CIE A Level Chemistry (9701) 2019-2021

Revision Notes

8.1.2 Interpreting Rf Values in GL Chromatography

Interpreting Rf Values in GL Chromatography

Features of a gas-liquid chromatogram

  • Peaks represent different molecules from the sample – each roughly taking the shape of a triangle
  • The area under each peak is the relative concentration of each component (the peak integration value)

Area under the peak = ½ x base x height

  • If the area under each peak is very small or unable to decipher, the height of peaks are used for further analysis

Analytical Techniques - Labelled GLC Chromatogram, downloadable AS & A Level Chemistry revision notes

To find the area under each peak, treat each peak as a triangle – see the examples shown using blue triangles in the diagram

Percentage composition of a mixture

  • The amount of a particular molecule in a sample can be calculated by using an expression
  • If a chromatogram shows peaks for alcohols A, B, C and D; To calculate the % composition of alcohol C, use this expression:

 Interpreting Rf Values in GL Chromatography equation

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Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.

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