Some salts while crystallising out from their solutions, combine with a definite quantity of water. Some of these salts lose this water on exposure to dry air. Certain water soluble substances, when exposed to atmosphere at ordinary temperatures, absorb moisture from atmospheric air forming a saturated solution.

(a) State the term used for a 'definite quantity of water' combined with a salt.

(b) What type of salts lose their water molecules ? Give two examples.

(c) Table salt forms a solution on exposure to air during rainy season. Explain.

(d) How can pure sodium chloride be obtained from the above table salt solution in (c) ?

(a) The definite quantity of water combined with a salt is called Water of Crystallisation.

(b) Salts that lose their water molecules on exposure to air are called Efflorescent salts.
Washing soda and magnesium sulphate heptahydrate are the two examples.

(c) Table salt forms a solution in the rainy season because it contains impurities like Magnesium chloride, which is deliquescent. It absorbs moisture from the air and dissolves in it, forming a solution.

(d) Pure sodium chloride can be obtained by evaporation or crystallisation.