Mixtures - AQADistillation

Learn more on distillation and chromatography in this podcast.

Listen to the full series on BBC Sounds.

Simple distillation

Simple distillation is used to separate a solvent from a solution. It is useful for producing pure water from seawater.

Simple distillation works because the dissolvedsolute has a much higher boiling point than the solvent. When the solution is heated, solvent vapour leaves the solution. It moves away and is cooled and condensed. The remaining solution becomes more concentrated as the amount of solvent in it decreases.

Fractional distillation

Fractional distillation is used to separate different liquids from a mixture of liquids. It is useful for separating ethanol from a mixture of ethanol and water, and for separating different fractions from crude oil.

Fractional distillation works because the different liquids have different boiling points. When the mixture is heated:

• vapours rise through a column which is hot at the bottom, and cooler at the top
• vapours condense when they reach a part of the column that is below the temperature of their boiling point
• each liquid is led away from the column

There are two ways of obtaining different liquids from the column:

• by collecting different liquids from different parts of the column - the substance with the lowest boiling point is collected at the top of the column
• by continuing to heat the mixture to increase the temperatures in the column - the substance with the lowest boiling point is collected first