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An azeotrope is a special mixture of 2 or more compounds (molecules). The ratio of the compounds, say in an azeotrope consisting of two compounds X and Y, is exactly the same in both the vapour form of the mixture, X:Y as in the liquid phase. Due to the uniformity of liquid and vapor, chemical composition of the azeotrope cannot be changed by simple boiling (distillation). This constant composition will (almost always) occur at a minimum or maximum temperature over the composition space. The exception for binary mixtures is the rare double azeotrope. The exception for three or more components is the intermediate boiling azeotrope (saddle azeotrope). For example, if there are 3 parts of liquid x to every 4 parts of liquid y, then you could not separate the two by boiling them because of the rates at which they boil. In order to enrich a mixture past the azeotrope (or "break" the azeotrope), one may use several techniques: 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 See also | ||||||||
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