Question

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

Answer 1

Hint: Copper is a very reactive metal and reacts quickly with electronegative elements. Moisture and gases present in air react with the reactive metals easily.

Complete step by step answer:
Copper reacts with oxygen and carbon dioxide in the presence of moisture in air and results in the formation of copper carbonate and copper oxide which are green in colour. Thus, it is observed that with time the copper vessels lose their brown shine and a green layer gets deposited over them. The reactions can be written as:
$
  2Cu + {O_2} \to 2CuO \\
  CuO + C{O_2} \to CuC{O_3} \\
 $
Lemon and tamarind have citric acid and tartaric acid in them. These acids react with copper carbonate and copper oxide to give respective salts which results in formation of copper salts and decolourisation of the green layer formed. The formed salts are then washed with water. Thus, tarnished copper vessels are cleaned with lemon or tamarind to regain its characteristic lusture.
Additional information: All the acids react with copper carbonate to give carbon dioxide, water and respective copper salts. Mostly the salts of copper are coloured in nature. All the sour substances containing acids can be used for the cleaning of copper substances. Vinegar can also be used to clean the copper vessels as it is acetic acid. It is perhaps the most commonly used chemical to clean copper surfaces.

Note:
Because citric acid kills bacteria, mold, and mildew, it's great for general disinfecting and cleaning. It's also effective at removing soap scum, hard water stains, calcium deposits, lime, and rust. Also, it serves as a preservative in many cleaning solutions.