Methods of Separation

• Distillation - used to separate out solutions

  (separate liquid and soluble solid from a solution)
• How simple distillation works?

  • the solution is heated, the water evaporates (Heating can be carried out using a Bunsen burner or water bath)
  • The vapor is cooled and condensed (This is done with the aid of cooling water jacket)
  • The newly condensed, pure liquid is collected in a new container
  • The rest of the solution remains in the flask
  • (Simple distillation only works when the components have very different boiling points)
• Fractional Distillation is used to separate mixtures of liquids (These liquids have different boiling points)
• How Fractional Distillation works?

  • the liquid with the lowest boiling point will evaporate first
  • the evaporating liquid will rise up a fractionating column
  • it will then be carried to a condenser (here it will reform as a liquid)
  • the temperature is then raised so that the second liquid can be collected
• Filtration - used to separate an insoluble solid from a liquid
• How filtration works?

  • a filter paper is placed in a funnel above a beaker
  • the mixture is poured into the funnel
  • the paper will only allow the smaller liquid particles to pass through
  • the solid particles will become trapped in the paper and remain as a residue
• Crystallization - separates soluble solids from a solution
• How crystallization works?

  • the solution is heated in a evaporating dish
  • some of the liquid evaporates, creating a more concentrated solution
  • as the solution cools, crystals of solute begin to form (this is because the solute is much less soluble when it is cold)
  • the crystals are filtered from the solution and dried
  • this is commonly demonstrated with copper sulphate (CuSO4) crystals
• Chromatography - another way to separate mixtures (mixtures are separated based on their solubilities in a particular solvent)
• How Chromatography works?

  • a pencil line is drawn on a sheet of paper (pencil marks are insoluble, so it will not dissolve in the solvent)
  • spots of different inks are added to the line at regular intervals
  • the paper is lowered into the solvent (this allows the solvent to travel up the paper)
  • as the solvent moves up the paper, it carries the dyes with it (some dyes will travel further than others based on their solubility)
• Chromatogram - shows the composition of mixtures

  • created when a mixture of different dyes are separated depending on their solubilities
• Rf Values - a ratio between the distance travelled by the solute and the distance travelled by the solvent
• How Rf values work?

  • the distance travelled by the solute is measured from the baseline to the center of the spot
  • Rf values are used to identify the components of mixtures
  • A substance will have the same Rf value in the same solvent( Rf values are often used by chemists to identify unknown substances
• Rf value formula: