Define water of crystallization. Give the chemical formula for two compounds as examples. How can it be proved that the water of crystallization makes a difference in the state and colour of the compounds?

Water of crystallization is the fixed number of water molecules present in one formula unit of a salt.

Examples:

CuSO₄.5H₂O - Blue vitriol
FeSO₄.7H₂O - Green vitriol

By heating these crystals they lose their water molecules and hence result in change in state and colour takes place.

Blue vitriol is blue in colour as it contains 5 molecules of water of crystallisation. When it is heated, it losses water of crystallisation and becomes anhydrous (CuSO₄) which is grey-white in colour.

On heating Green Vitriol, anhydrous Ferrous Sulphate (FeSO₄) is formed, which is white in colour. Anhydrous FeSO₄ on further heating, decompose forming ferric oxide, Sulphur dioxide and Sulphur trioxide gas is released.

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Updated on: 10-Oct-2022

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