Purity: Methods of Purification

Purity: Methods of Purification

Understanding Different Methods of Purification

  • Familiarise yourself with the different methods of purification such as simple distillation, fractional distillation, crystallisation, filtration, chromatography, and sublimation.

Simple Distillation

  • Understand that simple distillation is employed for separating a solvent from a solution or two miscible liquids with a significant difference in their boiling points.
  • Know that it involves heating the mixture, condensing the vapour produced, and collecting the distillate.

Fractional Distillation

  • Learn that fractional distillation is used to separate miscible liquids with close boiling points.
  • Note that it involves the use of a fractionating column which ensures that the vapour with a lower boiling point is fully condensed before the commencement of the second liquid’s boiling.


  • Learn that crystallisation is used to purify solids with the method based on the difference in solubility of the component substances in a solvent.
  • Know that the substance to be purified is dissolved in the minimum amount of hot solvent and as the solution cools, the solute recrystallises in the pure state.


  • Understand that filtration is a method used to separate an insoluble solid from a liquid in a solid-liquid mixture.
  • Be aware that it involves passing the mixture through a filter where the liquid particles pass through while the solid particles remain on the filter.


  • Realise that chromatography involves separation of dissolved substances due to their different abilities to travel across the surface of a material.
  • Understand that the substances are identified from their relative positions, or Rf values, in chromatography.


  • Understand that sublimation is the process of a substance transforming from a solid to a gas state without undergoing the liquid phase.
  • Note that this technique is used for purification when a substance is mixed with a sublimable impurity.