Separation techniques

• Filtration

  • separates a solid from a liquid or solution
  • the solid cannot fit through the small gaps in the filter paper so forms the residue, but the individual liquid particles and dissolved particles can pass through the filtrate

  
• Crystallisation:

  • obtains a dissolved solid (solute) from a solution
  • heating the solution causes the solvent to evaporate
  • when the solution becomes saturated, crystals of the solute start to form as the solvent is removed

  
• simple distillation:

  • obtains a solvent from a solution
  • heating the solution causes the solvent to evaporate
  • the solvent vapour is cooled in a condenser so that it condenses and the distillate can be collected separately from the solution

  
• fractional distillation:

  • obtains liquids from a mixture of liquids
  • different liquids have different boiling points, so each liquid in the mixture will evaporate at a different temperature to be condensed and collected

  
• paper chromatography info:

  • used to separate different dissolved substances such as the colouring additives in food
  • the relative solubility of each additive determines how fast it will travel up the chromatography paper when carried along by the solvent so the components end up being separated
• the more soluble, the faster the component moves
• a match is found when of the spots in the unknown sample is the same colour and at the same height (ie. the same Rf value) as the spot in the known sample
• paper chromatography method:

  1. draw a 'start line' using a pencil
  2. put your different inks on the start line
  3. the start line and the dots must be above the surface of the solvent
  4. make sure your paper is securely attached to a rod so it stays vertical without touching the beaker
  5. take the paper out of the solvent when your mobile phase is close to the top

  
• why do we use a pencil to draw the line for paper chromatography?


  so that it doesn't dissolve in the solvent and affect the results
• Rf = distance spot travelled by solute ÷ distance travelled by solvent