Question

Blue crystals of copper sulphate on heating in a dry test tube become colourless. Give reasons.

Answer 1

Blue crystals of copper sulphate are hydrated crystals. They contain water of crystallisation loosely attached to their molecules. On heating, they evaporated and changed to steam. This made the copper sulphate crystals anhydrous which changed their colour. This is a physical change which is reversible.

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Answer 2

this change in colour comes due to heating of cuso4 ,when it is heated it looses all of it's water and become anhyderous​. this is called water of crystallisation. this change can be reversed and blue color can be obtained back by adding water again
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