DP Chemistry (last assessment 2024)

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

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Date November 2022 Marks available [Maximum mark: 3] Reference code 22N.2.sl.TZ0.1e.iii
Level sl Paper 2 Time zone TZ0
Command term Calculate Question number e.iii Adapted from N/A
e.iii.
[Maximum mark: 3]
22N.2.sl.TZ0.1e.iii

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

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

(e.iii)

The absolute uncertainty in mass of the contents of the cold pack is ±0.01 g and in each temperature reading is ±0.2 °C. Using your answer in (e)(ii), calculate the absolute uncertainty in the mass of ammonium nitrate in the cold pack.

If you did not obtain an answer in (e)(ii), use 6.55 g, although this is not the correct answer.

[3]

Markscheme

«fractional / % uncertainty in ΔT =» 0.424.4 / 0.02 / 2«%» ✔


«fractional / % uncertainty in m =» 0.0125.32 / 0.0004 / 0.04«%»

OR

fractional / % uncertainty in m is much smaller than uncertainty in ΔT ✔


«2% x 8.01 g =» 0.2 «g» ✔

 

Award [3] for correct final answer.

Accept range of 0.1 g – 0.2 «g».

If 6.55 g used then the answer is 0.1 «g».

Examiners report

This question discriminated well between high achieving and low achieving candidates. Only about a fifth of the candidates propagated the uncertainties correctly throughout the calculation. Some candidates only obtained the first mark for the fractional/percentage uncertainty in the change in temperature.

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