A-LevelChemistryElectrochemistry9701/43 · May/June 2024 · Q413 Marks

Define standard electrode potential, Eº, including a description of standard conditions.

(a)Define standard electrode potential, Eº, including a description of standard conditions.[2]
(b)(i)An electrochemical cell is set up to measure Eº of the Ag+(aq)/Ag(s) electrode. Draw a labelled diagram of this electrochemical cell. Include all necessary substances. It is not necessary to state conditions used.[3]
(b)(ii)A separate electrochemical cell is set up using a lower concentration of Ag+(aq) than that used in (b)(i). Suggest how the electrode potential, E, for the Ag+(aq)/Ag(s) electrode would change from its Eº value. Explain your answer.[1]
(c)Define enthalpy change of solution, ΔHºsol.[1]
(d)(i)Some relevant energy changes for AgNO3 are shown in Table 4.1. [Table 4.1] Complete the energy cycle in Fig. 4.1 to show the relationship between the lattice energy, ΔHºlatt, of AgNO3(s) and the energy changes shown in Table 4.1. Include state symbols for all the species. [Figure 4.1][2]
(d)(ii)Calculate the lattice energy, ΔHºlatt, of AgNO3(s). ΔHºlatt = kJ mol-1[1]
(e)Suggest the trend in the magnitude of the lattice energies of the metal nitrates, NaNO3(s), Mg(NO3)2(s) and RbNO3(s). Explain your answer. most exothermic least exothermic[3]

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Mark scheme

Marking points from the official mark scheme (May/June 2024). The mark or mark type is shown in brackets.

[2] M1 voltage of a half-cell compared to SHE; M2 1 mol dm-3 AND 101 kPa AND 298 K
[3] [Diagram showing a standard hydrogen electrode (SHE) connected via a salt bridge to a silver electrode. SHE: Pt electrode, H2(g) bubbling, H+(aq) solution. Silver electrode: Ag(s) rod, Ag+(aq) solution. Voltmeter connecting the two electrodes, and a salt bridge connecting the two solutions.] M1 Pt; M2 gas delivery system H2; M3 voltmeter; Ag; Ag+; H+; salt bridge; wiring Pt to V to Ag
[1] E value would be more negative AND shifts Ag+ (+ e-) ⇒ Ag to the left
[1] enthalpy change when one mole of a solute dissolves in water
[2] [Energy cycle diagram: AgNO3(s) at the bottom. An arrow upwards from AgNO3(s) to Ag+(g) + NO3-(g) (labeled ΔHlatt). Two arrows downwards from Ag+(g) + NO3-(g) to Ag+(aq) + NO3-(aq) (labeled ΔHhyd(Ag+) and ΔHhyd(NO3-)). An arrow downwards from AgNO3(s) to Ag+(aq) + NO3-(aq) (labeled ΔHsol). All species must have correct state symbols (s, g, aq).] M1 two arrows in blue; M2 correct species in red with all state symbols
[1] ΔHlatt = -811.6 (kJ mol-1)
[3] M1 Mg(NO3)2(s), NaNO3(s), RbNO3(s); M2 Mg2+ has a higher charge than Na+ OR Rb+ AND Na+ has a smaller radius than Rb+; M3 correct statement relating magnitude of LE to attraction between ions OR strength of ionic bonds

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