Explain reflux, separating-funnel washing, drying, distillation and purity checks for an organic liquid in AQA RP10.
Make, separate and purify an ester
The liquid example in the AQA practical handbook is ethyl ethanoate, prepared from ethanol and ethanoic acid with an acid catalyst. The three separate jobs are to make the ester, remove impurities and isolate a dry liquid fraction. A reaction equation alone is not a complete preparation.
Reflux keeps volatile material in the reaction
Heat the mixture with a vertical condenser so vapour condenses and runs back into the flask. Reflux permits sustained heating with reduced loss of volatile reactants and products. It does not make a reversible reaction go to completion.
Cooling water enters at the bottom of the condenser jacket and leaves at the top, keeping the jacket full. The apparatus must communicate with the atmosphere through the intended open path. Never seal a heated reflux apparatus. Add anti-bumping granules before heating, not into a hot liquid. Use the approved electric heating arrangement for flammable organic liquids.
Diagram placeholder
Diagram placeholder — reflux versus distillation
Labels to include:
- Reflux: vertical condenser returns condensate to the reaction flask
- Distillation: angled condenser carries condensate to a receiver
- Water enters the lower jacket port and leaves the upper port
- Distillation thermometer bulb beside the side-arm entrance
- Heat source and anti-bumping granules in the starting flask
- An open pressure-relief path; no sealed heated system
Draw two apparatus panels. Reflux retains material for reaction; distillation removes a volatile fraction. Position the thermometer to measure vapour entering the condenser, not the liquid at the bottom of the flask.
Washing and separating remove different impurities
After cooling and following the prescribed work-up, use a separating funnel for immiscible organic and aqueous layers. A water wash removes water-soluble impurities. A carbonate wash neutralises acidic impurities and releases carbon dioxide, so pressure must be released frequently with the funnel directed safely away from people.
For an ethyl ethanoate/water system the ester-rich layer is normally the upper layer. That is a density result for this system, not a rule that all organic layers are on top. Identify layers from reliable density information or the approved drop test. Remove the stopper before draining through the tap so liquid flows freely.
Allow the layers to separate fully and keep the required product layer. Washing removes soluble impurities but leaves some dissolved water in the organic liquid; this is why a separate drying step follows.
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Diagram placeholder — separating funnel work-up
Labels to include:
- Stopper removed while draining
- Upper ester-rich layer in this particular system
- Lower aqueous layer
- Tap and receiving flask
- Label the product layer before discarding any liquid
- Carbonate wash: CO2 formation and frequent venting
Show a distinct interface. Add a note that the orientation of layers changes with density and solvent choice. Venting during washing and removing the stopper during draining serve different purposes.
Dry the organic layer before distilling
An anhydrous drying agent such as sodium sulfate or magnesium sulfate removes traces of water from a suitable organic liquid. Choose an agent compatible with the product and method. Swirl and allow adequate contact; persistent freely moving solid can indicate that enough drying agent has been used.
Separate the dry organic liquid from the solid by the prescribed decantation or filtration. The drying agent is not a reagent for removing every organic impurity. It also does not replace washing away residual acid.
Collect the appropriate boiling fraction
Distil the dried liquid and collect the fraction over the expected temperature interval, measuring the vapour temperature at the entrance to the condenser. Simple distillation is suitable where volatility differences are sufficient; a fractionating column improves separation when boiling points are close. Do not distil to dryness.
A boiling range close to a reliable reference supports purity, but boiling point depends on pressure and some mixtures have deceptively similar or constant boiling behaviour. A matching boiling point alone does not prove that the product contains no impurity. Combine it with appropriate analytical evidence.
AQA June 2023 Paper 2 Q06.4 and its report discuss fractional distillation for close-boiling liquids. June 2022 Q05 distinguishes washing, drying, apparatus and similar-boiling impurities. Learn the purpose of each step rather than treating all of them as “purification” with no explanation.
Worked limiting-reagent calculation
Original example: 4.60 g ethanol (Mr 46.0) reacts with 9.00 g ethanoic acid (Mr 60.0). Their amounts are 0.100 mol and 0.150 mol. The reaction is 1:1, so ethanol limits the theoretical product.
Ethyl ethanoate has Mr 88.0: theoretical mass = 0.100 × 88.0 = 8.80 g. Collecting 5.72 g of dry ester gives 5.72 ÷ 8.80 × 100 = 65.0%. Incomplete conversion at equilibrium, transfer losses and loss of product during washing or distillation can all lower the isolated yield.
If a volume is measured, convert it to mass using the supplied density before calculating moles or yield. Keep unrounded intermediate values and round the final answer appropriately.
Quick checks
Original Finesse questions. Reveal the indicative worked solutions after attempting each question; these are not official AQA mark allocations.
Q1. What does reflux achieve in an ester preparation?Show answer
It allows sustained heating while vapour condenses and returns to the flask, reducing loss of volatile substances. It does not force complete conversion in a reversible esterification.
Q2. Why vent a separating funnel during a carbonate wash?Show answer
Acidic impurities react with carbonate to produce CO2. Venting prevents pressure building up in the closed funnel.
Q3. Why does an ester need drying after an aqueous wash?Show answer
Some water remains dissolved in the organic layer. An appropriate anhydrous drying agent removes this water; washing and drying have different purposes.
Q4. A liquid product has volume 6.00 cm3 and density 0.880 g cm−3. The theoretical product mass is 8.80 g. Find the yield.Show answer
Actual mass = 6.00 × 0.880 = 5.28 g. Percentage yield = 5.28/8.80 × 100 = 60.0%.
Q5. Why can a fractionating column be needed, and why is a matching boiling point not conclusive evidence of purity?Show answer
A column provides repeated vaporisation and condensation, improving separation of close-boiling components. Similar boiling points or constant-boiling mixtures can still obscure impurities; use additional evidence where appropriate.
Sources
Sources and examiner guidance (reviewed 2 October 2026)
- AQA 7405 organic chemistry specification — 3.3.14 coverage and required skills.
- Chemrevise: Organic Synthesis — Coverage checklist; explanations, data exercises and quick checks on this page are original Finesse material.
- AQA June 2023 Paper 2 mark scheme — Q06.4 (pp25–26) and examiner report p5: separation of close-boiling liquids. Practical guidance is also grounded in the AQA handbook.
- AQA June 2023 Paper 2 examiner report — Read alongside the question-specific marking guidance; not a universal wording checklist.
- AQA June 2022 Paper 2 mark scheme — Q05 (pp22–24) and report p5: organic work-up, drying, apparatus and yield; Q10 (pp32–33) and report p7: synthesis involving amines.
- AQA June 2022 Paper 2 examiner report — Read with the matching question context described in the mark-scheme source.
- AQA practical handbook: Required Practical 10 — Solid preparation and melting point pp136–140; liquid preparation pp143–147. Follow your centre’s risk-assessed method.
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