How many molecules of water of crystallisation are there in
i. Plaster of Paris
ii. washing soda crystals?
(i) The chemical formula of Plaster of Paris is CaSO4. 1/2 H2O, so it has 1/2 molecules of water of crystallisation.
(ii) The chemical formula of Washing soda crystals is Na2CO3.10H2O, so it has 10 molecules of water of crystallisation.