Question

What is the difference between distillation under reduced pressure and steam distillation?

Answer 1

Steam distillation is based on Dalton’s law of partial pressure. It is employed for those liquids which are insoluble in water, have high boiling point, and contain non volatile impurities, when the sum of the partial pressure of steam and organic compound vapours equalise atmospheric pressure it start boiling, the vapours are collected and condensed. Ratio of the number of moles of components in the distillate is in the ratio of their respective vapour pressure. Ex., o-nitro phenol.
In Distillation under reduced pressure the external pressure is reduced, as a result the liquid boils at a lower temperature so that the decomposition of the compound does not occur. Glycerol and sugar are purified by this method. Ex., Glycerol