DP Chemistry (last assessment 2024)

Question 22N.2.sl.TZ0.1e.ii

Date	November 2022	Marks available	[Maximum mark: 2]	Reference code	22N.2.sl.TZ0.1e.ii
Level	sl	Paper	2	Time zone	TZ0
Command term	Calculate, Determine	Question number	e.ii	Adapted from	N/A

e.ii.

[Maximum mark: 2]

22N.2.sl.TZ0.1e.ii

Ammonium nitrate, NH₄NO₃, is used as a high nitrogen fertilizer.

Cold packs contain ammonium nitrate and water separated by a membrane.

(e.ii)

The change in enthalpy when ammonium nitrate dissolves in water is 25.69 kJ mol⁻¹. Determine the mass of ammonium nitrate in the cold pack using your answer obtained in (e)(i) and section 6 of the data booklet.

If you did not obtain an answer in (e)(i), use 3.11 × 10³ J, although this is not the correct answer.

[2]

Markscheme

« $2.58 \times 10^{3} J \times \frac{1 k J}{1000 J} \times \frac{1 m o l}{25.69 k J} =$ » $0.100$ «mol» ✔

« $0.100$ mol $\times 80.06$ g mol⁻¹ =» 8.01 «g» ✔

Award [2] for the correct final answer.

Accept range of $8.00 - 8.10$ «g».

If $3.11 \times 10^{3}$ J used then answer is $9.69$ «g».

Examiners report

The question was less familiar, however, almost half of the candidates obtained the mass of ammonium nitrate in the pack. This question discriminated well between high achieving and low achieving candidates.

Syllabus sections

Core

Core » Topic 5: Energetics/thermochemistry » 5.1 Measuring energy changes

Core » Topic 5: Energetics/thermochemistry

Question 22N.2.sl.TZ0.1e.ii

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