CHEMICAL REACTIONS AND EQUATIONS 45

3. Rancidity can be retarded by

keeping food in a refrigerator (see
Figure 59). The refrigerator has a low
temperature inside it. When the food is
kept in a refrigerator, the oxidation of
fats and oils in it is slowed down due to
low temperature. So, the development of
rancidity due to oxidation is retarded.
4. Rancidity can be retarded by
storing food in air-tight containers.
When food is stored in air-tight Figure 58. Unreactive gas nitrogen is used Figure 59. Rancidity can
containers, then there is little exposure in packaging some foods like potato chips also be prevented by keeping
to oxygen of air. Due to reduced to prevent their rancidity. the food in a refrigerator.
exposure to oxygen, the oxidation of fats
and oils present in food is slowed down and hence the development of rancidity is retarded.
5. Rancidity can be retarded by storing foods away from light. In the absence of light, the oxidation of
fats and oils present in food is slowed down and hence the development of rancidity is retarded.
We are now in a position to answer the following questions :
Very Short Answer Type Questions
1. What type of reaction is represented by the digestion of food in our body ?
2. Name the various types of chemical reactions.
3. Why does the colour of copper sulphate solution change when an iron nail is kept immersed in it ?
4. Write the balanced chemical equation for the following reaction :
Zinc + Silver nitrate  o Zinc nitrate + Silver
5. Which term is used to indicate the development of unpleasant smell and taste in fat and oil containing foods
due to aerial oxidation (when they are kept exposed for a considerable time) ?
6. What is the general name of the chemicals which are added to fat and oil containing foods to prevent the
development of rancidity ?
7. State an important use of decomposition reactions.
8. What are anti-oxidants ? Why are they added to fat and oil containing foods ?
9. Explain why, food products containing fats and oils (like potato chips) are packaged in nitrogen.
10. Give one example of a decomposition reaction which is carried out :
(a) with electricity
(b) by applying heat
11. What type of chemical reaction is used to extract metals from their naturally occurring compounds like
oxides or chlorides ?
12. Name two anti-oxidants which are usually added to fat and oil containing foods to prevent rancidity.
13. Write one equation each for the decomposition reactions where energy is supplied in the form of (a) heat,
(b) light, and (c) electricity.
14. In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper
metal. Write down the chemical equation of the reaction involved.
15. What type of reactions are represented by the following equations ?
(i) CaCO3  o CaO + CO2
(ii) CaO + H2O  o Ca(OH)2
(iii) 2FeSO4  o Fe2O3 + SO2 + SO3
(iv) NH4Cl  o NH3 + HCl
(v) 2Ca + O2  o 2CaO
46 SCIENCE FOR TENTH CLASS : CHEMISTRY

16. What type of chemical reactions take place when :

(a) a magnesium wire is burnt in air ?
(b) lime-stone is heated ?
(c) silver bromide is exposed to sunlight ?
(d) electricity is passed through water ?
(e) ammonia and hydrogen chloride are mixed ?
17. What type of chemical reactions are represented by the following equations ?
(i) A + BC  o AC + B
(ii) A + B  o C
(iii) X  o Y + Z
(iv) PQ + RS  o PS + RQ
(v) A2O3 + 2B  o B2O3 + 2A
18. Balance the following chemical equations :
Heat
(a) FeSO4  o Fe2O3 + SO2 + SO3
(b) Pb(NO3)2 (s) Heat
o PbO (s) + NO2 (g) + O2 (g)
19. Which of the following is a combination and which is a displacement reaction ?
(a) Cl2 + 2KI  o 2KCl + I2
(b) 2K + Cl2 o 2KCl
20. What type of reactions are represented by the following equations ?
(a) CaO + CO2  o CaCO3
(b) 2Na + 2H2O o 2NaOH + H2
(c) Mg + CuSO4  o MgSO4 + Cu
(d) NH4NO2  o N2 + 2H2O
(e) CuSO4 + 2NaOH  o Cu(OH)2 + Na2SO4
21. In the following reaction between lead sulphide and hydrogen peroxide :
PbS (s) + 4H2O2 (aq) o PbSO4 (s) + 4H2O (l)
(a) Which substance is reduced ?
(b) Which substance is oxidised ?
22. Identify the component oxidised in the following reaction :
H2S + Cl2 o S + 2HCl
23. When SO2 gas is passed through saturated solution of H2S, the following reaction occurs :
SO2 + 2H2S o 2H2O + 3S
In this reaction, which substance is oxidised and which one is reduced ?
24. Fill in the following blanks with suitable words :
(a) The addition of oxygen to a substance is called ......... whereas removal of oxygen is
called .........
(b) The addition of hydrogen to a substance is called ......... whereas removal of hydrogen is called .........
(c) Anti-oxidants are often added to fat containing foods to prevent ...............due to oxidation.

Short Answer Type Questions

25. What is an oxidation reaction ? Identify in the following reaction (i) the substance oxidised, and (ii) the
substance reduced :
ZnO + C  o Zn + CO
26. (a) What is a redox reaction ? Explain with an example.
(b) When a magnesium ribbon burns in air with a dazzling flame and forms a white ash, is magnesium
oxidised or reduced ? Why ?
(c) In the reaction represented by the equation :
MnO2 + 4HCl o MnCl2 + 2H2O + Cl2
(i) name the substance oxidised. (ii) name the oxidising agent.
(iii) name the substance reduced. (iv) name the reducing agent.
CHEMICAL REACTIONS AND EQUATIONS 47
27. (a) Define a combination reaction.
(b) Give one example of a combination reaction which is also exothermic.
(c) Give one example of a combination reaction which is also endothermic.
28. (a) Give an example of an oxidation reaction.
(b) Is oxidation an exothermic or an endothermic reaction ?
(c) Explain, by giving an example, how oxidation and reduction proceed side by side.
29. (a) What is the colour of ferrous sulphate crystals ? How does this colour change after heating ?
(b) Name the product formed on strongly heating ferrous sulphate crystals. What type of chemical reaction
occurs in this change ?
30. What is a decomposition reaction ? Give an example of a decomposition reaction. Describe an activity to
illustrate such a reaction by heating.
31. Zinc oxide reacts with carbon, on heating, to form zinc metal and carbon monoxide. Write a balanced chemical
equation for this reaction. Name (i) oxidising agent, and (ii) reducing agent, in this reaction.
32. Give one example of an oxidation-reduction reaction which is also :
(a) a combination reaction
(b) a displacement reaction
33. (a) What is the difference between displacement and double displacement reactions ? Write equations for
these reactions.
(b) What do you mean by a precipitation reaction ? Explain giving an example.
34. (a) Explain the following in terms of gain or loss of oxygen with one example each :
(i) oxidation (ii) reduction
(b) When copper powder is heated strongly in air, it forms copper oxide. Write a balanced chemical equation
for this reaction. Name (i) substance oxidised, and (ii) substance reduced.
35. (a) Define the following in terms of gain or loss of hydrogen with one example each :
(i) oxidation (ii) reduction
(b) When a magnesium ribbon is heated, it burns in air to form magnesium oxide. Write a balanced chemical
equation for this reaction. Name (i) substance oxidised, and (ii) substance reduced.
36. What is meant by (a) displacement reaction, and (b) double displacement reaction ? Explain with the help of
one example each.
37. (a) Why are decomposition reactions called the opposite of combination reactions ? Explain with equations
of these reactions.
(b) Express the following facts in the form of a balanced chemical equation :
“When a strip of copper metal is placed in a solution of silver nitrate, metallic silver is precipitated and a
solution containing copper nitrate is formed”.
38. (a) What happens when a piece of iron metal is placed in copper sulphate solution ? Name the type of
reaction involved.
(b) Write balanced chemical equation with state symbols for the following reaction :
Barium chloride solution reacts with sodium sulphate solution to give insoluble barium sulphate and a
solution of sodium chloride.
39. In the reaction represented by the following equation :
CuO (s) + H2 (g) o Cu (s) + H2O (l)
(a) name the substance oxidised (b) name the substance reduced
(c) name the oxidising agent (d) name the reducing agent
40. What happens when silver nitrate solution is added to sodium chloride solution ?
(a) Write the equation for the reaction which takes place.
(b) Name the type of reaction involved.
41. What happens when silver chloride is exposed to sunlight ? Write a chemical equation for this reaction. Also
give one use of such a reaction.
42. What happens when a zinc strip is dipped into a copper sulphate solution ?
(a) Write the equation for the reaction that takes place.
(b) Name the type of reaction involved.
48 SCIENCE FOR TENTH CLASS : CHEMISTRY

Long Answer Type Questions

43. (a) Explain the term “corrosion” with an example. Write a chemical equation to show the process of corrosion
of iron.
(b) What special name is given to the corrosion of iron ?
(c) What type of chemical reaction is involved in the corrosion of iron ?
(d) Name any three objects (or structures) which are gradually damaged by the corrosion of iron and steel.
44. (a) Explain the term “rancidity”. What damage is caused by rancidity ?
(b) What type of chemical reaction is responsible for causing rancidity ?
(c) State and explain the various methods for preventing or retarding rancidity of food.
45. (a) What happens when an aqueous solution of sodium sulphate reacts with an aqueous solution of barium
chloride ?
(b) Write the balanced chemical equation for the reaction which takes place.
(c) State the physical conditions of reactants in which the reaction will not take place.
(d) Name the type of chemical reaction which occurs.
(e) Give one example of another reaction which is of the same type as the above reaction.

Multiple Choice Questions (MCQs)

46. The removal of oxygen from a substance is called :
(a) oxidation (b) corrosion (c) reduction (d) rancidity
47. In the context of redox reactions, the removal of hydrogen from a substance is known as :
(a) oxidation (b) dehydration (c) reduction (d) dehydrogenation
48. The chemical reaction involved in the corrosion of iron metal is that of :
(a) oxidation as well as displacement (b) reduction as well as combination
(c) oxidation as well as combination (d) reduction as well as displacement
49. The term used to indicate the development of unpleasant smell and taste in fat and oil containing foods due
to aerial oxidation is :
(a) acidity (b) radioactivity (c) rabidity (d) rancidity
50. In order to prevent the spoilage of potato chips, they are packed in plastic bags in an atmosphere of :
(a) Cl2 (b) H2 (c) N2 (d) O2
51. A white precipitate can be obtained by adding dilute sulphuric acid to :
(a) CuSO4 solution (b) NaCl solution (c) BaCl2 solution (d) Na2SO4 solution
52. A white precipitate will be formed if we add common salt solution to :
(a) Ba(NO3)2 solution (b) KNO3 solution (c) AgNO3 solution (d) Mg(NO3)2 solution
53. Consider the following equation of the chemical reaction of a metal M :
4M + 3O2  o 2M2O3
This equation represents :
(a) combination reaction as well as reduction reaction
(b) decomposition reaction as well as oxidation reaction
(c) oxidation reaction as well as displacement reaction
(d) combination reaction as well as oxidation reaction
54. The process of respiration is :
(a) an oxidation reaction which is endothermic
(b) a reduction reaction which is exothermic
(c) a combination reaction which is endothermic
(d) an oxidation reaction which is exothermic
55. Which of the following can be decomposed by the action of light ?
(a) NaCl (b) KCl (c) AgCl (d) CuCl
56. Consider the reaction :
KBr (aq) + AgNO3 (aq)  o KNO3 (aq) + AgBr (s)
CHEMICAL REACTIONS AND EQUATIONS 49
This is an example of :
(a) decomposition reaction (b) combination reaction
(c) double displacement reaction (d) displacement reaction
57. You are given the following chemical equation :
Mg (s) + CuO (s)  o MgO (s) + Cu (s)
This equation represents :
(a) decomposition reaction as well as displacement reaction
(b) combination reaction as well as double displacement reaction
(c) redox reaction as well as displacement reaction
(d) double displacement reaction as well as redox reaction

Questions Based on High Order Thinking Skills (HOTS)

58. When a green iron salt is heated strongly, its colour finally changes to brown and odour of burning sulphur
is given out.
(a) Name the iron salt.
(b) Name the type of reaction that takes place during the heating of iron salt.
(c) Write a chemical equation for the reaction involved.
59. A colourless lead salt, when heated, produces a yellow residue and brown fumes.
(a) Name the lead salt.
(b) Name the brown fumes.
(c) Write a chemical equation of the reaction involved.
60. When hydrogen burns in oxygen, water is formed and when water is electrolysed, then hydrogen and
oxygen are produced. What type of reaction takes place :
(a) in the first case ?
(b) in the second case ?
61. A strip of metal X is dipped in a blue coloured salt solution YSO4. After some time, a layer of metal Y from
the salt solution is formed on the surface of metal strip X. Metal X is used in galvanisation whereas metal Y
is used in making electric wires. Metal X and metal Y together form an alloy Z.
(a) What could metal X be ?
(b) What could metal Y be ?
(c) Name the metal salt YSO4.
(d) What type of chemical reaction takes place when metal X reacts with salt solution YSO4 ? Write the
equation of the chemical reaction involved.
(e) Name the alloy Z.
62. When a black metal compound XO is heated with a colourless gas Y2, then metal X and another compound
Y2O are formed. Metal X is red-brown in colour which does not react with dilute acids at all. Gas Y2 can be
prepared by the action of a dilute acid on any active metal. The compound Y2O is a liquid at room temperature
which can turn anhydrous copper sulphate blue.
(a) What do you think is metal X ?
(b) What could be gas Y2 ?
(c) What is compound XO ?
(d) What is compound Y2O ?
(e) Write the chemical equation of the reaction which takes place on heating XO with Y2.
(f) What type of chemical reaction is illustrated in the above equation ?
63. A metal X forms a water soluble salt XNO3. When an aqueous solution of XNO3 is added to common salt
solution, then a white precipitate of compound Y is formed alongwith sodium nitrate solution. Metal X is
said to be the best conductor of electricity and it does not evolve hydrogen when put in dilute hydrohloric
acid.
(a) What is metal X ?
(b) What is salt XNO3 ?
(c) Name the compound Y.
50 SCIENCE FOR TENTH CLASS : CHEMISTRY

(d) Write the chemical equation of the reaction which takes place on reacting XNO3 solution and common
salt solution giving the physical states of all the reactants and products.
(e) What type of chemical reaction is illustrated by the above equation ?
64. Two metals X and Y form the salts XSO4 and Y2SO4, respectively. The solution of salt XSO4 is blue in colour
whereas that of Y2SO4 is colourless. When barium chloride solution is added to XSO4 solution, then a white
precipitate Z is formed alongwith a salt which turns the solution green. And when barium chloride solution
is added to Y2SO4 solution, then the same white precipitate Z is formed alongwith colourless common salt
solution.
(a) What could the metals X and Y be ?
(b) Write the name and formula of salt XSO4.
(c) Write the name and formula of salt Y2SO4.
(d) What is the name and formula of white precipitate Z ?
(e) Write the name and formula of the salt which turns the solution green in the first case.
65. A red-brown metal X forms a salt XSO4. When hydrogen sulphide gas is passed through an aqueous solution
of XSO4, then a black precipitate of XS is formed alongwith sulphuric acid solution.
(a) What could the salt XSO4 be ?
(b) What is the colour of salt XSO4 ?
(c) Name the black precipitate XS.
(d) By using the formula of the salt obtained in (a) above, write an equation of the reaction which takes
place when hydrogen sulphide gas is passed through its aqueous solution.
(e) What type of chemical reaction takes place in this case ?
66. When a strip of red-brown metal X is placed in a colourless salt solution YNO3 then metal Y is set free and
a blue coloured salt solution X(NO3)2 is formed. The liberated metal Y forms a shining white deposit on the
strip of metal X.
(a) What do you think metal X is ?
(b) Name the salt YNO3.
(c) What could be metal Y ?
(d) Name the salt X(NO3)2.
(e) What type of reaction takes place between metal X and salt solution YNO3 ?
67. A metal salt MX when exposed to light splits up to form metal M and a gas X2. Metal M is used in making
ornaments whereas gas X2 is used in making bleaching powder. The salt MX is itself used in black and
white photography.
(a) What do you think metal M is ?
(b) What could be gas X2 ?
(c) Name the metal salt MX.
(d) Name any two salt solutions which on mixing together can produce a precipitate of salt MX.
(e) What type of chemical reaction takes place when salt MX is exposed to light ? Write the equation of the
reaction.
ANSWERS
1. Decomposition reaction 4. Zn + 2AgNO3  o Zn(NO3)2 + 2Ag 5. Rancidity 6. Anti-oxidants
11. Decomposition reactions (carried out by electricity) 14. 2AgNO3 (aq) + Cu (s)  o Cu(NO3)2 (aq) +
2Ag (s) 15. (i) Decomposition (ii) Combination (iii) Decomposition (iv) Decomposition
(v) Combination 16. (a) Combination (b) Decomposition (c) Decomposition (d) Decomposition
(e) Combination 17. (i) Displacement reaction (ii) Combination reaction (iii) Decomposition
reaction (iv) Double displacement reaction (v) Displacement reaction 18. (a) See page 29 (b) See page
29 19. (a) Displacement reaction (b) Combination reaction 20. (a) Combination reaction
(b) Displacement reaction (c) Displacement reaction (d) Decomposition reaction (e) Double displacement
reaction 21. (a) H2O2 (b) PbS 22. H2S 23. Substance oxidised : H2S ; Substance reduced : SO2
24. (a) oxidation ; reduction (b) reduction ; oxidation (c) rancidity 25. (i) C (ii) ZnO 26. (b) Magnesium
is oxidised ; Addition of oxygen to magnesium takes place (c) (i) HCl (ii) MnO2 (iii) MnO2 (iv) HCl
31. ZnO + C o Zn + CO (i) Zinc oxide (ii) Carbon 34. (b) 2Cu + O2  o 2CuO (i) Cu (ii) O2
35. (b) 2Mg + O2  o 2MgO (i) Mg (ii) O2 37. (b) Cu (s) + 2AgNO3 (aq)  o Cu(NO3)2 (aq) +
2Ag (s) 39. (a) H2 (b) CuO (c) CuO (d) H2 43 (b) Rusting (c) Oxidation 44. (b) Oxidation
CHEMICAL REACTIONS AND EQUATIONS 51
45. (c) Solid sodium sulphate and Solid barium chloride (d) Double displacement reaction (e) Double
displacement reaction between silver nitrate solution and sodium chloride solution to form a white precipitate
of silver chloride and sodium nitrate solution 46. (c) 47. (a) 48. (c) 49. (d) 50. (c) 51. (c) 52. (c)
53. (d) 54. (d) 55. (c) 56. (c) 57. (c) 58. (a) Ferrous sulphate (b) Decomposition reaction (c) See
page 29 59. (a) Lead nitrate (b) Nitrogen dioxide (c) See page 29 60. (a) Combination reaction
(b) Decomposition reaction 61. (a) Zinc (Zn) (b) Copper (Cu) (c) Copper sulphate (CuSO 4 )
(d) Displacement rection ; CuSO4 (aq) + Zn (s)  o ZnSO4 (aq) + Cu (s) (e) Brass 62. (a) Copper
(Cu) (b) Hydrogen (H2) (c) Copper oxide (CuO) (d) Water (H2O) (e) CuO + H2  o Cu + H2O
(f) Displacement reaction (which is also a redox reaction) 63. (a) Silver (Ag) (b) Silver nitrate (AgNO3) (c)
Silver chloride (AgCl) (d) AgNO 3 (aq) + NaCl (aq)  o AgCl (s) + NaNO 3 (aq)
(e) Double displacement reaction 64. (a) Metal X : Copper ; Metal Y : Sodium (b) Copper sulphate, CuSO4
(c) Sodium sulphate, Na2SO4 (d) Barium sulphate, BaSO4 (e) Copper chloride, CuCl2 65. (a) Copper
sulphate (b) Blue colour (c) Copper sulphide (d) CuSO4 (aq) + H2S (g)  o CuS (s) + H2SO4 (aq)
(e) Double displacement reaction 66. (a) Copper (b) Silver nitrate (c) Silver (d) Copper nitrate
(e) Displacement reaction 67. (a) Silver (b) Chlorine (c) Silver chloride (d) Silver nitrate and Sodium
Light
chloride (e) Decomposition reaction; 2AgCl (s)   o 2Ag (s) + Cl2 (g)