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Relative Molecular Mass from a Mass Spectrometer

The structure of covalent compounds can be analysed by a mass spectrometer.The relative molecular mass of the element or compound can be obtained from the m/z ratio of the peaks.The mass spectrum of chlorine gas Cl2 is as follows:
The five peaks correspond to:
35Cl+  at m/z 35
37Cl+  at m/z 37

(35Cl 35Cl)+  at m/z 70
(35Cl 37Cl)+  at m/z 72
(37Cl 37Cl)+  at m/z 74
The molecular ion peak is the peak with the largest m/z ratio (ignoring any small M+1 peak) and the farthest to the right.Organic molecules sometimes have a very small M+1 peak due to the carbon-13 isotope.

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Specification: Edexcel Chemistry (8CH0), AS-level, Topic 1: Atomic Structure and the Periodic Table. Topic: Atomic Structure.

Key terms in this lesson

isotope
Atoms of the same element with the same number of protons but a different number of neutrons.

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