1) Copper sulphate pentahydrate Copper sulphate pentahydrate is a hydrated salt which contains 5 molecules of water of crytsallisation. Its chemical formula is CuSO4.5H2O. It is blue in colour. 2) Ferrous sulphate Ferrous sulphate is also a hydrated salt. The most commonly available form of hydrated ferrous sulphate contains seven molecules of water of crytsallisation and therefore it is represented by the chemical formula FeSO4.7H2O. This salt is blue-green in colour. 3) Na2CO3.10H2O sodium carbonate decahydrate Copper sulphate crystals are blue in colour. However, when copper sulphate is heated in a china dish for some time, the blue colour disappears and it becomes white-gray in colour. This is the anhydrous copper sulphate. The reaction is written as follows Thus the blue colour of copper sulphate crystals is due to water of crystallisation, which are lost when it is heated. Hence the blue colour of solution disappears. This proves that copper sulphate contains water of crystallisation.
