Are the Crystals of Salts really Dry ?

Copper sulphate crystals which seem to be dry contain water of crystallisation. When we heat the crystals, this water is removed and the salt turns white.
If moisten the crystals again with water, you will find that blue colour of the crystals reappears.
Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt. Five water molecules are present in one formula unit of copper sulphate. Chemical formula for hydrated copper sulphate is Cu SO4 . 5H2O.
Whether the molecule of Na2CO3 .10H2O is wet.
One other salt, which possesses water of crystallisation is gypsum.
It has two water molecules as water of cyrstallisation. It has the chemical formula CaSO4 .2H2O.

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