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.

When a copper vessel is exposed to moist air for a long time, a dull green colored layer is formed on it. This greenish layer is a mixture of copper hydroxide (Cu(OH)2) and copper carbonate (CuCO3). The reaction is 2Cu + H2O + CO2 + O2 → Cu(OH)2 + CuCO3. As these products are basic in nature, to clean them lemon or tamarind juice-like acidic substances are needed. These sour substances are effective in cleaning the copper vessels hence are considered for cleaning.