(a) Write the chemical formula of hydrated copper sulphate and anhydrous copper sulphate. Give an activity to illustrate how these two are inter convertible.
(b) Write chemical names and formulae of Plaster of paris and gypsum.

Explanation

(a) Hydrated copper sulphate- `CuSO_4. 5H2O`
Anhydrous coppper sulphate- `CuSO_4`
Activity (i) Heat a few crystals of copper sulphate in a dry boiling tube.
(ii) Add 2-3 drops of water on the sample of copper sulphate obtained after heating.
After heating, water is removed and salt turns white.
If crystals are moisten again with water, blue colour reappears. Water of crystallization is fixed number of water molecules present in one formulae unit of a salt. Five water molecules are present in one formula unit of copper sulphate.
(b) Calcium sulphate hemihydrate: `CaSO_4. 1//2 H_2O`
Calcium sulphate dihydrate: `CaSO_4. 2 H_2O`.