Worksheet: Mass Spectra

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

Q1:

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

Q2:

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

Q3:

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

Q4:

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.

Q5:

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.

Q6:

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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