Separating Techniques

• Filtration


  Used to Separate an Insoluble Solid from a Liquid
• Filtration


  1. Pour the liquid part of the mixture into a funnel

  2. Filter through paper

  3. Leaving behind the insoluble solid
• Crystallisation


  Separates a Soluble Solid from a Solution
• Crystallisation


  1. Pour the solution into an evaporating dish

  2. Gently heat to evaporate some water

  3. Once crystals start to form, remove from heat and let cool

  4. Filter out the crystals
• Separating rock salt

  • Grind up rock salt
  • Dissolve in water
  • Filter to remove insoluble sand
  • Evaporate to obtain pure salt crystals
• Salt dissolves in water, sand does not
• The sand stays on the filter paper, the dissolved salt goes through
• When the water evaporates, the salt forms crystals
• How to do Paper Chromatography

  1. Draw a line on a sheet of paper

  2. Add drops of different inks to the line

  3. Roll up the paper and place it in a container with solvent

  4. The solvent will travel up the paper, carrying the inks

  5. Each ink will move up the paper at a different rate

  6. When the paper is nearly at the top, remove it and let it dry

  7. The result is a pattern of spots called a chromatogram
• Chromatography


  A technique that separates mixtures based on the different rates at which the components move through a medium
• Chromatography works because different substances will move up the paper at different rates</b>
• The distance a substance moves up the paper depends on the substance and the paper used
• R_f value


  The ratio of the distance travelled by the solute to the distance travelled by the solvent
• Calculating R_f value


  Measure the distance travelled by the solute

  Measure the distance travelled by the solvent

  R_f = distance travelled by solute / distance travelled by solvent
• Chromatography is used to identify substances in a mixture
• Chemists use standard reference materials (SRMs) to check the identities of components in a mixture
• Uses of chromatography


  • Crime-fighting - identifying unknown substances
  • Identifying mysterious things in your hair
• On a paper chromatogram, chemical X travelled 2.1 cm, chemical Y travelled 3.6 cm and the solvent travelled 6.0 cm
• Distillation


  A process used to separate mixtures of liquids based on differences in their boiling points
• Simple Distillation


  1. The solution is heated

  2. The part of the solution with the lowest boiling point evaporates

  3. The vapour condenses back into a liquid and is collected

  4. The rest of the solution is left behind
• Simple Distillation

  • Can only separate substances with large differences in boiling points
  • Cannot separate a mixture of liquids with similar boiling points
• Fractional Distillation


  1. The mixture is heated in a fractionating column

  2. The different liquids evaporate at their different boiling points

  3. The vapours condense at different heights in the column

  4. The fractions are collected separately
• Fractional Distillation


  • Can separate a mixture of liquids with similar boiling points
  • Allows for the separation of the components of crude oil
• Propan-1-ol, methanol and ethanol have boiling points of 97 °C, 65 °C and 78 °C respectively