called Hoffman’s Voltameter. The voltameter is fitted with platinum electrodes, one of which is connected to the positive terminal of the battery and is called an anode, and the other is connected to the negative terminal and is called a ‘cathode’. The apparatus setup is shown in the figure.

Current enters water through anode and leaves through the cathode, decomposing water into hydrogen and oxygen. The hydrogen gets collected at cathode and the oxygen at anode. By Electrolysis of Brine: In the electrolysis of brine [sodium chloride solution], very pure hydrogen is obtained as a by - product, which is used for the manufacture of sodium hydroxide and chlorine.

NaCl

 aqueous solution 

electric  Na + + Cl current

electric H 2 O  H + + OH  current Along with sodium, some amount of hydrogen gas is also formed at the cathodes.

2H+ + 2e  H2 Along with sodium, some amount of hydrogen gas is also formed at the cathodes. Platinum electrodes III. From Natural Gas Acidulated Natural gas consists mainly of methane (CH4). water – + When natural gas is mixed with steam and passed over nickel and heated to 900°C, – + methane in it is oxidized to form hydrogen and Electrolysis of water carbon dioxide. CO2 is removed by pumping Acidulated water is poured into the the mixture in to water. CO2 dissolves in water voltammeter. Over each electrode, a test tube and hydrogen gas is collected in gas holders. which is filled with acidulated water is inverted. Electric current is passed through the water Nickel CH 4  2H 2 O   4H 2 + CO 2 900°C via the electrodes.  Methane   Steam  Hydrogen

Oxygen

Formative Worksheet 1.

Match the points pertaining to the occurrence and discovery of hydrogen in column I with the concluding facts in column II. Column-I

Column-II

1.

Lavoisier in 1783 established the name ‘hydrogen’

p.

The atmosphere around the sun and stars

2.

Hydrogen does not occur

q.

Water

3.

Hydrogen is present in traces in

r.

Meaning ‘water producer’.

4.

2.

A compound, one ninth by mass of which is s. In the free state on earth. hydrogen in the combined state is (A) 1 - r, 2 - s, 3 - p, 4 - q (B) 1 - s, 2 - p, 3 - q, 4 - s (C) 1 - p, 2 - q, 3 - s, 4 - r (D) 1 - q, 2 - p, 3 - r, 4 - s Match the following:

1.

Column-I Robert Boyle

a.

2. 3.

Henry Cavendish Lavoisier

b. c.

(A) 1 – b, 2 – c, 3 – a

Column-II Naming of hydrogen

Henry Cavendish Discovery of hydrogen and elementary character of hydrogen (B) 1 – a, 2 – c, 3 – b (C) 1 – c, 2 – b, 3 – a (D) 1 – b, 2 – a, 3 – c www.betoppers.com

7th Class Chemistry

68 3. 4.

5. 6.

7.

8.

9.

2K + 2H2O  A + H2 ; Mg + B  MgO + H2 ;Identify A & B represents. With which of the following, Zn when reacted does not liberate hydrogen? (A) Cold water (B) Dil. HCl (C) Dil. H2SO4 (D) Hot NaOH (20%) Mg reacts with very dilute HNO 3 at low temperature. Give reason. Assertion :Nitric acid is not used for preparing hydrogen from metals. Reason : Nitric acid is a strong oxidising agent and forms oxides of nitrogen rather than hydrogen. (A) Both assertion and reason are correct and reason is the correct explanation of assertion. (B) Both assertion and reason are correct but reason is not the correct explanation of assertion. (C) Assertion is correct and reason is incorrect. (D) Assertion is incorrect and reason is correct. Assertion : In the laboratory preparation of hydrogen, granulated zinc is preferred to pure zinc for the reaction with dilute acid. Reason : As granulated zinc is commercial, obtained from molten zinc, it may contain traces of impurities which are having a slight catalysing effect on the reaction. (A) Both assertion and reason are correct and reason is the correct explanation of assertion. (B) Both assertion and reason are correct but reason is not the correct explanation of assertion. (C) Assertion is correct and reason is incorrect. (D) Assertion is incorrect and reason is correct. Statement A: Hydrogen gas obtained in the laboratory has a peculiar smell. Statement B: Due to absence of the impurities in hydrogen gas, it produces peculiar smell. (A) ‘A’ is true, ‘B’ is false. (B) ‘A’ is false, ‘B’ is true. (C) Both ‘A’ and ‘B’ are true. (D) Both ‘A’ and ‘B’ are false. Pure hydrogen is prepared by passage of the gas through various solutions which respectively absorb each impurity. Match the impurity with the solution which absorbs it.

Impurity A. Arsine [AsH 3 ] B. Phosphine [ PH 3]

p) Potassium hydroxide solution

C. Hydrogen sulphide [H2 S] q) Fused calcium chloride D. Nitrogen dioxide [NO 2 ] r) Silver nitrate E. Sulphur dioxide [SO 2] solution F. Moisture s) Lead nitrate solution

10. Assertion : No flame should be brought near hydrogen gas. Reason : Large volume of hydrogen gas in air explodes vigorously. (A) Both assertion and reason are correct and reason is the correct explanation of assertion. (B) Both assertion and reason are correct but reason is not the correct explanation of assertion. (C) Assertion is correct and reason is incorrect. (D) Assertion is incorrect and reason is correct. 11. In the following sequence of reacting, identify X, Y, W and Z.  Red Hot Coke     X  Y + 770K     Steam Cold water  W g   W + Z  Pressure

Conceptive Worksheet 1.

2.

3.

4.

5.

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Removed by

The stars, including sun are mainly composed of: (A) Oxygen (B) Hydrogen (C) Carbon dioxide (D) Nitrogen dioxide Identify the element by studying its properties. (i) It is the lightest known element. (ii) It is known to be inflammable in air as the gas burns when kindled. (A) Nitrogen (B) Carbon dioxide (C) Argon (D) Hydrogen Choose the correct statement: (A) Every 1g of water contains 9g of Hydrogen. (B) Hydrogen exists freely in the atmosphere. (C) In combined state, hydrogen occurs as water. (D) The chief constituent of sun and stars in hydrogen. The most abundant element in the universe is: (A) Potassium (B) Oxygen (C) Hydrogen (D) Nitrogen Which of the following is the lightest gas? (A) Nitrogen (B) Helium (C) Oxygen (D) Hydrogen

Hydrogen

69

6.

Metal hydride on treatment with water gives: 12. Hydrogen can be prepared by : (A) H2O2 (B) H2 O (C) Acid (D) Hydrogen I) By the action of water or steam on metals. 7. Hydrogen combines with other elements by: II) By the action of dilute HCl or dilute H2SO4 on (A) Losing an electron active metals. (B) Gaining an electron III) By the action of concentrated alkali solution on (C) Sharing an electron metals like zinc, aluminium, lead and tin. (D) Losing, gaining and sharing of an electron. IV) By the electrolysis of water. 8. Which of the following metal is not used for (A) Only I and II (B) Only II and III preparing hydrogen from HCl (or) H2SO4? (C) Only III and IV (D) All the above (A) Mg (B) Fe (C) Pb (D) Zn 13. Zn + H2SO4  A + B; Identify A and B. 9. Hydrogen from ‘HCl’ can be prepared by using: A B (A) Cu (B) P (C) Mg (D) Hg (A) Zinc sulphate Hydrogen 10. Metals like Potassium, Sodium and Calcium react (B) Zinc sulphide Oxygen with acids to form their respective salts and hydrogen (C) Hydroxide Oxygen gas, but the reaction is: (D) Zinc oxide Hydrogen (A) Stable (B) Reversible 14. In Bosch’s process, which gas is utilised for the (C) Explosive (D) non-volatile production of hydrogen gas? 11. Which of the following cannot be used for the (A) Producer gas (B) Water gas preparation of H2? (C) Coal gas (D) All (A) Zn + HCl (dil)  (B) NaH + H2O  (C) Zn + HNO3 (dil.)  (D) All

4. Physical Properties Property Nature

Description • Pure hydrogen is colourless , odourless and tasteless gas • Impure hydrogen has fishy smell, because of phosphine and arsine gases as an impurity. • Nonpoisonous.

Density Solubility Boiling point

Hydrogen is lightest element. It is almost 14.6 times lighter than air. Hydrogen is practically insoluble in water. Liquid hydrogen boils at – 2530 C.

Freezing point: Liquefaction

Solid hydrogen melts at – 259.40 C. Hydrogen is a difficult gas to liquefy. It liquefies at a temperature of – 243 0 C at a pressure of 20 atm.

Adsorption or occlusion

The property by virtue of which certain substances adsorb gases on their outer surface is called adsorption. Ex: Palladium, gold, nickel, platinum.

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7th Class Chemistry

70

5. Chemical Properties a. Combustibility Hydrogen is a combustible gas, but it does not support combustion. In air or oxygen, it burns silently, with a very pale blue flame. However, if hydrogen is premixed with air or oxygen, it explodes with a pop sound, because of spontaneous combustion.

b. Action with Litmus Hydrogen is neutral towards litmus solution.

c. Action with non-metals (i)

Oxygen: Hydrogen burns silently in oxygen with a pale blue flame.

2H 2  O2   2H 2 O (ii) Chlorine: Equal volumes of H2 and Cl2 react slowly in diffused sunlight and explosively in direct sunlight. H2  Cl2   2HCl (iii) Nitrogen: Nitrogen reacts with hydrogen to form ammonia. N2  3H2   2NH3 ; Temp - 450 – 5000C, pressure: 200 – 900 atm, catalyst – finely divided iron and promoter is molybdenum. (iv) Sulphur: H2  S   H2 S

d. Action with Metals Most of the metals do not react with hydrogen. However, when dry hydrogen gas is passed over heated Na, K or Ca, they react to form their respective hydrides.  2K + H2   2KH 

2Na + H2   2NaH  Ca + H2   CaH2 The hydrides further react with cold water forming hydrogen.

CaH2 + 2H2O   Ca(OH)2 + 2H2

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e. Reducing properties of Hydrogen When hydrogen gas is passed over heated oxides of the less active metals such as zinc, iron, lead and copper, it reduces them to free metals and forms water. Metal oxide + Free metal +

Hydrogen Water

  

  

Zn +

H2O

Fe2O3 + 3H2



 

2Fe +

3H2O

PbO + H2

  

Pb +

H2O

ZnO + H2

 CuO + H2 H2O   Cu + Note: i) In the above reactions, the hydrogen is a reducing agent and hence, is oxidized to water. ii) In the above reactions, the metallic oxides are oxidizing agents and hence, are reduced to free metals. Hydrogenation – involves addition of hydrogen to organic compounds: Addition of hydrogen to organic compounds in the presence of a catalysts like platinum or nickel is

called hydrogenation. C2 H 6

H2C = CH2 + H2  

6. Test for Hydrogen Test - Observation Colour, odour, nature Colourless, odourless, neutral gas, lighter than air and density Combustibility of a) Pure hydrogen Burns quietly in air with a pale blue flame forming water as the only product. b) Hydrogen - air moisture Burns with a characteristic ‘popsound’

 2H 2  O 2  2H 2 O   

Hydrogen

71

7. Uses of Hydrogen As a fuel: It is present in coal gas ( 45 %) and water gas ( 50%) by volume. It produces a large amount of energy with the formation of water. It is an excellent non- polluting fuel. For cutting and welding purposes: The flame of hydrogen and oxygen can produce a temperature of 2800 0C. This flame is used for cutting and welding metals.

U S E S

For meteorological purposes: To study weather conditions. O F For the manufacture of industrial chemicals: Used extensively in the manufacture of NH 3 and HCl.

H Y D R O G E N

In hydrogenation reactions: Used in hydrogenation of oil [ ghee preparation ] and hydrogenation of coal.

In extraction of metals: Hydrogen acts as a reducing agent and reduces metallic oxides to metals. For making artificial petroleum: The artificial petroleum can be fractionally distilled so as to obtain various useful fractions like petrol, kerosene oil, diesel, etc.

Special Uses of Hydrogen Conversion of Oil to Ghee: Vegetable oils are hydrogen deficiently organic compounds. Oils are liquids at room temperature. Oils can be saturated with hydrogen and converted into vanaspati ghee. This is called hydrogenation. It is carried out by passing hydrogen through oil heated at 200°C, under pressure in the presence of finely divided nickel as catalyst.

Equation : CH 2 .O.OCC17 H33

CH 2 .O.OCC17 H 35

|

| Ni, 180°C

CH.O.OCC17 H33  3H 2  

CH.O.OCC17 H35

|

|

CH 2 .O.OCC17 H33

CH 2 .O.OCC17 H35

Thiolein

Tristearin

 Oil M.P.  5° C 

 Fat M.P.71°C 

Petrol from Coal with the help of Hydrogen: Petroleum is a mixture of compounds containing carbon and hydrogen. Some of these compounds can also be obtained by combining coal (carbon) with hydrogen. Hydrogen is bubbled through a suspension of powdered coal in heavy oil. Carbon from coal combines with hydrogen to give artificial petroleum, which on fractional distillation gives petrol, diesel, kerosene etc. Hydrogen – An efficient fuel: 1) Hydrogen has high heat of combustion. (Calorific value) 2) Hydrogen on combustion forms only water and no harmful gases. For the above reasons, hydrogen is a very efficient non - polluting fuel. The prominent hydrogen fuels are coal gas (H2 + CH4 + CO) and water gas (CO + H2). Liquid hydrogen is a good rocket fuel, as it occupies very little space. www.betoppers.com

7th Class Chemistry

72

Formative Worksheet 12. Match the following:(Select from (p, q, r) options given against each property). Property

P

Q

R

(A) Comparative density

1.1 times heavier than air

as heavy as air

14.4 times less dense than air.

(B) Solubility in water

fairly

Highly

slightly soluble

(C) Liquefaction

easy to liquefy

difficult to liquefy

(D) Nature

Acidic

Basic

13. Assertion : Hydrogen is used for filling balloons. Reason : Hydrogen is lighter than air. A balloon filled with hydrogen rises in the air and drifts in the wind. (A) Both assertion and reason are correct and reason is the correct explanation of assertion. (B) Both assertion and reason are correct but reason is not the correct explanation of assertion. (C) Assertion is correct and reason is incorrect. (D) Assertion is incorrect and reason is correct. Diffused sun light 14. H2 + Cl2   2HCl. Choose the correct statements for the above reaction. (A) Chlorine is a greenish yellow gas. (B) If the above reaction is exposed to direct sunlight, a blinding flash takes place. (C) The mixture of gas turns colourless, due to formation of hydrogen chloride. (D) All the statements are correct. 15. Statement A: Combustion of hydrogen is a highly exothermic reaction, results in formation of water. Statement B: Liquid hydrogen is polluting and it is not easy to store. (A) ‘A’ is true, ‘B’ is false. (B) ‘A’ is false, ‘B’ is true. (C) Both ‘A’ and ‘B’ are true. (D) Both ‘A’ and ‘B’ are false. 16. Hydrogen reduces : (by removing O) (i) ZnO to Zn (ii) S to H2S (iii) Fe2O3 to Fe (i) (ii) (iii) (A) False False True (B) True False True (C) True False False (D) False True True

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Neutral to litmus

17. Match the statements in column A with those in column B. Column A Column B 1. A metal used in p Lead converting vegetable oils to vegetable ghee. 2.

A flame used for cutting q and welding purpose

Hydrogen

3.

A gas used in filling weather observation balloons

Sodium hydroxide

r

4.

An alkali which reacts s Nickel with aluminium to form hydrogen. 5. A metal which does not T Oxyreact with dil. Sulphuric hydrogen. acid. 18. Hydrogen reduces certain metallic oxides to free metals. Give an equation of the following reductions. a) Black oxide formation b) Yellow amphoteric oxide formation c) Formation an oxide of iron

Conceptive Worksheet 15. Which one of the following is true for the physical properties of hydrogen? (A) Lightest known gas. (B) Almost soluble in water. (C) 14.6 times lighter than air. (D) Has characteristic odour. 16. The adsorption of hydrogen by platinum is known as: (A) Hydrogenation (B) Dehydration (C) Occlusion (D) Reduction 17. Which of the following gas is insoluble in water? (A) SO2 (B) NH3 (C) H2 (D) CO2

Hydrogen

73

18. Which of the following pairs of elements will react 5. to give a gas which dissolves in water to form an acid? (A) Hydrogen and oxygen (B) Hydrogen and chlorine (C) Hydrogen and nitrogen (D) All the above 19. Which of the following noble gas is next preferred to hydrogen for filling the balloons? (A) Ar (B) kr (C) Xe (D) He 20. With which of the following elements will hydrogen 6. react to give a gas that smells like rotten eggs? (A) O2 (B) Cl2 (C) N2 (D) S 21. The process of removing oxygen from the compounds containing oxygen is called: 7. (A) Oxidation (B) Synthesis (C) Reduction (D) Displacement 22. Hydrogen removes metals from: (A) Metal sulphates (B) Metal oxides (C) Metal nitrates (D) Metal sulphides

If a burning splinter is introduced into the mixture of hydrogen and air. It is observed that the: (i) The flame of splinter goes off. (ii) The gas explodes with a sharp pop sound and burns near the mouth of the cylinder. (i) (ii) (A) False False (B) True False (C) False True (D) True True Hydrogen can be prepared by mixing steam and water gas at 500°C in the presence of Fe3O4 and Cr2O3. This process is called. (A) Nelson process (B) Serpeck’s process (C) Bosch process (D) Parke’s process Which of the following statements is correct? (A) Hydrogen is an element which supports combustion. (B) Hydrogen is an element with colour and odour. (C) Hydrogen is an element which makes the sun shine. (D) All statements are incorrect. ummative orksheet 8. The ratio of volumes of hydrogen and oxygen in Statement I: The process of combination of two H2O is: nuclei of hydrogen to form a bigger nucleus of helium (A) 4:1 (B) 3:1 (C) 2:1 (D) 8:1 is called nuclear fusion. 9. Vegetable oils react with hydrogen in the presence Statement II: Nuclear fusion is not accompanied of catalyst (like nickel) to form solid fats. S u c h by the release of heat. addition of hydrogen is called: (A) Statement II only is true. (A) Hydrolysis (B) Hydrocatalysis (B) Statement I is true but II is false. (C) Hydrocatenation (D) Hydrogenation (C) Statements I and II are both false. 10. Hydrogen is used to produce an oxyhydrogen flame. (D) Statements I and II are both true. The temperature of oxyhydrogen flame is The reactive metals like sodium, magnesium, zinc around: or iron displace I from II . (A) 5000°C (B) 4000°C I II (C) 2800°C (D) 500°C (A) Carbon dioxide Distilled water 11. The suitable conditions for the manufacture of (B) Oxygen Salt water ammonia during Haber’s process are: (C) Hydrogen Water Temperature Pressure (D) Nitrogen Saline water (A) 200°C, 20 atm (B) 500°C, 200 atm Identify the correct options related to hydrogen: (C) 100°C, 1 atm (D) 300°C, 100 atm (A) Atomic weight is 1.008 12. Statement (S) : Hydrogen is known to be a clean (B) Valency is one fuel. (C) It is the lightest element Explanation (E) : Hydrogen is used to produce only (D) Hydrogen is the element that makes the sun hydrogen flame. shine. (A) Statement (S) is wrong i (ii) + H Zn + 2NaOH  2 (B) Statement (S) and explanation (E) are both I II incorrect (A) Cooling NaZnO2 (C) Statement (S) is correct but explanation (E) is (B) Boiling Na 2 ZnO2 incorrect (C) Melting Zn(OH)2 (D) Statements (S) and (E) are both correct (D) Freezing ZnO2

S 1.

2.

3.

4.

W

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7th Class Chemistry

74 13. Hydrogen is a reducing agent. It reduces (by adding 3. H): (A) O to H2O (B) Cl to HCl (C) N to NH3 (D) All 14. Which of the following statements are correct? (A) Oxy-hydrogen flame is used in welding and cutting of metal to produce high temperature. (B) Pure hydrogen burns quietly in air with a pale 4. blue flame forming water. (C) Oxy-hydrogen flame has low heat of combustion. (D) All the three statements are correct. 15. Hydrogen resembles in many of its properties with: (A) Halogens (B) Alkali metals (C) Both A and B (D) None of these 16. A reaction in which a metallic oxide loses its oxygen to form pure metal is called (p) reaction and the property of hydrogen is called its (q) property. (p) (q) 5. (A) Reducing Oxidation (B) Oxidising Reducing (C) Oxidation Oxidising (D) Reduction Reducing

2.

  2H  + O  36 grams of H O 2H 2O   2 2 2 is subjected to electrolysis. Find the number of atoms of hydrogen and oxygen liberated at STP. And also find the mass of hydrogen and oxygen formed at STP. Name the following: a) The element that reacts violently with water at room temperature. b) A hydride of divalent metal. c) A metal which cannot be used for preparation of hydrogen using dilute acids. d) The salt formed, when aluminium reacts with potassium hydroxide, during the preparation of hydrogen form alkalis. e) A metal which reacts wit dilute nitric acid at low temperature, liberating hydrogen. f) The chemical name of rust. g) The method of separation of liquid nitrogen, form liquid oxygen. h) The process of obtaining oxygen from water. i) A non – metallic oxide that acts as a reducing agent. j) A gas used along with acetylene, for welding and cutting of metals.

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Zn 

A

 Dil.Acid 



C + D 

B

 Metal chloride 

C

E  Rotten egg smell

C + Pb  CH 3COO 2



 Black

F

residue 

 G

Zn reacts with A and forms B & C. C reacts with D to form E. E reacts with lead acetate and forms F and G. Identify A, B, C, D, E, F and G, and give balanced equations.

HOTS Worksheet 1.

Substance A reacts with calcium to form B and C. ‘B’ is an inflammable gas, which on reacting with a gas D forms another gas E. ‘D’ is the gas, whose percentage is maximum in atmosphere. ‘E’ is a gas, that produces white dense fumes with HCl. Identify A, B, C, D and E. Show the balanced chemical equations to support you answer. Say true or False. i) Metals below hydrogen in metal activity series react with dilute acids to liberate hydrogen. ii) Magnesium with dilute HNO 3 produces hydrogen. iii) The reaction between potassium and water si violent and exothermic. iv) Mg, Al, Zn, Fe react with cold water, to liberate hydrogen. v) Reaction of iron and steam is reversible. vi) Hydrogen gas is collected by downward displacement of water.

IIT JEE Worksheet I.

Single Correct Answer Type

1.

Hydrogen is not obtained when zinc reacts with (A) Cold water (B) Dil. H2SO4 (C) Dil. HCl (D) Hot 20% NaOH Which metal adsorbs hydrogen ? (A) K (B) Al (C) Zn (D) Pd Hydrogen gas will not reduce (A) Heated cupric oxide (B) Heated ferric oxide (C) Heated stannic oxide (D) Heated aluminium oxide The sum of number of neutrons and protons in one of the isotopes of hydrogen is (A) 3 (B) 4 (C) 5 (D) 6 Hydrogen was discovered by (A) Scheele (B) Berzelius (C) Cavendish (D) Priestley The metal that does not displace hydrogen from one acid is (A) Hg (B) Zn (C) Al (D) Ca

2. 3.

4.

5.

6.

Hydrogen 7.

Nascent hydrogen consists of (A) Hydrogen atoms with excess energy (B) Hydrogen molecules with excess energy (C) Hydrogen ions in excited state (D) Solvated protons 8. Hydrogen molecules are (A) Monatomic and from x 22 ions (B) Diatomic and form x 22 ions (C) Diatomic and form X– ions (D) Monatomic and form X– ions 9. Moist hydrogen cannot be dried over concentrated H2SO4 because (A) It can catch fire. (B) It can be reduced by H2SO4 (C) It is oxidised by H2SO4 (D) It decomposes H2SO4. 10. Hydrogen has a tendency to gain one electron, in order to acquire helium configuration, It thus, resembles (A) Alkali metals (B) Noble gases (C) Halogens (D) Alkaline earth metals 11. Hydrogen is evolved by the action of cold dilute HNO3 on (A) Fe (B) Mg or Mn (C) Cu (D) Al 12. Deuterium an isotope of hydrogen is (A) Radio active (B) Non - radioactive (C) Heaviest (D) Lightest

II. Multiple Correct Answer Type 13. Hydrogen can be prepared from (A) Cold water (B) Hot water (C) Acids (D) Alkalis 14. Which of the following statements is/are correct? (A) Hydrogen is lightest element (B) Pure hydrogen is yellow in colour (C) Hydrogen is practically insoluble in water (D) Hydrogen is a tasteless gas 15. Which of the following is true for hydrogen? (A) It is present in coal gas and water gas. (B) It is used in study weather conditions high up

75 III. Paragraph Type

When hydrogen gas is passed over heated oxides of the less active metals such as zinc, iron, lead and copper, it reduces them to free metals and forms water.  16. x1 Fe2O3 +x2 H2   x3 Fe + x4 H2O x1 + x 2 + x 3 + x 4 = (A) 3 (B) 6 (C) 9 (D) 12  17. x1 PbO + x2 H2   x3 Pb + x3 H2O x1 + x 2 + x 3 + x 4 = (A) 2 (B) 4 (C) 8

(D) 16

 18. x1 ZnO + x2 H2   x3 Zn + x4 H2O x1 + x 2 + x 3 + x 4 = (A) 2 (B) 4 (C) 8 (D) 16

IV. Reasoning Type 19. Statement A: Nitric acid is not used for preparing hydrogen from metals. Statement B: Nitric acid is a strong oxidising agent and forms oxides of nitrogen rather than hydrogen. (A) ‘A’ is true, ‘B’ is false. (B) ‘A’ is false, ‘B’ is true. (C) Both ‘A’ and ‘B’ are true. (D) Both ‘A’ and ‘B’ are false. 20. Statement A: In the laboratory preparation of hydrogen, granulated zinc is preferred to pure zinc for the reaction with dilute acid. Statement B: As granulated zinc is commercial, obtained from molten zinc, it may contain traces of impurities which are having a slight catalysing effect on the reaction. (A) ‘A’ is true, ‘B’ is false. (B) ‘A’ is false, ‘B’ is true. (C) Both ‘A’ and ‘B’ are true. (D) Both ‘A’ and ‘B’ are false.

21. Statement A: Hydrogen gas obtained in the in the air. laboratory has a peculiar smell. (C) It is used in ghee preparation (D) Hydrogen acts as a oxidising agent and oxidises Statement B: Due to absence of the impurities in metals to metal oxides. hydrogen gas, it produces peculiar smell. (A) ‘A’ is true, ‘B’ is false. (B) ‘A’ is false, ‘B’ is true. (C) Both ‘A’ and ‘B’ are true. (D) Both ‘A’ and ‘B’ are false. www.betoppers.com

7th Class Chemistry

76

V. 22.

23.

Matrix Matching Match the points pertaining to the occurrence and discovery of hydrogen in column I with the concluding facts in column II. Column-I Column-II A. Lavoisier in 1783 established 1. The atmosphere around the sun and stars, the name ‘ hydrogen’ B. Hydrogen does not occur 2. Water C. Hydrogen is present in traces in 3. Meaning ‘water producer’. D. A compound, one ninth by mass of which 4. In the free state on earth. is hydrogen in the combined state is Pure hydrogen is prepared by passage of the gas through various solutions which respectively absorb each impurity. Match the impurity with the solution which absorbs it. Impurity A. B. C. D. E.

Removed by

Arsine [AsH3] Phosphine [ PH3] Hydrogen sulphide [H2S] Nitrogen dioxide [NO2] Sulphur dioxide [SO2]

1. Potassium hydroxide solution 2. Fused calcium chloride 3. Silver nitrate solution 4. Lead nitrate solution

F. Moisture



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Coal and Petroleum

By the end of this chapter, you will understand •

Formation of Coal

•

Coke

•

Coal tar

•

Coal gas

•

Formation of Petroleum

•

Refining of Petroleum

•

Natural Gas

•

Petro chemicals

1. Introduction We use various materials for our basic needs. Some of them are found in nature and some have been made by human efforts. Let’s look at few materials used by us in daily life that are natural and manmade. Natural Air

Man-made Paper

Wate r

Fibre glass

Soil

Plastic

Mine rals Wood

Cup Nylon

Air, Water, Soil and minerals are obtained from nature, they are called Natural Resources. Can we use all our natural resources forever ? Can air, water and soil be exhausted by human activities? Is water a limitless resource? In the light of the availability of various resources in nature, natural resources can be broadly classified into two kinds: A) Inexhaustible Natural Resources These resources are present in unlimited quantity in nature and are not likely to be exhausted by human activities. Examples: Sunlight, Air, Water, Soil, etc. B) Exhaustible Natural Resources The amount of these resources in nature is limited. They can be exhausted by human activities.

Chapter -5

Learning Outcomes

Examples: Forests, Wildlife, Minerals, Coal, Petroleum, Natural gas etc. In this chapter we will learn about some exhaustible natural resources like coal, petroleum and natural gas. These were formed from the dead remains of living organisms (fossils). So, these are all known as Fossil Fuels.

2. Coal You may have seen coal, or heard about it. It is as hard as stone and is black in colour. Coal is one of the fuels used to cook food. Earlier, it was used in railway engines to produce steam to run the engine. It is also used in thermal power plants to produce electricity. Coal is also used as a fuel in various industries. I) Formation of Coal Coal is called a fossil fuel because it was formed from the remains of vegetation that grew as long as 400 million years ago. It is often referred to as "buried sunshine," because the plants which formed coal captured energy from the sun through photosynthesis to create the compounds that make up plant tissues. The most important element in the plant material is carbon, which gives coal most of its energy. Most of our coal was formed about 300 million years ago, when much of the earth was covered by steamy swamps. As plants and trees died, their remains sank to the bottom of the swampy areas, accumulating layer upon layer and eventually forming a soggy, dense material called peat.

7th Class Chemistry

78

II)

A)

B)

C)

Over long periods of time, the makeup of the earth's surface changed, and seas and great rivers caused deposits of sand, clay and other mineral matter to accumulate, burying the peat. Sandstone and other sedimentary rocks were formed, and the pressure caused by their weight squeezed water from the peat. Increasingly deeper burial and the heat associated with it gradually changed the material to coal. Scientists estimate that from 3 to 7 feet of compacted plant matter was required to form 1 foot of bituminous coal. Coal formation is a continuing process (some of our newest coal is a mere 1 million years old). Today, in areas such as the Great Dismal Swamp of North Carolina and Virginia, the Okefenokee Swamp of Georgia, and the Everglades in Florida, plant life decays and subsides, eventually to be covered by silts and sands and other matter. Perhaps millions of years from now, those areas will contain large coal beds. Heating of Coal When heated in air, coal burns and produces mainly carbon dioxide gas. Coal is processed in industry to get some useful products such as coke, coal tar and coal gas. Co ke It is a tough, porous and black substance. It is almost pure form of carbon. Coke is used in the manufacture of steel and in the extraction of many metals. Coal Tar It is a black, thick liquid with unpleasant smell. It is a mixture of about 200 substances. Products obtained from coal tar are used as starting materials for manufacturing various substances used in everyday life and in industry, like synthetic dyes, drugs, explosives, perfumes, plastics, paints, photographic materials, roofing materials, etc. Interestingly, naphthalene balls used to repel moths and other insects are also obtained from coal tar. Note: These days, bitumen, a petroleum product, is used in place of coal-tar for metalling the roads. Coal Gas Coal gas is obtained during the processing of coal to get coke. It is used as a fuel in many

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industries situated near the coal processing plants. Coal gas was used for street lighting for the first time in London in 1810 and in New York around 1820. Now a days, it is used as a source of heat rather than light.

Formative Worksheet 1.

2.

3.

4.

Assertion (A): The resources are present in unlimited quantity in nature and are not likely to be exhausted by human activities are called Inexhaustible resources. Reason (R): Forests, wildlife, minerals are examples Inexhaustible resources. (A) A is correct and R is the correct explanation of A. (B) A is correct and R is not the correct explanation of A. (C) A is correct and R is wrong. (D) A is wrong and R is correct. Statement - I: Forests, wildlife, minerals, coal, petroleum, natural gas are the examples of exhaustible resources. Statement – II: The resources that can be exhausted by human activities are called exhaustible resources. (A) Statement - I is true, Statement - II is false. (B) Statement - I is false, Statement - II is true. (C) Both statements are true. (D) Both statements are false. Fill in the following blanks: i) __________was used in railway engines to produce steam to run the engine. ii) _________ is thermal power plants to produce electricity. Assertion (A): The slow process of conversion of dead vegetation into coal is called catenation. Reason (R): When heated in air, coal burns and produces mainly carbon dioxide gas. (A) A is correct and R is the correct explanation of A. (B) A is correct and R is not the correct explanation of A. (C) A is correct and R is wrong. (D) A is wrong and R is correct.

Coal and Petroleum 5.

6.

7.

79

Match the following: (A) Sunlight P. (B) Air Q. (C) Coal (D) Petroleum Match the following: (A) Coal P. (B) Coke

Q.

(C) Coal Tar

R.

(D) Coal gas

S.

3. Petroleum Exhaustible Resources In Exhaustible Resources

Black, thick liquid with unpleasant smell. Formed as a result of carbonisation. Tough, porous black susbstance It was used for street lighting for the first time in London

Fill in the blanks i) _________ is the pure form of carbon ( coke / Coal tar/ Coal gas) ii) _________ is a black, thick liquid with unpleasant smell ( coke / Coal tar/ Coal gas) iii) _________is obtained during the processing of coal to get coke. ( coke / Coal tar/ Coal gas)

Life in this generation has become fast and busy. If the development in technology is one reason, fast transportation is also one of the reasons. Now a days, travelling from one place to another has become very easy. Have you ever wondered what is the fuel used in automobiles, heavy motors etc for running? You know that petrol is used as a fuel in light automobiles such as motor cycles/ scooters and cars. Heavy motor vehicles like trucks and tractors run on diesel. Petrol and diesel are obtained from a natural resource called petroleum. A) Formation of Petroleum Formation of Petroleum: Petroleum was formed from organisms living in the sea. As these organisms died, their bodies settled at the bottom of the sea and got covered with layers of sand and clay. Over millions of years, absence of air, high temperature and high pressure transformed the dead organisms into petroleum and natural gas. Look at figure given below.

Conceptive Worksheet 1.

2.

3.

Assertion (A): Coal, Petroleum and Natural gas called fossil fuels Reason (R): Coal, Petroleum and Natural gas are formed by fossils, so they are called fossil fuels. (A) A is correct and R is the correct explanation of A. (B) A is correct and R is not the correct explanation of A. (C) A is correct and R is wrong. (D) A is wrong and R is correct. i) Which gas is produced when coal burns in air? ii) Name the gas which is formed when coal is heated in the absence of air. iii) What is the main use of coke? i) How many substances are found in coal tar? ii) Write the uses of coal. iii) Write the uses of coal tar.

It shows the deposits of petroleum and natural gas. You see that the layer containing petroleum oil and gas is above that of water. Why is it so? Recall that oil and gas are lighter than water and do not mix with it. B) Refining of Petroleum Petroleum is a dark oily liquid. It has an unpleasant odour. It is a mixture of various constituents such as petroleum gas, petrol, diesel, lubricating oil, paraffin wax, etc. The process of separating the various constituents/ fractions of petroleum is known as refining. It is carried out in a petroleum refinery.

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7th Class Chemistry

80

to global warming. It is therefore necessary that we use these fuels only when absolutely necessary. This will result in better environment, smaller risk of global warming and their availability for a longer period of time.

C) Various constituents of Petroleum and their Uses S.No. 1. 2. 3. 4. 5. 6. 7.

Constituents of Uses petroleum Petroleum Gas in Fuel for home and Liquid form (LPG) industry Motor fuel, aviation Petrol fuel, solvent for dry clearning Fuel for stoves, lamps Kerosene and for jet aircrafts Fuel for heavy motor Diesel vehicles, electric generators Lubricating oil Lubrication Ointements, candles, Paraffin wax Vaseline etc. Bitumen Paints, road surfacing

In India, the Petroleum Conservation Research Association (PCRA) advises people how to save petrol/diesel while driving. Their tips are:

Natural gas is a very important fossil fuel because it is easy to transport through pipes. Natural gas is stored under high pressure as compressed natural gas (CNG). CNG is used for power generation. It is now being used as a fuel for transport vehicles because it is less polluting. It is a cleaner fuel. The great advantage of CNG is that it can be used directly for burning in homes and factories where it can be supplied through pipes. Such a network of pipelines exists in Vadodara (Gujarat), some parts of Delhi and other places. 8.

A) Some Natural Resources are Limited You have studied in the beginning of the chapter that some natural resources are 9. exhaustible like fossil fuels, forests, minerals etc. You know that coal and petroleum are fossil fuels.

Moreover, burning of these fuels is a major cause of air pollution. Their use is also linked www.betoppers.com

•

Switch off the engine at traffic lights or at a place where you have to wait,

• •

Ensure correct tyre pressure, and

Formative Worksheet

In our country, natural gas has been found in Tripura, Rajasthan, Maharashtra and in the Krishna Godavari delta.

It required the dead organisms millions of years to get converted into these fuels. On the other hand, the known reserves of these will last atmost a few hundred years.

Drive at a constant and moderate speed as far as possible,

Ensure regular maintenance of the vehicle. B) Petrochemicals Many useful substances are obtained from petroleum and natural gas. These are termed as ‘Petrochemicals’. These are used in the manufacture of detergents, fibres (polyester, nylon, acrylic etc.), polythene and other manmade plastics. Hydrogen gas obtained from natural gas, is used in the production of fertilisers (urea). Due to its great commercial importance, petroleum is also called ‘black gold’.

4. Natural Gas

Natural gas is also used as a starting material for the manufacture of a number of chemicals and fertilizers. India has vast reserves of natural gas.

•

Assertion (A): Petroleum is called Black gold Reason (R): Due to its great commercial importance, petroleum is called black gold. (A) A is correct and R is the correct explanation of A. (B) A is correct and R is not the correct explanation of A. (C) A is correct and R is wrong. (D) A is wrong and R is correct. Statement - I: Petrol and diesel are obtained from a natural resource called petroleum. Statement – II: Petroleum has a pleasant odour. (A) Statement - I is true, Statement - II is false. (B) Statement - I is false, Statement - II is true. (C) Both statements are true. (D) Both statements are false.

Coal and Petroleum 10. Fill in the following blanks: i) The process of separating the various constituents/ fractions of petroleum is known as _____. ii) Many useful substances are obtained from petroleum and natural gas. These are termed as ________. 11. Assertion (A): Coal, petroleum and natural gas be prepared in the laboratory from dead organisms. Reason (R): They cannot be prepared in laboratory as their formation is a very slow process and conditions for their formation cannot be created in the laboratory. (A) A is correct and R is the correct explanation of A. (B) A is correct and R is not the correct explanation of A. (C) A is correct and R is wrong. (D) A is wrong and R is correct. 12. Match the following: (A) LPG P) Motor fuel, aviation fuel, solvent for dry cleaning (B) Petrol Q) Fuel for home and industry (C) Kerosene R) Ointments, candles, vaseline etc. (D) Paraffin wax S) Fuel for stoves,lamps and for jet aircrafts 13. Match the following: (A) Diesel P) Ointments, candles, vaseline (B) Lubricating oil Q) Paints, road surfacing C Bitumen R) Reducing the friction in vehicle engines D Paraffin wad S) Fuel for heavy motor vehicles, electric generators 14. Fill in the blanks i) ________ is obtained from the coal tar and used to repel moths and insects. ii) _________ is used for road surfacing these days. iii) The first oil was drilled at ____________.

81

Conceptive Worksheet 4.

i)

The expanded form of PCRA is _____________. ii) The expanded form of CNG is _____________. iii) The expanded form of LPG is _____________. 5. Why CNG is called clean fuel? 6. What are petrochemicals? What are their uses? 7. Why is natural gas called a very important fossil fuel in these days? 8. Why CNG is called clean fuel? 9. What are the harmful effects of using fossil fuels? 10. What are petrochemicals? What are their uses?

Summative Worksheet 1. 2.

5. 6. 7. 8.

What are natural resources? Explain with examples. Classify the natural resources on the basis of their availability. What are inexhaustible natural resources? Explain with example. What are exhaustible natural resources? Explain with example. What are fossil fuels? Name the main fossil fuels. What is Coal? Write its uses? What is coke? Write its uses. What is coaltar? What are its uses?

9.

What is coal gas? Write the uses of coal gas.

3. 4.

10. What is Petroleum? Why is it called black gold? 11. Where and when first oil well drilled in India as well as in world? 12. What do you mean by refining and petroleum refinery?

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7th Class Chemistry

82 7.

HOTS Worksheet 1.

Coal, petroleum, and methane are organic substances. They exist in different physical states. The physical states in which coal, petroleum, and methane respectively exist are (A) Solid, liquid, and liquid (B) Solid, liquid, and solid

8.

(C) Solid, liquid, and gas (D) Gas, liquid, and solid 2.

3.

4.

5.

Which of the following constituents of petroleum is used in paints and road surfacing? (A) Diesel

(B) Bitumen

(C) Paraffin wax

(D) Lubricating oil

A list of natural resources is given. I. Wind II. Coal III. Minerals IV. Petroleum V. Sunlight VI. Biomass Which of the following pairs of natural resources is exhaustible? (A) II and IV (B) I and V (C) IV and VI (D) V and VI Coal was formed over a long period of time under high pressure and temperature conditions by the decomposition of dead vegetation. This process of conversion of dead vegetation to coal is known as (A) Refining (B) Threshing (C) Condensation (D) Carbonization During the processing of coal to obtain i , ii is formed as a by-product. The information in which alternative completes the given statement? (A) (B) i ii

i

coal gas coke (C)

i

ii

coal tar coal gas 6.

ii

coke coal tar (D)

i

ii

coke coal gas

Which of the following products is not obtained from petroleum? (A) Coke (B) Diesel (C) Paraffin wax (D) Lubricating oil

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9.

A substance X is obtained from an exhaustible natural resource. It is a black and thick liquid with an unpleasant smell. It is a mixture of 175 “ 200 substances. Some of the products such as synthetic dyes, plastic paints, explosives, perfumes, etc are obtained using this resource. The substance X is (A) Coke (B) Coal tar (C) Bitumen (D) Lubricating oil Carbonization is a (A) Fast process in which dead vegetation converts into coal (B) Slow process in which dead vegetation converts into coal (C) Fast process in which dead organisms of the sea get converted into petroleum (D) Slow process in which dead organisms of the sea get converted into petroleum The slow process of the transition of dead i into coal is called ii . The information in which alternative completes the given statement? (A)

i

ii

vegetation condensation (B)

i

ii

vegetation carbonization (C)

i

ii

sea organisms carbonization (D)

i

ii

sea organisms condensation 10. Consider the following statements regarding fossil fuels. I Fossil fuels are the dead remains of living organisms that have been buried for a long time. II Excessive use of fossil fuels causes global warming and a depletion of natural resources. III Earthquakes occur as a result of burning fossil fuels. Among the given statements, (A) Only statement I is true (B) Only statement III is true (C) Statements I and II are true (D) Statements II and III are true

Coal and Petroleum

83

11. Which alternative incorrectly classifies a natural resource on the basis of its availability? (A)

Natural resource Classification Wild life

(B)

Natural resource Classification Minerals

(C)

Exhaustible

Exhaustible

Natural resource Classification Petroleum

Inexhaustible

(D) Natural resource Classification

Wind

Inexhaustible

12. Which of the following natural resources is exhaustible? (A) Wind (B) Coal (C) Sunlight (D) Biomass

13. Which of the following statements about fossil fuels is correct? (A) Only petroleum is prepared in the laboratory (B) Petrochemicals are products of coal and petroleum (C) Both coal and petroleum are prepared in the laboratory (D) Petrochemicals are products of petroleum and natural gas 14. Petroleum Conservation Research Association, under the Ministry of Petroleum and Natural Gas, does not encourage (A) Driving at a very high speed (B) Maintenance of vehicle by regularly servicing (C) Maintaining correct levels of pressure in the tyres (D) Switching off the vehicle engine at traffic intersections 15. Which of the following petroleum components is used as a solvent for dry cleaning? (A) Petrol (B) Kerosene (C) Paraffin wax (D) Lubricating oil



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7th Class Chemistry

By th e e n d o f th i s c h ap te r , yo u w i l l u n de r stan d • • •

1.

Slow and Fast Changes Reversible and Irreversible Changes Desirable And Undesirable Changes

• •

Introduction In our daily life, we observe many changes around us. Everything in this universe undergoes a change. These changes may be observed by us at school, home, playground, garden or any other place. For example, sudden change in weather, flowering of plants, melting of ice, ripening of fruits, drying of clothes, milk changing into curd, germination of seeds, cooking of food, rusting of iron, bursting of firecracker, etc., are the common changes that occur in day-to-day life. The changes can bring about different kinds of alterations in the things around us. Some of the alterations brought about are permanent in nature, and hence, cannot be reversed. However, some alterations are brought about in position, shape, size or state of the things. These alterations are temporary in nature, and hence, can be reversed. CLASSIFICATION OF CHANGES The changes taking place around us can be classified as under : (1) Slow and fast changes. (2) Reversible and irreversible changes. (3) Desirable and undesirable changes. (4) Periodic and non-periodic changes. (5) Physical and chemical changes

2.

Periodic And Non-periodic Changes Physical And Chemical Changes

Slow and Fast Changes Some changes are very fast. These changes occur within seconds or minutes. Examples : A boy blowing a balloon, bursting of a balloon, burning of a match stick, bursting ot a cracker, lighting of an electric bulb, spinning of a top, etc., are examples of fast changes Some changes take place very slowly. These changes may take hours, days, months or years to complete.

Chapter -26

Types of Changes

Learning Outcomes

Examples: 1. Germination of a mustard seed into a seedling may take a few days. The growth of a seedling into a full fledged mustard plant may take three months or more. 2. A baby grows into an adult in over 18 years. 3. Rusting of an iron nail in damp air may take a couple of days. 4. Milk changes into curd in 6 to 8 hours. 5. The water changes into ice in a fridge in a few hours. The change of seasons from summer to winter takes months.

3.

Reversible and Irreversible Changes A change which can be reversed is called a reversible change. In this change, the products formed can be converted back into their original forms. Examples: 1. Water can be changed into ice by placing it in the freezing chamber of the fridge. The ice so formed can be converted back into water by placing the ice outside the fridge. 2. An electric bulb can be made to give light by passing electric current through it. The bulb returns to its original state and does not give light when the electric current is switched off. 3. A piece of steel can be converted into a magnet by rubbing with a powerful magnet. The magnet so formed can be converted back into steel by hammering it or heating it strongly. A change which cannot be reversed is called an irreversible change. In this change, the products cannot be converted back into their original form.

7th Class Chemistry

86 Examples: 1. When a paper is burnt, it changes to ash and smoke. From ash and smoke, we cannot get back paper. Thus, the change is irreversible. 2. A candle, on burning, forms carbon dioxide gas and water vapour. These products cannot be converted back into a candle. 3. When a sparkle is set on fire, it burns with a bright flame. However, on cooling, the products do not change back into sparkle. 4. Similarly, curdling of milk, weathering of rocks, grinding of grains, cooking of food, falling of leaves from a tree, the ageing of human beings, animals and plants are irreversible changes.

6.

(A) Conversion of ice into water (B) Converting milk into curd (C) Stretching of a rubber band (D) Both (A) and (C) 7.

2.

3.

4.

5.

Water changes in to ice in fridge is : (A) Very fast change (B) Very slow change (C) Chemical change (D) Periodic change The change occur within seconds or minutes then it is: (A) Slow change (B) Very slow change (C) Desirable change (D) Very fast change Rusting of iron is : (A) Very fast change (B) Very slow change (C) Desirable change (D) Periodic change Column-I Column-II (A) Very fast change p) Germination of mustard seed (B) Reversible change q) A change cannot be reversed (C) Irreversible change r) Bursting of balloon (D) Very slow change s) Bursting of sparkle t) A change can be reversed Magnetization of a piece of steel is a/an: (A) Chemical change (B) Reversible change (C) Irreversible change (D) Periodic change

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Statement I : A change which can be reversed is called a reversable change. Statement II : Falling of leaves from a tree is reversible change. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I.

Formative Worksheet 1.

Identify an reversible change from the following options:

(C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true 8.

Identify which is true statement? (A) Lighting of electric bulb is reversable change. (B) Burning of paper is reversible change. (C) Burning of candle is reversible change. (D) Changing of seasons is slow change.

9.

Statement I : Curdling of milk, weathering of rocks are irreversible change. Statement II : Grinding of grains and cooking of food is reversible change. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true

10. Statement I : Flowering of plants is a reversible change. Statement II : Some of the changes are permanent in nature.. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true

Types of Changes

87

Conceptive Worksheet 1.

2.

3.

4.

5.

6.

Hammering or heating of iron is: (A) Periodic change. (B) Fast change. (C) Irreversible change. (D) Reversible change. Souring of milk is an example of a: (A) Physical change. (B) Irreversible change. (C) Reversible change. (D) Fast change. Evaporation is an example of : (A) Reversible change. (B) Irreversible change. (C) Chemical change. (D) None of these. Which of the following is a irreversible change? (A) Breaking of a glass tumbler. (B) Melting of wax. (C) Photosynthesis by plants. (D) Sublimation of camphor. Identify which one is true: (A) Germination of mustard seed into a seedling is a slow change (B) Spinning of a top is fast change (C) Rusting of iron nail is fast change (D) Milk changes into curd is a slow change Identify an irreversible change from the following : (A) Heating iron rod to red hot (B) Converting milk into curd (C) Stretching of a rubber band (D) Conversion of ice into water

4. Desirable Changes

And

Undesirable

A change brought about by a person or the nature, which desirable change. useful, is called a desirable change. Examples: 1. Formation of curd from rnilk is a desirable change. It is because curd is more easily digestible as compared to milk. 2. Formation of manure from animal dung and dead leaves is a desirable change. It is because waste materials are converted into useful manure which is good for raising crops. 3. Melting of snow on the mountains in the summer is a desirable change. It is because it brings fresh supply of water to the rivers.

4.

Change of weather from winter to summer is a desirable change. It is because the heat results in evaporation of water on a large scale. The water so evaporated changes to clouds and brings about rain which is good for the crops. A change brought about by a person or the nature, such that it has harmful effects is failed an undesirable change. Examples : 1. Food turning bad in summer is an undesirable change. It is because it not only spoils food, but people can get ill white eating such food. 2. Flooding of rivers in rainy seasons is an undesirable change. It is because the floods wash away the standing crops and cover the fertile soil with sand. 3. Breaking of glassware/glass article is an undesirable change. It is because the broken glass cannot be rejoined. 4. Rusting of articles of iron is an undesirable change. It is because rusting makes the articles of iron weak. It must be pointed out here that a change which is desirable at one i- time, may be undesirable at some other time. For example, if wood or coal is burnt in a proper place, the heat is produced which is a desirable change. It is because we can use the heat in cooking food er raising steam in factories. However, if a house or a factory catches fire, it also produces heat. This heat just causes destruction, and hence, is undesirable. Sometimes while carrying out desirable changes, some undesirable changes may also take place. The following examples will highlight the point : 1. The heat produced by the burning of petrol in the engines of cars or scooters is a desirable change. It is because it helps us to drive the cars and scooters. However, at the same time, the poisonous gases like carbon monoxide and nitric oxide are produced which are very harmful to health. This is an undesirable change. 2. In the thermal power stations, electricity is produced by producing heat energy from the burning of coal. It is a desirable change. However, burning of coal produces a lot of smoke and other poisonous gases. These gases arc harmful to health. This is an undesirable change. www.betoppers.com

7th Class Chemistry

88 Thus, to sum up, a change may be desirable for some people and undesirable for others. For example, when a farmer sprays chemicals on vegetables and fruits to kill insects, it is a desirable change for the farmer, because he gets a good crop. However, the chemicals used by the farmer may be harmful to the persons who are consuming his crop. Thus, it is an undesirable change. Similarly, cutting of forest for wood may be useful to some persons who need wood. However, cutting of wood disturbs the balance of nature, which can cause drought, water shortage, etc. Thus, while bringing about a desirable change, care should be taken that there is minimum of undesirable changes.

5. Periodic Changes

And

12. Identify the desirable and undesirable changes from the following: i)

The burning of petrol in the engines of vehicles help to drive.

ii)

The burning of petrol is the engine produce the poisonous gases like carbon monoxide and nitric oxide.

(A) i  Desirable change, ii)  Undesirable change (B) i, ii  Undesirable changes (C) i  Undesirable change. ii  Desirable change (D) i, ii  Desirable changes

Non-periodic

13. Statement I: The formation of curd from milk is a desirable change.

Periodic Changes: The changes which occur again and again, after fixed intervals of time, are called periodic changes. Examples : 1. Swinging of a clock pendulum is a periodic change. 2. Phases of moon is a periodic change. 3. Change of seasons is a periodic change. 4. High and low tides at sea is a periodic change. 5. Beating of heart is a periodic change. Non-Periodic Changes: The changes which do not repeat themselves at regular intervals of time are called non-periodic changes. Examples: 1. Earthquakes are non-periodic changes. 2. Land slides during rainy season are nonperiodic changes. 3. Falling of leaves from a tree is a non-periodic change. 4. Rusting of iron articles is a non-periodic change. 5. Sneezing, coughing, etc., are non-periodic changes.

Statement II : The curd is more easily digestible as compared to milk.

Formative Worksheet 11. Which of the following is/are undesirable changes? (A) Melting of snow on the mountains in the summer. (B) Rusting of articles of iron. (C) Flooding of rivers in rainy seasons. (D) Change of weather from winter to summer www.betoppers.com

(A) ‘A’ is true, ‘B’ is false (B) ‘A’ is false, ‘B’ is true (C) Both ‘A’ and ‘B’ are true (D) Both ‘A’ and ‘B’ are false 14. Identify which is false statement? (A) Food turning bad in summer is an undesirable change. (B) Breaking of glassware / glassy article is an desirable change. (C) Rusting of iron articles is desirable change. (D) The gases released from thermal power station are desirable change. 15. Statement I: Sneezing, coughing etc., are non-periodic changes. Statement II: The change which do not repeat themselves at regular intervals at time, are called non-periodic changes. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true

Types of Changes 16. Statement I: Cutting of wood is useful who need wood, however it disturbs the balance of nature and causes drought, water shortage etc., Statement II: A change which is desirable at one time, may be undesirable at some other time. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true 17. Identify which of the following statement is true? (A) Phases of moon is a periodic change. (B) Swinging of a clock pendulum is a non-periodic change. (C) Rusting of Iron articles is a non-periodic change. (D) Beating of heart is periodic change. 18. Statement I: If wood or coal is burnt in a proper place is a desirable change. Statement II: If a house or factory catches fire is undesirable change. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true

Conceptive Worksheet 7.

8.

9.

In the thermal power stations, electricity is produced by producing heat energy from the burning of coal. This is an example of : (A) Physical change (B) Periodic change (C) Desirable change (D) All the above. Sneezing and coughing are example of ___________ change (A) Fast change (B) Slow change (C) Non-periodicchange (D) Desirable change The changes which do not repeat themselves at regular intervals of time, are called: (A) Irreversable changes (B) Desirable changes (C) Non-periodic changes (D) Chemical changes

89 10. The change of seasons from winter to summer is an example of : (A) Non-periodic change (B) Irreversible change (C) A slow change (D) A desirable change 11. Identify the changes in the following: A) The heat produced by the burning of petrol in the engines of cars or scooters. B) Cutting of wood results in imbalance in nature. C) The poisonous gases like carbon monoxide and nitric oxide are produced, when fuels are burnt. D) To farmers, it is necessary spraying of chemicals on vegetables and fruits to kill insects. (A) A and B are desirable and B and C are undesirable (B) A and C are desirable and C and D are undesirable (C) B and C are desirable and A and B are undesirable (D) A and D are desirable and B and C are undesirable

6.

Physical Changes

And

Chemical

All substances around us undergo changes. In some cases, the changes are small and difficult to detect. In other cases, the changes are obvious and easy to detect. These changes generally get accelerated, if we heat the substances. Most of these changes can be classified under two headings : (i) Physical changes (ii) Chemical changes. Physical changes are generally temporary in nature and no new substances are formed. Chemical changes are generally permanent in nature and new substances are formed, which have entirely new properties. Experiments To Examine Changes In A Few Substances: Physical changes The changes are temporary in nature and can be reversed. Such changes are called physical changes. Experiment 1 Take a dry hard glass test tube and put in it about 2 g of candle wax. Meat the test tube gently on a Bunsen flame. What do you observe? The wax melts to form a colourless liquid. Now cool the tube by holding it in cold water. What do you observe? www.betoppers.com

7th Class Chemistry

90 The molten wax solidifies. Thus, we can say that on heating wax melts and on cooling, the liquid wax solidifies, but no new products are formed. Similarly, ice, ghee, butter, etc., melt on heating and solidify on cooling. Experiment 2 Zinc oxide is a white powder. Place about 2 g of zinc oxide in a dry test tube. Heat the test tube strongly. What do you notice after 2 minutes of heating? The zinc oxide changes to yellow colour. Cool the test tube. In a few minutes, the colour of zinc oxide changes to white colour. Thus, we can say that the change in zinc oxide was temporary in nature. Similarly, if we heat lead monoxide powder, which is yellow in colour, its colour changes to reddish brown. However, on cooling, its colour changes back to yellow. Experiment 3 Take about 50 cm3 of water in a beaker. Add a spoonful of common salt in it and stir. You will observe that salt dissolves in water. Now evaporate the salt solution on heated sand bath. It is observed that water disappears leaving behind common salt. Furthermore, the mass of common salt remains same. Thus, we can say that the above changes are (i) temporary in nature, (ii) no new products are formed, and (iii) there is no change in weight when change takes place. Experiment 4 Hold a short length of platinum wire or nichrome wire with the help of tongs. Hold the end of wire in a non-luminous Bunsen flame. What do you observe? The end of wire becomes red hot. Take out the end of wire from the Bunsen flame and allow it to cool. What do you observe? The wire regains its original colour. Thus, we can say that the change brought about in the appearance of the wire is temporary in nature. Similarly, when electric current flows through a bulb, its filament gets white hot and emits light. When current is switched off, the filament does not give off any light. Thus, the change in the appearance of the bulb is temporary in nature. Experiment 5 Take a bicycle spoke (wire fitted in wheel of bicycle) and rub it with a permanent bar magnet. Roll the iron wire in the iron filings. What do you www.betoppers.com

observe? Iron filings stick to the wire. Thus, we can conclude that wire has changed into a magnet. Now hit the wire against the table for 50 times. Again roll the wire in iron filings. It is observed that iron filings no longer stick to the iron wire. Thus, we can conclude that wire has lost its magnetic property. Thus, the changing of iron wire into a magnet is a temporary change and no new products are formed. Chemical Changes The changes are permanent in nature and cannot be reversed. Such changes are called chemical changes. Experiment 6 Hold a short length (about 50 cm) of magnesium ribbon in the fire tongs. Heat magnesium ribbon in the non-luminous flame for about 2 minutes. The magnesium ribbon burns with a brilliant white flame producing a large amount of heat and light. It leaves behind a white ash, which is commonly called magnesium oxide. The magnesium oxide, so formed, does not change to magnesium ribbon on cooling. Thus, we can conclude : (i) the change brought about in magnesium is permanent in nature; (ii) a new product is formed which has entirely different properties; and (iii) a large amount of heat and light energy are evolved. Experiment 7 Fix a candle on the table and light it. What do you observe after 10 minutes? (i) The candle burns to give heat and light energy. (ii) The candle does not regain its original size when put off. Thus, the burning of a candle is a permanent change which cannot be reversed. Actually, the candle burns to form new products, i.e., carbon dioxide gas and water vapour. Glowing splint bursts into flame Experiment 8 Take a hard glass test tube and put in it 2 g of red coloured mercuric oxide. Clamp the test tube on an iron stand. Heat the test tube strongly. You will notice that first of all the colour of mercuric oxide changes to black. On further heating, the test tube is filled with fumes. At this moment hold a glowing wooden splint in the test tube. The wooden splint of mercury bursts into flame. Also, tiny silvery droplets arc seen sticking to the cooler parts of test tube. On cooling the test tube, the change is not reversed.

Types of Changes Actually, on heating, mercuric oxide decomposes to form mercury and oxygen, i.e., two new products arc formed. The mercury vaporises and liquefies on the cooler parts of the test Heating mercuric oxide brings tube. The oxygen is responsible for the glowing splint to burst into flame, because it supports combustion. Thus, strong heating of mercuric oxide is a permanent change, which cannot be reversed. Furthermore, new products are formed. Experiment 9 Take a hard glass test tube and put in it 2 g of sugar. Heat the test tube strongly. What do you observe? The sugar melts and then turns brown. On further heating, it gives off steam which condenses on the cooler parts of the test tube. The residue left in the test tube is black in colour. On cooling, the change does not reverse itself. Thus, heating of sugar is a permanent change. Actually, sugar decomposes to form charcoal which is a form of carbon and is black in colour. It also gives off water in the form of steam. From the above experiments, it is clear that there are two types of changes which take place in the substances on heating.

Formative Worksheet 19. Identify which of the following is / are physical changing? (A) Melting of ice (B) Heating of zinc oxide (C) Heating of nicrome wire (D) Burning of magnesium ribbon. 20. Which of the following is / are a chemical change? (A) Burning of fuels (B) Burning of crakers (C) A strong heating of mercuric oxide (D) All the above 21. Identify the correct statement: (A) Heating of sugar is a permanent change. (B) Crystallisation of sugar is a chemical change. (C) Sugar decomposes to form charcoal which is a form of carbon. (D) Both 1 and 3. 22. When zinc hydroxide is heated, it decomposes to form zinc oxide. This is an example of : (A) Physical change (B) Periodic change (C) Chemical change (D) All the above

91 23. Statement I: On heating sugar decomposes to form charcoal is a chemical change. Statement II: The chemical changes are permanent in nature and cannot be reversed. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true 24. Identify the false statement: (A) Rusting is a physical change (B) Curdling of milk is a chemical change (C) Photosynthesis is a chemical change (D) Digestion of food is a physical change 25. Statement I : On strong heating mercuric oxide decomposes to form mercury and oxygen. Statement II: Strong heating of mercuric oxide is a permanent change, which cannot be reversed. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true 26. Statement I: Rusting of iron is a physical change. Statement II : When iron is left exposed to moist air for a few days, reddish brown powdery mass (rust) is found on its surface. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true 27. Statement-I : Burning of LPG is a chemical change. Statement-II : LPG burns with a pale blue flame and liberates colourless carbon dioxide gas which can be converted back to LPG. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true

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92

Conceptive Worksheet 12. Which one of the following is the correct statement(s): (A) Heating of sugar is a permanent change. (B) Sugar decomposes to form charcoal which is a form of carbon. (C) Powdering of sugar is a physical change. (D) All the above 13. In a change, energy is: (A) Absorbed (B) Evolved (C) Either absorbed or evolved (D) Neither absorbed nor evolved 14. A physical change is: (A) Permanent (B) Temporary (C) Both permanent and temporary (D) Neither permanent nor temporary 15. Which of the following is a chemical change? (A) Glowing of electric bulb. (B) Crushing an ice-cube. (C) Magnetizing an iron needle. (D) Burning of a match stick. 16. Burning of petrol or diesel is a/an: (A) Chemical change (B) Physical change (C) Reversible change (D) Periodic change Characteristics of Physical Changes (i) No new substances are formed during physical change: Ice, on heating, melts to form water. The water on further heating changes into steam. On cooling, the steam changes into water. On further cooling, the water solidifies to form ice. However, the molecules of ice, water or steam always contain two atoms of hydrogen and one atom of oxygen. Thus, we can say that no new substances are formed. Similarly, when we add common salt to water, salt solution is formed but no change takes place in its molecules. On evaporation, the water evaporates leaving behind salt. (ii) Physical changes can be generally reversed: The zinc oxide, on heating, changes to yellow colour. However, on cooling its colour changes to white. Similarly, when a piece of iron is stroked with permanent magnet, it gets magnetised. www.betoppers.com

7th Class Chemistry However, if magnetised iron is hammered, it loses its magnetism. The wax on heating changes into liquid state. However, liquid wax changes into solid on cooling. (iii) There is no change in weight during physical change: 10 g of solid ‘wax on melting will form 10 g of molten wax. If a salt solution is prepared by dissolving 20 g of salt in water, then on the evaporation of water, 20 g of salt is left behind. (iv) Only a little heat (if any) is absorbed or given off during physical change. If water changes into steam by absorbing a certain amount of heat energy, then steam will change into water by giving off the same amount of heat energy. The heat energy supplied during physical change, is in no way, utilised to change the composition of the molecules of a substance. Everyday examples of physical changes: Some of the very common examples of physical changes are given below : (i) Melting of ice or wax or butter or ghee. (ii) Freezing of water to ice or solidification of liquid wax to solid wax. (iii) Changing of water into steam by boiling. (iv) Evaporation of water by the heat of sun. (v) Condensation of water vapours, such as formation of clouds, mist, fog, etc. (vi) Glowing of an electric bulb on the passage of electric current, (vii) Magnetization of iron. (viii) Production of sound when two materials are hit together. (ix) Expansion or contraction of metals on heating, (x) Formation of solutions of soluble substances in water, (xi) Crystallisation of salts from their solutions. (xii) Change of colour due to heat as in case of zinc oxide or lead monoxide. (xiii) Beating of metals into sheets or drawing metals into wires, (xiv) Shaping of glass by heat.

Types of Changes

93

Formative Worksheet

Conceptive Worksheet

28. ‘x’ gms of solid wax on melting will form ____ gms of molten wax. (A) 2x gms (B) 4x gms (C)

1 gms(D) x gms x

29. Identify physical change(s)? (A) Formation of salt solution (B) Melting of wax (C) Evaporation of water (D) Magnetisation of iron 30. Statement I : 10g of solid wax at melting will form 10 g of molten wax. Statement II : Molecules of ice, water or steam always contain two atoms of hydrogen and one atom of oxygen. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true 31. Column-I Column-II On heating Change (A) Ice p) Salt (B) Salt solution q) Liquid wax (C) Solid wax r) Steam (D) Water s) Solid wax t) To form water 32. Statement I : Water changes into steam by absorbing a certain amount of heat energy. Statement II: Changing of water into steam by boiling is a chemical change. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true 33. Statement I : Water changes to steam by absorbing a certain amount of energy. Statement II: The heat energy supplied during the above change is utilised to change the composition of the molecules of a substance. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true

17. When we add common salt to water, salt solution is formed. Which of the following changes might have occurred in the salt solution? (A) The chemical composition of molecules changed slightly. (B) The mass of the salt solution increased. (C) Salt solution has some new substances. (D) The chemical composition remained the same. 18. The production of sound, when two materials are hit together is: (A) Physical change (B) Chemical change (C) Periodic change (D) None of these 19. Formation of salt solution is : (A) Periodic change (B) Chemical change (C) Physical change (D) Irreversible change 20. On heating zinc oxide change to : (A) White in colour (B) Brown in colour (C) Yellow in colour (D) Blue in colour 21. Which of the following is / are a physical change? (A) Liquification of gases to liquids (B) Melting of solids to liquids (C) Freezing of liquids to solids (D) Vaporisation of liquids to gases 22. Statement-I : A change which alters the specific properties of a material by bringing about a change in its composition, followed by change of state, is called chemical change. Statement -II : Decomposition of water into hydrogen and oxygen is physical change. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true Characteristics of a chemical change. (i) When a chemical change occurs new substances, with entirely new properties are formed. Candle wax on burning forms entirely new substances, i.e., carbon dioxide gas and steam. Mercuric oxide (red in colour) on strong heating forms new substances, i.e., mercury and oxygen gas. www.betoppers.com

7th Class Chemistry

94 Sugar on strong heating forms new substances, i.e., carbon and steam. Magnesium on burning forms entirely new substance, i.e., magnesium oxide. (ii) Chemical change cannot be easily reversed The carbon dioxide and steam formed during the burning of the candle, cannot be converted into wax by altering the conditions of experiment. Carbon and water vapour, formed during the heating of sugar, cannot be recombined to form sugar. Magnesium oxide formed during the burning of magnesium cannot be easily changed to original metal and oxygen. (iii) There is usually a change in weight during chemical reaction When magnesium is burnt in air, then the weight of white ash (magnesium oxide) is more than magnesium metal. For every 3 g of magnesium metal, 5 g of magnesium oxide is formed. When sugar is burnt, for every 7 g of sugar approximately 3 g of sugar charcoal is left. Similarly, when iron rusts, the weight of rusted iron is more than that of original metal, because the oxygen combines with iron. (iv) Lot of heat is usually given off or absorbed during, a chemical change When magnesium burns in air, it produces a large amount of heat and light energy. When mercuric oxide decomposes to form mercury and oxygen, it absorbs a large amount of heat energy. When sugar decomposes to sugar charcoal and steam, it absorbs large amount of heat energy. Everyday examples of chemical changes: Following are the common examples of chemical changes : (i) Cooking of food, (ii) Food turning bad after a few days, (iii) Curdling of milk. (iv) Fading the colours of clothes. (v) Germination of seeds, (vi) Ripening of fruits, (vii) Lighting of a match stick by striking match head with the side of match box. (viii) Digestion of food within our bodies, (ix) Respiration by humans, plants and animals. www.betoppers.com

(x) Decaying of old pieces of wood, (xi) Rusting of iron, (xii) Blackening of silverware, (xiii) Hardening of cement to form concrete block. (xiv) Fermentation of sugar solution to alcohol. (xv) Burning of wood, coal, kerosene oil, petrol or liquefied petroleum gas. Differences between physical and chemical changes Physical change

Chemical change

1) Change The change that The change that takes takes place in the place in the chemical physical properties composition of a of substances like substance. state, colour, volume, density etc. 2) Composition The identity of the The identity of the molecules or the molecule or the substance substance remains changes, and a new constant, as no new substance is formed, substance is formed. whose fundamental properties differ from those of the original substance. 3) Temporary or permanent change During a physical New molecules or change, the original substances, which substance can be cannot be converted to recovered merely the original substance, reversing the are formed. Hence, the conditions. Hence, chemical change is a physical change is permanent change. temporary change. 4) Recovery of original substances On reversing the On reversing the conditions, the original conditions, the original substance is recovered. substance cannot be recovered. 5) The weight of a substance The weight of a As a result of a substance, before and chemical change, the after a physical apparent weight of the change, remains substance formed constant. differs from the weight of the original substances.

Types of Changes

Formative Worksheet 34. If a small piece of quick lime is dropped in a beaker containing water. You can notice that water becomes very hot forming a milky white solution. What change does the above reactin illsutrate? (A) Change involving energy (B) Change involing time (C) Change involving concentration (D) Change involing volume 35. When water is added to concentrated sulphuric acid, heat is evolved but no new solution is formed and it is a reversible change. Therefore it is a: (A) Chemical change (B) Physical change (C) Physical and Chemical change (D) Neither Physical nor chemical change 36. Anhydrous copper sulphate turns blue, when a drop of water is poured over it. This illustrates: (A) Physical change (B) Chemical change (C) Slow change (D) Fast change 37. Which of the following is/are physical changes? (A) Freezing of ice. (B) Evaporation of water by the heat of sun. (C) Expansion and contraction of metals on heating. (D) Crystallisation of salts from their solutions. 38. Statement I : Candle wax on burning forms entirely new substances i.e., carbon dioxide gas and steam. Statement II: When the sugar burnt, for every 7 g of sugar approximately 3 g of sugar charcoal is left. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true 39. Study the following statements: i) Breaking of a glass pane is a physical change. ii) When a glass tumbler breaks into pices, the arrangement of molecules in glass changes. (A) (i) is true but (ii) is false (B) (i) and (ii) are both false (C) (ii) is true but (i) is false (D) (i), (ii) are both true

95 40. Choose the correct statements : (A) Heating of ammonium chloride strongly is a chemical change (B) Heating of zinc oxide is a physical change (C) Drying of a paint is a physical change (D) Condensation of water is a physical change 41.

heat Zn(OH)2 (s)   ZnO(s) + H2 O(g) heat ZnO(s)   ZnO(s) Cold and Hot and White Yellow (A) Physical change (B) Chemical change (C) Both physical and chemical change (D) Neither physical nor chemical change

Conceptive Worksheet 23.

24.

25.

Column-I Column-II (A) Sugar on strong heating p) Carbon dioxide and steam (B) Strong heating of mercuric oxide q) Carbon and steam (C) Burning of candle wax r) Magnesium oxide (D) Burning of magnesium s) Zinc oxide t) Mercury and oxygen When mix we iron fillings with sulphur and grind it, a ____A_____ takes place. If we heat the mixture a ____B_____ takes place. (A) A  Chemical change B  Physical change (B) A  Physical change B  Chemical change (C) A  Chemical change B  Chemical change (D) A  Physical change B  Physical change Which of the following, is true statement? (A) Chemical change cannot be easily reversible. (B) Ripening of fruits is chemical change. (C) Respiration by humans, plants and animals is physical change. (D) Fermentation of sugar solution to alcohol is chemical change. www.betoppers.com

7th Class Chemistry

96 26.

Heat (i) KNO3 (s)   KNO3 (l )

Heat (ii) 2KNO3 (l )   2KNO3 (l )  O2 (g) The above reaction illustrates: (A) (i) is a physical change (ii) is a chemical change (B) (ii) is a physical change (i) is a chemical change (C) (i) and (ii) both are physical changes. (D) (i) and (ii) both are chemical changes. 27. Statement I : In chemical change there is always net absorption or release of energy. Statement II: In physical change there is no net absorption or release of energy. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true

Summative Worksheet 1.

Sangita’s mother was making roti for  dinner. Sangita observed the steps followed by her mother to make roti and noted them down (as shown in the given table). I II III IV

2.

Sieving flour and bran Preparing dough by adding water to the flour Rolling out a roti from a ball of dough Baking of roti on the tawa

In the above list, the processes which are irreversible in nature are (A) I and II (B) I and III (C) II and IV (D) III and IV Raja cuts a square paper into two equal pieces. Then, he makes a toy aeroplane by folding one piece of the paper. He burns the other piece of the paper using a candle. He observed that three changes were involved in the whole process. He now wants to classify these changes as reversible and irreversible. In what manner should Raja classify the various changes?

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3.

(A)

Change Type of change I Irreversible II Reversible III Irreversible

(B)

Change Type of change I Reversible II Reversible III Irreversible

(C)

Change Type of change I Irreversible II Irreversible III Reversible

(D)

Change Type of change I Irreversible II Reversible III Reversible

Ramesh took some ice in a beaker and heated it on a burner. He added some salt to the water obtained and stirred it. He observed that the salt has disappeared. He then kept the beaker on the burner and boiled the water. Water gets evaporated leaving behind a white solid substance. Ramesh observed that the complete activity involves two major processes. Process I involves melting of ice to water, and process IIinvolves dissolving of salt in water. Which table lists the two processes correctly as reversible or irreversible? (A)

Process Type of change I Irreversible II Reversible

(B)

Process Type of change I Reversible II Reversible

(C)

Process Type of change I Irreversible II Irreversible

(D)

Process Type of change I Reversible II Irreversible

Types of Changes 4.

97

On burning a matchstick, new substances are 

, and the process is

.

The information in which alternative completes the given statement?

5.

(A)

i ii produced reversible

(B)

i produced

(C)

i ii not produced reversible

(D)

i ii not produced irreversible

ii irreversible

The tools that are used for digging soil are made by fixing an iron blade to a wooden handle. Normally, the ring of an iron blade is slightly smaller than the wooden handle. When the ring is heated, it easily fits into the handle and when it is cooled, the ring fits tightly into the handle. On heating, the iron ring the ring is

and on cooling

, and the whole process in nature.

The information in which alternative completes the given statement?

7.

Change Type of change Reversible (A) Melting of ice Sour ing of milk Irreversible

(A)

i contracts

iii expands

ii irreversible

Change Type of change Melting of ice Irreversible (B) Sour ing of milk Reversible

(B)

i contracts

iii expands

ii reversible

(C)

(C)

i iii ii expands contracts irreversible

i iii ii expands contracts reversible Ravi took some ice cubes in a kettle and closed its lid. Then, he kept the kettle on a burner. After sometime, he observed that the ice cubes have melted to form water. He also observed that steam was coming out of the spout of the kettle. The process that is involved in the formation of steam is called (A) expansion (B) boiling (C) evaporation (D) condensation Rajesh took some water in a kettle and closed its lid. He kept the kettle on the burner and placed an ice cooled plate just above the spout of the kettle.

(D) 6.

After sometime, he observed water drops falling from the plate. Which process is involved in the formation of the drops? (A) Evaporation (B) Condensation (C) Filtration (D) Decantation 8. Which of the following changes is an example of a reversible change? (A) Cutting of paper (B) Cooking of food (C) Melting of ice cream (D) Burning of a matchstick 9. A list of various changes is given. I. Burning of wood II. Melting of wax III. Dissolving sugar in water IV. Sawing of a piece of wood V. Ripening of fruits VI. Boiling of water In the given list, the irreversible changes are (A) II, IV, and VI (B) II, III,and VI (C) I, IV, and V (D) I, III,and V 10. Which table correctly lists the given changes as reversible or irreversible?

Change Type of change Melting of ice Reversible Sour ing of milk Reversible

Change Type of change Irreversible (D) Melting of ice Sour ing of milk Irreversible 11. The given table classifies some changes as reversible and irreversible.

Reversible change Folding of paper Boiling of water Cooking of food

Irreversible change Boiling of egg Burning of paper Rusting of iron

Which change is listed incorrectly in the table? (A) Boiling of water (B) Cooking of food (C) Boiling of egg (D) Folding of paper www.betoppers.com

7th Class Chemistry

98 12. Which of the following pairs of processes represents reversible change? (A) Melting and boiling (B) Cooking and boiling (C) Burning and melting(D) Cooking and burning 13.

HOTS Worksheet 1.

William makes a list of reversible and irreversible changes as shown in the given table. Reversible change Irreversible change Melt ing of ice Ripening of fruit Freezing of water Cooking of food Burning of sugar Digestion of food Which process is listed incorrectly in the given table? (A) Melting of ice (B) Burning of sugar (C) Cooking of food (D) Digestion of food 14. Identify the process I and II?

2.

 Water    Ice   Steam I

II

I

(A) Freezing

II Condensation

(B)

I II Evaporation Freezing

(C)

I II Condensation Melting

(D)

3.

I II Melting Evaporation

Process I Process II Reversible Reversible

(B)

Process I Reversible

(C)

Process I Process II Irreversible Reversible

(D)

Process I Process II Irreversible Irreversible

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Process II Irreversible

(A)

I II loose expansion

(B)

I II loose contraction

(C)

I tight

II expansion

(D)

I tight

II contraction

Which of the following changes is reversible? (A) Melting of ice (B) Souring of milk (C) Burning of wood (D) Ripening of fruits The information in which alternative is correctly matched? (A)

Change Type Cooking of food Reversible Digestion of food Irreversible

(B)

Change Type Cooking of food Irreversible Digestion of food Reversible

Change Type (C) Cooking of food Irreversible Digestion of food Irreversible

15. Neeta took some flour and prepared dough by adding water to the flour. She then rolled out a roti from  the  dough.  She  then  labelled  the  two processes as Process I and Process II. The information in which alternative correctly classifies the given process? (A)

During summers, the joints of a bridge become   because  of  . Which row correctly completes the given statement?

(D) 4.

Change Type Cooking of food Reversible Digestion of food Reversible

The given table lists some reversible and irreversible changes. The given table lists some reversible Reversible change Boiling of water Bending of wire Sour ing of milk

and irreversible changes. Irreversible change Cutting of trees Cooking of food Burning of wood

Which change is listed incorrectly in the given table? (A) Souring of milk (B) Cooking of food (C) Boiling of water (D) Bending of wire

Types of Changes 5.

6.

Which of the following changes is not a reversible change? (A) Water to ice (B) Water to vapours (C) Cow dung to biogas (D) Cold milk to hot milk Which of the following tables correctly lists the various processes as reversible and irreversible? (A)

(B)

(C)

(D)

7.

99 8.

Ramesh took some ice in a beaker and heated it on a burner. He added some salt to the water obtained and stirred it. He observed that the salt has disappeared. He then kept the beaker on the burner and boiled the water. Water gets evaporated leaving behind a white solid substance. Ramesh observed that the complete activity involves two major processes. Process I involves melting of ice to water, and process IIinvolves dissolving of salt in water. Which table lists the two processes correctly as reversible or irreversible?

Process Tearing a piece of paper Burning a piece of paper Rolling a roti Melting of ice Burning of candle

Change Reversible Irreversible Reversible Irreversible Reversible

Process Tearing a piece of paper Burning a piece of paper Rolling a roti Melting of ice Burning of candle

Change Irreversible Irreversible Reversible Reversible Irreversible

(B) Process Type of change I Reversible II Reversible

Process Tearing a piece of paper Burning a piece of paper Rolling a roti Melting of ice Burning of candle

Change Irreversible Irreversible Reversible Irreversible Reversible

(D) Process Type of change

Process Tearing a piece of paper Burning a piece of paper Rolling a roti Melting of ice Burning of candle

Change Reversible Irreversible Reversible Reversible Irreversible

Changes can be classified as reversible and irreversible changes. A list of some changes is given as follows. I. Freezing of water II. Folding a piece of cloth III. Mixing cement in water IV. Rusting of iron V. Souring of milk In the given list, which changes are irreversible? (A) I, III, and V (B) I, II, and III (C) II, IV, and V (D) III, IV, and V

(A) Process Type of change

I II

Irreversible Reversible

(C) Process Type of change

I II I II

Irreversible Irreversible Reversible Irreversible

9.

Changes can be classified as reversible and irreversible. The given table lists some reversible and irreversible changes. Reversible change Irreversible change Folding a piece of cloth Burning of paper Stretching a rubber band Melting of chocolate Which of the following changes is categorized incorrectly? (A) Folding a piece of cloth (B) Stretching a rubber band (C) Melting of chocolate (D) Burning of paper 10. Changes can be classified as reversible and irreversible changes. A list of some changes is given as follows. I. Freezing of water II. Folding a piece of cloth III. Mixing cement in water IV. Rusting of iron V. Souring of milk www.betoppers.com

7th Class Chemistry

100 In the given list, which changes are irreversible? (A) I, III, and V (B) I, II, and III (C) II, IV, and V (D) III, IV, and V 11. Which of the following processes is not a reversible process? (A) Folding of paper(B) Boiling of water (C) Boiling of egg (D) Heating of ice 12. Neeta took some flour and prepared dough by adding water to the flour. She then rolled out a roti from  the  dough.  She  then  labelled  the  two processes as Process I and Process II. The information in which alternative correctly classifies the given process? (A) Reversible

Process I

Process II Reversible

(B)

Process I Reversible

Process II Irreversible

(C)

Process I Process II Irreversible Reversible

IIT JEE Worksheet

Process I Process II (D) Irreversible Irreversible 13. The tools that are used for digging soil are made by fixing an iron blade to a wooden handle. Normally, the ring of an iron blade is slightly smaller than the wooden handle. When the ring is heated, it easily fits into the handle and when it is cooled, the ring fits tightly into the handle. On heating, the iron ring the ring

14. A list of various changes is given below. I. Cooking of food II. Burning of paper III. Baking  of roti on tawa IV. Expansion of a steel rim V. Melting  of  ice-cream VI. Souring of milk In the given list, the reversible changes are (A) IV and V (B) II and VI (C) I and IV (D) III and V 15. A metallic wire is fixed at both ends. This wire is being heated by a candle, as shown in the figure. On being heated, the wire (A) firstcontracts and then stiffens (B) first expands and then contracts (C) first contracts and then starts expanding (D) firstexpands and then sags down in the middle

I.

Single Correct Answer Type

1.

Which of the following is a reversible change? (A) Breaking of a glass tumbler (B) Melting of wax (C) Photosynthesis by plants (D) Curdling of milk Identify which is irreversible change (A) Falling of leaves from a tree (B) The ageing of plants (C) Weathering of rocks (D) All the above The farmers spray chemicals on vegetables and fruits to kill insects.This is example of: (A) Desirable change (B) Irreversaible change (C) Periodic change (D) Physical change Flooding of rivers in rainy season is an : (A) Reversible change (B) Undesirable change (C) Desirable change (D) Physical change Zinc oxide is yellow when hot and white when cold:

2.

and on cooling

, and the whole process 3.

is

in nature.

The information in which alternative completes the given statement? (A)

i iii ii contracts expands irreversible

(B)

i contracts

iii expands

ii reversible

(C)

i expands

iii contracts

ii irreversible

(D)

i expands

iii contracts

ii reversible

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4.

5.

This is an example of: (A) Chemical change. (B) Physical change (C) Both physical and chemical change (D) Neither physical nor chemical change

Types of Changes 6.

7.

8.

A banana browning in the air is a: (A) Chemical change .(B) Physical change. (C) Reversible change. (D) All the above. Formation of dew is: (A) Physical change (B) Chemical change (C) Reversible change (D) Both physical and chemical change A physical change is: (A) Permanent (B) Temporary (C) Both permanent and temporary (D) Niether permanent nor temporary

II. Multiple Correct Answer Type 9.

Which of the following is false statement(s)? (A) Burning of a match stick is a reversible change. (B) Rusting of an iron nail in damp air is fast change (C) Phenomenon of day and night is a non-periodic change (D) Breaking of a glass is a periodic change. 10. Identify that which is true related to desirable change? (A) Formation of curd from milk is desirable change. (B) Formation of manure from animal dung and dead leaves is desirable change. (C) Melting of snow on the mountains in the summer is desirable change. (D) Change of weather from winter to summer is a desirable change. 11. Which of the following is / are correct statement? (A) Heating of lead monoxide is physical change. (B) Changing of iron into magnet is a temporary change and no new products are formed. (C) Heating of sugar is permanent change. (D) Strong heating of mercuric oxide is a permanent change. 12. Identify, which of the following is correct statement? (A) Production of sound when two materials are hit together is a physical change. (B) Expansion or constraction of metals on heating is chemical change. (C) Shaping of glass by heating is chemical change.

101 13. Identify, which of the following is correct statement? (A) In chemical change specific properties of a substance change completely. (B) In physical change specific properties of the substance do not change. (C) Chemical change takes place in state, colour and texture. along with the change is composition (molecular properties) (D) In physical change molecular properties remains same. III. Paragraph Type The colour change in a banana peel is caused by chemical changes that are taking place in the cells of the bababa. A chemical change occurs when a substance reacts and form one or more new substances. 14. Which of the following is / are a chemical change?

15.

16.

17.

18.

19.

(A) Burning of fuels (B) Burning of crakers (C) A strong heating of mercuric oxide (D) All the above Identify the correct statement: (A) Heating of sugar is a permanent change. (B) Crystallisation of sugar is a chemical change. (C) Sugar decomposes to form charcoal which is a form of carbon. (D) Both 1 and 3. When zinc hydroxide is heated, it decomposes to form zinc oxide. This is an example of : (A) Physical change(B) Periodic change (C) Chemical change (D) All the above A change which some specific property of matter without any change in the composition of its molecules is called physical change. The production of sound, when two materials are hit together is: (A) Physical change(B) Chemical change (C) Periodic change (D) None of these Formation of salt solution is : (A) Periodic change(B) Chemical change (C) Physical change(D) Irreversible change On heating zinc oxide change to : (A) White in colour (B) Brown in colour (C) Yellow in colour (D) Blue in colour Cocking of food, food turning bad after few days. Curdling of milk, burning of wax, burning of fuels are the examples of a chemical change.

(D) Drawing metals into wires is physical change. www.betoppers.com

7th Class Chemistry

102 20. Study the following statements: i) Breaking of a glass pane is a physical change. ii) When a glass tumbler breaks into pices, the arrangement of molecules in glass changes. (A) (i) is true but (ii) is false (B) (i) and (ii) are both false (C) (ii) is true but (i) is false (D) (i), (ii) are both true 21. Choose the correct statements : (A) Heating of ammonium chloride strongly is a chemical change (B) Heating of zinc oxide is a physical change (C) Drying of a paint is a physical change (D) Condensation of water is a physical change 22.

heat Zn(OH)2 (s)   ZnO(s) + H2 O(g) heat ZnO(s)   ZnO(s)

Cold and Hot and White Yellow (A) Physical change (B) Chemical change (C) Both physical and chemical change (D) Neither physical nor chemical change

IV. Reasoning Type 23. Statement I: Agening of human beings are irreversible change. Statement II: A change in which cannot be reversed is called an irreversible change. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true 24. Statement I : Change of seasons is a periodic change. Statement II: The changes which occur again and again, after fixed intervals of time, are called periodic changes. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true www.betoppers.com

25. Statement I: On melting of butter the change is temporary in nature and no new substances are formed. Statement II: Physical changes are generally temporary in nature and no new substances are formed. (A) Both Statements are true, Statement II is the correct explanation of Statement I. (B) Both Statements are true, Statement II is not correct explanation of Statement I. (C) Statement I is true, Statement II is false. (D) Statement I is false, Statement II is true V. Matrix Matching 26. Column-I (A) Desirable change

Column-II p) Breaking of glass ware (B) Undesirable change q) Flooding of rivers (C) Periodic change r) Land slides (D) Non-periodic change s) Evaporation of water t) Change of weather from winter to summer

27. Column-I (A) Zinc oxide (B) Lead monoxide (C) Mercuric oxide (D) Sugar charcoal

Column-II p) Brown colour q) Red colour r) Black colour s) Yellow in colour t) White in colour

28. Column-I On heating (A) Ice (B) Salt solution (C) Solid wax (D) Water

Column-II Change p) Salt q) Liquid wax r) Steam s) Solid wax t) To form water 

IIT FOUNDATION Class VII

CHEMISTRY SOLUTIONS

© USN Edutech Private Limited The moral rights of the author’s have been asserted. This Workbook is for personal and non-commercial use only and must not be sold, lent, hired or given to anyone else.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without the prior written permission of USN Edutech Private Limited. Any breach will entail legal action and prosecution without further notice.

Utmost care and attention to the details is taken while editing and printing this book. However, USN Edutech Private Limited and the Publisher do not take any legal responsibility for any errors or misrepresentations that might have crept in.

Published by

:

USN Eductech Private Limited Hyderabad, India.

CONTENTS 1.

Language of Chemistry

..........

103 - 112

2.

Acids, Bases and Salts

..........

113 - 118

3.

Air and Its Components

..........

119 - 126

4.

Hydrogen

..........

127 - 130

5.

Coal and Petroleum

..........

131 - 134

6.

Types of Changes

..........

135 - 138

1. LANGUAGE OF CHEMISTRY SOLUTIONS

FORMATIVE WORKSHEET KEY Q.no 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Key A A B C MT C MT MT C D D D MT D D Q.no 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Key C MT D A D A D D D C C A D C D Q.no 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 Key D A,B B C C B,C MT D B B C B D C B Q.no 46 47 48 49 50 Key A C C C C

HINTS/ ANSWERS TO THE SELECTED QUESTIONS 1.

Compounds are formed when two or more elements combine chemically in fixed proportion. 2. The smallest particle of a compound having existence on its own is known as a molecule. 3. The properties of compound are similar to the properties of constituent elements. 4. Carbon (C) is an element and Carbon dioxide (CO2)is a compound. 5. A, B – r; C, D – p 6. 1 nm = 10–9 m = 10–7 cm 7. A – s; B – r C – q ; D – p 8. A – q; B – p C – s ; D – r 9. The smallest particle of matter that exist independently is called a molecule. 10. H2 is a diatomic molecule. He and Ne are the inert gases that exist independently in their atomic form. Hence are called mon atomic molecule. 11. Elementary molecules formed from same kind of atoms. Hence Cl2, O2 and O3 , all are elementary molecules. 12. Compound molecules are formed from the atoms of different elements. Here, Cl2, O3 and N2 are elementary molecules formed from same kind of atoms. H2O is a compound molecule fromed from the atoms of two different elements i.e., hydrogen and oxygen.

13. Sulphur, fluorine, ozone and helium exist as S8, F2, O3 and He in nature. Hence their atomicity is 8, 2, 3 and 1 respectively. Therefore, the right match is : A – u; B – q C – r ; D – p 14. The element with highest atomicity is carbon. Its atomicity is 60 in C– 60 molecule i.e., buckminister fullerene. 15. All the given molecules ( H2, F2, Cl2) are diatomic in nature. 16. Atomicity of ozone (O3) is 3. Therefore, x = 3. Atomicity of nitrogen (N2) is 2. Therefore, y = 2. The atomic number of the element = xy = 6 = carbon. 17. Carbonate ion = CO32–  Atomicity = 4 +3 Aluminium ion = Al  Atomicity = 1 +1 Cuprous ion = Cu  Atomicity = 1 +1 Sodium ion = Na  Atomicity = 1 Therefore, the right match is: A – s; B – p C – p ;D–p 18. (p) Sulphate ion  SO4 2– (q) Hydrogen  H+ (r) Hydride ion  H– (s) Nitrite ion  NO21– From the above, it is clear that sulphate and nitrite ions are polyatomic.

7th Class Chemistry

104 19. Cations are the postive ions formed by the loss of electrons. (A) Aluminium  Al+3 (B) Hydride  H– (C) Nitrite  NO2 – (D) Nitrate  NO3– From the atbove, it is clear that Aluminium is the cation. 20. Anions are the negative ions formed by the gain of electrons. (A) Nitride  N3– (B) Sulphide  S2– (C) Oxide  O2– All the above ions are anions. 21. O 2– 22. Ca = Ca+2 ; Mg = Mg+2 23. The elements with atomic numbers 1, 7 and 8 are hydrogen, nitrogen and oxygen respectively. All are non metals. 24. The atomic number of calcium is 20. 25. The number of protons in phosphorus is equal to the atomic number of phosphorus i.e., 15 26. The number of protons in sulphur is equal to the atomic number of sulphur i.e., 16. 27. Isotopes are defined as atoms having the same atomic number, but different mass numbers. 28. As istopes have same atomic number, they have same number of protons. As number of electrons in a neutral atom are equal to the number of protons, they have same number of electrons. As the chemical properties depends on the number of electrons in an atom, they have same chemical properties. 29. Isotopes contain an equal number of protons and electrons, but a different number of neutrons. 30. The atomic mass of an element is number of times an atom of an element is heavier than one-twelfth of the mass of carbon atom. That atomic mass of potassium 39. 31. Weight of one atom of an element = Atomic weight × amu.

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32. Atomic weight 

Weight of one atom of that element 1 weight of th of C 12atoms . 12

40  1.66 1024  40 1.66  1024  mass number = 40 and the element is either calcium or Argon.  Number of protons = 20 (or) 18. 34. Weight of He atom= 4 amu = 4 × 1.66 × 10–24g

33. Atomic weight 

Total weight 35. Number of atoms  weight of singleatom weight of single atom = (Atomic weight) amu = 39 amu = 39 × 1.66 × 10–24g. Total weight= Gram atomic weight = 39g 39g  Number of atoms  39  1.66  10 24 g

1024  6.023  1023 1.66 36. Atomic weight of silicon = 28  weight of one atom of silicon = 28amu  Weight of 100 atoms of silicon = 28 × 100 = 2800 amu. 37. The valency of lithium, barium, aluminium and zinc are 1, 2, 3 and 2 respectively. Therefore, the right match is: A – p ; B – q ; C – r; D – q. 38. (A) Nitride  N3–  valency = 3 

(B) Nitrate  NO3–  (C) Nitrite  NO2– 

valency = 1 valency = 1

(D) Sulphate  SO4–2  valency = 2 39. Valency of sulphide (S2–) is 2  x = 2 Valency of carbonate (CO32–) is 2  Valency of sulphite (SO32–) is 2  3– Valency of phosphate(PO3 ) is 3 

y=2 z=2 k=3

x y z 222  2 k 3 40. (P) Oxide  O 2–  valency = 2 3– (Q)Nitride  N  valency = 3 (R) Aluminium Al+3  valency = 3  (S) Magnesium  Mg+2  valency = 2 

Language of Chemistry Solutions

105

41. Iron has valency 2 and 3 in ferrous (Fe+2) and ferric (Fe+3)forms respectively. Silver has valency 1 and 2 in Argentous (Ag+1) and Argentic (Ag+2)forms respectively. 42. (i) Phosphate  PO33–  valency = 3 (ii)Nitrate  NO3–  valency = 1 + (iii) Potassium  K  valency = 1 (iv) Hydroxide  OH–  valency = 1 From the above it is clear that nitrate, postassium and hydroxide has same valency. 43.

Element Iron (Fe) Silver (Ag) Copper (Cu) Gold

47. i) The name of the element with lower valency in a compound ends with suffix ous. ii) The name of the element with higher valency ends with suffix ic. 48. The valency of Cu is 1 and 2 in ous and ic form respectively. Hence, when it combines with chlorine, it forms CuCl (Cu2Cl2) and CuCl2 respectively. 49.

M

N  M 3 N3  MN

3

3

50. The valency of Ferric is 3 and that of sulphate is 2. Therefore the formula of ferric sulphate is Fe2 (SO4)3

Valencies 2, 3 1, 2 1, 2 1, 3

44. The least valencies of iron, silver and lead are 2, 1 and 2 respectively, Therefore, x = 2, y = 1 and z = 2 x + z – y = 2 + 2 – 1 = 3 45. (i) Cations are formed by the loss of electrons and are basic radicals. (ii) Anions are formed by the gain of electrons and are acidic radicals. 46. In FeCl2, the valency of iron is 2. Whereas in FeCl3, it is 3.

51. a) Ca 3(PO4 )2 b) Na2S2O3 c) Mg3N2 d) MnO e) BaS f) Mg(NO3)2 52. C2 H 4 + 3O2 2CO2 + 2H2O  53. 2C2H 2 + 5O2 4CO2 + 2H2O  54. CH 4 + 2O2 CO 2 +  2H2 O 55. 2NH3 + 2Na 2NaNH2 + H2  56. Mn(OH)2 + 2Na2O2  Na2MnO4 + 2NaOH 57. Al2(SO4) 3 + 6NaOH 2Al(OH)3  + 3Na2SO4 58. 2KI + 3H2SO4  2KHSO4 + 2H2O + SO2 + I2 59. 2CuFeS2 + O2  Cu2S + 2FeS + SO2 60. 2FeS + 3O2 2SO2  2FeO +

CONCEPTIVE WORKSHEET KEY Q.no 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Key A B A D D C D C A B C D A D A D A Q.no 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 Key D A D D B A B C B A D B B B D A A Q.no 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 Key A,B C C B C A D A A B B A D B D

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7th Class Chemistry

106

HINTS/ ANSWERS TO THE SELECTED QUESTIONS 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

11. 12. 13.

14.

15.

16.

17. 18. 19. 20.

The basic form of matter that cannot be broken down into simpler substances is called an element. The smallest particle of matter that takes part in a chemical reaction is called an atom. Hydrogen is the smallest of all atoms. John Dalton introduced the symbols for the first time. The symbol for sodium is Na. The latin name of gold (Au) is Aurum. The latin name of Tungsten (W) is Wolfram. Symbols represents short hand notation of an element and one atom of that element. F2 is formed by same kind of atoms. Hence, it is an elementary molecule. The number of atoms constituting a molecule is known as its atomicity. For example the atomicity of Cl2 and O3 is 2 and 3 respectively. Ozone (O3) is a triatomic molecule. Helium (He), Neon (Ne) and Argon (Ar) are monoatomic molecules. In H2O, the mass contributed by hydrogens is 2 u. The mass contributed by oxygen is 16 u. Therefore, the ratio is 2 : 16 or 1 : 8. Ammonia = NH3 Therefore, the ratio of different element in ammonia is 1 : 3 Carbon dioxide= CO Therefore, the ratio of different element in carbon monoxide is 1 : 1 The charged species in which an atom or group of atoms posses a net electric charge is known as an ion or radical. Cations are formed by the loss of electrons and hence has postive charge. Carbonate ion (CO32–) is tetra atomic. Silver ion (Ag+) is a monoatomic ion. Ionic compounds are formed by the combination of ions. Na+ + Cl–  NaCl +2 – Mg + 2Cl  MgCl2 Ca+2 + O2–  CaO

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21. Atom is composed of fundamental particles like electrons, protons and neutrons. 22. In an atom, electrons keep revolving round the nucleus. And nucleus contain nucleons i.e., protons and neutrons. 23. The number of protons inside the atom of an element is known as atomic number. It is also equal to the number of electrons present in the neutral atom of an element. 24. The sum of protons and Neutrons inside the nucleus of an atom is called mass number. Mass number is also equal to the number of nucleons in an atom. 25. n = A – Z = 14 – 6 = 8 26. The atomic mass of chlorine is 35.5 27. The mass of one twelfth of mass of C-12 atom is equal to one atomic mass unit. 28. The atomc mass of calcium is 40. 29. Atomic mass of calcium is 40 and that of neon is 20. Therefore, the atomic mass of calcium is 2 times that of neon. 30. Atomic mass of carbon is 12 and that magnesium is 24. Therefore, the ratio is 1 : 2. 31. Atomic mass of sulphur = 32 and that of oxygen = 16. 32 = z × 16 z=2 32. Note: Change the (D) option to 1 : 4 : 4 Atomic mass of X = Half of that of oxygen (16)  Atomic mass of X = 8 Atomic mass of Y = Double of that of oxygen (16)  Atomic mass of Y = 32 Atomic mass of Z = 32 × atomic mass of hydrogen  Atomic mass of Y = 32 Ratio of atomic mass of X : Y : Z = 8 : 32 : 32 = 1 :4:4 33. The modern atomic weight scale is based on C – 12 isope’s atom. 34. 1 amu = 27

kg

1 th of C-12 = 1.66 × 10–24 g = 1.66 × 10– 12

Language of Chemistry Solutions

35. 1 amu =

107 46. Radicals are formed by the gain of electrons. Such radicals are called anions or negative radicals. 47. Metal phosphate = MPO4  Valency of metal = 3. Valency of nitrate (NO3–) is 1. Therefore, the formula of the metal nitrate is M (NO3 ) 3

1 th of C-12 = 1.66 × 10–24 g = 1.66 × 10– 12

27

36. 37. 38. 39.

40. 41. 42. 43.

44. 45.

kg The combining capacity of an element is called its valency. The valency of Aluminium (Al+3) is 3. The valency of sulphate ion (SO4–2) is 2. (A) Nitrite ion (NO2–)  Valency = 1 – (B) Nitrate ion (NO3 )  Valency = 1 +2 (C) Magnesium ion (Mg )  Valency = 2 + (D) Sodium ion (Na )  Valency = 1 –) The valency of hydroxide ion (IH is 1. Sulphur exibits variable valencies of 2, 4, 6. The formula of Calcium oxide is CaO. The number of electrons, lost, gained or shared with one atom of the element in order to acquine stable configuration of nearest noble gas element is called valency. An atom (or) a group of atoms which can exist independently with charge(s) is called molecule. Radicals are formed by the loss of electron (or) electrons. Such radicals are called cations or positive radicals.

48.

Na

PO 3  Na3PO 3

1

49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60.

3

The formula of sodium chloride is NaCl. Cu2S + CuSO4  3Cu + 2SO2 2Cu2 O + Cu2S  6Cu + SO2 2CuSO4 + 4KI  2CuI + I2 + 2K2SO4 3Fe + 4N2O  4N2 + Fe3O4 2CuCl2 + 2H2O + SO2  2CuCl + 2HCl + H2 SO4 4 2NaAg(CN)2 +Zn  2NaCN + Zn(CN)2 + 2Ag FeCl3 +3NH4 CNS  Fe(CNS)3 + 3NH4 Cl Ca 3(PO4 )2 +2H2 SO4  Ca(H2PO4)2+ 2CaSO4 CaCN2 +3H2O  CaCO3 + 2NH3 4Mg +10HNO3  4Mg(NO3 )2 + NH 4 NO 3 + 3H2 O 2Cu2S +3O2  2Cu2O + 2SO2

SUMM ATIVE WORKSHEET KEY Q.no

1

2

3

4

5

6

7

Key

C

C

A

C

B

D

C C B

Q.no

16

17 18

19 20 21

Key

D

D

C

B

A

9

10 11 12

13 14

15

C

A

C

D

A

C

C

HINTS / SOLUTIONS TO THE SELECTED QUESTIONS 1.

8

The law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction. Thus, the total mass before a reaction is equal to the total mass after the reaction.

2.

According to the law of conservation of mass, the total mass before a reaction is equal to the total mass after the reaction. Therefore, Mass of AgNO3 + Mass of HCl = Mass of AgCl + Mass of HNO3   x + 7.3 = 28.7 + 12.6   x = (28.7 + 12.6) – 7.3 = 34 g

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108 3.

It is given that the ratio by mass of carbon and oxygen in carbon dioxide is 3:8. Let the required mass of carbon and oxygen be 3x g and 8x g respectively. Now, 3x + 8x = 33  111x = 33   x = 3 Therefore, the required mass of carbon = 3 × 3 g = 9g And, the required mass of oxygen = 8 × 3 g = 24 g 4. The IUPAC approves the symbol Cu for copper. 5. The number of atoms constituting a molecule is known as its atomicity. A molecule of nitrogen molecule consists of two atoms of nitrogen. Hence, it is a diatomic molecule and its atomicity is 2. 6. A molecule of sodium oxide (Na2O) consists of one oxygen (O) and two sodium (Na) atoms. Atomic mass of Na = 23 u ; Atomic mass of O = 16 u Thus, the ratio by mass of atoms for Na2O can be calculated as: Na:O = 2 × 23 : 1 × 16 = 46:16 = 23:8 Or, O:Na = 8:23 7. A molecule of aluminium oxide (Al2O3) consists of two aluminium atoms and three oxygen atoms. Therefore, the ratio by the number of atoms for Al2 O3  is Al:O = 2:3. 8. Sulphide (S2–) ion is mono-atomic since it consists of only one single charged atom. 9. The symbols for sodium and carbonate ions are Na+ and  respectively. To write the chemical formula of the given compound, the constituent particles and their charges are written as shown in the figure. Then, by crossing over the charges of the combining particles, we get the chemical formula of sodium carbonate is Na2CO3. 10. The chemical formula of calcium hydroxide is Ca(OH)2 . Atomic mass of calcium (Ca) = 40 u Atomic mass of oxygen (O) = 16 u Atomic mass of hydrogen (H) = 1 u Molecular mass of any substance is the sum of the atomic masses of all atoms in a molecule of that substance. Thus, the molecular mass of Ca(OH)2 = 1× atomic mass of Ca + 2× atomic mass of O + 2× atomic mass of hydrogen = 1 × 40 + 2 × 16 + 2 × 1 = 40 + 32 + 2 = 74 u Hence, the molecular mass of calcium hydroxide is 74 u. www.betoppers.com

7th Class Chemistry 11. The molecular mass of any substance is the sum of the atomic masses of all atoms in a molecule of that substance. Molecular mass of magnesium chloride (MgCl2) = 1 × Atomic mass of Mg + 2 × Atomic mass of Cl = 1 × 24 + 2 × 35.5 = 24 + 71 = 95 u 12. Calculation of the formula unit mass is done in the same manner as that of the calculation of molecular mass. The formula unit mass of a substance is the sum of atomic masses of all atoms in a formula unit of that compound. The chemical formula of potassium chloride is KCl. Atomic mass of potassium (K) = 39 u Atomic mass of chlorine (Cl) = 35.5 u Thus, formula unit mass of potassium chloride (KCl) = 1 × atomic mass of K + 1 × atomic mass of Cl = 1 × 39 u + 1 × 35.5 u = (39 + 35.5) u = 74.5 u 13. Protons are subatomic particles that are positively charged. Neutrons are also sub-atomic particles that carry no charge. Hence, neutrons are neutral. 14. Protons and electrons have charge equal in magnitude but opposite in sign. Protons are positively charged and electrons are negatively charged. When the number of protons of an atom is more than the number of its electrons, then the atom is positively charged. Hence, an atom containing two protons and one electron is positively charged. 15. The mass number of an atom is the sum of the number of all the protons and neutrons present in that atom. Number of protons = 7 (given) Thus, the number of neutrons = 14 – 7 = 7 16. A neutral atom contains an equal number of protons and electrons. The given figure shows that the atom contains 15 electrons. Thus, the number of protons present in the atom is 15. The number of protons present in an atom represents the atomic number of the element. Thus, the atomic number of the given atom is 15, which represents the atomic number of phosphorus. Hence, the given figure represents the scematic atomic structure of phosphorus.

Language of Chemistry Solutions

109 would be positively charged. Similarly, if the number of protons is less than that of electrons, then the atom would be negatively charged. On the other hand, if the number of protons and electrons are equal in an atom, then the atom would be neutral. Hence, the atom having 8 protons and 7 electrons will be positively charged. 20. In a neutral atom, the numbers of protons and electrons are equal. Therefore, the atom of element X contains 10 protons. The atomic number of an element is the number of protons present in the atom of that element. Therefore, the atomic number of element X is 10. 21. In the nucleus of hydrogen, only one proton is present. There is no neutron present in the nucleus of a hydrogen atom.

17. Isotopes are atoms of the same element having the same atomic number, but a different mass number. Hydrogen has three isotopes. They are protium 11 H , deuterium

 H  , and tritium  H  . 2 1

3 1

4 1

H does not exist. 18. An isotope of uranium is used as a fuel in nuclear reactors. 19. Neutrons are neutral. Thus, the charge of an atom does not depend upon the number of neutrons it has. It depends upon the number of protons and electrons the atom has. The charges on a proton and on an electron are equal in magnitude, but opposite in sign. Protons are positively charged and electrons are negatively charged. Thus, if the number of protons is more than that of electrons in an atom, then the atom

HOTS WORKSHEET KEY Q.no

1

2

3

4

5

6

7

8

9

10

11 12 13 14

15

Key

A

C

A

A,B,C

C

D

D

B

MT

-

A

C

Q.no

16

17

19

20

21

22 23

24

C

A

D

A

C

A

34 A,B, C,D

35

36

37 38

39

C

MT

B

A

Key Q.no Key

31

18 A,B, D C,D 32 33

A

C

MT

C

HINTS/ ANSWERS TO THE SELECTED QUESTIONS 1. 2.

3. 4. 5. 6. 7.

The short hand representation of a compound is called formula. The formula gives the information of differnt kinds of elements and no. of atoms of each element present in a compound. Common salt is sodium chloride i.e., NaCl. Oxides formed from metals are metal oxides i.e., calcium oxide, copper oxide and mercury oxide. The formula of sulphur dioxide is SO2. The no. of atoms present in methane (CH4) is 5. 1 molecule of potassium nitrate (KNO3) contains 3 atoms oxygen. Therefore, 3 molecules of KNO3 contain 9 atoms of oxygen.

C 8. 9.

10. 11. 12. 13.

B

C

A

25 26 27 28 29 30 A,B B C A D MT C 40 D

Steam is water vapour has the same chemical composition as that of water i.e., H2O. a) Hydrogen chloride – HCl (C) b) Lead oxide – PbO (B) c) Washing soda – Na 2CO 3 (D) d) Iron sulphide – FeS (A) No question Baking soda is sodium bicarbonate (NaHCO3) Both the given statements are true. S8 contain 8 atoms of sulphur. www.betoppers.com

7th Class Chemistry

110 14. (A) Al2(SO4)3  4 × 3 = 12 oxygen atoms (B) 3KNO3 oxygen  3×3= 9 atoms (C) 2H2O  2 × 1= 2 oxygen atoms

15.

16.

17.

18. 19. 20. 21. 22.

23. 24. 25.

26. 27. 28.

(D) 4ZnO  4 × 1 = 4 oxygen atoms One molecule of zinc oxide (ZnO) contains 1 oxygen atom. Therefore, four molecules of ZnO contains 4 oxygen atoms. a) A gas with two oxygen atoms C a r b o n dioxide (CO2) (B) b) A gas with one chlorine atom Hydrogen chloride (HCl) (E) c) A gas with one oxygen atom C a r b o n monoxide (CO) , Steam (H2O) (C, D) d) A gas with four hydrogen atoms M e t h a n e (CH4 ) (A) i) Washing soda = Na 2CO3 .10H2 O ii) Common salt = NaCl iii) Blue vitriol = CuSO4.7H2 O iv) Lime stone. = CaCO3 All the given statements are correct. Aluminium sulphate = Al2(SO4)3 NaClO4 is the chemical formula of sodium per chlorate. Molecular formula of sulphur is S8. An ion (or) a radical formed by the acceptance of one electron is called monovalent electronegative ion. Bisulphite = HSO4– An ion (or) radical formed by the acceptance of two electrons is called bivalent electronegative ion. (A) Nitride  N 3– (B) Phosphide  P 3– (C) Phosphite  PO 3 3– (D) Carbonate  CO 3 2– From the above, it is clear that nitride, phosphide and phosphite are trivalent ions. Both the statements are true. Peroxide ion = O22– . Hydroxide ion = OH–.

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29. All the given radicals are electronegative. 30. (A) Hydride  H – (p) – (B) Nitrite (r)  NO 2 – (C) Nitrate (s)  NO 3

31.

32. 33. 34. 35. 36.

(D) Zincate  ZnO2 2– (s) (A) Phosphate  PO 4 3–– (B) Zincate  ZnO2 2– (C) Sulphide  S 2– (D) Acetate  CH3 COO – From the above, it is clear that phosphate ion is trivalent. Hydrogen sulphate = HSO4–. Formula of calcium chloride = CaCl2. All the given ions are bivalent. Oxide (O2–) is bivalent. (A) Cyanide  CN – (q) (B) Super oxide  O2

37.

38.

39. 40.

(p)

(C) Hydroxide  OH (r) – (D) Fluoride  F (s) i) Calcium sulphate  CaSO4 ii) Magnesium oxide  MgO iii) Potassium nitrite  KNO 3 From the given information, it is clear that the valency of metal is 1. Therefore, the formula of metal sulphate is MSO4. Valency of Ferric ion = 3. Therefore, the required formula is Fe2 (SO4)3. From the given information, it is clear that the valency of metal is 3. Therefore, the formula of metal nitrate is M (NO3)3.

Language of Chemistry Solutions

111

IIT JEE WORKSHEET Q.no Key Q.no

1 A

2

11 12 13 14 15 A,B, A,B, B A C B A B D C A A, B A,B, C B C,D D 17 18 19 20 21 22 23 24 25 26 27 28

16 Key A, B, A C, D

19. 29. 30.

3

4

5

6

7

8

9

10

B

B

C

C

A

B

D

B

B

5

2

Correction in the question: Change Fe+2 to Ca. A – r; B– s; C–p; D–q A – r; B– s; C–p; D–q

 

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112

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7th Class Chemistry

2. ACIDS, BASES & SALTS SOLUTIONS

FORMATIVE WORKSHEET KEY

1.

2.

3.

4.

5.

6. 7.

8.

9.

Q.no

1

2

3

4

5

6

7

8

9

10 11 12 13 14

15

Key

C

A

A

B

A

C

B

C

D

C

D

B

A

B

B

Q.no 16

17 18 19 20

21 22 23 24 25 26 27 28 29

30

Key

B

B

D

D

Q.no 31

32

Key

A

C

C

C

A

B

HINTS / SOLUTIONS TO THE All acids are sour in taste. Among the given substances, only lime juice is sour in taste. Hence, lime juice is an acid. An acid changes the colour of litmus paper to red. Among the given substances, only alcohol turns the colour of litmus paper to red. Hence, it is an acid. An acid changes the color of litmus paper to red, whereas a base changes the color of litmus paper to blue. An acid changes the colour of litmus paper to red, whereas a base changes the colour of litmus paper to blue. Vinegar changes the colour of litmus paper to red and soap solution changes the colour of litmus paper to blue. Hence, vinegar is acidic in nature, whereas the soap solution is basic in nature. An acid changes the colour of litmus paper to red, whereas a base changes the colour of litmus paper to blue. Since alcohol changes the colour of the litmus paper to red, it is acidic in nature. Citrus juice changes the colour of litmus paper to red as it is acidic in nature. Oranges, lemons, grapefruits contain vitamin C in the form of ascorbic acid and acids turns blue litmus red. Ascorbic acid is not found in acid rain. Ascorbic acid is also called vitamin C, which is present in citrus fruits. Lime water contains calcium hydroxide. It turns red litmus paper blue. Also, it gives a pink solution with phenolphthalein. Hence, it is basic in nature. Soda water contains carbon dioxide. It turns blue litmus paper red. Hence, it is acidic in nature.

D

A

A

C

B

D

C

SELECTED QUESTIONS Distilled water shows no colour change with either red or blue litmus paper. Hence, distilled water is neither acidic nor basic. It is neutral in nature. 10. Lactic acid is present in curd. 11. Litmus is the most commonly used natural indicator. It is extracted from lichens. It has a purple colour in distilled water. With acidic solutions, it turns red and with basic solutions, it turns blue. 12. Substances which are bitter in taste and feel soapy to touch are known as bases. For example, limewater and soaps are basic in nature. On the other hand, acid tastes sour. 13. An acid changes the colour of litmus paper to red, whereas a base changes the colour of litmus paper to blue. 14. Apart from being bitter in taste, a base changes the color of litmus paper to blue. Among the given substances, only baking soda is bitter in taste. Hence, it is a base. 15. The substances that are bitter to taste and soapy to touch are basic in nature. Among the given substances, baking soda and limewater are basic. 16. Alkaline solutions turn red litmus paper blue. Na2O + H2O  2NaOH (Alkali) 17. Calcium hydroxide is commonly known as slaked lime, which is obtained by the reaction of quick lime (calcium oxide) and water. 18. For treating the soil that is highly acidic, a base should be added to neutralise the effect. Thus, limewater, which is calcium hydroxide, can be added to the soil. Substances such as quick lime or calcium oxide can also be added.

7th Class Chemistry

114 19. Substances which are bitter to taste and soapy to touch are basic in nature. Thus, substance X is basic in nature. The colour of China rose indicator turns green with basic solutions and magenta with acidic solutions. Hence, substance X will turn the colour of China rose indicator to green. 20. A substance that turns red litmus to blue is basic in nature and the one that turns blue to red is basic in nature. Hence, liquid I is acidic and liquidII is basic in nature. Also, when an acid is mixed with a base, a salt is produced. This salt can be acidic, basic, or neutral in nature. 21. During indigestion, the stomach produces too much of acid, which causes pain and irritation. To get relief from this condition, a base is required to neutralize the excess acid produced. In this situation, milk of magnesia (an antacid) is taken. Milk of magnesia contains magnesium hydroxide, Mg(OH)2 , which is a mild base. It reacts with excess acid in the stomach and neutralizes it. 22. Neutralization reaction is the reaction between an acid and a base. In this reaction, the acid and base neutralize each other’s effect. A salt and water along with heat is produced in this reaction. Acid + Base  Salt + Water + Heat For example, hydrochloric acid and sodium hydroxide react to form sodium chloride (salt) and water with evolution of heat. HCl

Hydrochloric acid



NaOH   NaCl  H 2 O

Sodium hydroxide

Sodium chloride

Water

23. An acidic solution and a basic solution when mixed in suitable amounts, neutralise each other’s effect to produce salt and water. The reaction between an acid and a base is called a neutralisation reaction. A neutralisation reaction can be represented as: Acid + Base  Salt + Water + Heat Heat is generally evolved during the process. Hence, the reaction mixture will become hot. 24. Litmus paper changes its colour from red to blue in a basic solution and blue to red in an acidic solution and hence, soap bar is basic in nature and orange juice is acidic in nature.

25. Acids react with bases to produce salt and water. The reaction is called neutralization. Heat is also evolved during the process and this heat makes the reaction mixture hot. Thus, when dilute hydrochloric acid (an acid) is added to sodium hydroxide (a base), they react to produce sodium chloride (salt) and water along with the evolution of heat. Hence, the reaction mixture will become hot. 26. An acidic solution turns methyl orange to pinkish red. 27. The complete chemical reaction can be represented as HCl + NaOH  NaCl + H2O 28. In a neutralization reaction, an acid reacts with a base to form a salt and water. Sulphuric acid reacts with ammonium hydroxide to form ammonium sulfate (a salt) and water. Hence, this reaction is an example of a neutralization reaction. H2SO4 + 2 NH4OH  (NH4)2SO4 + 2 HOH Acid

 Salt + Water 29. Phenolphthalein is an indicator that remains colourless in an acidic solution. But, it gives a pink colour with basic solutions. Hence, when phenolphthalein is added to a base, the colourless basic solution will change to pink. 30. With China rose indicator, acids and bases give a dark pink and a green colour respectively. Neutral solutions will show no colour change with China rose indicator. Distilled water is neutral in nature. Hence, it will show no colour change with China rose indicator. 31. Turmeric is a natural indicator. With basic solutions, the colour of turmeric paste changes to red and with acidic solutions, it remains yellow. Soap is basic in nature. Hence, it will show a colour change with turmeric paste and will give red colour with it. 32. When hydrochloric acid reacts with sodium hydroxide, neutralisation reaction occurs. In this reaction, water and sodium chloride are formed. Sodium chloride is used as common salt. The given reaction can be represented by the following equation. HCl + NaOH  NaCl + H2O

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+ Base

Acids, Bases and Salts Solutions

115

CONCEPTIVE WORKSHEET KEY

6. 41. 42.

Q .n o

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

K ey

B

A

D

B

D

MT

C

A

A

B

B

B

B

C

C

Q .n o

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

B

D

A

B

A

K ey

C

C

B

C

B

B

C

C

B

C

Q .n o

31

32

33

34

35

36

37

38

39

40

K ey

B

D

D

C

B

A

C

A

D

C

A– s; B – r; C – q; D – p A– r; B – s; C – p; D – q A – s; B – r, C – q; D – p

SUMM ATIVE WORKSHEET KEY Q.no

1

2

3

4

5

6

7

8

9

10

Key

B

B

C

D

A

B

B

C

A

B

HINTS / SOLUTIONS TO THE SELECTED QUESTIONS 1.

China rose indicator produces green colour when added to a base. The original colour of China rose indicator is pink. It is prepared by adding some petals of China rose to warm water. The mixture is kept for some time until the colour becomes pink, as represented in the following figure.

2.

3.

4.

5. It gives dark pink colour with acidic solution and green colour with basic solution.

6.

With neutral solution, there is no change in the colour of China rose indicator. It remains pink.

As solution I changed red litmus to blue, it is basic. As solution II isnot affected by any litmus paper, it is neutral. Our stomach contains hydrochloric acid, which helps us digest food. During indigestion, excess acid is produced in the stomach which causes pain. This indigestion causes acidity in the stomach. Acids turn blue litmus paper red and bases turn red litmus paper blue. With neutral solutions, the colour of both blue and red litmus remains unaffected. Nitric acid is acidic in nature. Hence, it turns blue litmus paper red. Acids react with bases to produce salt and water. The reaction is known as neutralization. Heat is also evolved during the process. Thus, the word equation used to represent a neutralization reaction is: Acid + Base  Salt + Water + Heat Distilled water is neutral in nature. It shows no colour change with red and blue litmus paper. Lime water has calcium hydroxide in it. Calcium hydroxide is basic in nature. It turns red litmus paper blue. Also, it gives a pink colour with phenolphthalein indicator. Hence, lime water is basic in nature. www.betoppers.com

7th Class Chemistry

116 7.

Phenolphthalein gives a pink colour with basic solutions and it remains colourless with acidic solutions. Baking soda is sodium hydrogen carbonate, which is basic in nature. Thus, the solution of baking soda in water is basic. Hence, when a drop of phenolphthalein is added to a basic solution, then the colour of the solution changes to pink. 8. Acids turn blue litmus paper red and bases turn red litmus paper blue. Vinegar has acetic acid in it. Thus, acetic acid will change the colour of blue litmus paper to red. 9. Rose does not represent an indicator. When an acid or base solution is added to rose extract, there is no change in colour. Hence, we cannot distinguish between an acid or a base with the help of a rose. 10. The wastes from many factories generally contain acids. To neutralise their effect, basic substances should be added before these wastes are discharged in water bodies.

4.

5.

6.

HOTS WORKSHEET KEY Q.no

1

2

3

4

5

6

7

8

9

10 11

Key

A

A

C

B

C

B

A

B

B

C

A

HINTS / SOLUTIONS TO THE SELECTED QUESTIONS 1. Lemon juice is acidic in nature whereas limewater is basic in nature. On mixing the two solutions, salt and water are formed. This reaction is termed as neutralisation reaction. Heat is evolved during this reaction. In this reaction, both the acidic nature of the acid and the basic nature of the base are destroyed. Thus, it will have no effect on litmus solution. Also, it cannot be used to treat acidic soil. The correct answer is A. 2. Tamarind juice contains tartaric acid. On adding it to the turmeric paper, the colour remains yellow. With China rose indicator, a magenta colour is obtained. The red litmus paper remains unaffected. The correct answer is A. 3. Turmeric is a naturally occurring indicator. In acidic solutions, it remains yellow while in basic solution, it turns red in colour. In the given figure, the turmeric strip turns red on application of the substance ‘X’. Thus, X is basic in nature such as a soap solution. The correct answer is C. www.betoppers.com

7.

8.

9.

The substances that are used to test whether a substance is acidic or basic are known as indicators. China rose acts as an indicator. It can be prepared by boiling petals of China rose in water. It gives dark pink colour with acidic solutions and green colour with basic solutions. Soaps and shampoos are basic substances. Thus, the colour of the solution will turn to green. The correct answer is B. The chemical formula of oxalic acid is C2O2(OH)2. It is a naturally occurring component of green-leafy plants such as spinach. It is not present in citrus fruits such as oranges. Citrus fruits contain citric acid. The correct answer is C. Bases turn red litmus paper blue, and blue litmus paper remains unaffected in basic solutions. Hence, the substance mentioned above must be basic in nature. When an acid and a base are mixed, they neutralize the effect of each other. Since this substance can neutralize the effect of a sting, an ant’s sting must contain an acidic substance. The correct answer is B. Acids turn blue litmus red, and bases turn red litmus blue. On the other hand, neutral solutions do not change the colour of either red or blue litmus. Hence, the solution present in beaker III is neutral. Beaker I contains  an  acid  and  beaker II contains a base. When a suitable amount of acids and bases are mixed, they neutralize the effect of each other. Thus, the solution becomes neutral and such reactions are called neutralization reactions. By touching the beaker, Raju also observes that the reaction mixture has become hot. Heat is evolved or produced during the process and the produced heat raises the temperature of the reaction mixture. The correct answer is A. Acids are substances which are sour to taste. Hence, substance ‘X’ is acidic in nature. Acids turn blue litmus paper red, and red litmus paper remains unaffected with acidic solutions. Hence, substance ‘X’ will turn the colour of blue litmus paper red. The correct answer is B. Acids turn blue litmus paper red, and red litmus paper remains unaffected in acidic solutions. On the other hand, bases turn red litmus paper blue, and blue litmus paper remains unaffected in basic solutions.

Acids, Bases and Salts Solutions

117

Hence, X is  basic  in  nature,  while Y is  acidic  in nature. The correct answer is B. 10. Acids turn blue litmus paper red, and bases turn red litmus paper blue. On the other hand, both red and blue litmus papers remain unaffected with neutral solutions. Thus, the resulting solution obtained by mixing sodium hydroxide and hydrochloric acid is neutral in nature. It indicates that sodium hydroxide and hydrochloric acid have neutralized each other. He also observed that the resulting solution becomes hot, which means that heat is evolved or produced when sodium hydroxide reacts with hydrochloric acid. The correct answer is C. 11. Acids turn blue litmus paper red, while red litmus paper remains unaffected by acidic solutions. On the other hand, bases turn red litmus paper blue and blue litmus paper remains unaffected by basic solutions. Cola turns blue litmus paper red and does not change the colour of red litmus paper. Hence, cola is acidic in nature. The correct answer is A.

IIT JEE WORKSHEET Q.no Key Q.no Key

25. 26. 27.

1

2

3

4

5

6

7

8

9

10 11 12

B

A

C

A

C

C

C

D

A

C

A

A

13

14 15 A,B A,B A,D C C

16 17 18 19 20 21 22 23 24 A,B, A,B A,B B,C 1 7 5 7 7 C

A– s; B – r; C – q; D – p A– r; B – s; C – p; D – q A – s; B – r, C – q; D – p

 

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118

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7th Class Chemistry

3. AIR AND ITS COMPONENTS SOLUTIONS

FORMATIVE WORKSHEET KEY

Q.no

1

2

3

4

5

6

7

8

9

10

Key

D

A

D

B

A

A, B

C

A, B, D

a-3; b4; d-1

D

Q.no

11

12

13

14

15

16

17

18

19

20

Key

A

B

C

A

C

C

A, B, C, D

D

B, D

C

Q.no

21

22

23

24

25

26

27

28

29

30

Key

B

B

A

C

A

B

B

B

D

C

Q.no

31

32

33

34

35

36

37

38

39

40

Key

D

a-5; b2; c-1; d-3

A, B, C

A

B

A

C

A

A, B

B

Q.no

41

42

43

44

45

46

47

48

49

50

Key

A, B, C, D

C

B

A

A, B, C, D

A

D

A, B, C, D

B

B

Q.no

51

52

53

54

55

56

57

58

59

60

Key

B

A, B, C, D

A, B, C, D

A, B, C

A, B, C, D

B

A, B, C

A

a-4; b2; c-3; d-5, 3

B

Q.no

61

62

63

64

65

Key

B

D

7th Class Chemistry

120

CONCEPTIVE WORKSHEET KEY

Q.no

1

2

3

4

5

6

7

8

9

10

Key

B

D

A

D

C

B

B

B

A

A

Q.no

11

12

13

14

15

16

17

18

19

20

Key

D

B

C

B

C

A

B

A

D

B

Q.no

21

22

23

24

25

26

27

28

29

30

Key

B

C

D

D

D

A

C

D

B

B

Q.no

31

32

33

34

35

36

37

38

39

40

Key

D

A

C

D

B

D

B

A, B, C

A

C

Q.no

41

42

43

44

45

Key

A

A

B

B

A

SUMM ATIVE WORKSHEET KEY

Q.no.

1

2

3

4

5

6

7

8

9

10

Key

A

B

B

B

D

D

C

D

D

D

Q.no. 11 12 13 14 15 16 17 18 Key

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C

C

B

A

D

C

B

B

19 20 C

D

Air and its Components

121

HINTS / SOLUTIONS TO THE SELECTED QUESTIONS 1. Blowing air is called wind. In windmills, the energy of blowing air is used to rotate turbines and hence, to generate electricity. It is not used to propel sailing yachts. The correct answer is A. (OR) The energy of flowing water is used to generate electricity in hydropower plants. 2. Plants produce oxygen as a result of the process of photosynthesis. This is because they release more oxygen than what they take for respiration. The correct answer is B. 3. 78% of air is occupied by nitrogen, 21% by oxygen, and remaining 1% by other components of air such as carbon dioxide, dust, smoke, etc. Nitrogen and oxygen together comprise 99% of the total volume of air. The correct answer is B. 4. Air occupies and fills all the empty space. It forms a thin layer around earth called atmosphere. Oxygen is one of the components of air that is essential for burning. Nitrogen is not essential for burning. Hence, statement II is incorrect and statements I and III are correct. The correct answer is B. 5. Plants make their food in the presence of sunlight by using carbon dioxide present in the air. This process of making food by plants is known as photosynthesis. The correct answer is D. 6. Living organisms need oxygen for their survival. Oxygen in the air is used by the living organisms for the process of respiration. The relative percentages of the gases present in air are shown in the given pie chart. Carbon dioxide and other gases 1% Oxygen 21%

8.

9.

10.

11.

12.

13.

Water does contain air in a dissolved state. The aquatic organisms use this dissolved air to breathe. The correct answer is D. In the absence of air windmills do not produce electricity, birds and insects cannot fly, yachts, aeroplanes, gliders, etc. too do not move. The correct answer is D. When a lump of cotton is dropped into water, water displaces the air present inside the cotton and occupies that space. This air escapes from the cotton and appears as air bubbles. The correct answer is D. During the process of respiration in plants and animals, oxygen is consumed and carbon dioxide is released. During the process of photosynthesis, green plants consume carbon dioxide and release oxygen into the atmosphere. The level of oxygen and carbon dioxide in the atmosphere is thus maintained by plants and animals. The correct answer is C. Oxygen is used by living organisms during the process of respiration. This gas is also essential for the burning of objects. Green trees and plants produce oxygen. They consume carbon dioxide and release oxygen when they produce food by a process called photosynthesis. Thus, oxygen is the component of air that is essential during the process of burning. It is consumed by living organisms during respiration and is returned to the environment by green plants. The correct answer is C. An object burns in the presence of oxygen. During the burning process, carbon dioxide is released. Trees and plants produce food using carbon dioxide in the presence of sunlight by the process of photosynthesis. During this process, oxygen is released. During the respiration process, living organisms consume oxygen and release carbon dioxide into the air. O2

CO2

Nitrogen 78%

7.

From the above figure we conclude that oxygen contributes 21% of the composition of air. The correct answer is D. Moving air is called wind. Wind energy is used to produce electricity. The correct answer is C.

Burning

CO2

O2

Respiration

Photosynthesis

The correct answer is B.

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7th Class Chemistry

122 14. Dust comprises tiny, solid particles that are always present in air. As we inhale air, dust particles enter the nose. Fine hair and mucus present in the nostrils trap these dust particles and prevent them from entering the lungs. The correct answer is A. 15. Apart from the gases of nitrogen, oxygen, and carbon dioxide, particles of dust, smoke, and water vapour are also present in air. The gases of nitrogen, oxygen and carbon dioxide are not visible under sunlight. However, smoke, dust and water vapour can observed in the presence of sunlight. This is because dust, smoke, and water vapour reflect light. When a ray of sunlight enters a dark room through a tiny hole, the dust, smoke, and water vapour particles can be seen floating in air. The correct answer is D. 16. Plants make their own food in the presence of sunlight by using carbon dioxide that is present in the atmosphere. This process is known as photosynthesis. As a result of this process, plants release oxygen, which is essential for the survival of all living organisms. The correct answer is C. 17. Dust particles are pollutants and impurities that can cause harm if they enter the respiratory system. In order to prevent these from entering the body, fine hair and mucus is present inside the nostrils. The correct answer is B. 18. Humans release carbon dioxide gas during the process of respiration. In this process, humans inhale oxygen from the air and release carbon dioxide back into the air. The correct answer is B. 19. Although nitrogen is abundant in the atmosphere, it does not help in the process of burning. In fact, it is oxygen that is essential for the burning of any object. Without oxygen the process of burning cannot proceed. The correct answer is C. 20. Yacht is a type of boat that has a vertical flag and a mast. Moving air exerts a force on the mast along its direction. As a result, the yacht sails on the river in the direction of the moving air. Thus, the of source of energy that helps in the movement of the yacht is the moving air called wind energy. The correct answer is D.

HOTS WORKSHEET KEY 2

3

4

5

6

7

8

9

10

D

D

D

B

A

D

A

A

D

B

11 12

13 14 15 16 17

18

19 20

C

D

A

A

D

C

C

B

B

A

HINTS / SOLUTIONS TO THE SELECTED QUESTIONS 1. Burning or combustion is the process during which oxygen from the atmosphere is utilized to produce light and heat. In this process, carbon dioxide is produced. The correct answer is D. 2. Carbon dioxide is used by green plants to make food in the presence of sunlight. Living organisms consume oxygen and release carbon dioxide during respiration. When an object burns in the presence of oxygen, carbon dioxide gas is released. The correct answer is D. 3. Carbon dioxide and oxygen are respiratory gases. Most living organisms consume oxygen and release carbon dioxide. Green plants produce food using carbon dioxide and water in the presence of sunlight and chlorophyll. Oxygen is produced during this process of photosynthesis. Nitrogen is neither used for respiration nor is it a part of the photosynthesis process. Therefore, statements II and III are incorrect. The correct answer is D. 4. Air contains mostly nitrogen and oxygen. Together they make up 99% of air. Nitrogen makes up 78% and oxygen about 21% of air. Carbon dioxide, water vapour, and other gases add up to make the remaining 1% of air. Other gases Carbon dioxide

Oxygen Nitrogen

5.

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1

The correct answer is B. Wood cannot be burnt in the presence of strong winds. The correct answer is A.

Air and its Components 6.

7.

8.

9.

The height of the glass in container II is more than that in container I. Therefore, the glass in container II contains more air inside it. Air contains oxygen that supports burning. Therefore, the glass in container II has more oxygen. Hence, the candle in container II burns for a longer time than the candle in container I. When all the oxygen inside the glasses gets exhausted, the candles extinguish. Moreover, exhausted oxygen leaves vacant spaces inside the glasses. To fill up the vacant space left by the exhausted oxygen, water from the container rises up inside the glasses. Therefore, the water level rises more in container II than in container I. Therefore, after the experiment, Arunima is expected to observe that: 1. The candle in container I extinguishes first. 2. Water level in container II rises more than in container I. The correct answer is D. Air contains mostly nitrogen and oxygen. These two gases together constitute 99% of the atmosphere. Nitrogen constitutes 78% and oxygen about 21% of air. Carbon dioxide, water vapour, and other gases add up to constitute the remaining 1% of air. In the given pie-chart, the area covered under section II is the second largest and is almost 20% of the total area of the pie-chart. Therefore, the gas represented by section II is oxygen. The correct answer is A. Apart from the gases such as nitrogen, oxygen, water vapour, carbon dioxide, etc., dust particles are also present in air. Dust can be observed in the presence of sunlight as they reflect light. The correct answer is A. Almost all the objects contain carbon in it. When an object is burnt, oxygen reacts with the carbon present in the object and forms carbon dioxide. Therefore, statement I is correct. Carbon dioxide is released by all living beings during respiration while oxygen is consumed during respiration. Hence, statement II is correct. Carbon dioxide is consumed and used by green plants during photosynthesis to prepare food in the presence of sunlight. Therefore, statement III is incorrect. Therefore, among the given statements, II and III are incorrect. The correct answer is D.

123 10. When Mutum sits under a tree he feels cool and fresh. This is because all plants and trees release oxygen into the air. When people inhale this oxygen they feel fresh. Plants also release water vapour from their leaves by the process of transpiration. This vapour makes people feel relatively cool while sitting under a tree. The correct answer is B. 11. Traffic policemen manning busy intersections wear masks to protect themselves from the dust, smoke and pollutants that are released from various vehicles. These pollutants on entering the body can cause respiratory problems and other air-borne diseases. The correct answer is C. 12. Moving air is called wind. The energy possessed by moving air is called wind energy. This energy is harnessed by windmills to generate electricity. Blowing air rotates the turbines of the windmills in order to produce electricity. The correct answer is D. 13. Green trees and plants make their food by absorbing carbon dioxide from the air in the presence of sunlight. This process is known as photosynthesis. During photosynthesis, plants release oxygen into the air. This process helps in the cleaning up of the air. The correct answer is D. 14. The component of air that is released by animals through the process of respiration is carbon dioxide. In respiration animals inhale oxygen from the atmosphere and release carbon dioxide back into the air. Plants make their food in the presence of sunlight by using carbon dioxide present in the atmosphere. This process is known as photosynthesis. As a result of this process, plants release oxygen, which is essential for the survival of all living organisms. The correct answer is C. 15. The component of air that is released by animals through the process of respiration is carbon dioxide. During respiration animals inhale oxygen from the surrounding air and release carbon dioxide back into the air. Plants make their food in the presence of sunlight by using carbon dioxide present in the atmosphere. This process is known as photosynthesis. As a result of this process, plants release oxygen that is essential for the survival of all living organisms. The correct answer is C.

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7th Class Chemistry

124 16. Condensation is the process in which water vapour is converted into liquid or solid forms. This process takes place at low temperatures. Hence, one can see the water vapour present in the air when it condenses on a cold surface. For example, the accumulation of water drops on the exterior of a bottle of cold drink, when it is kept out in the open, is an example of the condensation of water vapour present in the air. . The correct answer is B. 17. The relative percentages of gases present in the air are shown in the following figure. Argon

Carbon dioxide

All others

Oxygen 21%

It is clear from the figure that nitrogen forms the maximum portion (78%) in the composition of air. The correct answer is B. 18. Living organisms need oxygen for their survival. Oxygen in the air is used by living organisms during the respiration process. The correct answer is A. 19. Small dust particles can be seen floating in the air when sunlight is allowed to enter a dark room through a small hole. Since smoke is composed of dust particles, it can be seen when sunlight enters a dark room through a small hole. The correct answer is A. 20. Wood is primarily composed of carbon. When it is burnt it produces carbon dioxide. This gas causes suffocation when inhaled. The correct answer is A.

Nitrogen 78%

IIT JEE WORKSHEET KEY Q.no.

1

2

3

4

5

6

7

8

9

10

Key

D

D

D

B

D

C

A

A

B

D

Q.no.

11

12

13

14

15

16

17

18

19

20

Key

A, B, D

A, B, C, D

A, B, C

A, B, C, D

A, B, C

B

D

B

A

A

Q.no.

21

22

23

24

25

26

27

28

29

30

Key

B

A

C

A

D

D

A

A

D

Q.no.

31

32

33

34

35

36

a-5; b-1; c-2; d-3

a-4; b-3; c-2; d-1

a-4; b-1; c-3; d-2

a-2; b-3; c-4; d-1

a-4; b-1; c-2; d-3

Key

HINTS / SOLUTIONS TO THE SELECTED QUESTIONS 1.

Oxygen is the component of air that is used in the burning of a candle. In fact, oxygen is essential for the burning of any object. Without oxygen, the process of burning cannot proceed. The correct answer is D.

2.

Plants make their food in the presence of sunlight by using carbon dioxide present in the air. This process of making food by plants is known as photosynthesis. The correct answer is D.

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3.

When a lump of cotton is dropped into water, water displaces the air present inside the cotton and occupies that space. This air escapes from the cotton and appears as air bubbles. The correct answer is D.

Air and its Components

125

4.

Condensation is the process in which water vapour 26. Every organism require air, water and food for is converted into liquid or solid forms. This process living. The substences exists in an impoper ratio in takes place at low temperatures. atmosphere. if solid, liquid and gaseous substences Hence, one can see the water vapour present in are present in higher volumes than required in air, it the air when it condenses on a cold surface. For is harmful to air. It is called air pollution. example, the accumulation of water drops on the 30. 76 exterior of a bottle of cold drink, when it is kept out 31. 0.07 in the open, is an example of the condensation of water vapour present in the air. . The correct answer is B. 5. Green trees and plants make their food by absorbing carbon dioxide from the air in the presence of sunlight. This process is known as photosynthesis. During photosynthesis, plants release oxygen into the air. This process helps in the cleaning up of the air. The correct answer is D. 6. The component of air that is released by animals through the process of respiration is carbon dioxide. During respiration animals inhale oxygen from the surrounding air and release carbon dioxide back into the air. Plants make their food in the presence of sunlight by using carbon dioxide present in the atmosphere. This process is known as photosynthesis. As a result of this process, plants release oxygen that is essential for the survival of all living organisms. The correct answer is C. 7. Wood is primarily composed of carbon. When it is burnt it produces carbon dioxide. This gas causes suffocation when inhaled. The correct answer is A. 8. Living organisms need oxygen for their survival. Oxygen in the air is used by living organisms during the respiration process. The correct answer is A. 9. Plants produce oxygen as a result of the process of photosynthesis. This is because they release more oxygen than what they take for respiration. The correct answer is B. 10. Yacht is a type of boat that has a vertical flag and a mast. Moving air exerts a force on the mast along its direction. As a result, the yacht sails on the river in the direction of the moving air. Thus, the of source of energy that helps in the movement of the yacht is the moving air called wind energy. The correct answer is D. 23. The air is absolutely essential for respiration for all forms of life. The precess of resperation is similar to the precess of burning, except that heat energy is released in controlled amount.



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126

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7th Class Chemistry

4. HYDROGEN SOLUTIONS

FORM ATIVE WORKSHEET 1. 2. 3. 4.

2.

9.

Lavoisier in 1783 established the name ‘ hydrogen’ meaning ‘water producer’. Hydrogen does not occur in the free state on earth. Hydrogen is present in traces in the atmosphere around the sun and stars A compound, one ninth by mass of which is hydrogen in the combined state is Water. The correct answer is (A) Robert Boyle prepared hydrogen in 1672, by 10. treating iron with sulphuric acid, but was unable to establish its elementary character. The credit of discovery of hydrogen goes to Henry Cavendish, who prepared it by the action of dilute 11. hydrochloric acid, with zinc in 1766. He not only established its elementary character, but also proved that, when hydrogen is burnt in air it forms water. 12. Because of its property of water formation, it was named hydrogen by Lavoisier in 1783, as hydrogen means water former in Greek language.

3.

2K + 2H2O  2KOH + H2 Mg + H2O

4.

5.

6.

7. 8.

 MgO + H2 Zn when reacted with cold water does not liberate hydrogen. When it reacts with steam, it liberates hydrogen. Magnesium and Manganese how ever, react with very dilute HNO3 at the low temperatures liberating hydrogen.Since, the oxidising action of the acid is much reduced due to dilution. Both assertion and reason are correct and reason is the correct explanation of assertion. The correct answer is (A). Assertion is correct and reason is incorrect. The correct answer is (C) The hydrogen evolved contains impurities such as NO2, SO2, CO2, H2S, etc. ‘A’ is true, ‘B’ is false. The correct answer is (A).

13.

14. 15. 16.

Pb(NO3 )2 solution

Impurities absorbed As H3(Arsene) and PH3 (Phosphine) H2S (Hydrogen Sulphide)

KOH solution

NO2, SO2 and CO3

Anhydrous CaCl2

Moisture (H2O)

Solution AgNO 3 solution

Both assertion and reason are correct and reason is the correct explanation of assertion. The correct answer is (A). 0

1000 C C  H 2 O    CO  H 2  

 Coke 

 steam 

Water gas 0

450 C  CO 2  2H 2    CO  H 2  H 2 O  Fe O Water gas

 steam 

2

3

Comparitive density – 14.4 less dense than air Solubility in water – Practically insoluble in water Liquefaction – Hydrogen is a difficult gas to liquefy. Nature – Hydrogen is neutral towards litmus solution. Both assertion and reason are correct and reason is the correct explanation of assertion. The correct answer is (A). All the statements are correct. The correct answer is (D). Both statements are false. The correct answer is (D). ZnO

+ H2

   Zn +

H2O

H2  S   H2 S  Fe2O3 + 3H2   2Fe + 3H2O The correct answer is (B).

7th Class Chemistry

128 17.

1. CH 2 .O.OCC17 H33

CH 2 .O.OCC17 H35

|

|

Ni, 180°C CH.O.OCC17 H 33  3H 2  

CH.O.OCC17 H 35

|

|

CH 2 .O.OCC17 H33

CH 2 .O.OCC17 H35

Thiolein

Tristearin

 Oil M.P.  5° C 



4.

+ H2

  Pb

+ H2O

b) ZnO

+ H2

   Zn

+ H2O

   2Fe

+ 3H2O

5.

6.

CONCEPTIVE WORKSHEET 1. 2. 3. 4. 5. 6. 7. 8.

9. 10. 11. 12. 13.

B D B, C, D C D D D Lead chloride or lead sulphate formed during the reaction of lead and HCl/H2SO4 are insoluble in water and hence, settle over the surface of lead. This in turn breaks the contact of acid with lead and reaction stops. Mg (s) + 2 HCl (aq)  MgCl2 (aq) + H2 (g) C C D Zinc reacts with sulphuric acid form zinc sulphate and hydrogen gas.

14.

Catalyst CO+ H 2 + H 2 O   CO 2 + 2 H 2   

15. 16. 17. 18. 20. 22.

A, C C Hydrogen is insoluble in water. B 19. D D 21. C B

Water gas

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C C Symbol Atomic weight Atomic number Electronic Configuration

a) PbO

c) Fe2O3 + 3H2

1. 2. 3.

 Fat M.P.71° C 

2. Oxyhydrogen flame 3.Hydrogen 4.sodium hydroxide 5.Lead 18.

SUMMATIVE WORKSHEET

7. 8. 9. 10. 11. 12. 13. 14. 15. 16.

: : :

H 1.008 1

:

K 1

Valency : 1 Zinc on boiling with sodium hydroxide form sodium zincate and liberate hydrogen gas. If a burning splinter is introduced into the mixture of hydrogen and air, it is observed that the flame puts of with pop sound. In Bosch process hydrogen gas can be prepared by mixing steam and water gas at 500°C in the presence of Fe3O4 and Cr2O4. D C D C B C D A,B C D

HOTS WORKSHEET 1.

 2H 2  O 2 from the equation, it is 2H 2 O  clear that on electrolysis 2 × 18gms of H2 O   2  2 gms of H2 and 32 gms of oxygen. (i) Mass of hydrogen formed = 4gms and Mass of oxygen formed = 32 gms.

(ii)No.of atoms of hydrogen =

Mass of hydrogen ––– (1) Mass of one atom of hydrogen

Mass of one atom of hydrogen = 1 amu = 1 × 1.66 × 10–24 gm Substituting the above values in eq. (1), we get

Hydrogen

129

No. of atoms of hydrogen



4  4  6.023  1023 24 1.66  10

IIT JEE WORKSHEET 1.

(a) Zn is less reactive metal. Hence, it does not liberate H2 with cold water.

2.

(d) The metal that adsorbs hydrogen is palladium.

Mass of oxygen ––– (1) Mass of one atom of oxygen

3.

(d) The affinity of Aluminium towards oxygen is more. Hence, H2 cannot reduce Al2O3

Mass of one atom of oxygen = 16 amu

4.

(a) The mass no, of the three isotopes of hydrogen protium (1H1), deuterium (1H2) and tritium (1H3) is 1, 2 and 3 respectively. Mass no. no. of neutrons + no. of protons. Therefore, the no.of neutrons and protons in tritium are 3.

5.

(C) Cavendish was the person who discovered and established elementary nature of H2.

atoms of oxygen. a) Postassium b) Calcium hydride c) Lead d) Potassium aluminate e) Magnesium f) Iron oxide g) Fractional distillation h) Electrolysis i) SO2 j) Oxygen

6.

(a) The metals which are placed below hydrogen, cannot displace H2 among the given element. Hg is the element which is placed below hydrogen. Hence, it does not give hydrogen.

7.

(a) Nascent hydrogen means, just born hydrogen. It possesses more energy and is highly reactive.

2HCl  Ca  H 2  CaCl 2

8.

(c) Hydrogen atoms being unstable, they exist as diatomic molecules and it forms both H+ & H– ions.

9.

(c) H2 undergoes chemical reaction (reduces) with the H2SO4. Hence, it is not suitable to dry H2.

10.

(c) Hydrogen is short of one electron to the nearest noble gas configuration (helium), like that of halogens.

11.

(b) Mangances and magnesium, the only metals that react with dil. HNO3 and form hydrogen.

12.

(b) The non radioactive isotope of hydrogen is deuterium..

No. of atoms of oxygen =

= 16 × 1.66 × 10

–24

Substituting the above value of eq. (2), we get No. of atoms of oxygen 

2.

3.

32  2  6.023  1023 16  1.66  1024

3H 2  N 2  2NH3 NH 3  HCl  NH 4 Cl (White dense fumes)

4. 5.

A = HCl; B = H2; C = CaCl2; D = N2; E = NH3 (i) False (ii) Ture(iii) True (iv) False (v) True (vi) True

Zn  2HCl  ZnCl2  H2  H 2  S  H 2S  H 2S  Pb  CH 3COO 2  PbS  2CH 3COOH

A = HCl B = ZnCl2 C = H2 D = S E = H2S F = PbS G = CH3COOH

13. A,B,C,D 14. Pure hydrogen in colourless, odourless and tasteless gas. So, the correct answers are A, C, D 15. A, B, C 16. Fe2O3 + 3H2

  

2Fe +

3H2O

So, x1 = 1 , x2 = 3, x3 = 2, x4 = 3 x1 + x 2 + x 3 + x 4 = 1 + 3 + 2 + 3 = 9 So, the correct answer is C. www.betopperss.com

7th Class Chemistry

130 17. PbO + H2

  

Pb +

H2O

So, x1 = 1 , x2 = 1, x3 = 1, x4 = 1 x1 + x 2 + x 3 + x 4 = 1 + 1 + 1 + 1 = 4 So, the correct answer is (B). 18. ZnO + H2

  

Zn +

H2O

So, x1 = 1 , x2 = 1, x3 = 1, x4 = 1 x1 + x 2 + x 3 + x 4 = 1 + 1 + 1 + 1 = 4 So, the correct answer is (B). 19. Nitric acid in the dilute form is not used in the preparation of hydrogen from metals. HNO3 is a powerful oxidising agent and the nascent oxygen formed on its decomposition oxidises the hydrogen to water. So, both ‘A’ and ‘B’ are true. So, the correct answer is (C). 20. Granulated zinc is placed at bottom of the Woulfe’s bottle and hydrochloric acid [or sulphuric acid] is added slowly from the thistle or dropping funnel. Hydrogen gas evolves with brisk effervescence. So, both ‘A’ and ‘B’ are true. So, the correct answer is (C). 21. Both ‘A’ and ‘B’ are true. So, the correct answer is (C). 22. A. Lavoisier in 1783 established the name ‘ hydrogen’ – Meaning ‘water producer’.

B.

Hydrogen does not occur – In the free state on earth.

C. Hydrogen is present in traces in – The atmosphere around the sun and stars D. A compound, one ninth by mass of which is hydrogen in the combined state is – water Composition

23.

Impurities absorbed

AgNO3 solution

As H3 (Arsene) and PH3 (Phosphine)

Pb(NO3) 2 solution

H2 S (Hydrogen Sulphide)

KOH solution

NO2 , SO2 and CO3

Anhydrous CaCl2

Moisture (H2 O)



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5. COAL & PETROLEUM SOLUTIONS

FORMATIVE WORKSHEET 1.

Forests, wildlife, minerals are examples Exhaustible resources. Therefore, A is correct and R is wrong. Therefore, the right answer is (c)

2.

Both the statements are correct. (c)

3.

i) Coal

4.

The slow process of conversion of dead vegetation into coal is called Carbonisation.

ii)

Coal

CONCEPTIVE WORKSHEET 1.

Both A and R are correct and R is the correct explanation of A. 2.

i) Carbon dioxide ii) Coal gas iii) It is used in the extraction of metals.

3.

i) Around 200 substances ii) a) Coal is used to cook food.

C + O2  CO2

b) It is used in thermal power plants to produce electricity.

So, A is wrong and R is correct. Therefore, the right answer is (d) 5.

A  Q; B  Q ; C  P; D  P

6.

A  Q; B  R; C  P; D  S

7.

i) Coke ii) iii) Coal gas

8.

Petroleum is a dark oily liquid. It is a mixture of various constituents. Its constituents very useful.

c) It is also used as industrial fuel. iii) a) It is used a source of various useful substances.

Coal tar

Due to its great commercial importance petroleum is also called black gold.

b) It is used to get naphthalene which is used to repel moths and other insects. c) It is used to make road surface. 4.

Petroleum is a dark oily liquid. It has an unpleasant odour.

i) Petroleum Conservation Research Association. ii) Compressed Natural Gas

A is correct and R is the correct explanation of A. 9.

Fossil fuels are formed from fossils. Coal, petroleum and natural gas are fossil fuels.

iii) Liquified Petroleum Gas 5.

CNG is called clean fuel because: (i)

It burns directly for burning.

Therefore, statement - I is true, Statement - II is false.

(ii)

It does not produce any pollution.

10.

i) Refining Petrochemicals

(iii)

No residue is left after burning of CNG.

(iv) It burns completely in the air.

11.

A is wrong and B is correct.

12.

A  Q; B  P; C  Q; D  R

13.

A  S; B  R; C  Q ; D  P

14.

i) Napthalene balls ii) Bitumen iii) Pennsylvania USA in 1859.

ii) 6.

Many useful substances are obtained from petroleum and natural gas. These are called petrochemicals. Petrochemicals are used in the manufacture of detergents, fibres, polythene and other plastics and fertilizers.

7th Class Chemistry

132

7.

Natural gas is a very important fossil fuel because it is easy to transport through pipes. It is used in the form of CNG as fuel and generation of power.

8.

CNG is called clean fuel because:

4.

The resources which are present in limited in nature and can be exhausted by human activities are called exhaustible natural resources. For example: forests, wildlife and minerals etc.

5.

The remains of dead plants and animals are called fossils. The fuels formed by the remains of dead plants and animals are called fossil fuels. Main fossil fuels are: coal petroleum and natural gas.

6.

Coal is a fossil fuel it is hard as stone.

(i) It burns directly for burning. (ii) It does not produce any pollution. (iii) No residue is left after burning of CNG. (iv) It burns completely in the air. 9.

10.

Harmful effects of burning fossil fuels are as following: (i) Burning of fossil fuels cause air pollution.

Uses:

(ii) They also cause global warming because they produce green house gas carbon dioxide gas on burning.

(ii) It is used in thermal power plants to produce electricity.

Many useful substances are obtained from petroleum and natural gas. These are called petrochemicals.

(iii) 7.

Petrochemicals are used in the manufacture of detergents, fibres, polythene and other plastics and fertilizers.

2.

The resources provided by nature or obtained from the nature are called natural resources. For example: air, water, soil and sunlight etc.

(ii) Exhaustible natural resources: Forests, Wild life, Minerals and Coal etc. 3.

8.

On the basis of the availability various natural resources in nature can be classifier. the following two groups: (i) In exhaustible natural resources: Air, Water, Soil, Sunlight, etc.

The resources which are present in unlimited quantity in nature and are not likely be exhausted by human activities are called inexhaustible natural resources. For example: Air, Sunlight etc.

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Coal is used to cook food.

It is also used as industrial fuel.

Coke is a tough porous and black substance. It is almost purest form of carbon. It is formed by heating coal in the absence of air. Uses:

SUMM ATIVE WORKSHEET 1.

(i)

9.

(i)

It is used in manufacture of steel.

(ii)

It is used in the extraction of metals.

Coaltar is a black thick liquid. It is a mixture of about 200 substances. Uses: (i)

It is used a source of various useful substances.

(ii)

It is used to get naphthaline which is used to repel moths and other insects.

(iii)

It is used to make road surface.

Coal gas is a by product formed when coal is heated in absence of air. Uses: (i)

It is used as fuel in many industries.

(ii)

Previously it is used for street lighting in London in 1810.

Coal and Petroleum

10.

Petroleum is a dark oily liquid. It is a mixture of various constituents. Its constituents very useful. Due to its great commercial importance petroleum is also called black gold.

11.

The world’s first oil well was drilled in Pennsylvania U.S.A. in 1859. The first oil well was drilled at Makum in 1867 in India.

133

5.

Coke, coal tar, and coal gas are products of destructive distillation of coal. During the processing of coal to obtain coke, coal gas and coal tar are obtained as by-products. The correct answer is D.

6.

Coke is obtained from coal, a fossil fuel. The correct answer is A.

12.

The process of separating various components or fraction of petroleum is called refining. The device where it is carried out is called petroleum refinery.

7.

HOTS WORKSHEET 1.

2.

3.

4.

Coal, petroleum, and methane are found in solid, liquid, and gaseous states respectively. The correct answer is C. The constituent of petroleum that is used in paints and road surfacing is Bitumen. The correct answer is B. Exhaustible natural resources are those resources in nature whose amount is limited and can be exhausted by human activities. Coal and minerals are found in limited quantities and their amount is depleting. They cannot be replenished. Therefore, coal and minerals are exhaustible natural resources. The correct answer is A. About 300 million years ago, there were dense forests in low lying wetland areas of the earth. These forests got buried under the soil because of some natural processes such as flooding. Over the course of time, more soil deposited over them and they were exposed to high temperature and pressure conditions. Under the said conditions, this vegetation got slowly converted into coal. This process is called carbonization. The correct answer is D.

Coal tar is obtained from coal, an exhaustible natural resource. It is a liquid that is a mixture of about 200 substances. It has an unpleasant smell. Synthetic dyes, plastic paints, explosives, perfumes, etc are obtained from coal tar. Hence, the substance X is coal tar. The correct answer is B.

8.

The process through which coal is formed is called carbonization. It is a slow process during which the dead vegetation such as trees and plants are converted into coal under very high temperature and pressure. The correct answer is B.

9.

Coal is form by a process called carbonization. In this process dead vegetation such as trees and plants get converted into coal under conditions of high temperature and pressure, deep under the Earth’s crust. The correct answer is B.

10.

Coal, petroleum, natural gas, etc. are fossil fuels. These are formed from the remains of dead organisms that were buried under the Earth’s crust over millions of years ago. Hence, statement I is correct. Fossil fuels are exhaustible natural resources because these are found in limited amounts. Excess use of fossil fuels causes global warming www.betoppers.com

7th Class Chemistry

134

and depletion of these resources. Hence, statement II is correct. Earthquake is a natural phenomenon that is caused by the movement of tectonic plates under the Earth’s crust. It is not caused by excess use/ burning of fossil fuels. Hence, statement III is incorrect. The correct answer is C. 11.

Petroleum is not an inexhaustible resource. The reserves of petroleum on Earth are limited; therefore it is an exhaustible resource. The correct answer is C.

12.

Coal is a natural resource. Coal is found in limited quantities and its amount is depleting. It cannot be replenished and therefore coal is an exhaustible natural resource. The correct answer is B.

13.

Many substances are obtained from petroleum and natural gas. Some of these products are fertilizers, detergents, fibres, nylon, polythene etc. These products are together called petrochemicals. The correct answer is D.

14.

The petroleum conservation research association (PCRA) of India is the prime body to issue advice that helps to conserve petrol/diesel. According to PCRA, driving at a very high speed consumes more fuel. Hence, driving at a moderate speed helps to conserve petrol/diesel. The correct answer is A.

15.

Petrol is not only used as a motor and aviation fuel but also as a solvent for dry cleaning. The correct answer is A.

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6. TYPES OF CHANGES SOLUTIONS

FORMATIVE WORKSHEET KEY Q.no

1

2

3

4

5

6

7

8

9

10

11

12 13

Key

B

D

B

MT

B

D

C

A,D

C

D

B,C

A

Q.no

16

17

18

19

20 21

22

23

24

25

26

27 28

Key

A

A,C,D

B

A, B, C

A

C

A

A,D

A

D

C

Q.no

31

32

33

34

35 36

38

39

C

C

A

B

B

A

40 A,B C,D

41

MT

37 A,B, C,D

Key

B

B

C

14

15

B,C,D

A

29

30

D A,B,C,D

B

C

4. a-4; b-5; c-2; d-1 31. a-5; b-1, c-2; d-3

CONCEPTIVE WORKSHEET KEY Q.no

1

2

3

4

5

6

7

8

9

10

11 12 13 14 15

Key

D

B

A

A,C,D

A,B,D

B

C

C

C

D

D

19

20

C

C

Q.no 16 17 18 Key A D A 23.

D

C

B

D

21 22 23 24 25 26 27 A,B, A,B C MT B A B C,D D

a-2; b-5; c-1; d-2

SUMM ATIVE WORKSHEET KEY Q.no

1

2

3

4

5

6

Key

C

A

B B

D

B B

7

8

9

C C

10 11

12 13 14 15

A

A

B

B

D

C

HINTS/ ANSWERS TO THE SELECTED QUESTIONS 1.

Changes that can be reversed are called reversible changes, and the changes that cannot be reversed are called irreversible changes. The dough prepared by mixing water and flour cannot be converted back into the original substance. Hence, preparing dough by adding water to the flour is an irreversible change. Also, baking of dough cannot be reversed back. Thus, baking of roti is also an irreversible change. Hence, processes II and IV are irreversible in nature.

7th Class Chemistry

136 2.

3.

4.

5.

The three changes that are involved in the process are cutting of paper, folding of paper, and burning of paper. When a square sized paper is cut into two smaller pieces, then those two pieces cannot be joined to get back the original sheet. Hence, the action cannot be reversed. Thus, change I can be classified as an irreversible change. A toy aeroplane is made by folding the piece of paper. A folded paper can be brought back to its original shape by unfolding it. Thus, folding of paper can be reversed. Hence, change II can be classified as a reversible change. On burning the paper, new substances are formed (ash and smoke). These substances cannot be converted back into the original substance. Thus, burning of paper cannot be reversed. Hence, change III can  be  classified  as  an  irreversible change. Ice melts on heating and changes into water. The change is reversible because on cooling it to a low temperature, water can again be converted into ice. Hence, process I is a reversible change. On adding salt to water, it dissolves in water. When this solution is heated, water evaporates leaving behind salt. Thus, on heating the salt solution, salt can be recovered. Hence, process II is also a reversible change. A process where a change can be reversed is called a reversible process. A process where a change cannot be reversed is called an irreversible process. When a matchstick is burnt, ash and gases are produced. Thus, the formation of new substances takes place. These new substances cannot be converted back into the original substance. Hence, the burning of a matchstick is an irreversible process. On heating, the iron ring becomes slightly larger and the handle easily fits into the ring. Thus, the iron ring expands on heating and the process is called expansion. On cooling, the iron ring contracts to its original size. Hence, the ring tightly fits inside the handle. As the iron ring contracts on cooling, the process is called contraction. Changes that can be reversed are called reversible changes. When the iron ring is heated, it expands in size. On the other hand when the iron ring is cooled, it comes back to its original size. Hence, it is a reversible process.

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6.

Steam is formed when water starts boiling. The changing of a liquid into a vapour at any temperature below its boiling point is called evaporation. Water is said to be boiling once the boiling point has been attained. 7. Water drops are formed due to the process of condensation. Water vapour (from the spout of the kettle) when exposed to the cold plate loses energy and changes to liquid water. 8. The process of a change in state of matter of a substance from a solid to a liquid is called melting. During the melting of ice cream, no new substance is formed, only a change in state of ice from a solid to a liquid takes place. The liquid substance formed by melting of ice cream can be converted back into solid ice cream by cooling it. Hence, melting of an ice cream is an example of a reversible change. 9. The changes that can be reversed are called reversible changes, and the changes that cannot be reversed are called irreversible changes. Burning of wood, sawing of a piece of wood, and ripening of fruits are irreversible changes as the substances obtained as a result of these changes cannot be converted back into the original substance. Hence, I, IV, and V are irreversible changes. 10. The changes that can be reversed are called reversible changes, and the changes that cannot be reversed are called irreversible changes. When ice melts, it changes into water. This water can be converted into ice by cooling it. Hence, melting of ice is a reversible change. On the other hand, milk cannot be obtained once it has gone sour. Hence, souring of milk is an irreversible change. 11. When food is cooked, new substances are formed. These new substances cannot be converted back into the original substance. Thus, cooking of food is an irreversible change. Hence, it is listed incorrectly in the table. 12. Melting is the process of phase change in which a substance changes from its solid state to its liquid state by absorbing heat. This process can be reversed by freezing the liquid. Boiling is the process of phase change in which a substance changes from its liquid state to its gaseous state by absorbing heat. The process can be reversed by condensing the gas. Hence, melting and boiling are reversible changes.

Types of Changes

137

13. When sugar is burnt, it is converted to carbon and water vapour. Sugar cannot be obtained from carbon and water vapour, i.e., the change is irreversible. Thus, the process of burning of sugar is incorrectly listed in the given table. 14. In the given figure, process I is the melting of ice to form water, while process II is the evaporation of water to form steam. 15. After preparing dough by adding water, the flour cannot be obtained back from the dough. Hence, process I is  irreversible. On the other hand, dough can be obtained back after a roti has  been  rolled.  Hence,  process II is reversible.

4.

HOTS WORKSHEET

6.

5.

KEY 1

2

3

4

5

6

7

8

A

A

C

A

C

B

D

B

9

10 11 12 13 14

15

C

D

D

C

C

D

A

HINTS/ ANSWERS TO THE SELECTED QUESTIONS 1.

2.

3.

When a substance is heated, its constituent particles move more vigorously. As a result, the average distance between the particles increases and the substance expands. Thus, during summers, the joints of a bridge expand and become loose. The changes that can be reversed are called reversible changes and the changes that cannot be reversed are called irreversible changes. When ice melts, it changes into water. The water obtained in this process can be converted back into ice by cooling it. Therefore, melting of ice is a reversible change. Changes that can be reversed are called reversible changes. Changes that cannot be reversed are called irreversible changes. When food is cooked, new substances are produced. The cooked food cannot be converted back into the raw material. Hence, cooking of food is an irreversible change. Similarly, digested food cannot be converted back into the form in which it was eaten. Hence, digestion of food is also an irreversible change.

7.

Changes that can be reversed are called reversible changes. Changes that cannot be reversed are called irreversible changes. During souring of milk, new substances are formed and those new substances cannot be converted back into the original substance. Hence, souring of milk is an irreversible change. Hence, it is listed incorrectly in the table. An irreversible change is defined as the change in which the product formed cannot be converted back into the original substance. Biogas is formed by cow dung through chemical processes. Once the gas is formed, it cannot be converted back into cow dung. Hence, the change is irreversible. Changes that can be reversed are called reversible changes and changes that cannot be reversed are called irreversible changes. When a piece of paper is torn, smaller pieces are obtained. These smaller pieces cannot be joined again to form the original sheet of water. Hence, it is an irreversible change. Burning a piece of paper leads to formation of ash. Since paper cannot be obtained back in the process, it is also an irreversible change. Burning of candle leads to consumption of wax with the formation of carbon dioxide and water vapours along with some smoke. A candle cannot be obtained back from these substances. Therefore, burning of candle is an irreversible change. A rolled roti can  be  converted  back  into  dough while water formed as a result of melting of ice can be converted back to ice by freezing. Hence, these changes are reversible in nature. Changes that can be reversed are called reversible changes. Changes that cannot be reversed are called irreversible changes. When we mix cement in water, the mixture hardens up. From this mixture, cement and water cannot be obtained back. Hence, it is an example of an irreversible change. Similarly, rusting of iron is an irreversible change. Once a part of any iron substance gets rusted, it is not possible to obtain back that iron part. Souring of milk is a result of bacterial actions with milk. Milk, once soured, cannot be converted back into the original substance. Hence, souring of milk is an irreversible change.

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7th Class Chemistry

138 8.

Ice melts on heating and changes into water. The change is reversible because on cooling it to a low temperature, water can again be converted into ice. Hence, process I is a reversible change. On adding salt to water, it dissolves in water. When this solution is heated, water evaporates leaving behind salt. Thus, on heating the salt solution, salt can be recovered. Hence, process II is also a reversible change. 9. Melting is the process in which a solid gets converted into its liquid state. During melting of chocolate, the chemical composition of the chocolate undergoing change remains the same. Only its state is changed from a solid to a liquid. Liquid chocolate formed on melting can be converted back into its solid state by cooling it. Hence, melting of chocolate is a reversible change and is listed incorrectly in the table. 10. Changes that can be reversed are called reversible changes. Changes that cannot be reversed are called irreversible changes. When we mix cement in water, the mixture hardens up. From this mixture, cement and water cannot be obtained back. Hence, it is an example of an irreversible change. Similarly, rusting of iron is an irreversible change. Once a part of any iron substance gets rusted, it is not possible to obtain back that iron part. Souring of milk is a result of bacterial actions with milk. Milk, once soured, cannot be converted back into the original substance. Hence, souring of milk is an irreversible change.

11. During the boiling of an egg, a new substance is formed as the chemical bonds present in the egg break. A boiled egg cannot be converted back into a raw egg by any physical or chemical process. Hence, the boiling of egg is an irreversible process. 12. After preparing dough by adding water, the flour cannot be obtained back from the dough. Hence, process I is  irreversible. On the other hand, dough can be obtained back after a roti has  been  rolled.  Hence,  process II is reversible. 13. On heating, the iron ring becomes slightly larger and the handle easily fits into the ring. Thus, the iron ring expands on heating and the process is called expansion. On cooling, the iron ring contracts to its original size. Hence, the ring tightly fits inside the handle. As the iron ring contracts on cooling, the process is called contraction. Changes that can be reversed are called reversible changes. When the iron ring is heated, it expands in size. On the other hand when the iron ring is cooled, it comes back to its original size. Hence, it is a reversible process. 14. Reversible changes are the changes that can be reversed and irreversible changes are the changes that cannot be reversed. Expansion of a steel rim is a reversible change because a steel rim expands on heating and contracts to its original size on cooling. Melting of ice-cream is also a reversible change because the original ice-cream can be obtained back on cooling. Hence, IV and V are  reversible  changes. 15. Solids increase in volume on heating. Hence, on being heated, the wire expands and sags down in the middle.

IIT JEE WORKSHEET

26.

Q.no

1

2

3

4

5

6

7

8

Key

B

D

A

B

B

A

A

B

Q.no

16

17

18 19

20

21

22

23

24

25

Key

C

A

C

A

A,B C,D

C

A

A

A

a-4; b-1; c-5; d-2

C

27.

9

A,B A,B C,D C,D

a-5; b-4; c-2; d-3

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10

11

12

A,B A, D C,D

28.

13

14

15

A,B, D

A

B

a-5; b-1, c-2; d-3