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

Explanation

Crystallisation : The compound which is to be purifiea 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 remain with the solution. Coloured impu rities 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 phe . nomenon is called sublimation.
Solid Vapour
The compound to be purified is taken in a beaker covered with a watch glass and heated. The compound sublimes and solidifies on the lower surface of the watch glass.-Impurities remain in the beaker. The compound is separated by scratch ing the watch glass.