(a) Why does common salt get wet during the rainy season?
(a) Why does common salt get wet during the rainy season?

(b) How can this impurity be removed?

(c) Name a substance which changes the blue colour of copper sulphate crystals to white.

(d) Name two crystalline substances which do not contain water of crystallisation.

(a) Table salt turns to water as it absorbs water and water vapor in the air, especially during the rainy season as it has high humidity. Pure sodium chloride is not edible, but the common type of salt trade contains contaminants such as magnesium chloride and calcium chloride.

(b) By transferring a stream of dry hydrogen chloride gas with a complete salt solution the impurities can be removed. It is produced as a precipitate pure sodium chloride that can be obtained by filtration and washing first with water and then with alcohol.

(c) Conc. sulphuric acid is a substance which changes the blue colour of copper sulphate crystals to white.

(d) Common salt (NaCl) and sugar (Glucose) are the two crystalline substances which do not contain water of crystallisation.