Corrosion


Physical and Chemical Change II - Concepts
Class - 7th CBSE Subjects
 
 
Concept Explanation
 

Corrosion

Corrosion: 

When a piece of iron is left in open for sometime, it acquires a film of brownish substance which is called rust. This process of change of iron to rust is called rusting of iron. Rust is different from iron. This rust is iron oxide. The chemical equation of rusting of iron can be represented as :

Iron(Fe)+Oxygen(O_{2})+Water(H_{2}O)rightarrow Rust(iron;oxide,Fe_{2}O_{3})

Prevention of Rusting:

(i) Galvanisation: It is considered as the best method to prevent rusting. It is the process of deposition of a thin layer of zinc on iron surface. It is done to prevent rusting of iron. Rusting can also be prevented by deposition of thin layer of chromium on iron articles. We use galvanised Iron (G.I) pipes to carry water in taps. It is estimated that about 15% of the total world production of iron is destroyed due to rusting.

(ii) Application of coat of paint or grease on the surface of iron also help in prevention of rusting.

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Sample Questions
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Question : 1

Which of the following are correct :

(a) When a piece of iron is left in open for sometime, it acquires a film of brownish substance which is called rust.

(b) Galvanisation is considered as the best method to prevent rusting.

(c) Application of coat of paint or grease on the surface of iron helps in prevention of rusting.

Right Option : D
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Question : 2

Which is the best method to prevent rusting?

Right Option : C
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Question : 3

Which of the following are correct :

(a) Presence of salts (electrolytes) in water makes the process of rusting faster.

(b) The process of rusting of iron is known as galvanisation.

(c) Essential Conditions For Rusting are Presence of moisture (water vapour) and Presence of air (or oxygen).

Right Option : C
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