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.

Explanation

Copper metal slowly reacts with water, carbon dioxide and oxygen present in air to form basic copper carbonate which is green in colour. Its layer slowly gets deposited on the surface of the metal. Now lemon
`2Cu + underset(("Present in air"))ubrace(H_(2)O+CO_(2)+O_(2)) rarr underset("Basic copper carbonate (green)")(Cu(OH)_(2)CuCO_(3))`
Juice contains citric acid while tartaric acid is present is tamrind. Both these acids reacts with basic copper carbonate to form soluble salts such as copper acetate (with citric acid) and copper tartarate (with tartaric acid). The equations for the reactions are complicated and are not given. These salts are removed from the surface of the copper metal and the surface of the metal shines.