State what happens when :
(a) Gypsum is heated at `373 K`
(b) Blue crystals of copper sulphate are heated
(c ) Excess of `CO_(2)` is passed through lime water.

Explanation

It turns into plaster of Paris `(CaSO_(4). ½H_(2)O)` by losing water molecules.
(b) It loses its crystalline structure and the characteristic blue colour and turns into a while powder.
(c ) The lime water first turns milky due to the formation of the insoluble Calcium carbonate. But with excess of the gas being passed it forms the soluble Calcium bicarbonate and the milky appearance disappears.