Question

How would you show that blue copper sulphate crystals contain water of crystallisation?

Answer 1

Copper sulphate crystals (CuSO₄.5H₂O) are blue in colour. When copper sulphate crystals are heated strongly, they lose all the water of crystallisation and form anhydrous copper sulphate (which is white).

\[\ce{\underset{(Blue)}{\underset{Hydrated copper sulphate}{CuSO4*5H2O}} ->[Heat] \underset{(White)}{\underset{ Anhydrous copper sulphate}{CuSO4}} + \underset{(Goes away)}{\underset{Water}{H2O}}}\]

Thus, on strong heating, blue copper sulphate crystals turn white (due to the loss of water of crystallisation).