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

(N/A) Crystallisation
Crystallisation is one of the most commonly used techniques for the purification of solid organic compounds.
Principle: It is based on the difference in the solubilities of the compound and the impurities in a given solvent. The impure compound is dissolved in a solvent in which it is sparingly soluble at room temperature but appreciably soluble at higher temperatures. The solution is concentrated to obtain a nearly saturated solution. On cooling the solution,the pure compound crystallises out and is removed by filtration.
Example: Pure aspirin is obtained by recrystallising crude aspirin. Approximately $2-4 \ g$ of crude aspirin is dissolved in about $20 \ mL$ of ethyl alcohol. The solution is heated to ensure complete dissolution. The solution is then left undisturbed until crystals start to separate out. The crystals are then filtered and dried.
$(b)$ Distillation
This method is used to separate volatile liquids from non-volatile impurities or a mixture of liquids that have a sufficient difference in their boiling points.
Principle: It is based on the fact that liquids having different boiling points vaporise at different temperatures. The vapours are then cooled and the liquids so formed are collected separately.
Example: $A$ mixture of chloroform $(b.p. = 334 \ K)$ and aniline $(b.p. = 457 \ K)$ can be separated by distillation. The mixture is heated in a round-bottom flask. Chloroform,being more volatile,vaporises first,passes into the condenser,and is collected as a liquid. Aniline remains in the flask.
$(c)$ Chromatography
It is one of the most useful methods for the separation and purification of organic compounds.
Principle: It is based on the difference in movement of individual components of a mixture through a stationary phase under the influence of a mobile phase.
Example: $A$ mixture of red and blue ink can be separated by chromatography. $A$ drop of the mixture is placed on the chromatogram. The component that is less adsorbed on the stationary phase moves faster with the mobile phase,while the more strongly adsorbed component moves slower.