rpa 6 : chromatography

• 1. use a ruler and draw a horizontal line on the chromatography paper
  2. the line should be 2cm from the bottom of the paper
  3. mark 5 pencil spots with 1cm gaps between them
  4. use a capillary tube to place a small dot of each colour
  5. pour water ( solvent ) at a depth of 1cm
  6. attach the paper to a glass rod using tape
  7. the pencil line must be above the water , the sides of the paper must not touch the beaker as it will interfere with the water and use a lid to prevent evaporation
  8. take the paper out after it moves 3/4 and mark with a pencil where the water reached and then hang the paper to dry
• how to identify the chemical

  • measure the distance from the pencil line to the centre of each spot ( mm )
  • measure the distance moved by water from the pencil line
  • distance moved by chemial / distance moves byy solvent = Rf value
  • look up the Rf value on a data base
• Rf values have no unit
• • several other chemicals may have the same Rf value so you would need to repeat the experiment using a different solvent
  • if the chemical has never been analysed before there will be no data on the data base and further analysis is required