Worksheet: Mass Spectra

In this worksheet, we will practice analyzing mass spectra to deduce the molar mass, likely composition, and structure of the analyte.


Which of the following chemical groups often display strong molecular ion peaks in mass spectra, due to their structural stability?

  • AAlkanes
  • BAlcohols
  • CCarboxylic acids
  • DAromatics
  • EAldehydes


Why might mass analysis of a nitrogen-containing molecule show a molecular ion peak with an odd 𝑚 / 𝑧 ratio?

  • AIt has rearranged via the McLafferty rearrangement
  • BIt contains an even number of nitrogen atoms
  • CThe mass analyzer needs to be recalibrated; nitrogen containing molecules always give an even 𝑚 / 𝑧 ratio
  • DIt contains an odd number of nitrogen atoms


In a mass spectrum of an alcohol, why is the molecular ion usually small or non-existent?

  • ARearrangement of the molecule to form an ester
  • BCleavage of the hydroxyl group
  • CFormation of a dimeric species
  • DCleavage of the C C bond adjacent to the hydroxyl group


Which of the following best describes the mass spectrum of fluorine ( F ) 2 ?

  • AIt consists of only one peak, since it is monoisotopic.
  • BIt is similar to the spectra of bromine and chlorine.
  • CIt consists of two peaks, separated by 2 Da.
  • DIt consists of two peaks, appearing at 19 Da and 38 Da.
  • EIt consists of three peaks, appearing at 20, 21 and 22 Da.


What is the likely explanation if a mass spectrum contains peaks at 35 and 37 Da?

  • AThe sample was analyzed in a gas mixture containing argon.
  • BThe sample is R b B r .
  • CThe sample was analyzed in a gas mixture containing krypton.
  • DThe sample contains chlorine.
  • EThe sample contains bromine.


What are the typical units for the 𝑥 -axis of a mass spectrum?

  • AWavenumbers ( ) c m 1
  • BParts per million (ppm)
  • CWavelength (nm)
  • DMass to charge ( 𝑚 / 𝑧 ) ratios
  • EMass (g)

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