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
  • BCarboxylic acids
  • CAlcohols
  • DAldehydes
  • EAromatics

Q2:

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

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

Q3:

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

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 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.

Q5:

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.

Q6:

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)

Q7:

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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