A Level Chemistry OCR A
Chapter 23 Redox and electrode potentials
Exam Booklet
, 1(a). Electrochemical cells contain two redox systems, one providing electrons and the other accepting electrons. The
tendency to lose or gain electrons is measured using values called standard electrode potentials.
Define the term standard electrode potential.
Include all standard conditions in your answer.
[2]
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, (b). The table below shows two redox systems and their standard electrode potentials, EƟ.
Redox system EƟ / V
Cu2+(aq) + 2e– ⇌ Cu(s) +0.34
+ –
Ag (aq) + e ⇌ Ag(s) +0.80
A standard Cu2+(aq) / Cu(s) half-cell is connected to a standard Ag+(aq) / Ag(s) half-cell. The potential of the cell
is measured.
Water is then added to the Cu2+(aq) / Cu(s) half-cell. This changes the position of equilibrium in the half-cell. The
cell potential increases.
(i) Write down the equation for the overall cell reaction.
[1]
(ii) Explain, in terms of equilibrium, why the cell potential increases.
[3]
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, (c). Aluminium—oxygen cells are being investigated for powering vehicles.
The reactions at each electrode are shown below.
(i) The standard electrode potential for the O2 / OH– redox system is +0.40 V.
The standard cell potential of an aluminium—oxygen cell is 2.71 V.
What is the standard electrode potential of the aluminium redox system in this cell?
standard electrode potential = _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ V [1]
(ii) Construct the overall cell equation for an aluminium—oxygen cell.
[2]
© OCR 2020. You may photocopy this page. 3 of 115 Created in ExamBuilder
Chapter 23 Redox and electrode potentials
Exam Booklet
, 1(a). Electrochemical cells contain two redox systems, one providing electrons and the other accepting electrons. The
tendency to lose or gain electrons is measured using values called standard electrode potentials.
Define the term standard electrode potential.
Include all standard conditions in your answer.
[2]
© OCR 2020. You may photocopy this page. 1 of 115 Created in ExamBuilder
, (b). The table below shows two redox systems and their standard electrode potentials, EƟ.
Redox system EƟ / V
Cu2+(aq) + 2e– ⇌ Cu(s) +0.34
+ –
Ag (aq) + e ⇌ Ag(s) +0.80
A standard Cu2+(aq) / Cu(s) half-cell is connected to a standard Ag+(aq) / Ag(s) half-cell. The potential of the cell
is measured.
Water is then added to the Cu2+(aq) / Cu(s) half-cell. This changes the position of equilibrium in the half-cell. The
cell potential increases.
(i) Write down the equation for the overall cell reaction.
[1]
(ii) Explain, in terms of equilibrium, why the cell potential increases.
[3]
© OCR 2020. You may photocopy this page. 2 of 115 Created in ExamBuilder
, (c). Aluminium—oxygen cells are being investigated for powering vehicles.
The reactions at each electrode are shown below.
(i) The standard electrode potential for the O2 / OH– redox system is +0.40 V.
The standard cell potential of an aluminium—oxygen cell is 2.71 V.
What is the standard electrode potential of the aluminium redox system in this cell?
standard electrode potential = _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ V [1]
(ii) Construct the overall cell equation for an aluminium—oxygen cell.
[2]
© OCR 2020. You may photocopy this page. 3 of 115 Created in ExamBuilder
