Explain cryatallization and sublimation phenomena whilch are used in the purification of organic compounds.

Explanation

Crystallisation : The compound which is to be purified is leached with a suitable solvent in a glass container. Then some impurities dissolve and others do not dissolve. Now, the container is heated. The compound starts dissolving and the solubility of the compound increases with increase in temperature. The solution is concentrated to near saturation and filtered while it is hot. On cooling the solution slowly the compound crystallises out. The crystals are separated by filtration under reduced pressure using Buckner funnel The soluble impurities remiain with the solution. Coloured impurities are removed by adsorbing them with activated charcoal.
2) Sublimation : Some solid substances on heating directly pass into vapour state without melting. Those vapours on cooling form directly solid without condensing to liquid. This phenomenon is called sublimation.
Solid`hArr`Vapour
The compound to be purified is taken in a beaker covered with a watch glass an heated. The compound sublimes and solidifies on the lower surface of the watch glass. Impurities remain in the bealter. The compound is separated by scratching the watch glass.