Mass spectrometry in organic analysisAQA A-Level Chemistry: Mind map

Exam questions on Mass spectrometry in organic analysis

1. A pure organic compound is analysed by mass spectrometry. In the mass spectrum, the peak with the highest mass-to-charge ratio (ignoring any very small peaks above it) is at m/z = 74.
   The compound is known to contain only carbon, hydrogen and oxygen. Explain why the m/z value of 74 alone cannot be used to find its molecular formula.2 marks
2. High-resolution mass spectrometry measures relative molecular masses to four decimal places. Precise relative atomic masses: H = 1.0078, C = 12.0000, N = 14.0031, O = 15.9949.
   A compound has a precise relative molecular mass of 46.0054. Calculate the precise relative molecular masses of C₂H₆O and CH₂O₂ and decide which is the molecular formula of the compound.2 marks
3. A pharmaceutical analyst finds that a compound containing only carbon, hydrogen and oxygen has a precise relative molecular mass of 88.0524 by high-resolution mass spectrometry. Precise relative atomic masses: H = 1.0078, C = 12.0000, O = 15.9949.
   The compound has a nominal mass of 88. Calculate the precise relative molecular masses of C₄H₈O₂ and C₅H₁₂O and deduce the molecular formula of the compound.3 marks