Question

Give a brief description of crystallization with an illustration.

Answer 1

Crystallisation is a process of removing impurity from the mixture and finally getting the pure desired compound. It includes the formation of crystals of pure compounds.

Complete step by step answer:
The process of formation of solid crystals from a homogeneous solution is called crystallization. In crystallisation, the impure substance is dissolved in a suitable solvent to reach its nearly saturated solution at a temperature higher than the room temperature and then left for cooling (generally on ice bath). Crystals are the most precise arrangement of molecules all the same fitting together in some sort of construction toy. The impurity is in some different shape and thus cannot fit in the crystal lattice. Each time we recrystallize, we get more of a purer and purer compound.
For example: when $1{\text{ }}g$ of $NBS$ (N -Bromo succinimide) is prepared, it is mixed with some organic flammable solvent like dimethyl ether and heated in an Erlenmeyer flask on hot plate to allow proper dissolution and after some time it is left for cooling in ice bath where the crystals of pure $NBS$ will form and the impurities like acetanilide are separated out.

Note: Crystallisation is basically based on the principle that the compound to be purified and the impurities present in it have differences in their solubilities. The solution is made concentrated by heating so that to achieve the saturation and then it is cooled where the pure compound forms crystal and the impurities can be separated out.