Corrosion | Rusting of iron | Chapter 7 | 9th Class Chemistry | Lec # 17

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Teacher/Instructor: Zulfiqar Ali Gujjar
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Corrosion
Q1: What is meant by corrosion?
Ans: The slow and continuous eating away of metal by the surrounding medium is called corrosion. It is redox reaction of air and moisture with metals.
For example; rusting of iron.
Q:2: Define rusting. (OR)
what is corrosion of iron?
Ans: Corrosion of iron is called rusting. Stains and dents on the surface of iron act as an anode region. At this point oxidation takes place.
The surface of iron contains moisture and a high concentration of oxygen which is called a cathodic region. At this point reduction takes place.
The Fe+2 spreads throughout the surrounding of water and react with O2 to form Fe2O3 .nH2O which is called rust.

It is redox reaction. The rust layer of iron is porous and does not prevent further corrosion. Thus rusting continues until all the piece of iron is eaten up.

Methods for prevention of corrosion.
Q: 3: Write methods for prevention of corrosion.
Ans: i) Removal of stains
ii) Using grease and paints
iii) Alloying
iv) Metallic coating
Q: 4: Why removal of stains is necessary to prevent from corrosion?
Ans: The region of stains in an iron rod act as the site for corrosion. If the surface of iron is properly cleaned and stains are removed, it would prevent corrosion.
Q: 5: What is role of paints and grease in prevention of corrosion?
Ans: Painting or greasing of the surface can prevent the corrosion of iron. Paints and grease provide protection against weathering and other atmospheric effects.
Q: 6: What is alloy? What is its role for corrosion?
Ans: A homogenous mixture of one metal with one or more metals is called alloy. Alloying of iron with other metals has proved to be very successful against rusting.
For example; stainless steel, which is good combination of Fe, Cr and Ni.
Q: 7: Write a note on metallic coating.
Ans: Coating of one metal on the surface of other metal is called metallic coating. It is widely used in food industry where container of iron is coated with tin or Cr. It is good method to prevent from corrosion.