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

(i) IT losses water molecules and become calcium sulphate hemihydrate, `CaSO_4. 1/2 H_2O` or plaster of paris.
(ii) Blue copper sulphate crystals on heating lose water of crystallisation and become white . When these crystals are left open, will absorb moisture from air and regain blue colour.
(iii) On passing `CO_2` gas through lime water , insoluble calcium carbonate is formed. On passing excess of `CO_2` soluble calcium bicarbonate is formed.
`Ca(OH)_2(aq)+CO_2(g) to CaCO_3(s)+H_2O(l)`
Insoluble
`CaCO_2(s)+CO_2(g) +H_2O (l) to Ca(HCO_3)_2 (aq)`
SOluble