Pure substances


  • n chemistry, a pure substance is a single element or compound, not mixed with any other substance.

Pure elements and compounds melt and boil at specific temperatures. Melting point and boiling point data can be used to distinguish pure substances from mixtures.

In everyday language, a pure substance can mean a substance that has had nothing added to it, so it is unadulterated and in its natural state, eg pure milk.

Students should be able to use melting point and boiling point data to distinguish pure from impure substances.



Key opportunities for skills development

Mixtures can be separated by physical processes such as

filtration, crystallisation, simple distillation, fractional distillation and chromatography. These physical processes do not involve chemical reactions and no new substances are made.

Students should be able to:

  • describe, explain and give examples of the specified processes of separation
  • suggest suitable separation and purification techniques for mixtures when given appropriate information.

WS 2.2 Plan experiments or devise procedures to make observations, produce or characterise a substance, test hypotheses, check data or explore phenomena.

WS 4.1 Use scientific vocabulary, terminology and definitions.