DP Chemistry (last assessment 2024)

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Question 20N.3.sl.TZ0.5a(ii)

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Date November 2020 Marks available [Maximum mark: 2] Reference code 20N.3.sl.TZ0.5a(ii)
Level sl Paper 3 Time zone TZ0
Command term Deduce Question number a(ii) Adapted from N/A
a(ii).
[Maximum mark: 2]
20N.3.sl.TZ0.5a(ii)
(a(ii))

Proteins are polymers of amino acids.

The mixture is composed of glycine, Gly, and isoleucine, Ile. Their structures can be found in section 33 of the data booklet.

Deduce, referring to relative affinities and Rf, the identity of A1.

[2]

Markscheme

Ile AND larger Rf ✔

more soluble in non-polar solvent «mobile phase»
OR
not as attracted to polar «stationary» phase ✔


Only award M2 if Ile is identified in M1.

Examiners report

Not well answered. Many candidates referred to glycine even when they had obtained the correct Rf value in 5a. Answers referring to Molar mass and isoelectric point were quite common. Some candidates that identified Ile correctly lost the first mark as didn't make any reference to the Rf. There was a clear lack of understanding that the Rf value was related to polarity not molar mass.

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