separation techniques

• 5 types of separation techniques

  • filtration
  • crystallisation
  • simple distillation
  • fractional distillation
  • paper chromatography
• Filtration

  used to separate a solid from a liquid.
• Filtration

  The substance left in the filter paper is called the residue
• Filtration

  The liquid that comes through the filter paper is called the filtrate
• Equipments needed for filtration:

  • filter paper
  • funnel
  • beaker
• Filtration can also be used to separate 2 solids if only one of them is soluble in water.
• Crystallisation

  used to separate a solute from a solution
• Equipments for crystallisation

  • gauze
  • tripod
  • bunsen burner
  • glass rod
  • evaporating dish
• Steps for crystilisation:

  • place the solution on the evaporation dish using a glass rod
  • Heat it gently using a bunsen burner
  • Stop when you see crystals start to form
  • Leave it to cool
  • Crystals then can be removed using filtration
• Simple distillation

  used to separate the components of a solution
• Steps for simple distillation

  • heat up the mixture
  • as it rises to the top of the flask, the pressure will force the gas down the condenser
  • the vapour will cool and condense into the liquid form as we pump cold water through the condenser
  • the liquid then run through the pipe and is collected in the beaker

  
• Fractional distillation

  used to separate a mixture of liquids that are miscible (becoming as one)
• Fractional distillation

  We separate the liquids by taking advantage of their different boiling points
• Fractional distillation

  e.g mixture of ethanol and water

  boiling point:

  ethanol: 78

  water: 100

  We heat the substance to the lowest boiling point (78), so that the ethanol can rise as a vapour whilst the water condenses back into the flask. After all the ethanol have been separated into the beaker, the water is left in the flask.

  
• Paper chromatography

  can be used to separate a variety of mixtures, but commonly used for coloured inks or food colouring
• Steps for paper chromatography

  • take a piece of chromatography paper and draw a line at the bottom of the paper using a pencil (also called the baseline)
  • add the sample of ink to the pencil line
  • find a beaker and fill with a shallow amount of solvent (e.g. water/ethanol etc)
  • place the chromatography paper in the beaker
  • make sure don't submerge the pencil line or dot of ink into the solvent
  • put lid on top to stop solvent from evaporating
  • wait for solvent to seep up the paper, the dyes will dissolve and move up with it
• Paper chromatography

  we use a pencil to draw the baseline because the ink of the pen might diffuse in the water or move up the chromatogrphy paper with the solvent
• Paper chromatography

  We don't submerge the baseline into the solvent because the dot of ink might diffuse into the solvent instead
• Paper chromatography - Rf value

  divide the distance travelled by the component by the distance travelled by the solvent