How Distillation Separates Mixtures

In simple distillation, a liquid mixture is heated in a flask. The component with the lower boiling point tends to enter the gas phase more readily. Vapour rises from the flask and passes into a condenser.

The condenser has a cool outer jacket surrounding an inner tube. As the vapour loses thermal energy, it changes back into a liquid. This liquid, called the distillate, collects in a separate container. Less volatile substances remain behind in the original flask.

Distillation does not create a new substance. It uses physical changes of state to separate existing components. The particles in the vapour are the same kind that were present in the liquid. They have simply been persuaded to change location through the traditional scientific method of heating something and watching it leave.

Simple distillation works well when separating a solvent from a dissolved solid. Salt water can be heated so that water vaporises and later condenses, while most of the salt remains in the flask. The collected water is separated from the salt, although additional treatment may be needed before it is safe to drink.

Separating two liquids is harder if their boiling points are close. Both may enter the vapour, so one round of evaporation and condensation gives only a partial separation. Fractional distillation improves the result by adding a fractionating column above the heated flask.

Inside the column, vapour repeatedly condenses and evaporates. The more volatile component becomes increasingly concentrated in the rising vapour, while the less volatile component tends to return to the flask. Industrial columns use many surfaces or trays to repeat this process efficiently. The column creates many small separation stages inside one piece of equipment.

Distillation is used in laboratories, petroleum refining, water treatment and the production of chemicals. It can require large amounts of energy because liquids must be heated and cooled. Some substances also decompose before boiling, so lower pressure or another separation method may be needed.

A careful setup should include:

• •A flask that is not sealed shut.
• •Controlled heating rather than an open flame when unsafe.
• •A thermometer positioned to measure vapour temperature.
• •Cooling water flowing through the condenser.
• •A separate container for the distillate.

Distillation separates substances by turning a more volatile liquid into vapour and then condensing it elsewhere. Simple distillation suits large boiling point differences or a solvent mixed with a solid, while fractional distillation handles closer boiling points. Follow vaporisation, travel and condensation, and the apparatus becomes a logical path rather than a glass maze.