Question

Write the name and formula of one salt each which contains:
(a) two molecules of water of crystallisation
(b) five molecules of water of crystallisation
(c) ten molecules of water of crystallisation

Answer 1

1. Gypsum (calcium sulphate crystals) contains two molecules of crystallisation in one formula unit and hence is written as CaSO₄.2H₂O. It is also called calcium sulphate dihydrate.
2. Copper sulphate crystals contain five molecules of crystallisation in one formula unit. The chemical formula is CuSO₄.5H₂O (copper sulphate pentahydrate).
3. Washing soda crystals (sodium carbonate crystals) contain 10 molecules of crystallisation in one formula unit. The chemical formula is Na₂CO₃.10H₂O (sodium carbonate decahydrate).