what is meant by the water of crystallization explain why crystalline salts contains water of crystallization
Answers
Take some crystals of blue vitriol (CuSO4.5H2O) in test tube. Heat the test tube on low flame of a burner. On heating, the crystalline structure of blue vitriol broke down to form a colourless powder and water came out. This water was part of crystal structure of blue vitriol. It is called water of crystalization. On adding water to the white powder a solution was formed which had the same colour as the solution in the first test tube. From this we come to know that no chemical change has occured in the crystals of blue vitriol due to heating. Losing water on heating blue vitriol, breaking down of the crystal structure, losing blue colour on adding water are all physical changes.
CuSO4. 5H2O Heat→ CuSO4+ 5H2O
(Blue) (White)
(anhydrous copper sulphate)
Similarly ferrous Sulphate crystals also contain 7 molecules of water of crystalization which are lost on heating. The reaction is represented as
FeSO4. 7H2O Heat→ FeSO4+ 7H2O
(Green) (White)
(anhydrous ferrous sulphate)
Ionic compound are crystalline in nature. These crystals are formed as a result of definite arrangement of ions. In the crystals of some compounds water molecules are also included in this arrangement. That is the water of crystalization. The water of crystalization is present in a definite proportion of the chemical formula of the compound.