Separation of Substances

• Why Separate Substances?

  • To remove harmful or unneeded components
  • To obtain useful components
  • To separate pure substances from mixtures

• Methods of Separation

  • Handpicking
    • Used for slightly larger impurities (stones from rice/pulses)
    • Separated by hand
  • Threshing
    • Used to separate grain from stalks
    • Beating stalks against a hard surface or using machines
  • Winnowing
    • Used to separate heavier and lighter components
    • Uses wind or blowing air (e.g., husk from grain)
  • Sieving
    • Used for components of different sizes
    • Fine particles pass through, larger impurities stay on the sieve (e.g., bran from flour)
  • Sedimentation & Decantation
    • Sedimentation: Heavy insoluble components settle down
    • Sediment is the solid at the bottom
    • Decantation: Pouring out the clear liquid without disturbing the sediment
  • Filtration
    • Used to separate insoluble solids from liquids
    • Uses a filter paper or strainer (e.g., tea leaves from tea)
  • Evaporation
    • Conversion of liquid into vapor
    • Used to recover solid dissolved substances (e.g., obtaining salt from sea water)
  • Condensation
    • Conversion of water vapor into its liquid form
    • Cooling steam on a plate above boiling water

• Can Water Dissolve Any Amount of Substance?

  • Solution: Formed when a substance dissolves in a liquid
  • Soluble: Substances that dissolve completely
  • Insoluble: Substances that do not dissolve
  • Saturated Solution: A solution in which no more substance can be dissolved at that temperature
  • Effect of Heating: Can dissolve more of a substance in a saturated solution