Lesson 8 of 8
Organic apparatus and tests
Connect reflux, distillation and observations to the chemistry.
A-Level 9476 (2026-2027)
I can explain qualitative organic analysis.Syllabus
Syllabus 9476, T7. Qualitative organic analysis
I can explain organic synthesis and purification.Syllabus
Syllabus 9476, T8. Organic synthesis and purification
Connect organic tests to apparatus and purification
Preserve volatile reactants, isolate a product and interpret functional-group evidence.
- Reflux for sustained heating
A vertical water-cooled condenser returns condensed vapour to the reaction flask. Keep the apparatus open to the atmosphere through the condenser; never seal a heated system.
- Distil when collecting a volatile fraction
Rearrange appropriately so vapour passes into a condenser and receiver. Put the thermometer bulb at the vapour entrance to the condenser when measuring the distillation temperature.
- Control heating and cooling
Run condenser water in at the lower connection and out at the upper. Use the specified suitable heat source, such as a water bath for an appropriate volatile/flammable system, and add anti-bumping material before heating when required.
- Purify and assess
Choose the supplied separation/purification method from the product properties. Yield measures recovered amount; an appropriate boiling/melting behaviour or other supplied evidence addresses purity.
Reflux returns condensed liquid to the reaction
A vertical condenser is open at the top. Vapour rises through its inner tube; cooled liquid runs back to the heated flask. Cooling water enters the lower jacket connection and leaves the upper connection. A water bath is shown as one suitable heat source.
Distillation sends the condensate to a receiver
Vapour leaves a heated flask through a side arm, passes the thermometer bulb, then condenses in a downward-sloping condenser and enters a separate open receiver. Cooling water enters at the low end and leaves at the high end.
Worked exampleChoose a purification step from the mixture
A supplied synthesis gives a neutral organic liquid P that is almost insoluble in water and does not react with a dilute carbonate wash. It is mixed with residual acid, water and a more volatile organic solvent. The question supplies distinct boiling ranges for P and the solvent.
Try it first. Then show the worked stepsHide the worked steps
- Use a separating funnel to separate the aqueous and organic phases after the specified wash. The acid reacts with carbonate and enters the aqueous phase as dissolved ions; vent the funnel appropriately because carbon dioxide is formed. Identify which layer contains P from the supplied density or a water-drop test, rather than assuming the organic layer is always on top.
- Retain the P-containing layer. Remove residual dissolved water with a suitable anhydrous drying agent that does not react with P, then remove that solid. Drying is different from removing an entire aqueous layer.
- Distil the dried liquid using the specified appropriate heat source. Collect the solvent fraction separately, then collect P over its supplied boiling range. This choice depends on a sufficient volatility difference and thermal stability.
- If P were instead a solid soluble in hot solvent but sparingly soluble when cold, choose recrystallisation: dissolve in minimal hot solvent, remove insoluble impurities if needed, cool to form crystals, then filter, wash sparingly with cold solvent and dry.
Each operation removes a named impurity by a stated property. Reflux helps a reaction proceed; it does not itself isolate a pure product.
| Test context | Positive evidence | Interpretation |
|---|---|---|
| Bromine water with an alkene | Orange solution is decolourised | Consistent with C=C, but other reactive groups may also consume bromine |
| Halogenoalkane hydrolysis then halide test | Heat with aqueous NaOH; acidify with dilute HNO3, then add AgNO3 | Precipitate colour supports the released halide; the covalently bound halogen is not tested directly as a free ion |
| Primary or secondary alcohol with heated acidified manganate(VII) | Purple colour is removed | Oxidation occurs; tertiary alcohols resist this oxidation under the usual conditions |
| Carbonyl compound with 2,4-DNPH | Orange precipitate | Carbonyl evidence; reagent excluded from hands-on H2 assessment |
| Aldehyde with Tollens reagent on warming | Silver mirror | Aldehyde oxidation; follow the supplied handling/disposal instructions |
| Aliphatic aldehyde with Fehling solution on warming | Red-brown precipitate | Distinguishes it from a typical ketone under these conditions |
| Methyl ketone or appropriate alcohol with alkaline iodine, warm | Pale-yellow precipitate | Iodoform evidence for CH3CO- or CH3CH(OH)-; ethanol/ethanal also give the test |
| Carboxylic acid with aqueous carbonate | CO2 evolves and is confirmed with limewater | Acidic enough to react with carbonate |
| Primary amide heated with aqueous NaOH | Ammonia evolves | Hydrolysis releases NH3; test with damp red litmus |
| Phenol or phenylamine with bromine water | Decolourisation and a white precipitate | Context is needed to distinguish the two; practical tests involving phenol itself are excluded |
Solid PCl5 gives steamy HCl fumes with suitable hydroxy compounds, including alcohols and carboxylic acids; it is not a unique alcohol test. PCl5, 2,4-DNPH and phenol are excluded from hands-on H2 tests. Large-scale synthesis involving reflux, distillation and purification is also not expected as an examination operation, although the principles and apparatus remain relevant.
Check your understanding
A volatile reactant must be heated for a long time with another reactant. Why heat under reflux rather than distil at once?
Show the answer
Reflux returns the condensed vapour, so the volatile reactant stays in the flask.
Distilling would remove the volatile reactant before it reacts. Reflux lets heating continue for as long as needed; distillation is used later to collect a product.