azeotrope, in chemistry, a mixture of liquids that has a constant boiling point because the vapour has the same composition as the liquid mixture. The boiling point of an azeotropic mixture may be higher or lower than that of any of its components. The components of the solution cannot be separated by simple distillation, and, therefore, such methods as adding a third component to change the volatility of the azeotrope or using two distillation columns operating at different pressures are used.