CBSE Class 12-science Answered

Very large deviations from ideality lead to a special class of mixtures known as azeotropes, azeotropic mixtures, or constant-boiling mixtures. Azeotrope is a special class of liquid mixture that boils at a constant temperature at a certain composition. At this condition, it behaves as if it was one component with one constant boiling point.

A boiling liquid mixture at the azeotropic composition produces a vapour of exactly the same composition, and the liquid does not change its composition as it evaporates.

Two types of azeotropes are known: minimum-boiling and maximum-boiling (less common). One of the best known minimum-boiling azeotrope is the ethanol-water system which at 1 atm occurs at 89.4 mole percent ethanol and 78.2 oC. Other examples are: