Blue crystals of copper sulphate turn white on heating because they lose their water of crystallisation. How many water molecules are present in one formula unit of these blue crystals?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 5
Blue copper sulphate crystals are \(\mathrm{CuSO_4\cdot5H_2O}\): one formula unit holds five water molecules of crystallisation. On heating they are lost and white anhydrous copper sulphate is left; adding water brings back the blue colour.