Filtration and Crystallisation

• Physical separation techniques can only be used to separate mixtures, they cannot be used to separate the elements in a compound
• Chemical reactions such as reduction or electrolysis can be used to separate the elements in compounds
• Filtration

  Used to separate an insoluble solid from a liquid
• Insoluble

  The solid will not dissolve in the liquid
• Example of insoluble solid and liquid

  • Silver chloride and water
• Filtration process

  1. Pour mixture into filter paper

  2. Liquid (filtrate) passes through

  3. Solid trapped in filter paper
• Crystallization

  Used to separate a soluble solid from a liquid
• Example of soluble solid and liquid


  • Sodium chloride and water
• Crystallization process

  1. Leave solution to evaporate

  2. Water evaporates

  3. Solid crystals left behind
• Heating can be used to speed up crystallization, but some chemicals may break down if heated