DP Chemistry (last assessment 2024)

Question 20N.3.hl.TZ0.12a

Date	November 2020	Marks available	[Maximum mark: 2]	Reference code	20N.3.hl.TZ0.12a
Level	hl	Paper	3	Time zone	TZ0
Command term	Show	Question number	a	Adapted from	N/A

[Maximum mark: 2]

20N.3.hl.TZ0.12a

$1.57 %$ of the mass of a rock weighing $46.5 kg$ is uranium(IV) oxide, ${UO}_{2}$ . $99.28 %$ of the uranium atoms in the rock are uranium-238, ${}^{238}U$ .

(a)

Show that the mass of the ²³⁸U isotope in the rock is $0.639 kg$ .

[2]

Markscheme

$« \frac{mass %}{fraction of U in {UO}_{2}} = » \frac{238.03}{238.03 + 2 \times 16}$ / $0.881$ / $88.1 %$ ✔

$46.5 « kg » \times 0.0157 \times 0.881 \times 0.9928 « = 0.639 kg »$ ✔

Award [1 max] for omitting mass composition (giving $0.725 k g$ ).

M2 is for numerical setup, not for final value of $0.639 k g$ .

Examiners report

This question was generally well answered. Many candidates approached this question using amount, in mol, and converting to mass at the end. Some candidates omitted the mass composition however, resulting in a mass of 0.725 kg, which yielded [1 max].

Syllabus sections

Core

Core » Topic 1: Stoichiometric relationships » 1.3 Reacting masses and volumes

Core » Topic 1: Stoichiometric relationships

Question 20N.3.hl.TZ0.12a

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