Topic 8 of 8
Organic apparatus and tests
Connect reflux, distillation and observations to the chemistry.
A-Level 9476 (2026-2027)
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 example
Choose 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.
- 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.