Lesson Worksheet: Mass Spectra Chemistry

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
  • BCarboxylic acids
  • CAlcohols
  • DAldehydes
  • EAromatics


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

  • ABecause it has rearranged via the McLafferty rearrangement
  • BBecause the mass analyzer needs to be recalibrated (nitrogen-containing molecules always give an even 𝑚/𝑧 ratio)
  • CBecause it contains an odd number of nitrogen atoms
  • DBecause it contains an even number of nitrogen atoms


In a mass spectrum of an alcohol, what is the reason for the molecular ion being usually small or nonexistent?

  • AThe cleavage of the CC bond adjacent to the hydroxyl group
  • BThe formation of a dimeric species
  • CThe rearrangement of the molecule to form an ester
  • DThe cleavage of 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 consists of two peaks, separated by 2 Da.
  • CIt consists of three peaks, appearing at 20, 21, and 22 Da.
  • DIt is similar to the spectra of bromine and chlorine.
  • EIt consists of two peaks, appearing at 19 Da and 38 Da.


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

  • AThe sample is RbBr.
  • BThe sample contains bromine.
  • CThe sample is analyzed in a gas mixture containing argon.
  • DThe sample is analyzed in a gas mixture containing krypton.
  • EThe sample contains chlorine.


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

  • AWavenumbers ()cm
  • BMass (g)
  • CMass to charge (𝑚/𝑧) ratios
  • DParts per million (ppm)
  • EWavelength (nm)


What is the most abundant ion in a mass spectrum, which is assigned a relative abundance of 100%, referred to as?

  • AThe blank correlation
  • BThe mother peak
  • CThe detection limit
  • DThe reference peak
  • EThe base peak

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