Chemistry a2

[Xtremite]

Hi guys again,

So here's my question. It's related to mass spectra.

Question 2, part (c) of this paper: http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s07_qp_4.pdf

Mark scheme: http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s07_qp_4.pdf

The examiner report states: Many candidates seem not to have been taught this new section of the Core syllabus, namely the
interpretation of mass spectra in terms of molecular fragments.

How do I do this?

 

[Nibz]

There isn't much to this question other than trying to figure out how you could use atoms/elements in the original compound (ammonium nitrate) to make fragments that would add up to each of the peaks in the question. My initial hunch was that A and B would be NH3 and NO2, but those don't balance (I mean even if only one mole of these gases is made, the Mr of NH4NO3 - 62 - is not equal to the combined Mr of both product gases - 17 + 46 = 63, so this must be dismissed.) Instead, chose two gases that would separately make up the maximum m/e values, 18 and 44 using onlu the elements provided. These would be H2O (18) and N2O (44). They even balance! 18 + 44 = 62. Then you can break these up to make each of the smaller values: O+ = 16, OH+ = 17. And N+ = 14, O+ = 16, N2+ = 28, NO+ = 30. (They'll all have positive signs 'cause the spectrometer only deals with positive ions.)

Here's the answer to your question. Thanks to abcde.
Topic moved to A-level section. Kindly post your doubts in the A-level sub-forum and not in IGCSE , here's one thread: https://www.xtremepapers.com/community/threads/chemistry-paper-4-theory-doubts-d.25868/