Which half-cell is on the left of a cell diagram?

The one where oxidation occurs, the negative electrode.

What do | and ‖ mean in a cell diagram?

| is a phase boundary; ‖ is the salt bridge.

Write the cell diagram for Zn and Cu half-cells.

Zn(s) | Zn²⁺(aq) ‖ Cu²⁺(aq) | Cu(s)

Why is platinum used in a Fe³⁺|Fe²⁺ half-cell?

Both ions are in solution, so an inert conducting electrode is needed.

Do you multiply E° by the number of electrons in a balanced equation?

No. E° is independent of the amount of substance.

Why must conditions be controlled when measuring E°?

Electrode reactions are equilibria, so temperature, concentration and pressure shift their position and the potential.

What happens to E for Ag⁺|Ag if [Ag⁺] falls below 1.00 mol dm⁻³?

The equilibrium shifts left, so the electrode becomes less positive.

Why are E° values called standard reduction potentials?

Every half-equation is written as a reduction: oxidised form + ne⁻ ⇌ reduced form.

What does a more negative E° say about the reduced form?

It is a stronger reducing agent.

What is the electrochemical series?

Half-equations listed in order of E°, from strongest reducing agents to strongest oxidising agents.

Which direction do electrons flow in the external circuit?

From the negative electrode (oxidation) to the positive electrode (reduction).

Electrochemical cells and cell potentialsEdexcel International A Level Chemistry: Flashcards

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How do you calculate E°cell?

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How do you calculate E°cell?: E°cell = E°(positive/right electrode) − E°(negative/left electrode).
Which half-cell is on the left of a cell diagram?: The one where oxidation occurs, the negative electrode.
What do | and ‖ mean in a cell diagram?: | is a phase boundary; ‖ is the salt bridge.
Write the cell diagram for Zn and Cu half-cells.: Zn(s) | Zn²⁺(aq) ‖ Cu²⁺(aq) | Cu(s)
Why is platinum used in a Fe³⁺|Fe²⁺ half-cell?: Both ions are in solution, so an inert conducting electrode is needed.
Calculate E°cell for Zn²⁺|Zn (−0.76 V) and Cu²⁺|Cu (+0.34 V).: +0.34 − (−0.76) = +1.10 V.
Do you multiply E° by the number of electrons in a balanced equation?: No. E° is independent of the amount of substance.
Why must conditions be controlled when measuring E°?: Electrode reactions are equilibria, so temperature, concentration and pressure shift their position and the potential.
What happens to E for Ag⁺|Ag if [Ag⁺] falls below 1.00 mol dm⁻³?: The equilibrium shifts left, so the electrode becomes less positive.
Why are E° values called standard reduction potentials?: Every half-equation is written as a reduction: oxidised form + ne⁻ ⇌ reduced form.
What does a more negative E° say about the reduced form?: It is a stronger reducing agent.
What is the electrochemical series?: Half-equations listed in order of E°, from strongest reducing agents to strongest oxidising agents.
Which direction do electrons flow in the external circuit?: From the negative electrode (oxidation) to the positive electrode (reduction).

Exam questions on Electrochemical cells and cell potentials

A cell is built from a zinc half-cell and a copper half-cell under standard conditions. Standard electrode potentials: Zn²⁺(aq)|Zn(s) −0.76 V; Cu²⁺(aq)|Cu(s) +0.34 V.
Write the overall ionic equation for the cell reaction, including state symbols, and state the direction of electron flow in the external circuit.2 marks
A student builds a cell from a silver half-cell and an iron(III)/iron(II) half-cell, both under standard conditions. Standard electrode potentials: Ag⁺(aq)|Ag(s) +0.80 V; Fe³⁺(aq)|Fe²⁺(aq) +0.77 V.
The student repeats the experiment using 0.50 mol dm⁻³ silver nitrate solution in the silver half-cell. Explain why the cell emf would no longer be the standard value of E°cell.2 marks
A data table gives these standard electrode potentials: Mg²⁺(aq)|Mg(s) −2.37 V; Ni²⁺(aq)|Ni(s) −0.25 V; Ag⁺(aq)|Ag(s) +0.80 V; Cl₂(g)|Cl⁻(aq) +1.36 V.
A cell is made from the Mg²⁺|Mg and Ni²⁺|Ni half-cells under standard conditions. Write the cell diagram and calculate E°cell.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).