Integrated Syllabus FOUNDATION OLYMPIAD& …Common misconception Fact 1. Physical changes are...

` 75Detailed solutionsfor all problems

of IIT Foundation &Olympiad Explorer

are available in this book

CLASS - VIIISolutions

CLASS - VIII

FOUNDATION OLYMPIAD&

IIT F

oundatio

n &

Olym

pia

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rer - C

hem

istry Cla

ss - VIII

CH

EM

IS

TR

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IntegratedSyllabus

CH

EM

IS

TR

Y

UNIQUE ATTRACTIONS

�

� Cross word Puzzles

� Graded Exercise

Basic Practice�

Further Practice�

Brain Nurtures�

� Numerical Problems

Conceptual Questions

� Multiple Answer Questions

� Paragraph Questions

� Assertion & Reason TypeQuestions

YOUR

COACH

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FOUNDATION & OLYMPIAD

E: X P L D R E: R

CHEMISTRY

CLASS - 8

BRAIN MAPPING ACADEMY

MapptngYour Future

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Published by:

Brain Mapping Academy#16–11–16/1/B, First Floor,Farhat Hospital Road,Saleem Nagar, Malakpet,Hyderabad–500 036Andhra Pradesh, India.✆ 040–65165169, 66135169E–mail: [email protected]: www.bmatalent.com

© Brain Mapping Academy

ALL RIGHTS RESERVEDNo part of this book 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 the publisher.

Publication Team

Content Team: E.V.S.S. Lakshmi & Sk. Jamila Begum

Design & Typing: V. Prasanna Kumari & M. Manjula

ISBN: 978-81-907285-6-0

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Every care has been taken by the compilers andpublishers to give correct, complete and updated information. In case there is any omission, printing mistake or anyother error which might have crept in inadvertently,neither the compiler / publisher nor any of thedistributors take any legal responsibility.

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Preface

Speed and accuracy play an important role in climbing the competitive ladder. Students

have to integrate the habit of being able to calculate and function quickly as well as efficiently

in order to excel in the learning culture. They need to think on their feet, understand basic

requirements, identify appropriate information sources and use that to their best advantage.

The preparation required for the tough competitive examinations is fundamentally different

from that of qualifying ones like the board examinations. A student can emerge successful in

a qualifying examination by merely scoring the minimum percentage of marks, whereas in a

competitive examination, he has to score high and perform better than the others taking the

examination.

This book provides all types of questions that a student would be required to tackle at the

foundation level. The questions in the exercises are sequenced as Basic Practice, Further Practice,

Multiple Answer Questions, Paragraph Questions, Numerical Problems, Conceptual Questions

and Brain Nurtures. Simple questions involving a direct application of the concepts are given

in Basic Practice. More challenging questions on direct application are given in Further Practice.

Questions involving higher order thinking or an open-ended approach to problems are given

in Brain Nurtures. These questions encourage students to think analytically , to be creative

and to come up with solutions of their own. Constant practice and familiarity with these

questions will not only make him/her conceptually sound, but will also give the student the

confidence to face any entrance examination with ease.

Valuable suggestions as well as criticism from the teacher and student community are most

welcome and will be incorporated in the ensuing edition.

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` 1. States of Matter .......................................... 01

2. Symbols, Formulae & Equations ............... 29

3. Transformation of substances ................... 51

4. Atomic Structure ........................................ 79

5. Water ........................................................... 101

6. Hydrogen & Oxygen .................................. 125

7. Carbon and its Compounds ....................... 154

8. Metals and Non-metals .............................. 181

9. Synthetic fibres and Plastics ...................... 199

Answers ....................................................... 213

Answers to Crossword Puzzles ................... 230

CONTENTS

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IIT Foundation & Olympiad Explorer Chemistry / Class -VIII

3. Transformation of substances © Brain Mapping Academy51

Common misconception Fact

1. Physical changes are reversible while chemical 1. A very common misconception. Chemicalchanges are not. changes are also reversible. In equilibrium

reactions, products can be reconverted toreactions leading to reversibility of chemicalchange. On the other hand, some physicalchanges are also hard to reverse foreg: crushing a rock.

2. Chemical reactions will continue until all the 2. In case of equilibrium reactions beforereactants are exhausted. exhaustion of reactants, products get

reconverted to reactants.

3. (i) Energy is used up in the chemical reactions. 3. Energy is not ”used up” or created in chemical(ii) Energy is created in chemical reaction. reaction instead, they are released or stored

in the form of chemical bonds betweenatoms.

4. A candle burning is endothermic since heat is 4. Heat is needed at the beginning to initiateused to burn wax. orneeded to initiate the reaction or activate

the reaction. Once activated, the reactionproceeds without further energy input, andreleases energy in the form of light.Therefore, it is an exothermic reaction.Another example is heating a piece ofmagnesium metal on bunsen burner.

SYNOPSIS

INTRODUCTION3.1

From the dawn of creation, the world has been subjected to the escapable phenomenoncalled change. In fact, the only thing which is permanent perhaps, is change. Change isinexorable law of nature. It has manifested itself in every branch of human activity.Chemistry is that branch of science which deals with the reactions of various substancesand the resulting changes. They range from very simple ones like change in state, colour,volume etc, to the more complex interconnecting reactions that keep our bodies alive.

Force and PressureForce and Pressure1Mathematical Induction

Chapter

3Transformation of Substances

Chapter

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Types of Changes

(i) Physical change (ii) Chemical change

Physical change3.2

The process where a change is occurring only in physical properties, without affectingthe identity of the molecules is called a physical change.In a physical change, the chemical composition remains the same and the originalsubstances can be regenerated by reversing the conditions.Hence, physical change is a temporary change.

Examples

Melting of ice, Melting of Wax

Chemical change3.3

The process in which the change is affecting the identity of a molecule by a change inchemical composition is called chemical change.In a chemical change, the original substance cannot be regenerated. Hence, it is apermanent change.

Examples

curdling of milk, burning of wood

Chemical reactions3.4

Physical state

Homogeneous Reaction

If all the reactants and products in a chemical reaction are in the same physical state,then the reaction is said to be a homogenous reaction. Same physical state means thatall of them are in gaseous state or in liquid state or in solid state.

Example

H2(g) + Cl2(g) → 2HCl (g)Hydrogen chlorine Hydrogen chlorideHeterogeneous Reaction

If all the reactant and products in a chemical reaction are not in the same physical state,then the reaction is said to be a heterogeneous reaction.Example

CaCO3(s) → CaO(s) + CO2 (g)Calcium carbonate calcium oxide Carbondioxidewww.bm

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Difference between exothermic and endothermic reactions:

Exothermic reaction Endothermic reaction 1. Heat is given out during the

reaction. 2. Heat liberated is indicated by a

positive sign on the product side. 3. An exothermic reaction is

represented Reactants Product + Heat 4. Energy of the reactants is greater

than the products.

1. Heat is absorbed during the reaction

2. Heat absorbed is indicated by a negative sign on the product side.

3. An endothermic reaction is represented as

Reactants Product � Heat 4. Energy of the reactants is lesser

than the products.

Irreversible Reaction

A reaction that occurs only in one direction, i.e., from reactants to products, is called anirreversible reaction.

Example

The reaction of quicklime with water to form hydrated lime is an irreversible reactions.

CaO (s) + H2O (l) → Ca(OH)2 + HeatCalcium oxide Water Calcium hydroxide (quick lime) (hydrated lime)Similarly, burning of natural gas is an irreversible reaction.

CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (g) + Heatmethane oxygen carbon dioxide water vapour

Reversible Reaction

A reaction that occurs in both directions is called a reversible reaction. The reactantchange to products and simultaneously products change to reactants. The reactants andproducts achieve a state of equilibrium with one another.

A reversible reaction is represented by two half � arrows between the reactants andproducts. One half � arrow points from reactants towards products and the other halfarrow points in the opposite direction.

Example

N2 (g) + 3H2 (g) � 2NH3 (g)Nitrogen Hydrogen Ammonia

Decomposition Reaction

A reaction in which a compound decomposes into two or more elements or compounds isknown as a decomposition reactions. When limestone is strongly heated, it decomposesinto quick lime (calcium oxide) and carbon dioxide.

Example

CaCO3 (s) → CaO (s) + CO2 (g)Calcium carbonate calcium oxide carbon dioxide

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Precipitation Reaction

A reaction in which a precipitate is formed is called a precipitation reaction. A precipitateis an insoluble product that separates out as solid particles at the bottom of the solution.

If we add a few drops of dilute hydrochloric acid to a solution of silver nitrate, a whiteprecipitate of silver chloride is formed.

Example

HCl (aq) + AgNO3 (aq) → AgCl (s) + HNO3 (aq)Hydrochloric acid Silver nitrate Silver chloride (ppt.) Nitric acid

Oxidation Reaction

A chemical reaction in which there is gain of oxygen or loss of hydrogen is called anoxidation reaction.

Example

When magnesium ribbon burns in oxygen, it forms magnesium oxide. Since oxygen hasbeen added to magnesium, the reaction is said to represent oxidation of magnesium.

2Mg (s) + O2 (g) → 2MgO (s)Magnesium Oxygen Magnesium oxide

Reduction Reaction

A chemical reaction in which there is gain of hydrogen or loss of oxygen is called areduction reaction.

Example

Consider the reaction between hydrogen and chlorine gases. If a mixture of H2 and Cl2gases are kept in sunlight, it reacts instantaneously to form hydrogen chloride gas.Since chlorine gains hydrogen, the reaction represents reduction of chlorine.

H2 (g) + Cl2 (g) → 2HCl (g) Hydrogen Chlorine Hydrogen chloride

Redox Reaction

In a chemical reaction, whenever one substance is oxidised, another substance is reduced.This means that oxidation and reduction reactions always occur simultaneously.

Example

2H2 (g) + O2 (g) → 2H2 O (l) Hydrogen Oxygen Water

Consider the reaction between hydrogen and oxygen. Here hydrogen gains oxygen, so itis oxidation reaction. And oxygen gains hydrogen, so it is reduction reaction.Similarly, consider the reaction between iron oxide and carbon monoxide to form ironand carbon dioxide. Since iron oxide loses oxygen, it is undergoing reduction while carbonmonoxide gains oxygen, it is undergoing oxidation reaction.

Fe2O3 (s) + 3CO (g) → 2Fe (s) + 3CO2 (g) Iron oxide Carbon monoxide Iron Carbon dioxide

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We see that every oxidation reaction is also a reduction reaction and vice versa. Hence,the chemical reactions involving reduction and oxidation are called redox reactions.

Oxidizing agent

Substances that help in oxidation of other substances are known as oxidising agentsFor example, in the reaction ZnO + C → Zn + CO

�C� undergoes oxidation by gaining �O� from ZnO. That is, ZnO helps C to get oxidisedby giving oxygen. Hence, Zn is the oxidising agent.

Similarly, oxidising agents also gain electrons or hydrogen and help the other substancesto get oxidised.

Reducing agent

Substances that help in reduction of other substances are known as reducing agents.For example, in the reaction. H2S + Cl2 → S + 2HCl

�Cl� undergoes reduction by gaining �H� from H2S. That is, H2S helps in reduction of �Cl�by giving hydrogen. Hence, H2S is the reducing agent.

Similarly, reducing agents also lose electrons or oxygen and help the other substancesto get reduced.

SOLVED EXAMPLES

Example 1:

Why is hydrogen placed in the metal reactivity series, though it is not a metal?

Answer:

Hydrogen is placed in the metal reactivity series, since it shows the following propertiesof metals:

Hydrogen atom has one electron in its valence shell and it readily loses its electron toform a positive ion like metals. Hence, hydrogen is placed in metal reactivity series.

Example 2:

When a piece of copper is dipped in silver nitrate solution, formation of a white silverycompound is observed. Explain.

Answer:

When a piece of �Cu� is dipped in AgNO3 solution, �Cu� disappears and a white silverycompound settles down. This process can be represented as,

( )3 3 2Cu 2AgNO 2Ag Cu NO+ → ↓ +

As copper (Cu) is present above silver (Ag) in reactivity series, it is more reactive thanAg.

Therefore, �Cu� loses electrons more easily than �Ag� and displaces �Ag� from silver ni-trate (AgNO3) solution, forming copper nitrate (Cu(NO3)2) and metallic silver (Ag) whichsettles down as a white compound.

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Example 3:Which of the following reactions are not possible and why?

1. 4 4FeSO Mg MgSO Fe+ → + 2. 4 4ZnSO Ag AgSO Zn+ → +

3. ( ) ( )3 32 2Pb NO Ca Ca NO Pb+ → + 4. 2 4 4 2H SO Cu CuSO H+ → +

5. 2 2HgCl Mg MgCl Hg+ → + 6. 22MgO 2Mg O→ +Answer:

We know that a more reactive metal replaces a less reactive metal from its salt solution.The reactivity series is as follows:

Potassium(K)

Sodium (Na)

Calcium (Ca)Magnesium(Mg)

Aluminium (Al)Zinc (Zn)

Iron (Fe)Tin (Sn)Lead (Pb)[Hydrogen]

Copper (Cu)

Mercury (Hg)Silver (Ag)

Gold (Au)

More reactive thanHydrogen

(More reactive)

(less reactive)

Descending

order of chemical

reactivity.

Less reactive thanHydrogen

Using the above reactivity series, let us identify the reactions that are not possible inthe given reactions.

1. 4 4FeSO Mg MgSO Fe+ → +This reaction is possible as �Mg� is more reactive than �Fe� (as evident from the reactivityseries). Hence, it can displace �Fe� from its solution (FeSO4).

2. 4 4ZnSO Ag AgSO Zn+ → +This reaction is not possible as �Ag� is less reactive than �Zn�. As per reactivity series, aless reactive metal cannot displace a more reactive metal from its salt solution. Hence,this reaction is not possible.

3. ( ) ( )3 32 2Pb NO Ca Ca NO Pb+ → +

This reaction is possible as �Ca� is more reactive than �Pb� (reactivity series). As a result,�Ca� can displace �Pb� from its solution [Pb(NO3)2].

4. 2 4 4 2H SO Cu CuSO H+ → +This reaction is not possible as �Cu� is less reactive than Hydrogen as per reactivityseries, as a result it cannot displace Hydrogen from its solution.

5. 2 2HgCl Mg MgCl Hg+ → +

This reaction is possible as �Mg� is more reactive than �Hg� as per reactivity series, as aresult �Mg� can displace �Hg� from its solution (HgCl2).

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6. 22MgO 2Mg O→ +

This reaction is not possible as formation of MgO is an example for chemical change andin a chemical change reverse reaction cannot take place (decomposition of MgO).

Example 4:Identify the type of chemical reactions.(A) H2 + Cl2 → 2HCl (B) CaO + H2O → Ca(OH)2

(C) CaCO3 → CaO + CO2 (D) FeSO4 + Mg → MgSO4 + Fe(E) 2KI + Pb(NO3)2 → 2KNO3 + PbI2 ↓Answer:

Reaction Explanation

(A) H2 + Cl2 → 2HCl Two elements H2 and Cl2 combine to form a singlecompound, HCl. Hence, it is a combinationreaction. As two elements combine to form acompound, it is an Element� Element combination

(B) CaO + H2O → Ca (OH)2 Two compound CaO and H2O combine to form asingle compound, Ca(OH)2. Hence, it is acombination reaction. As two compounds combineto form a new compound, it is a compound �compound combination.

(C) CaCO3 → CaO + CO2 The compound CaCO3 splits (decomposes) into twocompounds, CaO and CO2. Hence, it is a compound� compound decomposition.

(D) FeSO4 + Mg → MgSO4 + Fe Here, magnesium (Mg) is displacing, iron (Fe) fromits salt solution (FeSO4). Hence, it is adisplacement reaction.

(E) 2KI + Pb(NO3)2 → 2KNO3 + PbI2 ↓ The reactants potassium iodide and lead nitratereact to form potassium nitrate and lead iodide.From this it is clear that, radicals are interchangedby the decomposition of reactants. Hence, it is adouble decomposition reaction.

Example 5:Compound A reacts with compound B to form compounds C and D. �C� can easily dissolvein �D� and �D� on electrolysis gives hydrogen and oxygen. What type of compounds areA, B, C and D?Answer:

Compound D on electrolysis gives H2 and O2 and hence it is identified as H2O (water).∴ A + B → C + D (water)

Compound C easily dissolves in water, hence its a salt.∴ A + B → C + D (salt) (water)

Salt and water are the products of a neutralization reaction. Therefore, compounds Aand B are identified as Acid and Base.

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Example 6:Match the following equations with the type of reactions.(i) Al(OH)3 → Al2O3 + H2O (p) Neutralisation reaction.(ii) Zn + 2HCl → ZnCl2 + H2 (q) Decomposition reaction.(iii) CO2 + C → 2CO (r) Displacement reaction.(iv) 2NaOH + H2SO4 → Na2SO4 + 2H2O (s) Combination reaction.Answer:

(i) Al(OH)3 → Al2O3 + H2OIn this reaction, we have one reactant which decomposed to form more than oneproduct. Hence, the reaction is a decomposition reaction.

(ii) Zn + 2HCl → ZnCl2 + H2In this reaction, we have two reactants one of which is an element, that it is zinc (Zn).Zinc is displacing H2 from HCl to form ZnCl2. Hence this reaction is a displacementreaction

(iii) CO2 + C → 2COIn this reaction, two substances combine to form a single product. Hence, the reactionis a combination reaction. Here a compound and an element combine so it is anElement � Compound combination reaction.

(iv) 2NaOH + H2SO4 → Na2SO4 + 2H2OIn this reaction, two reactants react to form two products. Both the reactants and theproducts are compounds and it can be seen that the radicals got interchanged afterthe reaction. Hence, the reaction is a double decomposition reaction. The exchangeof radicals can be seen as follows:

2[Na + OH ] + [2H + SO ] [2Na + SO ] + 2[H + OH ]+ � + �2 + �2 + �

4 4

On the other side, a base reacts with an acid to form salt and water. Hence it is aneutralisation reaction. Therefore, the correct matches are i � q, ii � r, iii � s, iv � p.

Example 7:Double decomposition reactions take place in which new compounds are formed byinterchange of radicals. Complete the table given below representing double decompositionreactions.

(A) → [salt]

+ [water]

(B) Cu(OH)2 + �� → 2CuClsalt

+ [water]

(C) CuO + H2SO4 → [salt]

+ [water]

The above reactions are examples of _____ [Precipitation/neutralisation] reactions.

(D) → [salt]

+ [Precipitate] ↓

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(E) __________ + NH4OH → ( )[ ]4 42salt

NH SO + [ ]

2Precipatate

Cu(OH) ↓

(F) Pb(NO3)2 + ________ → [ ]

3salt

NaNO + [ ]Pr ecipitate

________ ↓

Solution:

(A) →[ ]Sodiumchloride

NaCl + [ ]

2waterH O

(B) Cu(OH)2 + 2HCl →[ ]

2Cupric chloride

CuCl + [ ]

2water

2H O

(C) CuO + H2SO4 → [ ]4

Copper sulphateCuSO +

[ ]2

w aterH O

The above reactions are examples of Neutralisation reactions.

(D) → [ ]Sodium chloride2NaCl + ( )

[ ]2

Ferrous hydroxide

Fe OH↓

(E) CuSO4 + 2 NH4OH → ( )[ ]

4 42Ammoniumsulphate

NH SO + ( )[ ]

2Copper hydroxide

Cu OH ↓

(F) Pb(NO3)2 + 2NaOH → [ ]3

Ammonium nitrate2NaNO + ( )

[ ]2

Lead hydroxide

Pb OH

Example 8:A substance X undergoes a chemical change involving the loss of Hydrogen and thisresults in the formation of a product Y. What type of agents are X and Y? (Reducingagent or Oxidising agent)Answer:

We know that, oxidising agent undergoes reduction and reducing agent undergoes oxi-dation. Hence, we need to know whether the substance has undergone oxidation orreduction. As X undergoes a chemical change by losing hydrogen atom, it is undergoesoxidation. Hence, it is a reducing agent. To the product Y, hydrogen is added, itundergoes reduction. Hence, Y acts as an oxidising agent.

Example 9:In the formation of a compound AB, atoms of element A lost two electrons each whileatoms of element B gained two electrons each. Which of the elements A or B is oxidisedin the formation of AB?Answer:

It is to be noted that the substance that undergoes oxidation is said to be oxidised andthe substance that undergoes reduction is said to be reduced. As A loses 2 electrons, itundergoes oxidation and hence is oxidised.B gained 2 electrons, it undergoes reduction and hence is reduced.Therefore, the element A is oxidized in the formation of AB.

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utilizes the light energy of the Sun trapped by chlorophyll, the green pigment in theleaves. In this process, as energy is absorbed in the form of light, the reaction can becalled an endothermic reaction.Within the plants, glucose first gets converted into starch. Then the carbon atoms areused to build proteins and the other complex compounds needed for life.

Example 12:The equation below shows the reaction between nitrogen and oxygen.

( ) ( ) ( )2 2 2N g 2O g 66kJ 2NO g+ + →

(a) Is this an exothermic or endothermic reaction? Explain your answer.Solution:

(a) Endothermic reaction. 66 kJ of heat energy is absorbed in this reaction.

Example 13:In an experiment, the weight of carbon in carbon dioxide was found to be 25%. In anotherexperiment, 1.2 g of carbon on heating produces 4.8 g of carbondioxide. Show that theresults prove the law of constant proportions.Solution:

Case � I Case � II (Ist experiment) (IIst experiment)

% of carbon in CO2 = 25% Weight of carbon = 1.2 g

⇒ % of oxygen = 75% (100% � 25%) Weight of carbon dioxide = 4.8 g

∴ the ratio of weights of carbon and % of carbon in carbon dioxide

oxygen is 25% : 75% = 1 : 3 = weightof carbon

100weightof carbon dioxide

×

= 1.2 1

100 100 25%4.8 4

× = × =

⇒ % of oxygen = 100% � 25% = 75%

∴ The ratio of weights of carbon and oxygenis 25% : 75% = 1 : 3

From both the above cases, it is clear that the ratio of weights of carbon and oxygen is1 : 3. Thus, the results prove the law of constant proportions.www.bm

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Example 14:1.375 g of cupric oxide was reduced by heating in a current of hydrogen, and the weightof copper that remained was 1.098 g. In another experiment, 1.179 g of copper wasdissolved in nitric acid and the resulting copper nitrate was converted into cupric oxideby ignition. The weight of cupric oxide formed was 1.476 g. Show that these resultsillustrate the law of constant proportions.

Solution:

Case � I Case � IIWeight of cupric oxide taken = 1.375 g Weight of cupric oxide formed = 1.476 gWeight of copper left = 1.098 g Weight of copper taken = 1.179 g

⇒ Weight of oxygen present in cupric ⇒ Weight of oxygen present in cupricoxide oxide= weight of cupric oxide � wieght of copper = weight of cupric oxide � weight of copper= 1.375 gm � 1.098 gm = 0.277 g = 1.476 gm � 1.179 gm = 0.297 g

We know that % of oxygen in cupric oxide = weightof oxygen incupricoxide

100weightof cupricoxidetaken

×

Applying the above formula in both the cases, we get

% of oxygen in cupric oxide = 0.277

100 20.151.375

× =

% of oxygen in cupric oxide = 0.297

100 20.121.476

× =

In both the cases, percentage of oxygen in cupric oxide is 20%. Hence, it proves thelaw of constant proportions.

Example 15:Carbon reacts with oxygen to produce CO (Carbon monoxide) and CO2 (Carbon dioxide).The atomic weights of Carbon and Oxygen are 12 and 16 respectively. Show that theresults illustrate law of multiple proportions.Solution:

For compound CO

Elements Carbon Oxygen

No. of atoms Atomic weight Weight of each element

1 12 12

2 16 16

For compound CO2

Elements Carbon Oxygen

No. of atoms Atomic weight Weight of each element

1 12 12

1 16 32

Ratio of weights of carbon and oxygen in the compound CO is 12 : 16 = 3 : 4Ratio of weights of carbon and oxygen in the compound CO2 is 12 : 32 = 3 : 8The ratio of weights of the element oxygen, combining with a part of carbon in thetwo compounds, is 4 : 8 = 1 : 2.

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CONCEPT MAP T

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Summative Exercise

SECTION – A

BASIC PRACTICE

FILL IN THE BLANKS

1. Decomposition is reverse of __________ reaction.

2. In double decomposition reaction __________ are exchanged.

3. A decomposition reaction taking place due to passage of electric current is called__________.

4. Formation of SO3 from SO2 and O2 is a __________ reaction.

5. Heat is released in _________ reactions.

6. Zn displaces __________ from CuSO4 solution.

7. Presence of soluble impurities __________ the boiling points of liquid.

8. In oxidation reaction either __________ is added or __________ is removed.

9. Oxidising agent undergoes __________.

10. A reaction in which there is transfer of electrons from one reactant to another is calleda __________.

11. Addition of silver nitrate to sodium chloride solution causes preciptation of silver chlo-ride. This is an example of ____________ reaction.

12. Burning magnesium ribbon in air to form magnesium oxide is an example of ________reaction.

13. Digestion of food is an example of _________ change.

14. Respiratory reaction is an example of __________ change.

15. Dissolution of salt in water is a __________ change.

TRUE OR FALSE

16. Endothermic reactions are accompanied by absorption of heat.

17. In redox reactions, oxidation and reduction take place simultaneously.

18. Combination is the reverse of decomposition reaction.

19. Neutralisation is a double displacement reaction.

20. Two elements combine to form one compound in a displacement reaction.

21. Formation of calcium oxide and carbon dioxide by heating limestone is an example ofdouble decomposition reaction.

22. Reaction of hydrochloric acid with zinc oxide to form zinc chloride and water is a neutral-ization reaction.

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23. Heating of sugar solution is a chemical change.

24. Reaction of magnesium ribbon with dilute sulphuric acid to form magnesium sulphateand hydrogen is a combination reaction.

25. Melting of butter is a physical change.

MATCH THE FOLLOWING

26. Column - I Column - II

(A) Expansion or contraction of metals (p) Physical change on heating or cooling

(B) Action of heat on zinc hydroxide (q) Chemical change

(C) A stone place under sunlight (r) Combination of physical and chemical change

(D) Shaping of glass by heating (s) Neither a physical nor a chemical change.


(A) Absorption of energy (p) Physical change

(B) Curdling of milk (q) Exothermic reaction

(C) Glowing of an electric bulb (r) Chemical change

(D) Releasing of energy (s) Endothermic reaction


(A) H2+Cl2 → 2HCl p) Decomposition of a compound intotwo elements.

(B) CaO + H2O → Ca(OH)2 (q) Combination of two elements toform a new compound.

(C) 2HgO heat→ 2Hg + O2 (r) Decomposition of a compound intoa compound and an element.

(D) 2KClO3 heat→ 2KCl + 3O2 (s) Combination of two compounds to

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FURTHER PRACTICE

MULTIPLE CHOICE QUESTIONS

1. Which of the following statements is correct?(A) Physical changes are irreversible(B) All chemical changes are reversible(C) New substances are formed during a physical change.(D) Chemical change produces new substances.

2. Identify the physical change in the following:(A) Reaction of zinc metal with dilute sulphuric acid.(B) Formation of solutions of soluble substances in water.(C) Burning of coal(D) Photosynthesis

3.heating heatingcooling cooling

Ice water steam�� . Identify the type of change.

(A) Physical change (B) Chemical change(C) Both physical and chemical changes (D) None

4. Chemical reaction does not involves:(A) Absorption (or) release of energy (B) Forming of new substances (or) products(C) Two (or) more reactants (D) None of the above

5. In which type of change, we observe alteration only in specific property of matter but notcomposition?(A) Chemical change (B) Physical change(C) Both physical and chemical change (D) None of the above

6. The formation of nitrous oxide from nitrogen and oxygen is the example for:(A) Decomposition reaction(B) Chemical combination of one element and one compound(C) Chemical combination of two compounds(D) Chemical combination of two elements

7. Chemical combination involves:(A) Combination of two atoms.(B) Combination of only same type of elements.(C) Combination of only same type of compounds.(D) Combination of any two or more elements or compounds.

8. + � + � + � + �A B + C D A D + C B→ .

Identify the above generalised type of reaction.(A) Chemical replacement reaction (B) Chemical double decomposition reaction(C) Chemical displacement reaction (D) Chemical combination reaction

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9. Identify the following reactions as endothermic or exothermic.

(i) 2NaHCO3 + Heat energy → Na2CO3+ H2O + CO2

(ii) 2Mg + O2 → 2MgO + energy

(i) (ii)(A) Exothermic Endothermic(B) Endothermic Exothermic(C) Exothermic Exothermic(D) Endothermic Endothermic

10. Which type of chemical decomposition reaction is the following reaction?

Cu(OH)2 heat→ CuO + H2O

(A) Decomposition of one element into one compound and one element.(B) Decomposition of a compound into two new compounds.(C) Decomposition of one compound into two elements.(D) Decomposition of one compound into one compound and one element.

11. (i) Reaction between calcium oxide and water is a _____ reaction.(ii) Reaction of mercuric oxide with strong heat is a _____ reaction. (i) (ii)(A) Decomposition Combination(B) Combination Combination(C) Combination Decomposition(D) Decomposition Decomposition

12. The reaction Pb(NO3)2 + 2 NaI → 2 NaNO3 + PbI2 ↓ is classified as

(A) combination reaction (B) decomposition reaction

(C) single replacement reaction (D) double replacement reaction

13. 4 Al + 3O2 → 2Al2O3

In the above equation, identify the oxidising agent.(A) Al (B) O2 (C) Al2O3 (D) Both �a� and �c�

14. �Nitric oxide reacts with oxygen to form reddish brown nitrogen dioxide gas�. Choosethe correct equation for the above reaction.

(A) 2NO + O2 → 2NO2 (B) N2O + O2 → NO2 + NO

(C) NaNO3 heat→ 2 NaNO2+ O2 (D) 2NO3 + O2 → 2NO2 + 2 O2

15. Choose the incorrect statement:(A) Combination of two different elements is possible.(B) Decomposition of single compound is not possible.(C) Decomposition of a chemical compound into two new compounds is possible.(D) Combination of an element with a compound to form a new product is possible.

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(A) Law of multiple proportions (B) Law of reciprocal proportions(C) Law of conservation of mass (D) Law of constant proportions

25. Which one of the following pairs of compounds illustrates the law of multiple proportions?(A) H2O, Na2O (B) MgO, Na2O (C) Na2O, BaO (D) SnCl2, SnCl4

MULTIPLE ANSWER QUESTIONS

1. Chemical change involves:(A) No change in weight of the reacting substance.(B) Change in the composition.(C) Absorption (or) the release of energy.(D) Formation of precipitate.

2. Choose the incorrect statement(s).(A) Chemical reactions are characterised by the change in colour.(B) Chemical reactions are not alone characterised by change in state.(C) Physical changes are characterised by change in colour of reacting substances.(D) Physical changes are not reversible.

3. The reaction, AB → A + B is a:

(A) Decombination reaction (B) Combination reaction(C) Chemical composition (D) Decomposition reaction

4. Identify the combination reaction in the following:

(A) NH3 + HCl → NH4Cl (B) NaCl + KOH → NaOH + KCl

(C) 2CO + O2 → 2 CO2 (D) Cu(OH)2 heat→ CuO + H2O

5. Identify the correct combination reaction of two compounds to form a new product.

(A) H2 + Cl2 → 2HCl (B) 2CO + O2 → 2 CO2

(C) CaO + H2O → Ca(OH)2 (D) NH3 + HCl → NH4Cl

6. �Reaction of potassium iodide solution with lead nitrate solution� is the example of:(A) Chemical replacement reaction (B) Neutralisation reaction(C) Precipitation reaction (D) Chemical double decomposition reaction

7. Chemical compounds are formed to have constant composition irrespective of their(A) Method of formation (or) Source (B) Conditions for formation(C) Substances taken for formation (D) Time of formationwww.bm

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ASSERTION AND REASON TYPE QUESTIONS

The questions given below consists of statement of an Assertion and a Reason. Use thefollowing key to choose the appropriate answer.(A) If both assertion and reason are CORRECT and reason is the CORRECT explanation

of the assertion.(B) If both assertion and reason are CORRECT, but reason is NOT THE CORRECT

explanation of the assertion.(C) If assertion is CORRECT, but reason is INCORRECT.(D) If assertion is INCORRECT, but reason is CORRECT.(E) If both assertion and reason are INCORRECT.

1. Assertion: Physical change of a substance involves change in all properties andcomposition of its molecules.

Reason: The change of a substance with alteration of composition of its moleculeswithout any change in its specific property is called physical change.

2. Assertion: Burning of coal is a physical change.

Reason: When coal is burnt, the chief component, carbon is changed to carbon dioxide.This process cannot be reversed.

3. Assertion: �A golden yellow precipitate of lead iodide is formed when colourless leadnitrate solution is mixed with colourless solution of potassium iodide.� So,it is a chemical change.

Reason: Formation of new products in the reaction with the precipitate indicates achemical change.

4. Assertion: Beating of metals into sheets is a physical change.

Reason: The conversion of metals into sheets involves no chemical reaction andsheets can be easily reconverted into metals with some external conditions.So, it is reversible.

5. Assertion: Catalyst is a substance which takes part in a chemical reaction, undergoeschemical change and alters the rate of a reaction.

Reason: Catalyst is a substance which does not take part in a chemical reaction, butchanges the rate of a reaction.

6. Assertion: When an electric current is passed through an aqueous solution of sodiumchloride, sodium ions move towards cathode and chloride ions move towardsanode.

Reason: Cathode is a negatively charged electrode and therefore attracts Na+ ions.Anode is a positively charged electrode and therefore attracts Cl� ions

7. Assertion: The process of depositing a thin and compact layer of a superior metal overan inferior metal by the process of electrolysis is known as electroplating.

Reason: Electroplating is a process to improve the appearance of the articles.

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8. Assertion: The laws of chemical combination ultimately led to the idea of �atoms� beingthe �smallest unit of� matter.

Reason: The laws of chemical combination played a significant role in the developmentof Dalton�s atomic theory of matter.

Paragraph Questions

Passage - I

Limestone is held with tongs and heated on the flame directly. It crumbled to give whitepowder of calcium oxide. After cooling, when water is added to it a hissing sound is heardand water started boiling. If it is allowed to stay over night, a clear solution (top layer) istaken and for this experiment below as lime water.

When carbon dioxide is bubbled into testtube a clear solution of lime water, turbidityappears first and later a white precipitate of calcium carbonate is formed. Carbon dioxideis continued to passed into the same solution and the solution again became clear becauseof formation of calcium bicarbonate. On heating the contents of the tube, white precipitateof calcium carbonate reappears.

(i) On heating limestone, the following are formed.

(A) calcium hydroxide, carbon dioxide (B) calcium bicarbonate

(C) calcium oxide and carbon dioxide (D) calcium oxide and water

(ii) Passing of carbon dioxide to lime water gave the following initially

(A) calcium bicarbonate and carbon dioxide (B) calcium carbonate and water

(C) calcium carbonate and carbon dioxide (D) calcium oxide and water

(iii) Heating of calcium bicarbonate gave the following:

(A) calcium oxide and carbon dioxide (B) calcium carbonate, water and CO2

(C) calcium bicarbonate and CO2 (D) calcium hydroxide and carbon dioxide

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SECTION – B


1. What type of reaction is the reaction of quick lime with water?

2. 4 Al + 3O2 → 2Al2O3 In the above equation, identify the oxidising agent.

3. Fe + S → FeS. In the above reaction,` how many number of electrons are lost bythe iron atom and how it acts?

4. Calcium carbonate decomposes on heating to form calcium oxide and carbon dioxide.According to law of conservation of mass, if 5.6 gms of calcium oxide and 4.4 gms ofcarbon dioxide are formed, how much calcium carbonate was taken?

5. We have seen combination or synthesis, decomposition, double decomposition anddisplacement reactions. Identify the nature of the following reactions: Write againsteach.(A) CaO + H2O → Ca(OH)2

(B) 2NaHCO3 heat→ Na2CO3 + H2O + CO2

(C) 4Fe + 3O2 + 3H2O → 2Fe2O3 + 3H2O(D) CaCl2 + 2AgNO3 → 2AgCl ↓ + Ca(NO3)2

(E) CaCO3 heat→ CaO + CO2

(F) 2KI + Cl2 → 2KCl + I2

6. What happens when(A) a copper rod is placed in FeSO4 solution?(B) an iron rod is placed in CuSO4 solution?

7. Classify the following combination reactions into different types.(A) Na2O + H2O → 2NaOH (B) 4Fe + 3O2 → 2Fe2O3(C) MgCl2 + 3O2 → Mg(ClO3)2

8. Arrange the following in the increasing order of their reactivity:Ca, Cu, Hg, Al, Ag, K, Zn.

9. Name of the oxidising agent in the following reactions.(A) ZnO + C → Zn + CO (B) Cl2 + H2S → 2HCl + S(C) 4HCl + MnO2 → MnCl2 + 2H2O + Cl2

10. Hydrogen and Oxygen combine in the ratio of 1 : 8 by mass to form water. What mass ofOxygen gas would be required to react completely with 3 grams of hydrogen gas?

11. In two different experiments, copper oxide was obtained from copper. The ratio of massof copper and mass of oxygen found in the two experiments are same. They are in theratio of 4 : 1. What do you infer about the experiments?

12. In an experiment 1.288 g of copper oxide was obtained from 1.03 g of copper and 0.258 gof oxygen. Calculate the ratio of copper and oxygen in the sample?

13. Certain non-metal X forms two oxides I and II. The mass percentage of oxygen in I(X4O6)is 43.7 which is same as that of X in the 2nd oxide. Find the formula of 2nd oxide.

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SECTION – C

Previous Contest Questions

1. The strongest reducing agent is:

(A) HNO2 (B) H2S (C) H2SO3 ((D) SnCl2

2. Which substance is serving as a reducing agent in the following reaction?

FeSO4 + Mg → MgSO4 + Fe

(A) Mg (B) SO4�2 (C) Fe ((D) MgSO4

3. In the reaction, 3 224Fe 3O 4Fe 6O+ −+ +� Which of the following statements is

incorrect?

(A) It is a redox reaction (B) Metallic iron is a reducing agent(C) Fe3+ is an oxidising agent (D) Metallic iron is reduced to Fe3+

4. In the reaction, 2 4 2 4 2 22Ag 2H SO Ag SO SO 2H O+ → + + , sulphuric acid acts as:(A) oxidising agent (B) reducing agent(C) catalyst (D) acid and oxidant

5. When iron is added to CuSO4 solution, copper is precipitated. It is due to _________.(A) oxidation of Cu2+ (B) reduction of Cu2+

(C) hydrolysis of CuSO4 (D) ionisation of CuSO4

6. An oxidising agent is a substance which can _____.(A) accept electrons (B) donate electrons(C) accept protons (D) donate protons

7. The reaction, ( ) ( )2Zn aq 2e Zn s+ −+ → is:

(A) oxidation (B) reduction (C) redox reduction (D) none

8. The reaction, 2 4 2 42K MnO Cl 2KMnO 2KCl+ → + , is an example of ________.(A) oxidation (B) reduction (C) neutralisation (D) chlorination

9. In the reaction, ( ) ( ) ( )2Cu s 2Ag aq Cu 2Ag s+ ++ → +(A) Cu(s) is oxidised to Cu2+ (B) Cu(s) reduced to Cu2+ (aq)(C) Ag (aq) is oxidised to Ag (s) (D) both Cu(s) and Ag+(aq) are oxidised.

10. Which of the following reactions involves oxidation and reduction?

(A) NaBr HCl NaCl HBr+ → + (B) 3 3HBr AgNO AgBr HNO+ → +

(C) 2 2H Br 2HBr+ → (D) 2 2 4 2 4 2Na O H SO Na SO H O+ → +

11. In the reaction between zinc and iodine, zinc iodide is formed. What is being oxidised.(A) zinc ions (B) iodide ioins (C) zinc atom (D) iodine

12. In the reaction, 2 3 2Cl OH Cl ClO H O− − −+ → + + chlorine is ________.(A) oxidised (B) reduced(C) oxidised as well as reduced (D) neither oxidised nor reduced

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13. Oxidation is defined as __________.(A) gain of electrons (B) loss of electrons(C) gain of electrons (D) loss of neutrons

14. In the rusting of iron, 2 2 34Fe 3O 2Fe O+ → , iron is:(A) reduced (B) oxidised (C) precipitated (D) hydrolysed

15. Which of the following reactions indicates the oxidising behaviour of H2SO4?

(A) 5 2 4 3 2 22PCl H SO 2POCl 2HCl SO Cl+ → + +

(B) 2 4 4NaCl H SO NaHSO HCl+ → +

(C) 2 4 2 4 22NaOH H SO Na SO 2H O+ → +

(D) 2 4 2 2 22HI H SO I SO 2H O+ → + +

Brain Nurtures

1. When a zinc strip is placed in blue copper sulphate solution, the colour fades away andthe solution turns colourless. Why?

2. Ramu has a copper coin. But he wants a silver coin. As a chemist, can you help him getthe silver coin by giving him the right solution from those given below.

(A) Cu(NO3)2 (B) AgNO3 (C) both

3. We often see beautiful hydrogen gas balloons flying in the sky. Hydrogen gas is filledinto these balloons from a cylinder. Can you guess how the hydrogen gas is produced inthis cylinder? Which of the following reactions produces hydrogen in the cylinder.

(A) Zn + HCl (B) Ag + HCl (C) Cu + HCl (D) AgCl + HCl.Explain?

4. Copper sulphate solution is placed in an iron pot and left over night. The next morning,a number of holes are formed in the iron pot. But, when iron sulphate solution is placedin a copper pot and left over night, the copper pot remained as it was. Why?

5. An element �A� forms a sulphide A2S. In terms of loss or gain of electrons, find out whichatom is oxidised and which atom is reduced?

6. In a solution of lead acetate, a strip of metal �M� is dipped. After some time, a whitecoating of lead is observed on the metal strip. Which is more reactive �M� or lead?

7. We have seen metal activity series. Similarly we also have halogen activity series, Cl,Br, I. Applying the same principle of metal activity series, can you answer the followingquestions:

When chlorine is passed into KBr solution, a deep red coloured liquid is formed. Whenchlorine is passed into KI solution, a violet coloured solution is formed. Explain?

8. When 0.28 g of iron filings were heated in a current of dry air, 0.36 g of iron oxide isformed. Find the weight of oxygen that combines with this weight of metal, with thehelp of law of conservation of mass.

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CROSS WORD PUZZLE

ACROSS

2 The gas displaced by Zn on reaction with HCl

4 A reaction that occurs in both directions

6 Decomposition of lime stone gives quick lime

8 Heat is evolved during a chemical reaction

9 Reaction of an acid and a base

10 Loss of oxygen

DOWN

1 Type of change, magnetisation of iron

3 Loss of hydrogen

5 Heat is absorbed during a chemical reaction

7 Type of change, curdling of milk

1

2

3

4 5

6

7

8

9

10

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` 75Detailed solutionsfor all problems

of IIT Foundation &Olympiad Explorer

are available in this book

CLASS - VIIISolutions

CLASS - VIII

FOUNDATION OLYMPIAD&

IIT F

oundatio

n &

Olym

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d E

xplo

rer - C

hem

istry Cla

ss - VIII

CH

EM

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TR

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IntegratedSyllabus

CH

EM

IS

TR

Y

UNIQUE ATTRACTIONS

�

� Cross word Puzzles

� Graded Exercise

Basic Practice�

Further Practice�

Brain Nurtures�

� Numerical Problems


� Multiple Answer Questions

� Paragraph Questions

� Assertion & Reason TypeQuestions

YOUR

COACH

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