CAIE A Level Chemistry 9701 · Analytical techniques
A student records the mass spectrum of a volatile organic compound, X, which contains only carbon, hydrogen and bromine. The molecular ion peak, M+, appears at m/e = 122, with a relative abundance of 50. A peak at m/e = 124 has a relative abundance of 48. The base peak is at m/e = 43.
Explain what these data show about the molecular mass of X, the number of bromine atoms in one molecule of X, and the identity of the ion responsible for the base peak.
4 marks, so the mark scheme is looking for about 4 separate creditworthy points. Making the same point twice in different words earns it once.
Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.
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