DP Chemistry (last assessment 2024)

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Question 19M.3.hl.TZ2.27a

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Date May 2019 Marks available [Maximum mark: 3] Reference code 19M.3.hl.TZ2.27a
Level hl Paper 3 Time zone TZ2
Command term Describe Question number a Adapted from N/A
a.
[Maximum mark: 3]
19M.3.hl.TZ2.27a

The presence of alcohol in the breath can be detected using a breathalyzer.

(a)

Describe how a fuel cell breathalyser works.

[3]

Markscheme

Any three of:
ethanol «in breath» is oxidized «to ethanoic acid»  [✔]
electrons pass through external circuit/meter [✔]
«to cathode where» O2 is reduced [✔]
current is proportional to alcohol concentration [✔]

 

Note: Accept equations for oxidation of ethanol or reduction of oxygen.

Examiners report

While many scored the first marking point, full marks were rarely seen. Many candidates mixed up this and a dichromate breathalyser.

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