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The reaction of ethene with aqueous potassium manganate (VII), KMnO4, produces ethane-1,2-diol, CH2OHCH2OH.
Data: molar mass of ethane- 1,2 diol = 62 g mol-1
In an experiment, KMno4 containing only 18O reacts with ethene.

Suggest how the mass spectrum of ethane- 1,2 diol data could be used to decide whether the oxygen atoms in ethane- 1,2 diol came from manganate (VII) ion, water, or a combination of the two.

Reply 1

booklover1313

Original post by Jab/Soledad

So normal water contains oxygen with a Mr of 16, whilst the KMnO4 contains a heavy isotope of Oxygen, 18O (with 2 more neutrons). The mass spectrum will show a different level of deflection based on the mass (and charge) of the molecule. If the oxygen came from the H20, the ethane-1,2 diol would have a lower mass than if the oxygen came from the KMnO4. So you could compare ethene-1,2 diol that was made with 'normal KMnO4' and see if its deflected more. If so, that implies it is lighter than the one made in the question, so the one in the question must contain the heavier isotope of Oxygen, which came from the KMnO4. If there is no difference, then the oxygens must weigh the same, so the oxygen came from the H20.