Corrosion and its Prevention


 
 
Concept Explanation
 

Corrosion and its Prevention

Corrosion:

It is the slow process of eating away of metals by the reaction of atmospheric air and moisture, e.g. rusting of iron, tarnishing of silver, formation of green coating over copper etc.

When a copper vessel is exposed to moist air for long, it acquires a dull green coating. The green material is a mixture of copper hydroxide Cu(OH)_{2}  and copper carbonate CuCO_{3} . The reaction involved is

  2Cu+H_{2}O+CO_{2}+O_{2}rightarrow Cu(OH)_{2}+CuCO_{3}

•  Iron reacts with oxygen and moisture present in the atmosphere to form a brown, flaky substance called rust. Rusting of iron in an undesirable reaction because the layer of rust formed falls off, exposing the metal to further rusting.

4Fe + 3O_2 + 3H_2O rightarrow Fe_2O_3 + 2Fe(OH)_2

Prevention of Corrosion:

Rusting of iron is prevented by galvanizing, by making alloys, painting greasing or oiling and tin- planting and chromium plating which are explained below:·  

1. Galvanisation: The process of coating iron and steel objects with a thin layer of zinc is called galvanization. It is done by dipping the object in molten zinc.The galvanized article is protected against rusting even if the zinc coating is broken.·

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Sample Questions
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Question : 1

Silver articles become _________________  after some time when exposed to air.

Right Option : A
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Question : 2

Silver article turns black after a period of time due to formating of _________________

Right Option : B
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Question : 3

Rusting of iron can be prevented by ______________

Right Option : D
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