Alcohols
A-level Chemistry (7405) · exam-style practice, examiner-report intelligence and the tools that drill it.
The topic on one screen
- Classify first: primary, secondary or tertiary decides what oxidation can do.
- Oxidising agent = acidified potassium dichromate(VI) (K2Cr2O7 / H2SO4), orange → green. Primary → aldehyde (distil off) → carboxylic acid (reflux); secondary → ketone; tertiary → no reaction.
- Distil to stop at the aldehyde (removes it before it oxidises further); reflux to push a reaction to completion without losing volatile reactants.
- Dehydration (elimination of water) with hot concentrated H2SO4 or H3PO4 gives an alkene.
- Esterification: alcohol + carboxylic acid, conc. H2SO4 catalyst, gives an ester + water (reversible).
- Purifying an organic liquid: wash, dry with anhydrous MgSO4 (a drying agent), then distil; purity shows as a sharp boiling point close to the data-book value.
Where students actually lose marks
The requirement to acidify potassium dichromate(VI) with sulfuric acid was well known — but say 'acidified', or write K2Cr2O7 with H2SO4. A bare 'potassium dichromate' can cost the reagent mark.
June 2023 Paper 2 examiner report (Q06.1)
Only about 30% knew that purity is linked to a sharp boiling point close to the known value from a data source. Either point earns the mark — don't just say 'measure the boiling point'.
June 2024 Paper 2 examiner report (Q04.5)
Identifying the most likely impurity as the alcohol with a similar boiling point (so it distils over with the product) was poorly answered. Link impurity to boiling point, not just 'leftover reactant'.
June 2022 Paper 2 examiner report (Q05.5)
Try it — exam-style
State the reagent and conditions to oxidise a primary alcohol all the way to a carboxylic acid, and how you would change the conditions to stop at the aldehyde.
2-methylpropan-2-ol is warmed with acidified potassium dichromate(VI). State and explain what you would observe.
Propan-2-ol is heated with concentrated sulfuric acid. Name the type of reaction, the organic product and why the acid is described as a catalyst.
Write the equation for the reaction of ethanol with ethanoic acid, name the catalyst, and name the organic product.
A crude ester is shaken with anhydrous magnesium sulfate and then filtered. Explain the purpose of this step, and state how you would confirm the final ester is pure.
Questions are written in the style of past AQA papers (source shown on each) — never copied from them.
Get the printable question packfree accountDrill it properly
Stuck on alcohols?
Oxidation conditions and the reflux-vs-distil choice are classic dropped marks — I teach the exact wording examiners reward, and the first lesson is free.