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The molecules ethanol and nitrogen dioxide have the same molar mass (M = 46 g mol⁻¹) - VCE - SSCE Chemistry - Question 3 - 2010 - Paper 1
Question 3
The molecules ethanol and nitrogen dioxide have the same molar mass (M = 46 g mol⁻¹). They can be easily distinguished by mass spectrometry. The mass spectra of the... show full transcript
Worked Solution & Example Answer:The molecules ethanol and nitrogen dioxide have the same molar mass (M = 46 g mol⁻¹) - VCE - SSCE Chemistry - Question 3 - 2010 - Paper 1
Step 1
a. Write an equation showing how either an ethanol molecule or a nitrogen dioxide molecule becomes ionised in the mass spectrometer.
Answer
An ethanol molecule, C₂H₅OH, can become ionised as follows:
This reaction shows the interaction of an ethanol molecule with an electron, resulting in the formation of a positively charged ion and the release of two electrons.
Step 2
b. Which mass spectrum cannot be that of nitrogen dioxide? What evidence does the mass spectrum provide to support your answer?
Answer
The mass spectrum that cannot be that of nitrogen dioxide is Spectrum A. The presence of a prominent peak at m/z 30 indicates a molecular species that could correspond to an ethanol fragment, since nitrogen dioxide (NO₂) does not fragment to produce a peak at this m/z ratio. The peak pattern also suggests different fragmentation behavior consistent with ethanol rather than nitrogen dioxide.
Step 3