- Salts exist in the form of formula units
- To these formula units of a salt, a fixed number of molecules of water remain attached. This is known as the Water of Crystallization.
Copper Sulphate (CuSO 4 ) is ideally white and powdery and does not have any water (anhydrous).
When we add water to these crystals they turn blue due to the formation of Copper pentahydrate (CuSO 4 .5H 2 O).These 5 water molecules present in the structure of salts hydrating the salt is called water of crystallisation .