DP Chemistry (first assessment 2025)

Question 19M.2.HL.TZ2.19b

Date	May 2019	Marks available	[Maximum mark: 2]	Reference code	19M.2.HL.TZ2.19b
Level	HL	Paper	2	Time zone	TZ2
Command term	Determine	Question number	b	Adapted from	N/A

[Maximum mark: 2]

19M.2.HL.TZ2.19b

(b)

The cell potential for the spontaneous reaction when standard magnesium and silver half-cells are connected is +3.17 V.

Determine the cell potential at 298 K when:

[Mg²⁺] = 0.0500 mol dm⁻³
[Ag⁺] = 0.100 mol dm⁻³

Use sections 1 and 2 of the data booklet.

[2]

Markscheme

«E = Eᶱ $\frac{{RT}}{{nF}}$ × lnQ»

lnQ = « $\frac{{[{\text{M}}{{\text{g}}^{2 + }}]}}{{{{[{\text{A}}{{\text{g}}^ + }]}^2}}} = \frac{{0.0500}}{{{{0.100}^2}}} = \ln 5.00 =$ » 1.61 [✔]

E = «3.17 V $- \frac{{8.31{\text{ J }}{{\text{K}}^{ - 1}}{\text{ mo}}{{\text{l}}^{ - 1}} \times 298{\text{ K}}}}{{2 \times 96500{\text{ J }}{{\text{V}}^{ - 1}}{\text{ mo}}{{\text{l}}^{ - 1}}}} \times \ln \frac{{0.0500}}{{{{0.100}^2}}} = 3.17 - 0.021 = +$ »3.15 «V» [✔]

Note: Award [2] for correct final answer.

Examiners report

The cell potential was correctly calculated by several candidates with some candidates managed an ECF mark for an error in the calculation. Unfortunately, the ln Q part was frequently wrong due to candidates forgetting to square the denominator.

Syllabus sections

Reactivity 3. What are the mechanisms of chemical change? » Reactivity 3.2—Electron transfer reactions » Reactivity 3.2.13—Standard cell potential, E⦵cell, can be calculated from standard electrode potentials. E⦵cell has a positive value for a spontaneous reaction. Predict whether a reaction is spontaneous in the forward or reverse direction from E⦵ data.

Question 19M.2.HL.TZ2.19b

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