DP Chemistry (last assessment 2024)

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Question 20N.2.sl.TZ0.a(v)

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Date November 2020 Marks available [Maximum mark: 2] Reference code 20N.2.sl.TZ0.a(v)
Level sl Paper 2 Time zone TZ0
Command term Explain Question number a(v) Adapted from N/A
a(v).
[Maximum mark: 2]
20N.2.sl.TZ0.a(v)

Chlorine undergoes many reactions.

Explain the presence and relative abundance of the peak at m/z=74.

[2]

Markscheme

«diatomic» molecule composed of «two» chlorine-37 atoms ✔

chlorine-37 is the least abundant «isotope»
OR
low probability of two Cl37 «isotopes» occurring in a molecule ✔

Examiners report

This was the lowest scoring question on the paper, that was also left blank by 10% of the candidates. About 20% of the candidates identified the peak at m/z = 74 to be due to a molecule made up of two 37Cl atoms. And only very few candidates commented that the low abundance of the peak was due to the low abundance of the 37Cl isotope. A common incorrect answer was that chlorine has an isotope of mass number 74.

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