Question

Paheli bought a statue made of copper. To her surprise it acquired a dull green coating after a couple of months. Explain the reason.

Answer 1

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 (CuCO₃) 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.