Distillation

Simple distillation

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

Simple distillation works because the dissolved solute has a much higher boiling point than the solvent. When the solution is heated, solvent vapour evaporates from the solution. The vapour is cooled and condensed. The remaining solution becomes more concentrated as the amount of solvent in it decreases.

Salty water is heated.

1. Salty water is heated

Fractional distillation

Fractional distillation is used to separate the different liquids from a mixture of liquids. It 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 cold at the top
  • vapours condense when they reach a part of the column that is below the temperature of their boiling point
  • the liquid flows out of 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. Different fractions are separated from crude oil this way.
  • By continuing to heat the mixture to increase the temperatures in the column. The substance with the lowest boiling point is collected first. Ethanol is separated from a mixture of ethanol and water this way.
In the first stage of ethanol distillation, water and ethanol solution is heated.

1. Water and ethanol solution is heated