Salts- Water of Crystalization

Crystals of some salts have some fixed amount of water molecules attached to them. Such salts are called hydrated salts and the water molecules attached to them are called water of crystallization.

On heating the hydrated salts lose their water molecules( water of crystallization). In doing so they lose their colour and shape and form a powdery substance. The compound left after heating is called anhydrous salt. Anhydrous regain the colour after the addition of water for eg. Copper Sulphate loses its blue colour after heating and regains its colour after addition of water.

The water of crystallization is always mentioned after a dot(.) for eg. Copper Sulphate is CuSO4.5H2O.


1. Common Salt [NaCl] : It is used as table salt. It is used for preservation of food in pickling. It is used to preserve raw hides. It is used in the manufacture of chemicals such as chlorine, caustic soda (NaOH) and washing soda (Na2CO3).

2. Baking Soda [NaHCO3] : It is used for making baking powder. It is used for preparing antacid tablets, for controlling acidity in the stomach.

3. Washing Soda [Na2CO3] : It is used by washermen to wash clothes. It is used in manufacture of glass and caustic soda. It is used in fire extinguishers. It is used in the manufacture of detergents.

4. Chile Salt Petre [(NH4)2CO3] : It is used in the manufacture of nitric acid, gun powder and fire works.

5. Nitre [KNO3] : It is used as a fertilizer. It is also used in the manufacture of gun powder, fire works and Nitric acid.

6. Smelling salt [(NH4)2CO3] : It provides relief from common cold.

7. Epsom Salt [MgSO4] : It is used as a laxative by patients suffering from constipation.

8. Green Vitriol [FeSO4.5H2O] : It is used in making blue – black inks and in curing leather.

9. Blue Vitriol [CuSO4.5H20] : It is used as fungicide in agriculture. It is used in dyeing and printing industry. It is used in electroplating copper metal.

10. Plaster of Paris [CaSO4.1/2H2O] : It is used for making statues. It is used for setting broken bones.

11. Potash alum [K2SO4.Al2(SO4)3.24H2O] : It helps in rapid settling of suspended impurities in water. It is used for the purification of water.

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