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Question
If copper is kept exposed to damp air for a considerable time, it gets a green coating on its surface. This is due to the formation of ______.
Options
hydrated copper sulphate
copper oxide
basic copper carbonate
copper nitrate
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Solution
If copper is kept exposed to damp air for a considerable time, it gets a green coating on its surface. This is due to the formation of basic copper carbonate.
Explanation:
When copper is exposed to damp air for a long time, it slowly undergoes corrosion by reacting with atmospheric carbon dioxide, oxygen, and water vapour. This chemical reaction forms a green layer on its surface, which is a basic mixture of copper carbonate and copper hydroxide [CuCO3.Cu(OH)2]. The other options are incorrect because copper oxide is black or brown, while copper sulphate and copper nitrate typically form blue or blue-green crystals under different laboratory conditions, rather than a natural corrosion patina.
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