Using chromatograms

• R₁ value


  The ratio between the distance travelled by the dissolved substance and the distance travelled by the solvent
• R₁ value


  • The further a substance moves through the stationary phase, the larger the R₁ value
• Calculating R₁ value

  1. distance moved by substance (B)

  2. distance moved by solvent (A)

  3. R₁ = distance moved by substance (B) / distance moved by solvent (A)
• Chromatography experiment


  • Measuring distance moved by red spot (B)
  • Measuring distance moved by solvent (A)
  • Calculating R₁ = 29 mm / 41 mm = 0.70731
• The R₁ value of a chemical will change if you change the solvent
• Using chromatography to identify substances in mixtures

  • Run a pure sample of a substance (reference) next to the mixture
  • If the R₁ value of the reference compound matches one of the spots in the mixture, the substance could be in the mixture
• Identifying substances in a mixture


  • The mixture contains 3 different substances
  • Reference A has moved the same amount as one of the spots in the mixture, so the mixture probably contains substance A
  • Reference C has moved the same amount as one of the spots in the mixture, so the mixture probably contains substance C
• If the R₁ values match in one solvent, you can check to see if the chemicals are the same by repeating with a different solvent. If they match again, it's likely that they're the same