Water of Crystallisation
The salts that have water of crystallisation are called hydrated salts. For example, there are 5 molecules of water attached to the copper sulphate crystal. Its formula is written as CuSO4
O. It has a typical blue colour. If this water is removed by heating, the salt becomes non-crystalline and its colour becomes white. The salts from which their water of crystallisation has been removed are called anhydrous salts. They do not have a crystalline structure. The water molecules are also attached to the salts like potash alum, copper sulphate, ferrous sulphate and washing soda. These water molecules are loosely attached to salt and are called water crystallisation.