Question

What is meant by water of crystallisation in a substance? How would you show that blue copper sulphate crystals contain water of crystallisation?

Answer 1

The water of crystallization means having a fixed number of molecules present in one formula of a unit of salt. Crystal salts with water of crystallization are known as hydrates. The other names of water crystallization are crystallization water or water of hydration. These crystals are easily affected by heat.
When copper sulphate crystals are heated strongly, they lose all the water of crystallisation and form anhydrous copper sulphate, which is white. As the blue colour of the crystals disappeared on heating, we can conclude that the colour was due to water crystallisation. This proves that blue copper sulphate crystals contain water of crystallisation.