Question

You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.

Answer 1

Tarnishing of copper:

• Copper carbonate is formed when copper combines with damp carbon dioxide in the air, and the bright brown surface of the copper vessel is overlaid by a green coating of Copper carbonate.
• $$\begin{gathered} 2\mathrm{Cu}\left(\mathrm{s}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to {\mathrm{CuCO}}_3.\mathrm{Cu}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right) \\ \mathrm{Tarnished}\mathrm{copper} \end{gathered}$$
• Lemon or tamarind citric acid destroys the covering by neutralizing the base Copper carbonate.
• As a result, to restore their luster, corroded copper vessels are cleaned with lemon or tamarind juice