Chromatography

• Paper chromatography method


  1. Draw horizontal pencil line on chromatography paper

  2. Mark 5 pencil spots across the line

  3. Use capillary tube to put small spots of known and unknown food colors onto the pencil spots

  4. Pour water into beaker to 1cm depth

  5. Attach paper to glass rod and lower into beaker

  6. Remove paper when water has travelled 3/4 up

  7. Mark point where water reached

  8. Hang paper up to dry
• Paper chromatography


  • Used to identify substances
  • Required practical
• Unknown color separates into 3 spots


  Indicates it is a mixture of 3 colors
• Spots in unknown color line up with spots in known colors A, C, D


  Indicates unknown color is a mixture of A, C, D
• Unknown color does not contain color B

  Indicates it does not contain color B
• RF value


  • Ratio of distance moved by chemical to distance moved by solvent
  • Used to identify chemicals by looking up in a database
• Several different chemicals could have the same RF value, so further analysis may be needed
• If a chemical has not been analyzed before, there will not be an RF value in the database, so further analysis is required