Azeotrope
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An azeotrope is a liquid mixture of two or more components which has a unique constant boiling point. This azeotrope may boil at a higher, lower, or intermediate temperature, relative to the constituent liquids, and the liquid retains the same composition as it is boiled. As a consequence, the vapor has the same composition as the liquid and simple distillation will not separate the constituents as it would with most liquid mixtures, to get a higher concentration it is necesary use azeotropic distillation.
The word azeotrope comes from the Greek "zein tropos", or "constant boiling". An azeotrope is said to be positive if the constant boiling point is at a temperature maximum, and negative when the boiling point is at a temperature minimum. The vast majority of azeotropes are minimum boiling. All liquid mixtures which are immiscible and which form azeotropes are minimum boiling.
Examples of azeotropes
- nitric acid (68.4%) / water, boils at 122°C
- perchloric acid (28.4%) / water, boils at 203°C (negative azeotrope)
- hydrofluoric acid (35.6%) / water, boils at 111.35°C (negative azeotrope)
- ethanol (95%) / water, boils at 78.2°C
- sulphuric acid (98.3%) /water, boils at 330°C
- acetone / methanol / chloroform form an intermediate boiling azeotrope