Question

Whay do we observe when crystals of copper sulphate are heated

Answer 1

The blue coloured copper sulphate crystals turns white due to the loss of water molecules. ... When copper sulphate is heated, it looses water molecules and hence it looses blue colour. On heating, ferrous sulphate crystals lose water and anhydrous ferrous sulphate(FeSO4) is formed.
hope you understood
; )

Answer 2

it changes its color to white as it loses the water of crystallization.