Quick answer: Electrochemistry links redox reactions to electrical energy. This AP Chemistry worksheet on electrochemistry gives 20 problems from easy to hard: reading a lead-copper cell, magnesium and silver cell and will the iron nail react?. The worked answers are on a separate page, and the worksheet is a free printable PDF.
These 20 problems train the Unit 9 skills: labelling cells, calculating E°cell, linking voltage to ΔG° and K, applying the Nernst equation and using Faraday’s law for electrolysis.
They climb from recall through multi-step calculations to AP-style reasoning, suitable for AP Chemistry and first-year university courses. Use the table of potentials from the lesson when a value is not given.
Level: AP Chemistry · Curriculum: AP Chem Unit 9
Problem 1 Reading a lead-copper cell ★★★
Emma in Leeds builds the cell in the diagram. The voltmeter reads 0.47 V.2. State the direction of electron flow in the wire.
3. State which way nitrate ions move in the salt bridge.
Problem 2 Magnesium and silver cell ★★★
Kofi in Accra looks up E°(Mg²⁺/Mg) = −2.37 V and E°(Ag⁺/Ag) = +0.80 V.1. Decide which half-cell is the cathode.
2. Calculate E°cell.
3. Write the balanced overall equation.
Problem 3 Will the iron nail react? ★★★
Bilal in Lahore drops one iron nail into zinc sulfate solution and another into copper(II) sulfate solution. E°: Fe²⁺/Fe = −0.44 V, Zn²⁺/Zn = −0.76 V, Cu²⁺/Cu = +0.34 V.1. Calculate E° for Fe + Zn²⁺ → Fe²⁺ + Zn.
2. Calculate E° for Fe + Cu²⁺ → Fe²⁺ + Cu.
3. State which nail changes and describe what Bilal sees.
Problem 4 From current to electrons ★★★
Wanjiru in Nairobi passes 0.250 A through a cell for 2.00 h. Use F = 96 485 C/mol and NA = 6.022 × 10²³ mol⁻¹.1. Convert the time to seconds.
2. Calculate the charge in coulombs.
3. Calculate the moles of electrons.
4. Calculate the number of electrons.
Problem 5 Balancing aluminium and copper ★★★
Mei in Singapore pairs aluminium (E° = −1.66 V for Al³⁺/Al) with copper(II) (E° = +0.34 V).1. Write the oxidation and reduction half-reactions.
2. Multiply them so the electrons cancel and write the overall equation.
3. State n and calculate E°cell.
Problem 6 The hydrogen electrode ★★★
Aarav in Pune is told that all reduction potentials are measured against the standard hydrogen electrode (SHE).1. State the standard conditions of the SHE.
2. In a cell of SHE and Cu²⁺/Cu (E° = +0.34 V), identify the cathode.
3. Use E°(Zn²⁺/Zn) = −0.76 V to decide if zinc reacts with 1.0 mol/dm³ hydrochloric acid.
Problem 7 Electrolysis of molten potassium bromide ★★★
Diego in Texas electrolyses molten KBr with inert electrodes, as in the diagram.2. Write the half-reaction at each electrode.
3. Explain why a battery is needed.
Problem 8 Free energy of a copper-silver cell ★★★
Cu + 2Ag⁺ → Cu²⁺ + 2Ag. E°(Ag⁺/Ag) = +0.80 V, E°(Cu²⁺/Cu) = +0.34 V.1. Calculate E°cell.
2. State n.
3. Calculate ΔG° in kJ/mol.
Problem 9 Equilibrium constant for iron and copper ★★★
Fe + Cu²⁺ → Fe²⁺ + Cu. E°(Cu²⁺/Cu) = +0.34 V, E°(Fe²⁺/Fe) = −0.44 V. Use log K = nE°/0.0592.1. Calculate E°cell.
2. Calculate log K and K.
3. Comment on the extent of reaction.
Problem 10 Nickel plating a bracket ★★★
Chiamaka in Lagos nickel-plates a brass bracket with Ni²⁺ + 2e⁻ → Ni, using 1.50 A for 25.0 min. M(Ni) = 58.69 g/mol.1. Calculate the charge passed.
2. Calculate the moles of nickel deposited.
3. Calculate the mass of nickel.
Problem 11 How long to deposit silver? ★★★
Mei in Singapore wants 5.00 g of silver from Ag⁺ + e⁻ → Ag at a steady 2.00 A. M(Ag) = 107.87 g/mol.1. Calculate the moles of silver needed.
2. Calculate the charge required.
3. Calculate the time in minutes.
Problem 12 Cell voltage at other concentrations ★★★
A Zn/Cu cell at 25 °C has [Zn²⁺] = 0.050 mol/dm³ and [Cu²⁺] = 0.80 mol/dm³. E° = 1.10 V and n = 2.1. Write the expression for Q.
2. Calculate Q and log Q.
3. Use the Nernst equation to find E.
Problem 13 Reading a Nernst graph ★★★
The graph shows E against log Q for one cell at 25 °C.2. Use the points (−2, 1.16) and (2, 1.04) to find the slope.
3. Use slope = −0.0592 / n to find n.
Problem 14 Galvanic against electrolytic ★★★
Compare a galvanic cell and an electrolytic cell. Cover the energy change, the sign of the anode, the sign of ΔG° and the source of the electrons.Problem 15 Galvanised and tin-plated steel ★★★
Wanjiru in Nairobi compares a galvanised (zinc-coated) roofing sheet with a tin-plated can, both scratched to expose the iron. E°: Zn²⁺/Zn = −0.76 V, Fe²⁺/Fe = −0.44 V, Sn²⁺/Sn = −0.14 V.1. Explain which coating still protects the iron.
2. Explain what happens to the iron under the tin.
Problem 16 Permanganate and iron(II) titration cell ★★★
Aarav in Pune builds a cell with platinum electrodes in acidified MnO₄⁻/Mn²⁺ (E° = +1.51 V) and Fe³⁺/Fe²⁺ (E° = +0.77 V).1. Explain why platinum electrodes are used.
2. Write the balanced overall equation in acid.
3. Calculate E°cell and ΔG° in kJ/mol.
Problem 17 Aluminium smelting ★★★
A smelter reduces Al³⁺ to Al in molten cryolite with a steady 5.00 × 10⁴ A for 1.00 h. M(Al) = 26.98 g/mol.1. Calculate the mass of aluminium in kilograms.
2. Calculate the moles of O₂ released if 2O²⁻ → O₂ + 4e⁻ is the anode reaction.
3. Explain why aqueous Al³⁺ cannot be electrolysed to give aluminium, using E°(H₂O/H₂ in base) = −0.83 V and E°(Al³⁺/Al) = −1.66 V.
Problem 18 A concentration cell ★★★
A cell has two copper electrodes, one in 0.0010 mol/dm³ Cu²⁺ and the other in 1.0 mol/dm³ Cu²⁺, joined by a salt bridge. n = 2.1. State E°cell and explain why the cell still gives a voltage.
2. Identify the anode.
3. Calculate E at 25 °C.
4. Predict E after a long time.
Problem 19 Spot the errors ★★★
A student writes: “Zn + 2Ag⁺ → Zn²⁺ + 2Ag, so E°cell = 2(0.80) − (−0.76) = 2.36 V. Then ΔG° = −1 × 96 485 × 2.36 = −228 kJ/mol.”1. Identify the two mistakes.
2. Give the correct E°cell.
3. Give the correct ΔG° in kJ/mol.
Problem 20 Two cells in series ★★★
The same current passes through two electrolytic cells in series, one of CuSO₄(aq) and one of AgNO₃(aq). In the first, 0.640 g of copper is deposited in 30.0 min. M(Cu) = 63.55 g/mol, M(Ag) = 107.87 g/mol.1. Calculate the moles of electrons passed.
2. Calculate the mass of silver in the second cell.
3. Calculate the current in amperes.
