Liquid-Liquid Mixtures

• Separating funnel


  • used to separate immiscible liquids
  • when a heterogenous mixture settles into separate layers, each component is removed by opening the tap at the bottom and collecting the liquids in separate flasks
• Chromatography


  • used to separate mixture of substances which have different solubilities in a given solvent
  • Chromatograms show the separated substances on the paper after chromatography
  • more soluble substances will move more rapidly towards the solvent front, separating the mixture into its components
  • Rf (retention factor) value = distance travelled by substance / distance travelled by solvent
  • locating agents, which react with colourless substances to form coloured spots, can be used to analyse chromatograms which are colourless. UV light can also be used.
• Uses of Chromatography


  • can be used to identify unauthorised substances like pesticides and poisons in food
  • detect small quantities of banned substances in an athlete's urine or blood sample
  • separate components like DNA fragments in samples for forensic investigations
• Fractional Distillation


  • Used when two liquids are miscible and the boiling points of the liquids are different

  1. As the solution is heated, both liquids rise up the column
  2. water has higher boiling point that ethanol. Water vapour condenses on the cool surface of the fractionating column an the liquid water returns to the flask
  3. ethanol continues to rise, and at its boiling point, it exits the column through the sidearm at the top
  4. the hot ethanol vapour cools and condenses into a liquid as it travels through the inner tube of the condenser
  5. liquid ethanol flows into the conical flask
• Uses of Fractional Distillation


  • Oil refineries separate different substances from crude oil
  • liquefied air is separated to produce nitrogen, oxygen and argon gas
  • ethanol produced by glucose fermentation is extracted in breweries