Water of Crystallization : Water of crystallization is the fixed number of water molecules present in one formula unit of a salt in its crystaline form.
Ex : CuSO4 • 5H2O.
It means that five water molecules are present in one formula unit of copper sulphate.
Activity to show the water of crystallization :
1. Take a few crystals of copper sulphate in a dry test tube and heat the test tube.
2. We observe water droplets on the walls of the test tube and salt turns white.
3. Add 2 – 3 drops of water on the sample of copper sulphate obtained after heating.
4. We observe, the blue colour of copper sulphate crystals is restored.
Reason :
1. In the above activity copper sulphate crystals which seem to be dry contain the water of crystallization, when these crystals are heated, water present in crystals is evaporated and the salt turns white.
2. When the crystals are moistened with water, the blue colour reappears. Removing water of crystallization.
