DP Chemistry (last assessment 2024)

Question 18N.3.hl.TZ0.c

Date	November 2018	Marks available	[Maximum mark: 2]	Reference code	18N.3.hl.TZ0.c
Level	hl	Paper	3	Time zone	TZ0
Command term	Determine	Question number	c	Adapted from	N/A

[Maximum mark: 2]

18N.3.hl.TZ0.c

The presence of very small amounts of lead in calcium-based antacids can be determined using inductively coupled plasma-mass spectroscopy (ICP-MS).

Electrolysis is used to obtain lead from Pb²⁺ (aq) solution.

Determine the time, in hours, required to produce 0.0500 mol lead using a current (I) of 1.34 A. Use section 2 of the data booklet and the equation, charge (Q) = current (I) × time (t, in seconds).

[2]

Markscheme

«Faraday’s constant, F = 9.65 × 10⁴ C mol^‒1 and 1 A = 1 C s^–1»
Q «= 0.0500 mol × 2 × 96500 C mol^‒1» = 9650 «C» ✔

t « $= \frac{Q}{I} = \frac{{9650\,{\text{C}}}}{{1.34\,{\text{C}}\,{{\text{s}}^{-1}}}} \approx 7200\,{\text{s}}$ so $\frac{{7200\,{\text{s}}}}{{60 \times 60\,{\text{s}}\,{{\text{h}}^{-1}}}}$ » = 2.00 «hours» ✔

Award [2] for correct final answer.

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Options » A: Materials » A.2 Metals and inductively coupled plasma (ICP) spectroscopy

Options » A: Materials

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