What is azeotropes ? Explain their types.

Explanation

Some liquids on mixing, form azeotropes which are binary mixtures having the same composition in liquid and vapour phase and boil at a constant temperature. In such cases, it is not possible to separate the components by fractional distillation.
There are two types of azeotropes called minimum boiling azerotrope and maximum boiling azeotrope.
(i) Minimum Boiling azeotrope : The solutions which show a large positive deviation from Raoult.s law form minimum boiling azeotrope at a specific composition.
For example : ethanol - water mixture on fractional distillation gives a solution containing approximately 95% by volume of ethanol. Once this composition, known as azeotrope composition, has been achieved, the liquid and vapour have the same composition, and no further separation occurs.
(ii) Maximum Boiling azeotropes : The solutions that show large negative deviation from Raoult.s law form maximum boiling azeotrope at a specific composition.
Example : Nitric acid and water is an example of this class of azeotrope. This azeotrope has the approximate composition, 68% nitric acid and 32% water by mass, with a boiling point of 393.5 K.