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.
[3 marks]
Total for this question: 3
Chemistry
Alcohols
AQA 3.3.5
A-level Chemistry (7405) · exam-style practice, examiner-report intelligence and the tools that drill it.
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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
Medium
ORIGINAL · after June 2023 Paper 2 Q06.1
Easy
ORIGINAL
2-methylpropan-2-ol is warmed with acidified potassium dichromate(VI). State and explain what you would observe.
[2 marks]
Total for this question: 2
Medium
ORIGINAL
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.
[3 marks]
Total for this question: 3
Medium
ORIGINAL
Write the equation for the reaction of ethanol with ethanoic acid, name the catalyst, and name the organic product.
[3 marks]
Total for this question: 3
Medium
ORIGINAL · after June 2024 Paper 2 Q04.5
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.
[2 marks]
Total for this question: 2
Questions are written in the style of past AQA papers (source shown on each) — never copied from them.
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