Chapter 1

Chemical Reactions and Equations

In-text question set 1
1. Why should a magnesium ribbon be cleaned before burning in the air?
Solution:
Magnesium ribbon should be cleaned before burning in air because Magnesium metal reacts with
the atmospheric oxygen and forms Magnesium Oxide (MgO) layer which is a very stable
compound. In order to prevent further reactions with Oxygen, it is therefore necessary to clean the
ribbon by to remove the layer of MgO.

2. Write a balanced equation for the following chemical reactions.

i) Hydrogen + Chloride → Hydrogen chloride
ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
iii) Sodium + Water → Sodium hydroxide + Hydrogen
Solution:
i) H2 + Cl2 → 2HCl
ii) 3BaCl2 + Al2(SO4)3 →3BaSO4 + 2AlCl3
iii) 2Na + 2H2O → 2NaOH + H2

3. Write a balanced chemical equation with state symbols for the following reactions
i) Solutions of Barium chloride and Sodium sulphate in water react to give insoluble
Barium sulphate and solution of Sodium chloride.
ii) Sodium hydroxide solution in water reacts with the hydrochloric acid solution to
produce Sodium chloride solution and water.
Solution:
i) BaCl2 + Na2SO4 → BaSO4 + 2NaCl
ii) NaOH + HCl → NaCl + H2O

In-text question set 2

1. A solution of a substance, ‘X,’ is used for whitewashing.
i) Name the substance ‘X’ and write its formula.
ii) Write the reaction of the substance ‘X’ named in (i) above with water.
Solution:
i) The substance ‘X’ which is used in whitewashing is quick lime or Calcium Oxide and its
formula is CaO.
ii) CaO + H2O → Ca(OH)2

2. Why is the amount of gas collected in one of the test tubes in Activity 1.7 double the
amount collected in the other? Name this gas.
Solution:
In activity 1.7, gas collected in one of the test tubes is double of the amount collected in the other
because water gets hydrolysed to release H2 and O2 gas. Here, after electrolysis two molecules of
Hydrogen and one molecule of oxygen gas are released; hence, the amount of Hydrogen collected
would be double than that of oxygen.

In-text question set 3

1. Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
Solution:
When an iron nail is dipped in the copper sulphate solution, iron displaces copper from the copper
sulphate because iron is more reactive than copper. Therefore, the colour of the copper sulphate
solution changes. The reaction is Fe + CuSO4 → FeSO4 + Cu
2. Give an example of a double displacement reaction other than the one given in Activity
1.10.
Solution:
Reaction Between silver nitrate (AgNO3) and Sodium chloride (NaCl) is an example of a double
displacement reaction. During the reaction, negative and positive ions trade positions as a result of
the formation of white silver chloride precipitate. The chemical reaction is given below.
Ag+ + NO3– + Na+ + Cl– → AgCl + Na+ + NO3–

3. Identify the substances that are oxidised and that are reduced in the following equation.
i) 4Na(s) + O2(g) → 2Na2O(s)
ii) CuO(s) + H2(g) → Cu(s) + H2O(l)
Solution:
The Sodium (Na) in the first equation is getting oxidized with the addition of Oxygen (O2), and the
Copper (Cu) in the second equation is reduced due to the addition of Hydrogen (H2).

Exercise Question:
1. Which of the statements about the reaction below are incorrect?
2PbO(s) + C(s) → 2Pb(s) + CO2(g)
a) Lead is getting reduced
b) Carbon Dioxide is getting oxidised
c) Carbon is getting oxidised
d) Lead oxide is getting reduced
i) (a) and (b)
ii) (a) and (c)
iii) (a), (b) and (c)
iv) all the above
Solution:
(i) (a) and (b)

Explanation: (a) Because Oxygen is being removed and (b) Because the removed oxygen from
Lead is added to the elemental Carbon.

2. Fe2O3 + 2Al → Al2O3 + 2Fe

The above reaction is an example of a
1) Combination reaction
2) Double displacement reaction
3) Decomposition reaction
4) Displacement reaction

Solution:
4. Displacement reaction.
Explanation: The Oxygen from the Ferrous oxide is getting displaced to the Aluminium metal to
form Aluminium Oxide. In this reaction, Aluminum is a more reactive metal than Fe. Therefore,
Al will displace Fe from its oxide. This type of chemical reaction, called displacement reaction, is
in which one of the elements displaces another. Here, less reactive metal is displaced by more
reactive metal. Since one-time displacement is occurring, it is called a single displacement
reaction.

3. What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct
answer.
 1. Hydrogen gas and Iron chloride are produced.
2. Chlorine gas and Iron hydroxide are produced.
3. No reaction takes place.
4. Iron salt and water are produced.

Solution:
1. Hydrogen gas and Iron chloride are produced.

Explanation: The Chlorine from Hydrogen chloride is displaced by the Iron fillings to undergo
the following reaction.
2HCl + Fe → FeCl2 + H2

4. What is a balanced chemical equation? Why should a chemical equation be balanced?

Solution:
A balanced equation is the one in which number of different atoms on both the reactant and
product sides are equal. Balancing chemical equations is necessary for the reaction should obey
The Law of Conservation of mass. Balancing the chemical equation has no defined method and is
purely a trial-and-error attempt.

5. Translate the following statements into chemical equations and balance them.
a) Hydrogen gas combines with nitrogen to form ammonia.
b) Hydrogen sulphide gas burns in the air to give water and sulphur dioxide.
c) Barium chloride reacts with aluminium sulphate to give Aluminium chloride and a
precipitate of barium sulphate.
d) Potassium metal reacts with water to give potassium hydroxide and Hydrogen gas.
Solution:
(a) Unbalanced: H2 + N2 → NH3
Balanced: 3H2 + N2 → 2NH3
(b) Unbalanced: H2S + O2 → H2O + SO2
Balanced: 2H2S + 3O2 → 2H2O + 2SO2
(c) Unbalanced:
BaCl2 + Al2(SO4)3 → AlCl3 + BaSO4
Balanced: 3BaCl2 + Al2(SO4)3 → 2AlCl3 + 3BaSO4
(d) Unbalanced: K + H2O → KOH + H2
Balanced: 2K + 2H2O → 2KOH + H2

6. Balance the following chemical equations.

a) HNO3 + Ca(OH)2 → Ca(NO3)2 + H2O
b) NaOH + H2SO4 → Na2SO4 + H2O
c) NaCl + AgNO3 → AgCl + NaNO3
d) BaCl2 + H2SO4 → BaSO4 + HCl
Solution:
a) 2HNO3 + Ca(OH)2 → Ca(NO3)2 + 2H2O
b) 2NaOH + H2SO4 → Na2SO4 + 2H2O
c) NaCl + AgNO3 → AgCl + NaNO3
d) BaCl2 + H2SO4 → BaSO4 + 2HCl

7. Write the balanced chemical equation for the following reactions. Calcium hydroxide +
Carbon dioxide → Calcium carbonate + Water
Zinc + Silver nitrate → Zinc nitrate + Silver
Aluminium + Copper chloride → Aluminium chloride + Copper
Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride Solution:
2Ca(OH)2 + 2CO2 → 2CaCO3 + 2H2O
Zn + 2AgNO3 → Zn(NO3)2 + 2Ag
2Al + 3CuCl2 → 2AlCl3 + 3Cu
BaCl2 + K2SO4 → BaSO4 + 2KCl

8. Write a balanced chemical equation for the following and identify the type of reaction of
each case. KBr + BaI2 → KI + BaBr2
ZnCO3 → ZnO + CO2
H2 + Cl → HCl
Mg + HCl → MgCl2 + H2
Solution:
2KBr + BaI2 → 2KI + BaBr2 (Double Displacement Reaction)
ZnCO3 → ZnO + CO2 (Decomposition Reaction)
H2 + Cl → 2HCl (Combination Reaction)
Mg + 2HCl → MgCl2 + H2 (Displacement Reaction)

9. What is meant by exothermic and endothermic reactions? Give examples.

Solution:
An endothermic reaction occurs when energy is absorbed from the surroundings in the form of
heat (For example, Photosynthesis, melting of ice, evaporation). Conversely, an exothermic
reaction is one in which energy is released from the system into the surroundings (Examples:
Explosions, concrete setting, nuclear fission and fusion).

10. Why is respiration considered to be an exothermic reaction?

Solution:
For the survival of life, we require energy. We obtain this energy from the food we eat. The food
molecules, through the process of digestion, is broken down into simpler molecule like glucose.
These substances come in contact with the Oxygen present in our body cells to form Carbon
dioxide and water along with a certain amount of energy (Respiration process). Since the energy is
in the form of heat (that maintains our body temperature), respiration is considered to be an
exothermic reaction. The reaction taking place is:
C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy
11. Why are decomposition reactions called the opposite of Combination reactions? Write
equations for decomposition reactions.
Solution:
Combination reaction is said to be the reaction between two or more molecules to form a larger
molecule; whereas the decomposition reaction is defined as the splitting of larger molecules into
two or more smaller molecules. This essentially explains that the decomposition reaction is the
opposite of the combination reaction.

In most cases, the decomposition reaction is endothermic since the heat from the surrounding or
induced heat is used to break the bonds of the larger molecule. A few examples of decomposition
reactions are
ZnCO3 → ZnO + CO2
CaCO3 + Energy → CaO + CO2
2HgO → 2Hg + O2

12. Write one equation each for decomposition reactions in which energy is supplied in the
form of heat, light or electricity.
Solution:
(a) Thermal decomposition reaction (Thermolysis)

Decomposition of potassium chlorate: When heated strongly, potassium chlorate decomposes into
potassium chloride and oxygen. This reaction is used for the preparation of oxygen.
2KClO3 + Heat → 2KCl + 3O2

(b) Electrolytic decomposition reaction (Electrolysis)

Decomposition of sodium chloride: On passing electricity through molten sodium chloride, it

decomposes into sodium and chlorine.
electricity
2NaCl 2Na +Cl2

(c) Photodecomposition reaction (Photolysis)

Decomposition of hydrogen peroxide: In the presence of light, hydrogen peroxide decomposes
into water and oxygen.
light
2H2O2 2H2O

13. What is the difference between displacement and double displacement reactions? Write
relevant equations for the above.
Solution:
A displacement reaction is one when a more reactive substance displaces a less reactive one from
its salt solution, whereas a double displacement reaction is one where a mutual exchange of ions
happens between two compounds.

In a displacement reaction, only a single displacement takes place, whereas in the double
displacement reaction, as the name suggests, two displacement takes place between the molecules.
Example:
Displacement reaction
Mg + 2HCl → MgCl2 + H2
Double displacement reaction
2KBr + BaI2 → 2KI + BaBr2

14. In the refining of Silver, the recovery of silver from Silver nitrate solution involves
displacement reaction by Copper metal. Write down the reaction involved.
Solution:
Cu(s) + 2AgNO3(aq) → Cu(NO3)2(aq) + 2Ag(s)

15. What do you mean by a precipitation reaction? Explain by giving examples.

Solution:
When two solutions containing soluble salts are combined, a double displacement reaction takes
place in which the ions are exchanged between the compounds. When one of such compounds
formed is in solid form (that is insoluble in aqua), then it settles down at the bottom of the
container. This solid is known as the precipitate and the respective reaction is termed as the
precipitation reaction. A few examples of precipitation reactions are

CdSO4(aq) + K2S(aq) → CdS(s) + K2SO4(aq)

2NaOH(aq) + MgCl2(aq) → 2NaCl(aq) + Mg(OH)2(s)

16. Explain the following in terms of the gain of oxygen with two examples each.
 a) Oxidation
b) Reduction
Solution:
(a) In a chemical reaction, when the oxygen is added to the element to form its respective oxide it
is the element being oxidised. Example:
4Na(s) + O2(g) → 2Na2O(s)
H2S + O2 → H2O + SO2

(b) In a chemical reaction, when the oxygen is removed from the compound, then it is said to be
reduced. Example:
CuO(s) + H2(g) → Cu(s) + H2O(l)
2HgO → 2Hg + O2

17. A shiny brown coloured element ‘X’ on heating in the air becomes black in colour. Name
the element ‘X’ and the black-coloured compound formed.
Solution:
The shiny brown-coloured element is Copper metal (Cu). When the metal is heated in air, it reacts
with atmospheric oxygen to form copper oxide. Hence, the black-coloured compound is copper
oxide.
2Cu(s) + O2(g) → 2CuO(s)

18. Why do we apply paint on iron articles?

Solution:
Iron articles are painted to prevent them from rusting. When left unpainted, the metal surface
comes in contact with the atmospheric oxygen and in the presence of moisture it from Iron(III)
oxide. But if painted, the surface does not come in contact with moisture and air, thus prevents
Rusting.

19. Oil and Fat containing food items are flushed with Nitrogen. Why?
Solution:
The main purpose of flushing Nitrogen into food packets that contain oil and fat items is to prevent
Rancidity which occurs when the oil or fat reacts with the oxygen letting out an unpleasant smell
and taste. Therefore, by flushing Nitrogen, an unreactive surrounding is created, thus preventing
rancidity.

20. Explain the following terms with one example each.

a) Corrosion
b) Rancidity
Solution:
(a) Corrosion is a process where a refined metal is oxidised by atmospheric oxygen to form a more
stable compound, such as oxides. The metal gradually degrades during the corrosion process.
Rusting of iron is a good example of corrosion where the iron is converted to Iron oxide. Millions
of dollars are spent annually in preventing rusting from bridges and other monuments.
(b) The condition produced by the aerial oxidation of the oil and fat present in the food material
that produces an unpleasant taste and smell. The rancidity is retarded when the food is kept inside
the refrigerator since the low temperature does not promote the oxidation reaction.
 Additional Questions
Chapter 1
Chemical Reactions and Equations
1 Marks Questions
1. Some crystals of copper sulphate were dissolved in water. The colour of the
solution obtained would be
a) green
b) red
c) blue
d) brown.
Ans. (c) blue

2. When dilute HCl is added to zinc pieces taken in a test tube

a) No change takes place
b) the colour of the solution becomes yellow.
c) A pungent smelling gas gets liberated.
d) small bubbles of H 2 gas appear on the surface of zinc pieces
Ans. (d) small bubbles of H2 gas appear on the surface of zinc pieces

3. PbS reacts with ozone (O3) and forms pbso4. As per the balanced equation, molecules of
ozone required for every one molecule of PbS is / are
a) 4
b) 3
c) 2
d) 1
Ans. (a) 4

4. Chemically rust is
a) Hydrated ferrous oxide
b) hydrated ferric oxide
c) only ferric oxide
d) none of these
Ans. (b) hydrated ferric oxide

5. Which of the following reactions is not correct

a) Zn + CuSO 4 → ZnSO 4 +Cu
b) 2Ag + Cu(NO 3)2 → 2AgNO 3 + Cu
c) Fe + CuSO 4 → FeSO 4 +Cu
d) Mg + 2HCl → MgCl 2 + H 2
Ans: (b) 2Ag + Cu(NO3)2 → 2AgNO3 + Cu

6. Copper displaces which of the following metals from its salt solution:
a) ZnSO 4
b) FeSO 4
c) AgNO 3
d) NiSO 4
Ans. (c) AgNO3

7. In an electrolytic cell where electrolysis is carried, anode has:

a) Positive change
b) Negative charge
 c) Connected to negative terminal of the battery
d) None of these is correct.
Ans. (a) Positive change

8. The reaction H2+Cl2 → 2HCl represents :

a) Oxidation
b) Reduction
c) Decomposition
d) Combination
Ans. (d) Combination

9. In the reaction PbO + C → Pb + CO

a) Pbo is oxidised
b) C act as an oxidising agent
c) C act as a reduction agent
d) Reaction does not represent redox reaction.
Ans. (c) C act as a reduction agent

10. A substance which oxidizes itself and reduces other is known as

a) Oxidising agent
b) reducing agent
c) Both (a) and (b)
d) None of these.
Ans. (b) reducing agent

11. Take about 5 ml of dil. HCl in a test tube and add a few pieces of fine Zn granules to
it. Which gas is evolved?
a) Chlorine
b) Hydrogen
c) HCl
d) Nitrogen
Ans. (b) Hydrogen

12. Dissolving suger is an example of-

a) Physical change
b) Chemical change
c) Redox Reaction
d) None of these.
Ans. (a) Physical change

13. Heat is evolved diving

a) Endothermic Reaction
b) Displacement Reaction
c) Combustion Reaction
d) Combination Reaction
Ans. (c) Combustion Reaction

14. Which of the following is not a balanced equation?

a) Fe + Cl2 → FeCl3
b) Mg + CuSO 4 → MgSO 4 + C4
c) NaOH + HCl → NaCl +H 2O
d) Zn + S → ZnS
 Ans: (a) Fe + Cl2 → FeCl3

15. The reaction between lead nitrate and potassium iodide present in aqueous
solutions is an example of
a) Decomposition Reaction
b) Displacement Reaction
c) Double Displacement Reaction
d) Neutralisation Reaction
Ans. (c) Double Displacement Reaction

16. What happens when dilute hydrochloric acid is added to iron filling? Tick the
correct answer

a) Hydrogen gas and iron chloride are produced.

b) Chlorine gas and iron hydroxide are produced
c) No reaction takes place
d) Iron salt and water are produced
Ans. (a) is correct

2 Marks Questions
1. Identify the type of chemical reaction
(i) A→B+C
(ii) AD + CD → AD +CB
Ans. (i) Decomposition reaction
(ii) Double displacement reaction

2. Why does not silver evolve hydrogen on reacting with dil H2So4?
Ans. Silver do not evolve hydrogen on reacting with dil. H 2SO 4 as silver is less
reactive metal than hydrogen.

3. Way do diamond and graphite, the two allotropic forms of carbon evolve
different amounts of heat on combustion?
Ans. Diamond and graphite are the two allotropes of carbon but they do not evolve
same amount of heat on combustion because they differ in the arrangement of carbon
atoms and also their shapes one different.

4. What is the sole of oxidizing agent is a reaction?

Ans. The oxidizing agent supply the oxygen in a reaction or it removes the
hydrogen.

5. What happens chemically when quick lime is added to water?

Ans. When quick lime is added to water calcium hydroxide (slaked lime) is formed
with a hissing sound and lot of heat is evolved during the reaction. The reaction
involved is
CaO (s)+ H 2O(Quick Lime) → Ca (OH) 2 (s) + Heat (Shaked Lime)

6. Why a combustion reaction an oxidation reaction?

Ans. Combustion reaction because it is always carried out in the presence of air or
oxygen for e.g. CH 4 (g) + 2O 2 (g) → Co2 (g) +2H 2O (l)

7. Why are food particle preferably packed in aluminum foil?

 Ans. Aluminium foil do not corrode in atmosphere even if kept for a long time
because a protective coating of aluminium oxide (Al2O 3) is formed on the surface of
the foil and stops any further reaction of the metal with air and water thus food
particles do not get spoiled.

8. What happens to lime water when Co2 gas is bubbled through it in excess?
Ans. When CO 2 gas is bubbled through lime water in excess then initially it
becomes milky but then its milkiness disappears.

9. Why is a Combustion reaction an oxidation reaction?

Ans. Combustion is an oxidation reaction as it is always carried out in the presence
of oxygen. For example: CH 4 + 2O 2 → CO 2 + 2H 2O.

10. Identify the type of chemical reaction

(i) A +B → C
(ii) A + BC → AC + B
Ans: (i) Combination reaction
(ii) Displacement reaction

11. Why cannot a chemical change be normally reversed?

Ans. Chemical change cannot be reversed back because products so formed in a
chemical reaction are totally different from the reactants.

12. Identify the substance oxidized and reduced in the reaction.

CuO(s) + Zn(s) → ZnO(s) + Cu(s).
Ans. The substance oxidized is Zinc oxide and the copper oxide get’s reduced to
copper.

13. A student took 2-3 g of a substance X in a glass beaker & poured water over it slowly.
He observed bubbles along with hissing noise. The beaker becomes quite hot. Identify X.
What type of reaction is it?
Ans. X = Calcium oxide (Quick lime), Combination reaction.

14. A substance X used for coating iron articles is added to a blue solution of
a reddish brown metal Y,the color of the solution gets discharged Identify X
and Y & also the type of reaction.
Ans. X= Fe, Y = Cu, Displacement reaction.

15. A student burnt a metal A found in the form of ribbon. The ribbon burnt with a
dazzling Flame & a white powder B is formed which is basic in nature. Identify A &
B. Write the Balanced chemical equation.
Ans. X = Mg, Y = MgO, Mg + O 2 → 2MgO

16. Why should a magnesium ribbon be cleaned before burning in air?

Ans. Magnesium ribbon is cleaned before burning to remove the protective
layer of basic magnesium carbonate from the surface of magnesium ribbon.

17. Write the balanced chemical equation with state symbols for the following
reactions?
Ans. Balance chemical reaction with state symbols are as follows-
(i) BaCl2(aq) + Na2 SO4 (aq) → BaSO 4 (s) + 2NaCl (aq)
 (ii) NaOH (aq) + HCl (aq) → NaCl (aq) + H2O

18. A solution of a substance ‘X’ is used for white washing

i. Name the substance ‘X’ and writes its formula.
ii. Write the reaction of the substance ‘X’ named in (i) above with water
Ans. (i). The substance whose solution is water is used for white washing is
calcium oxide. Its formula is CaO.
(ii). CaO (s) + H2O → Ca(OH)2 (s)

19. Which of the following statement about the reaction below are incorrect?
2PbO (s) + C (s) → 2Pb (s) + CO2 (g)
a) Lead is getting reduced.
b) Carbon dioxide is getting oxidized
c) Lead oxide is getting oxidized
d) Lead is getting reduced
(i) (a) and (b)
(ii) (a) and (c)
(iii) (a), (b) and (c)
(iv) All
Ans. As statement (a) and (b) are incorrect, answer (i) is correct.

20. In refining of silver, the recovery of silver from silver nitrate solution involved
displacement by copper metal. Write down the reaction involved.
Ans. The reaction involved is: Cu(s) + 2AgNO 3(aq) → Cu(NO 3)2(aq) + 2Ag(s)

21. What do you mean by a precipitation reaction? Explain by giving examples.

Ans. A chemical reaction in which an insoluble substance (precipitate) is formed is
called precipitation reaction. For example
AgNO 3 + NaCl → AgCl + NaNO 3

22. A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name
the element ‘X’ and the black coloured compound formed.
Ans. The brown coloured element ‘X‘ is copper. On heating in air it forms
copper oxide, which is black in colour.
2CuS + O 2 → 2CuO

23. Why do we apply paint on iron articles?

Ans. We apply paint on iron articles to prevent rusting. Iron articles do not
come in contact of atmospheric oxygen and moisture and thus the rusting is
prevented.

24. Oil and fat containing food items are flushed with nitrogen. Why?
Ans. Oil and fat containing items get rancid due to oxidation with atmospheric
oxygen. To prevent rancidity food items are flushed with nitrogen. Nitrogen do not
reacts with oil and fat containing items.

3.Marks Questions
1. (a) Define Rusting
(b) Why do you apply paint an iron article?
Ans. (a) The process of slow eating of the surface of metal iron when exposed to air
for a longer period of time is called rusting.
 (b) We apply paint on iron articles because it forms a protective coating on the
surface of iron and we can protect it against rusting.

2. White the balanced reactions for the following

(i) Potassium Bromide (aq) + Barium iodide (aq) → Potassium iodide (aq) +
Barium Bromide(aq)
(ii) Zinc carbonate (s) → Zinc oxide (s) + carbon dioxide (g)
(iii) Hydrogen (g) + chlorine (g) → Hydrogen chloride
Ans. (i)2KBr(aq) + Bal 2(aq) → 2KI(aq) + BaBr 2(aq)
(ii) ZnCO 3(s) → ZnSO 4 + CO 2(g)
(iii) H 2(g) +Cl2(g) → 2HCl(g)

3. The reaction is given by

Zn + H2SO4 → ZnSO4 + H2
I. White the ionic equation for the reaction
II. The ionic equations can be represented by two half equations. Write these equations.
III.Explain why this is a redox reaction
Ans. (i) Zn + 2H+ → Zn2+ + H2
(ii)The half ionic equations are-
Zn → Zn2+ + 2e⁻
2H+2e⁻ → H2
(iii) The first half represents oxidation since these is loss of electrons and second
half represents reduction as there is gain of electrons.

4. What are neutralization reactions? Why are they named so? Give one example?
Ans. A neutralization reaction is the chemical reaction between an acid and base
dissolved in water
For eg →KOH(aq) + NHO3(aq) → KNO3(aq) + H2O(aq)
It is called neutralization reaction because both KNO 3 and H2O formed as the products, are
neutral in nature.

5. Identify the type of reaction in the following

a) ZnCO3 + 2HCl (aq) → ZnCl2 (aq) + H2CO3 (aq)
b) 2NaBr (aq) +Cl (g) → 2Nacl (aq) + Br2 (aq)
c) 2CuO (S) Heat 2Cu (s) + O2 (g)

Ans. (a) Double decomposition reaction.

(b) Displacement reaction.
(c)Decomposition reaction.

6. A student dropped few pieces of marble in dilute hydrochloric acid contained in a

test tube. The evolved gas was then passed through lime water. What change would
be observed in lime water? Write balanced chemical equation for both the change
observed?
Ans. When marble reacts with dil. HCl, CO 2 gas evolved
CaCO 3 (s) +2HCl (aq) → CaCl2 (aq) + H 2O (l) + CO 2 (g)
When this gas is evolved and is passed through lime water, becomes milky due to
the formation of insoluble Calcium carbonate
Ca (OH) 2 + CO 2(g) → CaCO 3(s) + H2O (l)
But when milkiness disappears i.e. when CO 2 gas is passed in excess through
CaCO 3 (s) CaCO 3 (s) + CO 2 (g) +H 2O (l) → Ca (HCO 3)2 (aq)
7. In the reaction MnO2 +4HCl → MnCl2 + 2H2O +Cl2
(a) Name the substance oxidised.
(b) Name the oxidising agent.
(c) Name the reducing agent and the substance reduced.
Ans. (a) HCL has been oxidized to Cl2
(b) MnO 2
(C) HCL is the reducing agent and Mno2 has been reduced to MnCl2
8. Give one example each of
(a) Thermal decomposition
(b) Electrolytic decomposition
(c) Photo decomposition
Ans. (a) MgCO 3 (s) Heat MgO (s) +CO2 (g)
(b) 2H2O (l) Electric Current 2H2 (g) +O2 (g)
(c) 2H2O2 (l) Light 2H 2 O (l) +O 2 (g)

9. Write three equations for decomposition reaction where energy is supplied

in the form of heat, light and electricity?
Ans: (i) MgCO3 Heat MgO +CO2
(ii) 2AgCl Light 2Ag +Cl 2
(iii) 2NaCl electricity 2Na + Cl 2

10. When you mix solutions of lead (II) nitrate and potassium iodide,
(i) What is the colour of the precipitate formed? Name the compound evolved?
(ii) Write a balanced chemical reaction?
(iii) Is this a double displacement reaction?

Ans. (i) The precipitate is yellow in colour and the compound is lead (II) Iodide.
(ii) Pb(NO 3 ) 2 (aq) + 2kI(aq) → PbI 2 (s) + 2KNO 3 (aq)
(iii) Yes it is a double displacement reaction.

11. Transfer the following into chemical equations and balance them.
(i) Hydrogen gas combines with nitrogen to from ammonia.
(ii) Hydrogen sulphide gas burns in air to give water and sulphurdioxide.
(iii) Potassium metal reacts with water to give potassium hydroxide and hydrogen
gas.

Ans: (i) 3H 2 + N 2 → 2NH 3

(ii) 2H 2 S + 3O 2 → 2H 2 O + 2SO 2
(iii) 2K + 2H 2 O → 2KOH + H 2

12. Balance the equations.

(i) NHO3 + Ca(OH)2 → Ca(NO 3 ) 2 + H 2 O
(ii) NaCl + AgNO 3 → AgCl + NaNO 3
(iii) BaCl 2 + H 2 SO 4 → BaSO 4 + HCl

Ans: (i) 2NHO 3 + Ca(OH)2 → Ca(NO 3 ) 2 + 2H 2

(ii) NaCl + AgNO 3 → AgCl + NaNO 3
(iii) BaCl 2 + H 2 SO 4 → BaSO 4 + 2HCl
13. A compound ‘X’ is used for drinking, has pH =7.Its acidified solution undergoes
decomposition in presence of electrictiy to produce gases ‘Y’ and ‘Z’ The volume of
Y is double than Z. Y is highly combustible whereas Z is supporter of combustion.
Identify X, Y & Z and write the chemical reactions involved.
Ans: 2H2O(l) → H2(g) + O 2(g)
X Y Z

14. An aqueous solution of metal nitrate P reacts with sodium bromide solution to
form yellow ppt of compound Q which is used in photography. Q on exposure to
sunlight undergoes decomposition reaction to form metal present in P along with
reddish brown gas. Identify P &Q. Write the chemical reaction & type of chemical
reaction.
Ans: P = Ag NO 3, Q = AgBr 2AgBr (s) → 2Ag(S) + Br2(g)
,
Photochemical decomposition.

15. Bhawana took a pale green substance A in a test tube. And heated it over the
flame of a burner. A brown colored residue B was formed along with evolution of
two gases with burning smell of sulphur. Identify A & B. Write the chemical
reaction involved.
Ans: 2FeSO 4(s) Heart Fe2O 3(s) + SO 2(g) + SO 3(g)
A(green) B(brown)

16. A reddish brown vessel developed a green colored solid X When left open in air for a
long time. When reacted with dil H2SO4 , it forms a blue colored solution along with brisk
efficient due to colourless & odourless gas Z. X decomposes to form black colored oxide Y
of a reddish brown metal along with gas Z, Identify X, Y, & Z.
Ans:
X = CuCo3 Cu(OH), Y = CuO, Z = CO2

17. A student has mixed the solutions of lead (II) nitrate and potassium iodide.
(a) What was the colour of the precipitate formed? Can you name the compound?
(b) Write the balanced chemical equation for this reaction.
(c) What type of reaction is it?
Ans. (i) Yellow, Lead iodide
(ii) Pb(NO3)2 +Kl → Pbl2 +2KNO3
(iii) Double displacement reaction

18. Name the type of reaction seen in the diagram below. Write the reaction for the
Same.
Ans. Displacement Reaction
Fe(s) + CuSO 4 → FeSO 4aq + Cu
Oxygen and is being oxidized.

19. A student dropped few pieces of marble in dilute HCI contained in a test tube.
The gas evolved was passed through lime water. What change would be observed in
lime water? Write chemical reactions for both the changes observed.
Ans.
Ca (OH) 2(aq) + CO 2 (g) → CaCO 3(s) + H 2O(l)
Ca(OH) 2(aq) + CO 2(g) → CaCO 3(s) + H 2O(l)
(Calcium (Calcium
Hydroxide) carbonate)
20. Astha has been collecting silver coins and copper coins. One day she observed a black
Coating on silver coins and a green coating on conner coins. Which chemical phenomenon is
responsible for these coatings? Write the chemical name of black and green coatings?
Ans. Corrosion is responsible for this coating. Black coating is due to formation of
Ag2 S And green coating is due to formation of CuCO 3, Cu (OH) 2

21. Write the balance equation for the following reactions Give reasons for the following
reactions?
i. Hydrogen + Chlorine → Hydrogen chloride
ii. Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium
chloride
iii. Sodium + water → Sodium hydroxide + water

Ans. The chemical equations are as follows-

(i) H 2 +Cl2 → 2HC
(ii) 3BaCl 2 + Al2 (SO 4)3 → 3BaSO 4 + 2AlCl3
(iii) Na + 2H 2O → 2NaOH +H 2

22. Fe2O3 + 2Al → Al2O3 + 2Fe

The above reaction is an example of a
(a) combination reaction
(b) double displacement reaction
(c) decomposition reaction
(d) displacement reaction
Ans. This is an example of displacement reaction because Fe in FeO 3 has
been displaced by Al. Hence correct answer is (d).

23. What is balanced chemical equation? Why should chemical equation be

balanced?
Ans. The reaction in which the number of atoms of each element is equal on the reactant
side and product side is called balanced equation. Chemical reaction should be balanced
because only a balanced equation tells us the relative quantities of different reactants and
products involved in the reaction.

24.Why respiration is considered an exothermic reaction? Explain.

Ans. During respiration, we inhale oxygen from the atmosphere which reacts with
glucose in your body cells to produce carbon dioxide and water.

C6H 12O6 (aq) + 6O2 → 6CO2 (g) + 6H2 O (l) + heat

Heat is liberated in this process; hence respiration is considered an exothermic

reaction.

5 Marks Questions
1. You are given with
a) Iron Nails
b) CuSO4 solution
c) Bacl2
 d) Cu powder
e) Ferrous sulphate crystal
f) Quick lime.
Make five reactions that can take place from these materials.
Ans: (i) BaCl2(aq) + CuSO4(aq) → BaSO4(aq) + CuCl2(aq)
(ii) 2Cu(s) + O2(g) → 2CuO(s)
(iii) 2FeSO 4(s) heat Fe2O3 + SO 2 + SO 3
(iv) FeSO 4-7H2O heat Fe2SO3(s) + 7H 2O
(v) CaO(s) + H 2O → Ca(OH)2(s) + Heat

2. A metal is heated with dil. H2SO4. The gas evolved is collected by the method shown
in the figure: Answer the following

(a) Name the gas.

(b) Name the method of collection of gas.
(c) Is the gas soluble or insoluble in water?
(d) Is the gas lighter or heavier than air?

Ans. (a) H 2 gas

(b) Gas is collected over water by a method called downward displacement method.
(c) Since collected over water so it is insoluble.
(d) The gas is lighter than air.

3. With the help of an activity show that iron is more reactive than copper?
Ans. First take some aqueous solution of Cuso 4 (blue is colour) and dip iron nails
into it leave for half an hour the blue colour of the solution changes into light green.
At the same time brown deposit appears on the nails. This happens because iron is
placed above copper in reactivity series hence it displaces copper from cuso 4
solution. The brown deposit is of copper.
i.e. Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)

4. Observe the following activity & answer the questions

a. Do you observe anything happening around the zinc granules?
b. Is there any change in its temperature?
c. Why is glass tube not dipped in dil H2SO4 ?
d. How is H2 gas collected by downward displacement or upward displacement of
water?
e. Is H2 gas soluble or insoluble in water?
f. Is H2 gas heavier or lighter than air?

Ans. a. Bubbles of hydrogen gas.

b. Yes temperature will increase.
c. H 2 SO 4 will rise in glass tube, preventing H2 to evolve
d. downward displacement
e. Insoluble
f. lighter than air

5. A reddish brown metal X when heated in presence of oxygen forms a black

compound Y Which is basic in nature when heated with hydrogen gas gives back X.
Identify X & Y. Write the chemical reaction between Y & H2 Identify the substance
being oxidized & reduced.
Ans. Oxygen reacts with copper to form copper oxides which has black colour
2Cu(s) + O2(g) → 2Cuo(s)
Air Black
CuO + H 2 Heat Cu + H2O

The copper (II) ovide is losing oxygen and is being reduced. The hydrogen is
gaining

6. Why does the colour of copper sulphate solution change when an iron nail is
dipped in it?
Ans. When iron nail is dipped in copper sulphate solution, than iron sulphate
solution and copper solution and copper metal are formed:
CuSO4 (aq) + Fe (s) → FeSO4 (aq) + Cu (s)
In this reaction, iron displaces copper from copper sulphate solution. The deep blue
colour of copper sulphate fades due to the formation of light green solution of iron
sulphate.

7. Identify the substances that are oxidized and the substances that are reduced in
the following reactions.
(i) 4Na (s) + O2 (g) 2Na2O (s)
(ii) CuO (s) + H2 → Cu (s) + H2O (l)
Ans. (i) 4Na + O 2 → 2Na2O
In this reaction, Na is oxidized because it combines with O 2 to form Na 2O. O 2
is reduced because it is converted into Na 2O.
(ii) CuO + H 2 → Cu + H2O
In this reaction, CuO is reduced because it loses oxygen. H 2 is oxidized because
it combines with oxygen of CuO to form water

8. Translate the following statements into chemical equations and then balance them.
(a) Hydrogen gas combines with nitrogen to form ammonia.
 (b) Hydrogen sulphide gas burns in air to give water and Sulpher dioxide.
(c) Barium chloride reacts with aluminum sulphate to give aluminum chloride
and precipitate of barium sulphate
Ans. (a) H 2 +N2 → NH3
3H 2 +N2 → 2NH3

(b) H2S + O 2 → H2O + SO 2

2H 2S + 3O 2 → 2H2O + 2SO 2

(c)BaCl2 + Al2(SO 4)3 → AlCl3 +BaSO 4

3BaCl2 + Al2(SO 4)3 → 2AlCl3 +3BaSO 4

(d) K + H 2O → KOH + H 2
2K + 2H 2O → 2KOH + H 2

9. Balance the following chemical equations:

(e) HNO3 + Ca(OH)2 → Ca(OH)2 àCa(NO3)2 +H2O
(f) NaOH +H2SO4 → Na2SO4 +H2O
(g) NaCl +AgNO3 → AgCl + NaNO3
(h) BaCl2 +H2SO4 → BaSO4 +HCl

Ans. Balanced chemical equation are

(a) 2HNO 3 + Ca(OH)2 → Ca(OH)2 àCa(NO 3)2 +2H 2O
(b) 2NaOH +H 2 SO 4 → Na2SO 4 +2H 2O
(c) NaCl +AgNO 3 → AgCl + NaNO3
(d) BaCl2 +H 2SO 4 → BaSO 4 +2HCl

10. Write the balanced chemical equations for the following reactions.
a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
b) Zinc + Silver nitrate → Zinc nitrate + Silver
c) Aluminum + Copper chloride → Aluminum chloride +Copper
d) Barium chloride + Potassium sulphate → Barium sulphate + potassium chloride
Ans. Balanced chemical equation for reactions are
(a) Ca(OH)2 + CO2 → CaCO 3 + H2O
(b) Zn + 2AgNO 3 → Zn(NO 3)2 +2Ag
(c) 2Al + 3Cl2 → 2AlCl3 + 3Cu
(d) BaCl2 + K2SO4 → BaSO 4 + 2KCl

11. Write the balanced chemical equation for the following and identify the type of
reaction in each case.
a) Potassium bromide (s) + Barium iodide (aq) → Potassium iodide (aq) + Barium
bromide(s)
b) Zinc carbonate (s) → Zinc oxide (s) + Carbon dioxide (g)
c) Hydrogen (g) + Chlorine (g) → Hydrogen chloride (g)
d) Magnesium (s) + Hydrochloric acid (aq) → Magnesium chloride (aq) + Hydrogen
(g)

Ans. Balanced equations are

 a) 2KBr (aq) + BaI2 ( aq) → 2KI (aq) + Br2 (displacement reaction)
b) ZnO 3 (s) → ZnO (s) + CO 2 (g) (decomposition reaction)
c) H 2 (g) + Cl2 (g) → 2HCl (combination reaction)
d) Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g) (displacement reaction)

12. What does one mean by exothermic and endothermic reactions? Give examples.
Ans. A reaction in which energy is released in the form of heat or light is called
exothermic reaction. Example of exothermic reaction are:
CH4 + 2O 2 → CO2 + 2H2O + heat
2Al + FeO 3 → Al2O 3 + Fe + heat
A reaction in which energy is absorbed from the surrounding and cooling is
produced is called endothermic reaction. Example of exothermic reaction are:
(a) CaCO 3 → CaO + CO2
(b) N2 + O 2 → 2NO

13. Why decomposition reactions are called the opposite of combination

reactions? Write equations for these reactions.
Ans. NH4Cl (s) → HCl (g) + NH 3 (g)
In a decomposition reaction, a single substance breaks down into two or more
substance while in a combination reaction, two or more substances react to produce
one substance. Therefore, decomposition reactions are called opposite of
combination reactions.
Example of decomposition reaction: Example of combination reaction:
CaO (s) + CO 2 (g) → CaCO 3 (s)

14. Write one equation each for decomposition reactions where energy is supplied
in the form of heat, light or electricity.
Ans. Decomposition by heat:
CaCO 3(S) + heat → CaO (s) + CO 2 (g)
Decomposition by electricity:
2H2O + light → 2H2 (g) + O2 (g)
Decomposition by light:
2AgBr (s) + light → 2Ag (s) + Br2

15.What is difference between displacement and double displacement reactions?

Write equations for these reactions.
Ans. In displacement reaction, more reactive element displaces the less reactive
element from its compound. For example
Zn (s) + CuSO4 (aq) → ZnSO4 (aq) + Cu (s)
But in double displacement reaction, exchange of ions takes place. For example
HCl (aq) + AgNO 3 (aq) → AgCl (s) + HNO 3 (aq)

16. Explain the following in terms of gain and loss of oxygen with two examples
each?
a) Oxidation
b) Reduction
Ans. Oxidation- addition of oxygen or removal of hydrogen in a chemical reaction
is called oxidation reaction. For example
2Cu +O 2 → 2CuO
 4Al + 3O 2 → 2Al2O3
Reduction- addition of hydrogen or removal of oxygen in a chemical reaction is
called oxidation reaction. For example
CuO +H 2 → Cu +H2O
H2S + Cl2 → 2HCl +S

17. Explain the following terms with one example each.

a) Corrosion
b) Rancidity.
Ans. Corrosion- action of air, water, acid or other substance on metal surface to form oxides
and carbonates is called corrosion. Corrosion of iron is called rusting. Green coating on
copper and black coating on silver is examples of corrosion.
Rancidity-change in smell of food item containing fat and oil when kept open for
longer time due to oxidation is called rancidity. To prevent rancidity food items
are flushed with nitrogen or kept in airtight containers.

Assertion and Reason Questions

Following questions consist of two statements – Assertion (A) and Reason (R). Answer these
questions selecting the appropriate option given below:
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
1. Assertion (A) : Decomposition of vegetable matter into compost is an example of exothermic
reactions.
Reason (R) : Exothermic reaction are those reactions in which heat is evolved.
Ans: a

2. Assertion (A) : When HCl is added to zinc granules, a chemical reaction occurs.
Reason (R) : Evolution of a gas and change in colour indicate that the chemical reaction is taking
place.
Ans: b

3. Assertion (A) : Calcium carbonate when heated gives calcium oxide and water.
Reason (R) : On heating calcium carbonate, decomposition reaction takes place.
Ans: d

4. Assertion (A) : Brown fumes are produced when lead nitrate is heated.
Reason (R) : Nitrogen dioxide gas is produced as a byproduct due to the decomposition of lead
nitrate.
Ans: a

5. Assertion (A) : White silver chloride turns grey in sunlight.

Reason (R) : Decomposition of silver chloride in presence of sunlight takes place to form silver
metal and chlorine gas.
Ans: a

6. Assertion (A): Pungent smelling gas is produced when sulphur burns in air.
Reason (R) : Sulphur trioxide is formed on reaction of sulphur with oxygen.
Ans: c
7. Assertion (A) : In a reaction of copper with oxygen, copper serves as a reducing agent.
Reason (R) : The substance which gains oxygen in a chemical reaction acts as a reducing agent.
Ans: a

8. Assertion (A) : In electrolysis of water, the volume of hydrogen liberated is twice the volume
of oxygen formed.
Reason (R) : Water (H,0) has hydrogen and oxygen in the ratio of 1:2 by volume.
Ans: c

9. Assertion (A): Corrosion of iron is commonly known as rusting.

Reason (R) : Corrosion of iron occurs in presence of water and air.
Ans: b

10. Assertion (A) : The balancing of chemical equations is based on law of conservation of mass.
Reason (R) : Total mass of reactants is equal to total mass of products.
Ans: a

11. Assertion (A): In a balanced chemical equation, total mass of the reactants is equal to the total
mass of the products.
Reason (R): Mass can neither be created nor destroyed during a chemical change.
Ans: a

12. Assertion (A): Iron articles are painted so as to prevent them from rusting.
Reason (R): When the surface of iron is coated with paint, its surface does not come in contact
with oxygen and moisture therefore rusting does not take place.
Ans: a

13. Assertion (A) : Chemical reaction changes the physical and chemical state of a substance.
Reason (R) : When electric current is passed through water (liquid), it decomposes to produce
hydrogen and
oxygen gases.
Ans: b

14. Assertion (A): When calcium carbonate is heated, it decomposes to give calcium oxide and
carbon dioxide.
Reason (R): The decomposition reaction takes place on application of heat, therefore, it is an
endothermic reaction.
Ans: b

15. Assertion (A): Zinc reacts with sulphuric acid to form zinc sulphate and hydrogen gas and it is
a displacement reaction.
Reason (R): Zinc reacts with oxygen to form zinc oxide
Ans: b

16. Assertion (A): Chips manufacturers usually Ilush bags of chips with gas such as nitrogen to
prevent the chips from getting oxidised.
Reason (R): This increases the taste of the chips and helps in their digestion.
Ans: c

17. Assertion (A): Exposure of silver chloride to sunlight for a long duration turns grey due to the
formation of silver by decomposition of silver chloride.
Reason (R): In this process, sublimation of silver chloride takes place.
Ans: c

18. Assertion (A): Rusting of iron metal is the most common form of corrosion.
Reason (R): The effect of rusting of iron can be reversed if they are left open in sunlight.
Ans: c

19. Assertion (A): AgBr is used on photographic and X-ray film.

Reason (R): AgBr is photosensitive and changes to Ag and bromine in presence of sunlight and
undergoes decomposition reaction.
Ans: a

20. Assertion (A): Magnesium ribbon keeps on burning in atmosphere of nitrogen.

Reason (R) : Magnesium reacts with nitrogen to form magnesium nitride and this reaction is
combination reaction.
Ans: a

21. Assertion (A): A lead nitrate on thermal decomposition gives lead oxide, brown coloured
nitrogen dioxide and oxygen gas.
Reason (R): Lead nitrate reacts with potassium iodide to form yellow ppt. of lead iodide and the
reaction is double displacement as well as precipitation reaction.
Ans: b