Paper 1 Q30 — Oxidising four primary alcohol groups

Organic — full oxidation of primary alcohols to carboxylic acids; atom bookkeeping

What the examiners said

“Candidates were required to deduce that four carboxylic acid groups and four molecules of water are made when the four primary alcohol groups are oxidised with excess oxidising agent. Option C was the most common incorrect answer based on incorrect numbers of hydrogen atoms lost and oxygen atoms gained.”

Try the question

A molecule has four −CH₂OH (primary alcohol) groups, all oxidised to completion with excess oxidising agent. What forms?

Examiner report: “Option C (right product, wrong H/O count) was the most common error.”

Explore — oxidise a primary alcohol, atom by atom

Step a single −CH₂OH through aldehyde to acid and watch the atom counter. Then scale to four groups to get the whole-molecule change and the water produced.

Oxidation stage: alcohol Number of −CH\u2082OH groups: 4

The whole-molecule answer is just the single-group change times four: four −COOH and four molecules of water. Getting the per-group +1 O / −2 H right is the whole question.

Original reconstruction inspired by the misconceptions described in the Singapore-Cambridge GCE A-Level H1 Chemistry 8873 November 2023 Examiner Report. Not the actual examination question. For classroom exploration.

Made by lookang, using Claude Fable 5. More resources: iwant2study.org