Question

There are different types of chemical reactions occurring around us or being carried

out for the benefit of mankind, e.g. combination reactions, decomposition reactions,

displacement reactions, precipitation reactions, reduction-oxidation (redox) reactions,

photochemical reactions etc.

Now answer the following questions: (5)

i. Combustion of coke is a combination reaction. CO2

is not a pollutant. Then why is

combustion of coke harmful?

ii. Which reaction followed by two combination reactions are involved in white wash

of walls?

iii. Give one use of tin plating in daily life.

iv. How photochemical reactions have played an important role in photography?​

Answer 1

Answer:

(i) CO2 is not a pollutant when present in the atmosphere upto a certain per cent. Rather, it helps to maintain the temperature of the earth. Combustion of coke is harmful as it increases the concentration of CO2 in the atmosphere causes global warming (greenhouse effect).

(ii) Decomposition of limestone (CaCO3) gives quicklime (CaO) which combines with water to form slaked lime, Ca(OH)2 which after putting on the walls, combines with CO2 of the air to form CaCO3.

(iii) Tiffin boxes made up of steel are either tin plated or nickel plated to protect them from rusting. However, tin-plating is preferred because tin is non-poisonous and hence, does not contaminate the food kept in them.

Chromium plating is done on bicycle handles and car bumpers made up of iron to protect them from rusting and give them a shining appearance.

(iv) A photographic film used in black and white photography is a celluloid film coated with silver chloride. Its working is based on the decomposition of silver chloride in the presence of sunlight.

Explanation: