Azeotropes

 Azeotropes 

A mixture of two liquids which has a constant boiling point and composition throughout distillation.

1. Azeotropes are binary mixtures having the same composition in liquid and vapour phase and boil at a constant temperature.
2.  Minimum boiling azeotrope The solutions which show a large positive deviation from Raoult’s law form minimum boiling azeotrope at a specific composition.
3.  For example, ethanol-water mixture containing approximately 95% of ethanol forms an azeotrope with boiling point 351.15 K.
   

Maximum boiling azeotrope :

1.  The solutions that show large negative deviation from Raoult’s law form maximum boiling azeotrope at a specific composition.
2. Nitric acid and water mixture containing 68% nitric acid forms an azeotrope with a boiling point of 393.5K 

An azeotrope  or a constant boiling point mixture is a mixture of two or more liquids whose proportions cannot be altered or changed by simple distillation. This happens because when an azeotrope is boiled, the vapour has the same proportions of constituents as the unboiled mixture.