Describe the crystallisation technique used for the purification of organic compounds.

(N/A) 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 suitable solvent. The compound is generally more soluble in a hot solvent and less soluble in a cold solvent.
Method:
$1$. The impure compound is dissolved in a minimum amount of a suitable solvent in which it is sparingly soluble at room temperature but appreciably soluble at higher temperatures.
$2$. The solution is heated to dissolve the compound completely and then filtered while hot to remove insoluble impurities.
$3$. The hot solution is then allowed to cool slowly. As the solution cools,the pure compound crystallises out.
$4$. The crystals are separated from the remaining liquid (mother liquor) by filtration. The mother liquor contains the impurities and a small quantity of the dissolved compound.
$5$. If the compound is highly soluble in one solvent and very little soluble in another,crystallisation can be carried out using a mixture of these solvents.
$6$. Impurities that impart colour to the solution are removed by adsorbing them onto activated charcoal.
$7$. Repeated crystallisation is necessary for the purification of compounds containing impurities with comparable solubilities.
Flowchart:
Solution of crystals of impure compound $\rightarrow$ Filtrate $\rightarrow$ (Precipitate: crystals of pure compound) $AND$ (Filtrate: mother liquor containing impurities + very little quantity of compound).