Question

when we heat blue coloured crystals of copper sulphate. they became colourless. why?

Answer 1

This is because they lose the water of crystallization, and hence become colourless. The colour is due to this water of crystallization: $\blue{\mathrm{CuSO_4.5H_2O}}$

Answer 2

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When we heat blue coloured question of $CuSO_4$ then dehydrate the copper sulphate and make it white in colour.

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