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Question
Paheli bought a statue made up of copper. To her surprise, it acquired a dull green coating after a couple of months. Explain the reason.
Solution
When a copper statue (or 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)z] and copper carbonate (CuC03) formed due to the reaction of copper with moist air. The following is the reaction.
\[\ce{2Cu + \underset{Moist air}{(H2O + CO2 + O2)} -> \underset{Green coating}{Cu(OH)2 + CuCO3}}\]
The green coating is commonly known as ‘basic copper carbonate’ and the formation of green coating on copper objects show the corrosion of copper.
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