chromatogrphy

• Investigate chromatography using inks/food colourings


  1. Draw pencil line 2 cm from bottom of chromatography paper

  2. Mark 5 pencil spots along horizontal line

  3. Use capillary tube to place dots of 4 known food colourings and unknown mixture

  4. Place chromatography paper in beaker with 1 cm water, cover with lid

  5. Wait for water to travel most of way up paper

  6. Remove paper, draw line at solvent front, leave to dry

  7. Calculate Rf values, compare known and unknown
• Chromatography paper


  • Pencil must be used to draw line as it is insoluble in solvent
  • Depth of water in beaker must be below substances to avoid washing them away
• Rf value


  Distance travelled by substance ÷ distance travelled by solvent front
• If Rf value of known food colouring matches Rf value of spot in unknown mixture, it's likely this food colouring is in the mixture
• Stationary phase


  Chromatography paper