Filtration, evaporation, crystallisation

• Separating soluble and insoluble solids from liquids

  1. Filtration

  2. Evaporation

  3. Crystallization
• Mixture


  Liquid and insoluble solid
• Solution


  Liquid and soluble solid (solute) in water (solvent)
• Filtration


  1. Pour mixture through filter paper with tiny holes

  2. Allows liquid to pass through

  3. Leaves solid behind on paper
• Cannot filter out soluble solids that have dissolved in a liquid
• Evaporation


  1. Place solution in evaporating dish/crucible

  2. Slowly heat to evaporate solvent

  3. Leaves behind dry crystals of solid
• Evaporation

  • Relatively quick and easy
  • Some solids may decompose when heated (thermal decomposition)
• Crystallization


  1. Place solution in evaporating dish

  2. Heat gently, e.g. in water bath

  3. Allow to cool, more crystals will form

  4. Filter out crystals

  5. Dry the crystals
• Solids are less soluble at colder temperatures
• Crystallization is a slower technique than evaporation, used for solids susceptible to thermal decomposition