Question

The green coating on copper when exposed to air and moisture is
a) CuCO3.Cu(OH)3
b) CuS
c) CuO
d) CuCO3

Answer 1

Answer:

c) CuO copper forms a black oxide

Answer 2

Answer:

CuCO3.Cu(OH)3

Explanation:

Copper metal when exposed to air turns green in colour due to corrosion. When copper vessel is exposed to air in rainy season, the metal reacts with gases, moisture and atmospheric gases to form a mixture of copper carbonate and copper hydroxide. This gives a green colour to the surface of copper metal.  

The reaction is as follows:

2Cu+H2 O+CO2 +O2 →Cu(OH)2 +CuCO3

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Hence, copper becomes green when exposed to moist air for a long period of time due to the formation of a layer of basic carbonate of copper on the surface of copper.

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