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
Official 2025-2027 spec · A2 LevelThese are the exact learning outcomes Cambridge sets for this topic. The candidate is expected to be able to do each of these on the relevant paper.
- predict the identities of substances liberated during electrolysis from the state of electrolyte (molten or aqueous), position in the redox series (electrode potential) and concentration
- state and apply the relationship F = Le between the Faraday constant, F, the Avogadro constant, L, and the charge on the electron, e
- calculate: (a) the quantity of charge passed during electrolysis, using Q = It (b) the mass and/or volume of substance liberated during electrolysis
- describe the determination of a value of the Avogadro constant by an electrolytic method ⦵ ⦵
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
- › Standard cell potential is the potential difference between two half-cells under standard conditions; electrode potential refers to a single half-cell against SHE.
- › Check that n is the number of moles of electrons and F is the Faraday constant (96500 C mol–1).
- › Standard cell potential is the potential difference between two half-cells under standard conditions, not the potential of a single electrode.
- › Carefully memorize and apply the Nernst equation: E = Eo + (0.059/z) log [oxidised species] / [reduced species].
- › Refer to the SHE as a 'half-cell' or 'electrode' and specify all standard conditions: 101 kPa and 1.00 mol/dm3.
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?
First calculate Q = It = 2A * (30 * 60)s = 3600 C. Then find moles of electrons: moles = Q/F = 3600/96500 = 0.0373 mol. H₂ requires 2 electrons: moles of H₂ = 0.0373/2 = 0.0186 mol. Finally, volume = moles * 24000 cm³ = 447 cm³.
During the electrolysis of concentrated NaCl(aq), which product is preferentially discharged at the anode, and why?
Chlorine gas (Cl₂) is preferentially discharged at the anode because it has a lower (less positive) electrode potential compared to oxygen from water, and the high concentration of Cl⁻ further favors its discharge.
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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All Chemistry FlashcardsMore topics in Unit 24 — Electrochemistry
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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