Lemon or tamarind is used for cleaning copper vessels turned greenish. Comment on the above statement.
Hint: Copper undergoes oxidation in air to form black copper oxide. So think about the reaction between copper oxide in air. Lemon and tamarind contain acid which is responsible for the removal of green coating.
Complete step by step answer: When copper is exposed in air it undergoes oxidation and forms black copper oxide. Copper oxide reacts slowly with carbon dioxide in air and gains a green coat. This green substance is copper carbonate. Lemon and tamarind contain acid. The acid dissolves the green coating of basic copper carbonate present on the surface of a tarnished copper utensil and makes it shiny again.
Additional Information:-The citric acid is present in the lemon or tamarind neutralizes the basic copper carbonate and dissolves the layer. That is why, the tarnished copper vessels are cleaned with lemon or tamarind juice to give the surface of the copper vessel its characteristic lustre. Copper is a soft, malleable and ductile metal with very high thermal and electrical conductivity. Copper oxide dissolves in acid. A freshly exposed surface of pure copper has a pinkish-orange color. Copper is used as a conductor of heat and electricity, as a building material and as a constituent of various metal alloys. Copper is one of the few metals that occur in nature in a directly usable metallic form.
Note: The acid present in lemon and tamarind is citric acid. It is responsible for the shiny layer of the tarnished copper vessel by dissolving the greenish coating or layer of copper utensils or copper vessels.