Azeotropes are special types of solutions that are binary mixtures of two or more liquids that exhibit the same concentration level in the liquid and vapor phase. These mixtures can either have a lower boiling point or a higher boiling point of the components, and simple distillation cannot alter their proportions. Azeotropes do not follow Raoults Law, which means that they are not ideal solutions and show deviation from Raoults Law. There are different types of azeotropic mixtures, including:
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Minimum Boiling Azeotropes or Negative Azeotrope: This type of azeotrope has a boiling point lower than its constituents. For example, ethanol consisting of a weight concentration of approximately ninety-five per cent and four per cent of water.
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Maximum Boiling Azeotropes or Positive Azeotrope: This type of azeotrope has a boiling point higher than its constituents. For example, a mixture of hydrochloric acid and water.
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Heterogeneous and Homogeneous Azeotropes: A minimum-boiling azeotrope may be produced by adding a compound forming an azeotrope (trainer), which cannot be differentiated by the conventional distillation in an established azeotropic or closely boiling mixture.
Azeotropes are used for the separation of constituents of zeotropic mixtures. For example, it is very difficult to separate pure acetic acid from a solution of acetic acid and water. Ethyl acetate forms an azeotrope with water and boils at 70.40C. So, by adding ethyl acetate in the mixture of acetic acid and water as an entertainer (solvent), it is possible to distil away the azeotrope (ethyl acetate and water) and leave nearly pure acetic acid in the distillation flask.
