Chemical Reactions and Equations

Q.1. What is the general name of substances which are added to fat & oil containing
food to prevent rancidity. (1 Mark)

Ans. Antioxidants

Q.2. Write balanced chemical equation for the reaction of barium chloride with
Aluminium sulphate. (1 Mark)

Ans. 3 BaCl2 + Al2­ (SO4)3 3 BaSO4 +2AlCl3.

Q.3. Identify the substance that is oxidised and the substance that is reduced in the
following reaction. 4 Na+O2 2 Na2O (1 Mark)

Ans. Substance Oxidised Na
Substance reduced O2

Q.4. Why does the colour of copper sulphate solution fade when iron nail is dipped in
it. (2 Mark)
Ans. The solution changes into iron sulphate Fe+CuSO4 FeSO4 + Cu

Q.5. What happens when quick lime is added to water? Write the chemical equation.
Which type of reaction is it endothermic or exothermic? (2 Mark)
Ans. Calcium oxide reacts vigorously with water to produce slaked lime (Calciumm hydroxide)
CaO+H2O Ca (OH)2­ +Heat energy. It is an exothermic reaction.

Q.6. Silver chloride turns grey when kept in sunlight. Write chemical equation for it.
What type of reaction is it? (2 Mark)

Ans. 2 Ag Cl Sunlight 2 Ag (S) + Cl2 (g). It is a decomposition reaction
where light energy is absorbed. So it is an endothermic reaction.

Q.7. What happens when potassium iodide solution is added to lead nitrate solution? Give equation of the reaction involved. What type of reaction is represented by this example? (3marks)

Ans. When potassium iodide solution is added to lead nitrate solution, then a yellow
precipitate of lead iodide is formed alongwith potassium nitrate solution
Pb(NO3)2 (aq) + 2KI (aq) PbI2 (S) + 2 KNO3 (aq)
This is an example of a double displacement reaction. It is also a precipitation

Q.8. When a green iron salt is heated strongly, its colour finally changes to black and the odour of burning sulphur is given out.

a) Name the iron salt.

b) Name the type of reaction that take place during the heating of iron salt.
c) Write a chemical equation for the reaction involved. (3 Marks)

Ans:- a) Ferrous Sulphate
b) Thermal decomposition
c) 2 FeSO4 (S) Heat Fe2O3(s) + SO2 (g) + SO3 (g)
(Ferrous sulphate) (ferric oxide)
Green Colored Reddish brown.

Q. 9. Which type are the following reactions?
a) NH4Cl NH3 + HCl.
b) Fe + CuSO4 Fe SO4 + Cu
c) Ag NO3 + NaCl AgCl + NaNO3
d) PbO2 + SO2 PbSO4
e) CaCO3 CaO +CO2 (5 Marks)

Ans. a) Thermal decomposition reaction
b) Displacement reaction
c) Double displacement reaction
d) Combination reaction.
e) Thermal decomposition reaction

Q.10. Write balanced chemical equations for the following reactions:-
(5 Marks)
a) Dilute Sulphuric acid is poured on zinc granules
b) Iron reacts with steam
c) Carbon dixide reacts with water in the process of photosynthesis
d) Limestone is heated strongly.
e) Silver chloride is kept in sunlight in a china dish.

a) Zn + H2SO4 ZnSO4 + H2.
b) 3 Fe + 4H2O Fe3O­4 + 4 H2
c) 6CO2 + 6H2O Sunlight C6H12O6 +6O2
d) CaCo3 Heat Chlorophyll CaO +Co2
e) 2 Ag Cl 2 Ag + Cl2