Ions present
List every ion in the solution, including H⁺ and OH⁻ from the water.
AQA 8462 · Aqueous electrolysis · Higher
Aqueous electrolysis: when hydrogen wins the cathode
The product-prediction mark, and both half-equations. Predicting the wrong species at an electrode takes the half-equation with it.
Reviewed family · Studara-authored items · No grade-uplift claim
The lost mark
One answer. Several places the method can fail.
Studara does not reduce the response to right or wrong. The reviewed contract checks these states independently.
Cathode product
Compare the metal with hydrogen in the reactivity series to decide which is discharged.
Both half-equations
Write balanced half-equations at each electrode with the correct direction of electron transfer.
Why it goes wrong
The diagnosis stays uncertainty-safe.
A wrong response can support a specific measured diagnosis. A blind multiple-choice diagnostic records only a possible cause until later working provides stronger evidence.
01
The error
Naming the metal as the cathode product regardless of its reactivity — in aqueous solution, a metal more reactive than hydrogen leaves hydrogen discharged instead.
02
Why it survives revision
For copper and for silver, the simple rule gives the right answer, and those are the demonstrations electrolysis is usually introduced with. The rule is confirmed in the lab before the exception is ever met.
The worked repair
Repair the smallest broken step.
Teaching is not evidence. This one move is the repair; the proof checks begin after it disappears.
Compare the metal against hydrogen in the reactivity series before naming the cathode product. Less reactive than hydrogen: the metal. More reactive: hydrogen.
What happens after the repair
Correction is the start, not the result.
Immediate
Asked again straight away, on a different question
The repair leaves the screen and a new authored item checks the method unassisted. Being taught something is never evidence that it was learned, so this is the first stage that counts at all.
Delayed
Asked again after at least 1 day
A parallel form of the same method, unassisted, with the repair no longer on screen. A retest in the same session does not count.
Transfer
Asked again when the surface changes
The transfer form changes the anion to a halide, so the anode product changes as well and the two electrodes cannot be reasoned about as one memorised pair.
Exam
Asked again under exam conditions
Timed, carrying the mark tariff, in an exam-like response format and aligned to the specification. Any one of those missing and the evidence is refused.
REVIEWED BOUNDARY
This page covers one reviewed family: Aqueous electrolysis · Higher. Predict competing electrode products, balance both half-equations, and preserve oxidation/reduction direction. Other families within the same GCSE Chemistry topic are outside this reviewed journey, and Studara does not apply the proof label to material that has not been reviewed. No grade-uplift claim is made anywhere on this site.
Straight answers
Before you use this guide.
Why is hydrogen produced instead of the metal?
In an aqueous solution, if the metal is more reactive than hydrogen, hydrogen is discharged at the cathode instead. The metal only appears when it is less reactive than hydrogen — copper and silver, for example.
What is produced at the anode?
A halide ion is discharged as the halogen. If no halide is present, oxygen is produced from hydroxide ions.
Does Studara guarantee a higher grade?
No. Studara has not run a controlled outcome study and publishes no grade-uplift claim. What has been measured, what is withheld, and the metric that failed its bar are all on the public evidence page.
Turn this method into evidence