The copper sulphate crystals has formula CuSO4. 5H2O .
It contains 5 water molecules known as water of crystallisation.
When the crystals are heated, these water molecules are removed and the salt turns white.
If the crystals are again moistened with water, the blue colour of the crystals reappears.
Final Answer: When the crystals of copper sulphate are heated. water molecules are removed and the salt turns white.