Azeotropic mixtures are binary mixtures having the same composition in liquid and vapour phase and boil at a constant temperature. Hence, they behave as a single component.
The most common example is the azeotrope between water and ethanol (grain alcohol). Water boils at 100 ºC, and ethanol boils at 78.3 ºC. The mixture will boil at 78.2 ºC and have a composition of 95% ethanol and 5% water by volume. This is a binary azeotrope because it involves two components.
- There are also azeotropes between three components, and these are called ternary azeotropes. A common ternary azeotrope found in solvent recycling is Acetonitrile, water and methanol.
- Their mixture can either have a higher boiling point than either of the components or have a lower boiling point.
- Azeotropes occur when a fraction of the liquids cannot be altered by distillation. Azeotropes exist in a solution at a boiling point specific to that component.