Give a brief description of the principles of the following techniques taking an example in each case. 
(a) Crystallisation    (b) Distillation      
(c) Chromatography

Crystallisation:
This is a most common method for the purification of solid organic compounds. It is based on the fact that certain organic compounds are partly soluble in a solvent at room temperature and solubility increases with increases in temperature. Example: separation of sugar from a mixture of sugar and common salt by using ethanol.

Distillation:
This method is based on the principle that at constant pressure every pure liquid boils at a definite temperature called its boiling point. The method is used for the purification of those liquids which boil without decomposition provided the impurities are non-volatile. The method is applied for the purification when the two liquid differs in the boiling points by 30-50K.
Chromatography
The technique dependes on the distribution of the mixture between two phases, one fixed and the other mobile. The fixed phase may bean absorbent column (a solid chemical compound) or a paper strip. The moving phase may be a liquid or gas. the mixture to be separted is dissolved in the moving phase and passed over the fixed phase. There are three types of chromatography.
i) adsorption chromatography
ii) partition chromatography
iii) gas chromatography