Question

Give a brief description of crystallization with an illustration.

Answer 1

Crystallization $\to$ The process by which a pure substance is separated from its solution in the form of crystals is known as crystallisation.

The impure substance is dissolved in a suitable solvent in which it is sparingly soluble at room temperature. The solution is concentrated by heating to get nearly a saturated solution. When this saturated solution is cooled, crystals of the pure substance will separate out.

Example: Crystallization of potash alum

Potash alum (phitkari) is highly soluble in water. The commercial sample is shaken with water when alum dissolves. The insoluble impurities are removed by filtration. The solution is then heated and then cooled. On cooling, pure crystals of alum separate. The soluble impurities are left behind.