Mixtures of two liquids which boil at a constant temperature and can be distilled unchanged in their composition are called azeotropic mixtures. These are formed by non-ideal solutions and are of two types.
(i) Maximum boiling azeotropes: These are mixtures of two liquids whose boiling points are more than either of the two pure components. These are formed by non-ideal solutions showing negative deviation, e.g. HNO3 (68%) + water (32%) mixture which boils at 393-5 K.
(ii) Minimum boiling azeotropes: These are mixtures of two liquids whose boiling points are less than either of the two pure components. These are formed by non-ideal solutions showing positive deviation, e.g. ethanol (95-5%) + water (4.5%) mixture which boils at 351-15 K.
