Copper becomes green when exposed to moist air for a long period. This is due to :
the formation of a layer of cupric oxide on the surface of copper.
the formation of a layer of basic carbonate of copper on the surface of copper.
the formation of a layer of cupric hydroxide on the surface of copper.
the formation of basic copper sulphate layer on the surface of the metal.
As learnt in the concept
Corrosions -
Slow formation of undesirable compounds such as oxides, sulphides or carbonates at the surface of metals by reaction with moisture and other atmospheric gases is known as corrosion.
When copper is exposed to moist air for extended periods of time, it forms a lays of basic sulphate on its surface. This is corrosive and results in losses.
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