CIE A Level Chemistry (9701) 2019-2021

Revision Notes

8.1.3 Mass Spectrometry

Mass Spectrometry: Deducing Molecular Formula

  • Each peak in the mass spectrum corresponds to a certain fragment with a particular m/e value
  • The peak with the highest m/e value is the molecular ion (M+) peak which gives information about the molecular mass of the compound
  • The molecular ion is the entire molecule that has lost one electron when bombarded with a beam of electrons

Mass Spectrometry Deducing Molecular Formula equation

  • The [M+1] peak is a smaller peak which is due to the natural abundance of the isotope carbon-13
  • The height of the [M+1] peak for a particular ion depends on how many carbon atoms are present in that molecule; The more carbon atoms, the larger the [M+1] peak is
    • For example, the height of the [M+1] peak for a hexane (containing six carbon atoms) ion will be greater than the height of the [M+1] peak of an ethane (containing two carbon atoms) ion

Author: Francesca

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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