Page 63 - Ripples SCIENCE 7 - TEJPUR Edition 2024 Answer Key

Since iron is more reactive than copper, so it displaces copper from the solution. As a

result, copper starts sticking to the surface of iron fillings, froming a layer of copper
metal. This layer of copper metal gives the iron fillings their brown colour.

Also the blue colour of the copper sulphate solution changes to light green. It is
because of the formation of a new substance called iron sulphate.

CuSO + Fe  FeSO + Cu
4
4
Copper sulphate Iron Iron sulpahte Copper
5. Explain two most common exothermic reactions taking place in nature.
Ans. Two of the most common exothermic reactions taking place in nature are :

(a) Combustion of organic matters : We know that combustion is a rapid chemical
change or reaction between a fuel (mostly organic matter) and oxygen resulting

in the release of heat and light. For example , burning of wood or other biomass
in a fire. Organic materials in the wood react with oxygen, producing carbon

dioxide, water vapour and releasing energy in the form of heat and light.
(b) Respiration in Living Organism : Respiration is a biochemical process where

organic matter react with oxygen to produce carbon dioxide water and energy
in the form of ATP. For example, respiration in animals and plants involves the

breakdown of glucose with oxygen to release energy in the form of heat.
6. How can rusting of iron be prevented?

Ans. Rusting can be prevented by the following methods.
(a) Painting, greasing or oiling regularly prevents rusting of iron objects. These

prevent the surfaces of iron objects from coming in direct contact with the air
& moisture.

(b) Galvanisation is the process of deposition of a thin layer of zinc on iron objects.
Zinc reacts with air and moisture to form a layer of zinc oxide. This layer prevents

rusting.
(c) Rusting can be prevented by using alloys. An alloy is a substance made by mixing

two or more metals or a metal and a non-metal. This process is called alloying.

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