Chemistry

(i) Separation by fractional distillation :
Fractional distillation is the process of separating two (or more) miscible liquids by distillation, the distillate being collected in fractions boiling at different temperatures. A mixture of two miscible liquids can be separated by the process of fractional distillation. The separation of two liquids by fractional distillation depends on the difference in their boiling points. Fractional distillation is carried out by using a fractionating column.
Example.
Alcohol and water are miscible liquids. The boiling point of alcohol is 78ºC and the boiling point of water is 100ºC. Since the boiling points of alcohol and water different, therefore, a mixture of alcohol and water can be separated by fractional distillation. The mixture of alcohol and water is heated in a distillation flask fitted with a fractionating column. When the mixture is heated, both alcohol and water form vapours as their boiling points approach. The alcohol vapour and water vapour rise up in the fractionating column. The upper part of the fractionating column is cooler, so as the hot vapours rise up in the column, they get cooled, condense and trickle back into the distillation flask.
The more volatile liquid distils over first, and the less volatile liquid distils over later. A mixture of alcohol and water can be separated by fractional distillation.