DP Chemistry (last assessment 2024)

Question 18N.3.hl.TZ0.15c

Date	November 2018	Marks available	[Maximum mark: 2]	Reference code	18N.3.hl.TZ0.15c
Level	hl	Paper	3	Time zone	TZ0
Command term	Determine	Question number	c	Adapted from	N/A

[Maximum mark: 2]

18N.3.hl.TZ0.15c

Chemical energy from redox reactions can be used as a source of electrical energy.

(c)

A voltaic cell consists of a nickel electrode in 1.0 mol dm⁻³ Ni²⁺ (aq) solution and a cadmium electrode in a Cd²⁺ (aq) solution of unknown concentration.

Cd (s) + Ni²⁺ (aq) → Cd²⁺ (aq) + Ni (s) E^Θ_cell = 0.14 V

Determine the concentration of the Cd²⁺ (aq) solution if the cell voltage, E, is 0.19 V at 298 K. Use section 1 of the data booklet.

[2]

Markscheme

«E = E^Θ− $\left( {\frac{{RT}}{{nF}}} \right)$ lnQ»

$0.19 = 0.14 - \left( {\frac{{8.31 \times 298}}{{2 \times 96500}}} \right)\,{\text{ln}}\,\left( {\frac{{\left[ {{\text{C}}{{\text{d}}^{2 + }}} \right]}}{{\left[ 1 \right]}}} \right)$

0.05 = –0.01283 ln [Cd²⁺]

ln[Cd²⁺] = – 3.897 ✔

[Cd²⁺] = 0.020 «mol dm^–3» ✔

Award [2] for correct final answer.

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Options » C: Energy » C.6 Electrochemistry, rechargeable batteries and fuel cells (HL only)

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