Grade 13 — Term 2

Electrochemistry

What you must know

• Thermodynamic spontaneity relation: ΔG° = -nFE°cell. A positive E°cell indicates a spontaneous cell reaction under standard conditions.
• Cell shorthand notation: Anode (oxidation) | electrolyte || electrolyte | Cathode (reduction); double vertical line represents the salt bridge.
• Salt bridge role: maintains electrical neutrality by ion migration (e.g. KNO₃ or KCl) without allowing bulk solution mixing.

Try one question

For the standard galvanic cell: Zn(s) | Zn²⁺(aq, 1.0 mol dm⁻³) || Cu²⁺(aq, 1.0 mol dm⁻³) | Cu(s), given E°(Zn²⁺/Zn) = -0.76 V and E°(Cu²⁺/Cu) = +0.34 V, what is the standard electromotive force (E°_cell) and the spontaneous oxidation reaction?

1. A. -1.10 V with reduction of Zn²⁺(aq) + 2e⁻ → Zn(s) at the cathode
2. B. +1.10 V with oxidation of Zn(s) → Zn²⁺(aq) + 2e⁻ at the anode
3. C. +0.42 V with reduction of Cu²⁺(aq) + 2e⁻ → Cu(s) at the anode
4. D. +1.10 V with oxidation of Cu(s) → Cu²⁺(aq) + 2e⁻ at the anode

Show the answer

Answer: B. +1.10 V with oxidation of Zn(s) → Zn²⁺(aq) + 2e⁻ at the anode. Zinc has a more negative standard reduction potential (-0.76 V vs +0.34 V for Cu), meaning Zn oxidizes more readily than Cu. Thus, Zn acts as the anode: Zn(s) → Zn²⁺ + 2e⁻ (oxidation). Cu²⁺ acts as the cathode: Cu²⁺ + 2e⁻ → Cu(s) (reduction). E°_cell = E°_cathode - E°_anode = +0.34 V - (-0.76 V) = +1.10 V.

A model question written by Idasara on the exam pattern. It is not from a past paper.