Class 12 Chemistry Electrochemistry Corrosion


We all must have observed newly bought iron, silver or coper articles appears very shiny but with passage of time they get dull. This is due to the layer of metal oxide that develops on their surface. Rusting of iron, silver jewellery getting tarnished or copper articles getting covered by green layer. Metals react with atmospheric oxygen and produces metal oxides that are basic in nature because they react with water to form bases.

  • In case of rusting of iron, the iron reacts with the oxygen present in air and moisture and develops rust (hydrated iron (III) oxide).

Fig. Iron chain left in moist air got rusted

Corrosion causes damage to car bodies, bridges, iron railings, ships and to all objects made of metals, especially those of iron.

  • In case of rusting of copper, the metallic copper reacts with oxygen, carbon-dioxide and atmospheric moisture and develops a green coloured coating of copper hydroxide and copper carbonate.

Fig. Copper developing green coloured rust on exposure to moist air

  • In case of tarnishing of silver articles, the metallic silver reacts with hydrogen sulphide or sulphur present in air and gets tarnished.

Fig. Tarnished silver Vs polished silver



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