Question

What is water of crystallization? Give the name and formulae of any five salts that have water of crystallization.

Answer 1

Part 1: Water of crystallization

• The fixed amount of water that is chemically bonded to a crystal structure and is necessary for certain salts to crystallize out from their aqueous solutions is called its water of crystallization.
• The crystals contain salts and water combined in definite proportions, the water is lost on heating.
• It is responsible for the shapes of its crystals.

Part 2: Examples

• The crystals of blue vitriol i.e., hydrated copper sulphate (CuSO₄.5H₂O) are blue in colour. the crystals are formed by the combination of 1 mole of CuSO₄ with 5 moles of H₂O.
• The crystals of washing soda i.e., sodium carbonate decahydrate (Na₂CO₃.10H₂O) contain 10 moles of water of crystallization.
• The crystals of gypsum i.e., calcium sulphate (CaSO₄.2H₂O ) contain 2 moles of water of crystallization.
• The crystals of green vitriol i.e., ferrous sulphate (FeSO₄.7H₂O) contain 7 moles of water of crystallization.
• The crystals of Epsom salt i.e., magnesium sulphate (MgSO₄ .7H₂O) contain 7 moles of water of crystallization.