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.


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)2] and copper carbonate (CuCO3) formed due to the reaction of copper with moist air. The following is the reaction:

$2Cu + H_2O + CO_2 + O_2 → Cu(OH)_2 + CuCO_3$ 

This is known as the corrosion of copper.

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