DP Chemistry (last assessment 2024)

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Question 20N.3.hl.TZ0.d

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Date November 2020 Marks available [Maximum mark: 1] Reference code 20N.3.hl.TZ0.d
Level hl Paper 3 Time zone TZ0
Command term Comment Question number d Adapted from N/A
d.
[Maximum mark: 1]
20N.3.hl.TZ0.d

Aspirin is formed by reacting salicylic acid with ethanoic anhydride. The structure of aspirin is given in section 37 of the data booklet.

Comment on the risk of overdose when taking aspirin as an analgesic, referring to the following values, for a person weighing 70 kg:

Minimum therapeutic dose =0.5 g

Estimated minimum lethal dose =15 g

[1]

Markscheme

low/medium risk «of overdosing» AND «estimated» lethal dose is 30 times/much larger than therapeutic dose OR
30 times the dose results in chance of dying ✔

Accept “30 and low/medium risk due to large therapeutic index”.
Do not accept “low/medium risk AND large therapeutic window”.
Do not accept “30 times the dose” alone for the mark.

Examiners report

Few scored this mark. Most knew the overdose risk was low but referred to a large therapeutic window instead of a large therapeutic index. Many also did not quantify the therapeutic index by working out that the estimated lethal dose is actually 30 times the therapeutic dose.

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