Crystallization is the process of obtaining crystals of a solid from its saturated solution. Crystallization can be used for the separation of two salts with different solubilities and also the purification of salt that contains insoluble solid impurities.
The salt can either be dissolved at a high temperature and the solution cooled to allow crystals to settle out or the solution of the salt can be heated to evaporate part of the solvent, in order to obtain a saturated solution. On cooling, crystals will appear. Filter the crystal and dry the salt in a filter paper.
To obtain purer crystals, the crystallization process is repeated on a given solid sample using a fresh solvent.
Fractional crystallization is based on the difference in solubility of solids in a given solvent. It is a process whereby a mixture of two or more solid substances is crystallized one after the other from the same solution.
On cooling, the least soluble solid crystallizes out first leaving behind the other with higher solubility.