Why is it not possible to obtain pure ethanol by fractional distillation? What
general name is given to binary mixtures which show deviation from Raoultslaw and whose components cannot be separated by fractional distillation.How many types of such mixtures are there?
1. It is not possible to obtain 100 % ethanol from ethanol- water mixture even by fractional distillation. This is due to the fact that ethanol forms azeotropic solution with ​water at the concentration 95 % by volume.
As soon as this composition is achieved, the vapour and solution exist with same composition and no furthur seperation occurs.
2. Binary mixture which shows deviation form raoults law and which cannot be separated by fraction distillation are known as azeotropes.
Basically there are two azeotropic mixture
1. Minimum boiling azeotrope : They shows large positive deviation form Raoults law, for example : 95 % ethanol by volume.
2. Maximum boiling azeotrope :They shows large negative deviation form Raoults law, for example : 68 % nitric acid by mass.
As soon as this composition is achieved, the vapour and solution exist with same composition and no furthur seperation occurs.
2. Binary mixture which shows deviation form raoults law and which cannot be separated by fraction distillation are known as azeotropes.
Basically there are two azeotropic mixture
1. Minimum boiling azeotrope : They shows large positive deviation form Raoults law, for example : 95 % ethanol by volume.
2. Maximum boiling azeotrope :They shows large negative deviation form Raoults law, for example : 68 % nitric acid by mass.