GCSE Combined Science (AQA)

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Purity: Melting & Boiling Points

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Chemical analysis Purity, formulations and chromatography

Purity: Melting & Boiling Points

3:11 Identifying Pure Substances and Mixtures
Spec 4.8.1.1
Previous Cracking Next Formulations
  • Everyday language defines a substance as pure if nothing is added and it is in its natural state.
  • Example: Orange juice made only from oranges is considered 100% pure.
  • Pure in chemistry means a single element or compound not mixed with any other substance.
  • Pure gold is an example of a pure substance, consisting only of gold atoms.
  • Pure water contains only water molecules; drinking water is not pure due to minerals like calcium, potassium, and zinc.
  • Pure substances melt and boil at specific temperatures, shown by flat sections on a heating curve graph.
  • Impure substances melt and boil over a range of temperatures, lacking flat sections on a graph.
  • Melting and boiling point data can distinguish pure substances from mixtures.
  • A pure substance's graph has horizontal lines during changes of state, while an impure substance's graph does not.

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