A-LevelChemistryElectrochemistry9701/41 · Oct/Nov 2025 · Q411 Marks

Define standard cell potential, E°cell. Include a description of standard conditions.

(a)Define standard cell potential, E°cell. Include a description of standard conditions.[2]
(b)(i)The Daniell cell is an electrochemical cell consisting of a Cu2+(aq)/Cu(s) electrode and a Zn2+(aq)/Zn(s) electrode. Draw a labelled diagram of this electrochemical cell. Include all necessary substances and relevant pieces of apparatus needed to measure the E°cell. It is not necessary to state the conditions used.[3]
(b)(ii)State the charge carriers that transfer current through the solutions and through the wire. the solutions _________________________ the wire _________________________ [1][1]
(b)(iii)The standard electrode potential, E°, for the Zn2+(aq)/Zn(s) electrode is –0.76 V. Water is added to a standard Zn2+(aq)/Zn(s) electrode. The new concentration of Zn2+(aq) is 0.25 mol dm−3. Use the Nernst equation to calculate the electrode potential, E, for this new Zn2+(aq)/Zn(s) electrode. E (Zn2+(aq)/Zn(s)) = _________________________ V [2][2]
(c)(i)An electrochemical cell consists of a ZnO/Zn electrode and a MnO2/Mn2O3 electrode in an alkaline electrolyte. The standard cell potential, E°cell, for this cell is +1.47V. The half-equation at each electrode when this cell is discharging is shown. Zn + 2OH¯ → ZnO + H2O + 2e¯ 2MnO2 + H2O + 2e¯ → Mn2O3 + 2OH¯ Use this information to determine the change in oxidation state of manganese when this cell is discharging. from _________________________ to _________________________ [1][1]
(c)(ii)Write the equation for the overall reaction that occurs when this cell is discharging.[1]
(c)(iii)The E° for the ZnO/Zn electrode is –1.28 V. Calculate the standard electrode potential, E°, for the MnO2/Mn2O3 electrode. E° (MnO2/Mn2O3) = _________________________ V [1][1]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2025). The mark or mark type is shown in brackets.

[1] M1: potential difference / voltage / EMF AND between two half-cells / two electrodes (in a cell)
[1] M2: (at concentration of) 1 mol dm-³ AND (pressure of) 1 atm/101 kPa AND (temperature of) 298K/25 °C
[1] M1: salt bridge labelled AND voltmeter/V AND wire to electrode and liquid level shown [complete circuit]
[1] M2: Cu(s) AND Cu2+(aq)
[1] M3: Zn(s) AND Zn2+(aq)
[1] ions AND electrons
[1] M1: Nernst equation E = E° + (0.059/z) log(Zn2+/Zn)
[1] M2: E = −0.76 + (0.059 / 2) log(0.25) = −0.778 V OR E = −0.76 + (8.31 × 298) / (96 500 × 2) In(0.25) = −0.778 V min 2sf
[1] (from) +4 (to) +3
[1] Zn + 2MnO2 → ZnO + Mn2O3
[1] Eº (MnO2/Mn2O3) = 1.47 – 1.28 = (+)0.19 V