Separating a liquid from a mixture – fractional distillation

Fractional distillation is a method for separating a liquid from a mixture of two or more liquids. For example, liquid ethanol can be separated from a mixture of ethanol and water by fractional distillation. This method works because the liquids in the mixture have different boiling points. When the mixture is heated, one liquid evaporates before the other.

Water and ethanol solution are heated in a flask over a bunsen burner, pure vapour is produced in the air above the solution within the flask.

A water and ethanol mixture is heated in a flask using an electric heater. Vapour forms in the air above the mixture in the flask.

One way to check the purity of the separated liquids is to measure their boiling points. For example, pure ethanol boils at 78°C and pure water boils at 100°C.