It is generally true that a negative azeotrope boils at a higher temperature than any other ratio of its constituents. Indeed 110☌ is the maximum temperature at which any hydrochloric acid solution can boil. Hydrogen chloride boils at –84☌ and water at 100☌, but the azeotrope boils at 110☌, which is higher than either of its constituents. Positive azeotropes are also called minimum boiling mixtures.Īn example of a negative azeotrope is 20.2% hydrogen chloride and 79.8% water (by weight). It is generally true that a positive azeotrope boils at a lower temperature than any other ratio of its constituents. Indeed 78.1☌ is the minimum temperature at which any ethanol/water solution can boil. Ethanol boils at 78.4☌, water boils at 100☌, but the azeotrope boils at 78.1☌, which is lower than either of its constituents. The boiling point of an azeotrope is either less than the boiling points of any of its constituents (a positive azeotrope), or greater than the boiling point of any of its constituents (a negative azeotrope).Ī well known example of a positive azeotrope is 95.6% ethanol and 4.4% water (by weight). 7 Use of azeotropes to separate zeotropic mixturesĮach azeotrope has a characteristic boiling point.6.6 Pervaporation and other membrane methods.6.4 Distillation using a dissolved salt.
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