8 exam-style question sets on Electrochemistry (Paper 2), each with a hint and a fully worked answer. The app holds 40 questions on this section in total, including variants of every set below, and lets you mark yourself part by part.
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Question 1
Zinc granules react with dilute sulfuric acid at 25 °C according to the following balanced equation:
Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g)
Separately, the galvanic cell shown in the diagram consists of a Ni | Ni²⁺ half-cell and an Ag | Ag⁺ half-cell, connected by a salt bridge, operating under standard conditions.
- aUse oxidation numbers of EACH of the reactants to explain why the reaction of zinc with dilute sulfuric acid is a redox reaction. (2)
- bWrite down the FORMULA of the oxidising agent in this reaction. (1)
- cWhen copper granules are added to dilute sulfuric acid at 25 °C, NO reaction is observed. Explain this observation by referring to the relative strengths of the REDUCING agents involved. (2)
- dWill bromine water oxidise iodide ions in a potassium iodide solution at 25 °C? Choose from YES or NO. Explain the answer by referring to the relative strengths of the OXIDISING agents involved. (3)
- eWrite down the balanced net ionic equation for the reaction that takes place in the Ni–Ag galvanic cell. (3)
- fThe Ni half-cell is now replaced by a Mg | Mg²⁺ half-cell (a STRONGER reducing agent) while the same Ag half-cell is used under the same conditions. How will this affect the initial emf of the cell? Choose from INCREASES, DECREASES or NO EFFECT. (1)
This question has a diagram, shown in the app.
Hint
Track how each oxidation number changes, then use the table of standard reduction potentials to compare agent strengths.
Worked answer
a) Zn: oxidation number increases from 0 to +2 (Zn is oxidised). ✓ H: oxidation number decreases from +1 to 0 (hydrogen is reduced). ✓ Because oxidation numbers change (electrons are transferred), this is a redox reaction.
b) H₂SO₄ ✓ (accept H⁺(aq) / H₃O⁺(aq))
c) Copper is a WEAKER reducing agent than H₂ ✓, so Cu cannot donate electrons to H⁺ ions / cannot be oxidised by the dilute acid ✓ – hence no reaction.
d) YES ✓ Br₂ is a STRONGER oxidising agent than I₂ ✓, so Br₂ accepts electrons from the I⁻ ions and oxidises them to I₂. ✓
e) Oxidation: Ni → Ni²⁺ + 2e⁻; Reduction: Ag⁺ + e⁻ → Ag (×2)
Net ionic equation: Ni(s) + 2Ag⁺(aq) → Ni²⁺(aq) + 2Ag(s) ✓✓✓ (correct reactants and products ✓ atoms balanced ✓ charge balanced ✓)
f) INCREASES ✓ (E°cell = E°cathode − E°anode rises from 0,80 − (−0,27) = 1,07 V to 0,80 − (−2,36) = 3,16 V.)
Modelled on Nov 2024 Paper 2, Question 8 — same skills, new scenario.
Question 2
A copper strip is placed in a beaker containing a 1 mol·dm⁻³ nickel(II) sulfate solution at 25 °C. A learner claims that the following reaction will take place:
Cu(s) + Ni²⁺(aq) → Cu²⁺(aq) + Ni(s)
Separately, the galvanic cell shown in the diagram is set up with a magnesium electrode in a 1 mol·dm⁻³ Mg(NO₃)₂ solution and a silver electrode in a 1 mol·dm⁻³ AgNO₃ solution at 25 °C, connected by a salt bridge.
- aBy means of a calculation of the cell potential, determine whether the learner's claimed reaction is SPONTANEOUS or NON-SPONTANEOUS. (5)
- bState TWO functions of the salt bridge in the galvanic cell. (2)
- cWrite down the cell notation for the galvanic cell. (3)
- dCalculate the initial emf of the galvanic cell under standard conditions. (4)
This question has a diagram, shown in the app.
Hint
For the claimed reaction, take the reduced species as the cathode in E°cell = E°cathode − E°anode; a negative E°cell means non-spontaneous.
Worked answer
a) In the claimed reaction Ni²⁺ would be reduced (cathode) and Cu oxidised (anode):
E°cell = E°cathode − E°anode ✓ = (−0,27) − (+0,34) ✓✓ = −0,61 V ✓
Since E°cell < 0, the reaction is NON-SPONTANEOUS ✓ (nothing happens to the copper strip).
b) The salt bridge completes the circuit by allowing ions to move between the two half-cells ✓ and it maintains electrical neutrality in the electrolyte solutions ✓.
c) Mg(s) | Mg²⁺(aq) || Ag⁺(aq) | Ag(s) ✓✓✓ (anode half-cell on the left ✓ salt bridge symbol ✓ cathode half-cell on the right ✓)
d) E°cell = E°cathode − E°anode ✓ = 0,80 − (−2,36) ✓✓ = 3,16 V ✓
Modelled on Nov 2024 Paper 2, Question 9 — same skills, new scenario.
Question 3
A standard galvanic cell is set up with a zinc electrode in a Zn²⁺(aq) solution and a copper electrode in a Cu²⁺(aq) solution, as shown in the diagram.
Which ONE of the following combinations of the metal used as CATHODE and the direction of ELECTRON FLOW in the external circuit is CORRECT?
This question has a diagram, shown in the app.
Hint
Compare E° values: the electrode of the half-cell with the higher reduction potential is the cathode.
Worked answer
B. E°(Cu²⁺/Cu) = +0,34 V is higher than E°(Zn²⁺/Zn) = −0,76 V, so reduction occurs at the copper electrode (cathode) while zinc is oxidised at the anode; electrons therefore flow from Zn to Cu in the external circuit. A is wrong: Zn is the anode, not the cathode. C is wrong on both counts: the cathode is Cu and electrons do not flow towards the anode. D correctly names Cu as cathode but reverses the electron flow — electrons leave the anode (Zn), they do not leave the cathode.
Question 4
An electrolytic cell is used to electroplate a steel spoon with silver. The spoon and a pure silver rod are dipped into a silver nitrate solution and connected to a battery.
Consider the following statements:
(i) The spoon must be connected as the cathode.
(ii) The mass of the silver rod decreases during electroplating.
(iii) The concentration of Ag⁺(aq) in the solution decreases steadily during electroplating.
Which of the statements above are TRUE?
Hint
The object to be plated must be where reduction happens; the pure-metal anode replenishes the ions.
Worked answer
A. (i) is true: Ag⁺ ions must be reduced onto the spoon (Ag⁺ + e⁻ → Ag), so the spoon is the cathode. (ii) is true: the silver rod is the anode and is oxidised (Ag → Ag⁺ + e⁻), so it loses mass. (iii) is false: the Ag⁺ removed at the spoon is replaced by Ag⁺ released at the silver anode, so the concentration stays approximately constant. B, C and D are wrong because each includes the false statement (iii).
Question 5
The galvanic cell shown in the diagram operates under STANDARD conditions. A zinc electrode dips into a zinc nitrate solution and a copper electrode dips into a copper(II) nitrate solution. The two half-cells are connected by a salt bridge, and a voltmeter is connected across the electrodes.
- aWrite down TWO conditions that must apply for this cell to operate under standard conditions. (2)
- bWhich electrode, Zn or Cu, is the anode? Give a reason for the answer by referring to the relative strengths of the reducing agents. (2)
- cWrite down the half-reaction that takes place at the cathode. (2)
- dWrite down the cell notation for this cell. (3)
- eCalculate the initial reading on the voltmeter. (4)
This question has a diagram, shown in the app.
Hint
The metal that is the stronger reducing agent is oxidised at the anode. Use E°cell = E°cathode − E°anode with the standard reduction potentials.
Worked answer
a) Temperature of 25 °C (298 K) ✓ and electrolyte concentrations of 1 mol·dm⁻³ ✓ (pressure 101,3 kPa also accepted as one condition).
b) Zn ✓. Zinc is a STRONGER REDUCING AGENT than copper, so zinc is oxidised (loses electrons) at the anode. ✓
c) Cu²⁺(aq) + 2e⁻ → Cu(s) ✓✓
d) Zn(s) | Zn²⁺(aq) || Cu²⁺(aq) | Cu(s) ✓✓✓ (anode on the left ✓ salt bridge symbol ✓ correct formulae with phases ✓; concentrations of 1 mol·dm⁻³ may be shown)
e) ✓
✓✓
V ✓
Modelled on Nov 2025 Paper 2, Question 8 — same skills, new scenario.
Question 6
The cell in the diagram is used to refine silver. Electrode P is a bar of impure silver that contains COPPER as the only impurity. Electrode Q is a thin sheet of pure silver. The electrolyte is a silver nitrate solution, AgNO₃(aq).
After the switch has been closed for T hours:
- 0,12 mol of silver has been deposited on electrode Q
- the amount of Ag⁺(aq) ions in the electrolyte has DECREASED by 0,02 mol
Take M(Ag) = 108 g·mol⁻¹.
- aWrite down the energy conversion that takes place in this cell. (1)
- bWhich electrode, P or Q, is connected to the POSITIVE terminal of the battery? (1)
- cWrite down the half-reaction that takes place at electrode Q. (2)
- dHow will the concentration of Cu²⁺(aq) ions in the electrolyte change during the refining process? Choose from INCREASES, DECREASES or REMAINS THE SAME. Explain the answer by referring to the relative strengths of the oxidising agents present. (3)
- eCalculate the mass of silver that dissolved from electrode P during the T hours. (4)
This question has a diagram, shown in the app.
Hint
The impure metal must be the anode. Silver deposited at Q comes partly from silver dissolving at P and partly from the drop in Ag⁺ in the electrolyte.
Worked answer
a) Electrical energy is converted into chemical energy. ✓
b) P ✓ (the impure silver must be the anode, where oxidation occurs).
c) Ag⁺(aq) + e⁻ → Ag(s) ✓✓ (reduction at the cathode Q)
d) INCREASES ✓. The copper impurity is oxidised at the anode and goes into solution as Cu²⁺. ✓ Ag⁺ is a STRONGER OXIDISING AGENT than Cu²⁺, so only Ag⁺ ions are reduced at the cathode — the Cu²⁺ ions stay in solution and accumulate. ✓
e) n(Ag deposited) = 0,12 mol, but the electrolyte supplied only 0,02 mol, so:
mol ✓✓
✓ g ✓
Modelled on Nov 2025 Paper 2, Question 9 — same skills, new scenario.
Question 7
A standard galvanic cell is set up using Cu(s)|Cu²⁺(aq) and Ag(s)|Ag⁺(aq) half-cells.
E°(Cu²⁺/Cu) = +0,34 V; E°(Ag⁺/Ag) = +0,80 V
Which ONE of the following statements about this cell is CORRECT?
This question has a diagram, shown in the app.
Hint
The half-cell with the higher E° undergoes reduction.
Worked answer
B. E°(Ag⁺/Ag) > E°(Cu²⁺/Cu), so Ag⁺ is reduced at the silver electrode (the cathode) while copper is oxidised at the anode. A: copper is the anode. C: Cu²⁺ is PRODUCED by oxidation, not reduced. D: silver is deposited, not oxidised.
Modelled on Nov 2025 Paper 2, Question 1.9 — same skills, new scenario.
Question 8
A steel spoon is electroplated with nickel using a nickel rod and a NiSO₄(aq) electrolyte, as shown in the diagram. Which ONE of the following gives the correct ANODE together with the correct REACTION AT THE CATHODE?
This question has a diagram, shown in the app.
Hint
In electroplating the object is the cathode; the plating metal is the anode.
Worked answer
D. The spoon to be plated is the cathode, where Ni²⁺(aq) + 2e⁻ → Ni(s) deposits nickel; the nickel rod is the anode and dissolves to replenish the Ni²⁺ ions. A and C: the spoon cannot be the anode. B: gives an OXIDATION half-reaction as the cathode reaction.
Modelled on Nov 2025 Paper 2, Question 1.10 — same skills, new scenario.