Question

(a) Why common salt gets wet during rainy season?
(b) Give four substances which contain water of crystallisation and write their common name.

Answer 1

(a) Common salt contains magnesium chloride as an impurity. Magnesium chloride is a deliquescent compound. It absorbs moisture from air. Thus, common salt reacts with excess moisture present in the atmosphere and becomes wet.

(b) The four substances that contain water of crystallisation are given in the table below:

Substance Containing Water of Crystallisation	Formula	Common Name
Sodium carbonate decahydrate ​	${\mathrm{Na}}_2{\mathrm{CO}}_3.10{\mathrm{H}}_2\mathrm{O}$	Washing soda
Copper sulphate pentahydrate	${\mathrm{CuSO}}_4.5{\mathrm{H}}_2\mathrm{O}$	Blue vitriol
Ferrous sulphate heptahydrate	$\mathrm{F}\mathrm{e}{\mathrm{SO}}_4.7{\mathrm{H}}_2\mathrm{O}$	Green vitriol
Calcium sulphate dihydrate	${\mathrm{CaSO}}_4.2{\mathrm{H}}_2\mathrm{O}$	Gypsum