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

Copper acquires a dull green coating when kept for a few months:

• Upon exposure to air, the copper metal gains a dull green color on its surface, due to the corrosion of Copper.
• Copper metal, upon exposure to the atmosphere, forms a mixture of Hydroxide and Carbonate of copper, which is also called basic carbonate.
• This mixture is obtained by reaction of the metallic copper with the moisture present in the air which contains oxygen gas and carbon dioxide.
• Due to the formation of these compounds, the surface of metallic Copper is covered with a green layer containing Copper hydroxide and Carbonate.
• The balanced chemical reaction for the conversion of Copper into a mixture of Hydroxide and Carbonate of copper can be given as :$\underset{\left(\mathrm{Copper}\right)}{2\mathrm{Cu}\left(\mathrm{s}\right)}+\underset{\left(\mathrm{Water}\right)}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}+\underset{\left(\mathrm{Carbon}\mathrm{dioxide}\right)}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}+\underset{\left(\mathrm{Oxygen}\right)}{{\mathrm{O}}_2\left(\mathrm{g}\right)}\to \underset{\left(\mathrm{Copper}\mathrm{hydroxide}\right)}{\mathrm{Cu}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right)}+\underset{\left(\mathrm{Copper}\mathrm{carbonate}\right)}{{\mathrm{CuCO}}_3\left(\mathrm{s}\right)}$

Hence, why Copper acquired a dull green coating after a couple of months has been explained above.