Electrolysis
Cambridge A-Level Chemistry (9701) · Unit 24: Electrochemistry · 8 flashcards
Electrolysis is topic 24.1 in the Cambridge A-Level Chemistry (9701) syllabus , positioned in Unit 24 — Electrochemistry , alongside Standard electrode potentials E. In one line: The Faraday constant (F) is the magnitude of electric charge per mole of electrons. It is related to the Avogadro constant (L) and the elementary charge (e) by the equation: F = Le.
Marked as A2 Level: examined at A Level in Paper 4 (A Level Structured Questions) and Paper 5 (Planning, Analysis and Evaluation). It is not tested on the AS-only papers (Papers 1, 2 and 3).
The deck below contains 8 flashcards — 2 definitions, 4 key concepts and 2 calculations — covering the precise wording mark schemes reward. Use the 2 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
The Faraday constant (F)
The Faraday constant (F) is the magnitude of electric charge per mole of electrons. It is related to the Avogadro constant (L) and the elementary charge (e) by the equation: F = Le.
What the Cambridge 9701 syllabus says
2025-2027 syllabus, in our words · A2 LevelWhat the syllabus expects you to be able to do in this topic, in plain English. For the exact wording, see the official syllabus (PDF).
- Predict which substances are released in electrolysis, using whether the electrolyte is molten or aqueous, the position of the species in the redox series (electrode potentials) and concentration.
- State and apply F = Le, where F is the Faraday constant, L is the Avogadro constant and e is the charge on one electron.
- Calculate: (a) the charge that flows during electrolysis, from Q = It; (b) the amount of substance released in electrolysis, as a mass and/or a volume.
- Describe how a value for the Avogadro constant can be found by an electrolysis experiment.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9701 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Electrolysis
- › In the electrolysis of aqueous solutions, remember that water is reduced to H2 gas if the metal is high in the reactivity series.
State the three factors that determine the products formed during the electrolysis of an aqueous solution.
The products depend on: 1) The state of the electrolyte (aqueous vs. molten), 2) The position of the ions in the electrochemical series (electrode potential), and 3) The concentration of the ions in solution.
Define the Faraday constant (F).
The Faraday constant (F) is the magnitude of electric charge per mole of electrons. It is related to the Avogadro constant (L) and the elementary charge (e) by the equation: F = Le.
What is the equation used to calculate the quantity of charge (Q) passed during electrolysis?
The quantity of charge (Q) is calculated using the equation: Q = It, where I is the current (in amperes) and t is the time (in seconds).
How can electrolysis be used to determine the Avogadro constant?
By electrolyzing a known mass of a substance (
What volume of hydrogen gas (at RTP) is produced during the electrolysis of water by a current of 2A for 30 minutes?
Q = It = 2 A x (30 x 60) s = 3600 C. Moles of electrons = Q/F = 3600/96500 = 0.03731 mol. 2H⁺ + 2e⁻ -> H₂, so moles of H₂ = 0.03731/2 = 0.01865 mol. Volume at RTP = 0.01865 x 24000 cm³ = 448 cm³.
During the electrolysis of concentrated NaCl(aq), which product is preferentially discharged at the anode, and why?
Chlorine (Cl₂) is discharged at the anode. On E⦵ values alone oxygen would be expected, because E⦵(O₂/H₂O) = +1.23 V is less positive than E⦵(Cl₂/Cl⁻) = +1.36 V. However, the two values are close, and in concentrated NaCl(aq) the very high concentration of Cl⁻ ions makes Cl⁻ oxidation favoured, so Cl₂ is released.
Explain why different products may be obtained when electrolyzing molten NaCl compared to aqueous NaCl.
In molten NaCl, only Na⁺ and Cl⁻ are present, so Na(l) and Cl₂(g) are produced. In aqueous NaCl, H₂O is present and can be reduced to H₂(g), while either Cl⁻ or H₂O can be oxidized, depending on concentration (Cl⁻ favored when concentrated).
Define electrolysis.
Electrolysis is the process of using an electric current to drive a non-spontaneous chemical reaction. It occurs in an electrolytic cell, which consists of electrodes immersed in an electrolyte.
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Electrolysis sits alongside these A-Level Chemistry decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Electrolysis deck
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