3. Separation Techniques

1. Filtration
  • Separates a mixture of insoluble solid & a liquid.
  • Recovers the insoluble solid as the residue and the liquid as filtrate.
  • e.g. mixture of calcium carbonate and water.
  • Calcium carbonate is obtained as residue (insoluble solid) and water is obtained as the filtrate (liquid).
 
2. Evaporation and Crystallisation
  • To recover solute from solution
  • Evaporation: For solutes which do not decompose upon heating e.g. sodium chloride
  • Crystallisation: For solutes which decompose upon heating e.g. nitrates, sulfates & hydrated crystals
 
Steps :
  • Heat solution until it is saturated.
  • Allow the saturated solution to cool to form crystals.
  • Filter, wash and dry the crystals.
 
  • Saturated solution is a solution which contains the maximum amount of solute in a given volume of solvent at a given temperature.
  • The higher the temperature, the more solute can be dissolved.

3. Simple Distillation
  • To recover solvent from a solution as distillate.
  •   e.g. pure water (distillate) is obtained from seawater.

Things to note :
  • The bulb of the thermometer must be at same level as distilling arm to measure temperature of pure vapour.
  • Boiling stones are added to ensure smooth boiling.
  • Water enters from bottom of condenser and water exits from top of condenser.
    
4. Fractional distillation
  • Separates mixtures of miscible liquids with different boiling points.
  • First fraction is the one with the lowest boiling point.
  • Separates components in liquid air & crude oil/petroleum

5. Paper Chromatography
  • Principle: Different components in the mixture have different solubilities in the same solvent. The more soluble component, the further it travels up the chromatogram. 
  • Pure substance produces one spot only.
  • Locating agent is used to make colourless components visible.

6. Sublimation
  • A process whereby a substance changes from the solid sate to the gaseous state without melting.
  • Recovers iodine & ammonium chloride.

7. Separating funnel
  • Separates  immiscible liquids e.g. oil and water