The Water of crystallization is a definite number of water molecules attached to each formula unit of a salt in its crystalline form.
Water of crystallization are the water molecules which form part of the structure of a crystal (of a salt).
The water of crystallisation gives the crystals of the salts their shape and in some cases imparts them colour
Copper sulphate crystals contain 5 molecules of water of crystallization in one formula unit and hence written as:CuSO4. 5H2O These are blue in color.
The salts which have lost their water of crystallisation are known as Anhydrous salts
ACTION OF HEAT ON HYDRATED SALTS
When copper sulphate crystals are heated strongly, they lose all the water of crystallisation and form anhydrous copper sulphate which is white in color.
This is due to the loss of water of crystallisation:
