Q24 of 79 Page 3

The copper vessels used in homes are found to be coated with green colour. Answer the following.
a) What is the chemical composition of the green coating?
b) Why do copper vessels form such a green coating?
c) What is the name of the phenomenon, responsible for the green coating?
d) Copper vessels are best cleaned with tamarind or lemon juice, but not with soap. Why?

a) Green coloured coating on copper is due to the formation of basic copper carbonate, CuCO3.Cu(OH)2. b) Copper forms green coating of basic copper carbonate as it reacts with water, atmospheric oxygen and carbon dioxide.c) Corrosion phenomenon is responsible for the formation of basic copper carbonate (green).d) Since basic copper carbonate is basic in nature, it can be removed by tartaric acid present in tamarind or citric acid, present in lemon. Soap is basic in nature. So copper vessels are best cleaned with tamarind or lemon.

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ii) What is the blue colour of crystalline copper sulphate due to?