Disclaimer:
The exact reagents, reactions, processes and equipment used in practical activities may vary between schools, colleges, and exam board exemplar methods. The essential techniques, skills, and learning objectives remain the same. Always follow the instructions, risk assessments, and safety guidance provided by your teacher or centre.

PRACTICAL 5 – Distillation of a Product from a Reaction

Aim:
To prepare cyclohexene by dehydrating cyclohexanol and to distil the cyclohexene from the reaction mixture.

Overview:
Dehydrate cyclohexanol using an acid catalyst, then distil, separate, dry, and test the cyclohexene product.

Alternative a: Preparation of Cyclohexene by Dehydration of Cyclohexanol

Key Concepts:

Elimination reaction
Use of distillation
Separation and purification
Confirmation of product identity

Apparatus and Chemicals:

Distillation apparatus (semi-micro or Quickfit) with thermometer
Cyclohexanol
Concentrated phosphoric acid
Anti-bumping granules
Measuring cylinders (10 cm³ and 25 cm³)
Separating funnel
Saturated sodium chloride solution
Anhydrous calcium chloride or drying agent
Acidified potassium manganate(VII) solution (test for alkene)
Sample container
Gloves and fume cupboard

Method Summary:

AQA A-Level Chemistry diagram of a distillation setup showing flask, condenser, thermometer and receiver for separating cyclohexene

Add 20 cm³ cyclohexanol to a 50 cm³ flask. Record the mass added.
Add 8 cm³ concentrated phosphoric acid with frequent shaking.
Add anti-bumping granules. Set up distillation apparatus.
Gently heat to distil off liquids boiling below 100 °C.
Collect distillate and transfer to a separating funnel. Add 50 cm³ saturated NaCl. Shake and separate layers.
Discard lower aqueous layer. Transfer upper layer (crude cyclohexene) to flask.
Dry using anhydrous calcium chloride or magnesium sulfate. Allow to stand until clear.
Decant into a pre-weighed container. Record mass and calculate % yield.

Test for Alkenes (Cyclohexene Product):

Mix 1 cm³ distillate with equal volume of acidified KMnO₄.
Shake well. Decolorisation confirms C=C bond.

AQA A-Level Chemistry test showing acidified potassium manganate(VII) decolorised by cyclohexene confirming presence of a carbon–carbon double bond

Alternative b: Preparation of Ethanal by Oxidation of Ethanol

Aim:
To oxidise ethanol to ethanal and distil ethanal from the reaction mixture.

Key Concepts:

Controlled oxidation
Distillation at low temperature
Confirmation by silver mirror test

Apparatus and Chemicals:

Simple distillation/Quickfit apparatus
Acidified sodium dichromate(VI)
Ethanol
Anti-bumping granules
Silver nitrate, sodium hydroxide, and ammonia (for Tollens’ reagent)
Thermometer, teat pipette
Ice/water bath

Method Summary:

AQA A-Level Chemistry schematic showing controlled oxidation of ethanol to ethanal and immediate distillation at low temperature

Measure 12 cm³ acidified sodium dichromate into a boiling tube.
Cool the tube in a water bath.
Measure 2 cm³ ethanol and add it dropwise to the cooled oxidising agent.
Add anti-bumping granules and assemble distillation setup.
Gently distil 5 cm³ of the product. Keep collection tube cold in ice bath.
Test distillate with Tollens’ reagent: formation of silver mirror confirms presence of ethanal.

Test for Aldehydes (Ethanal Product – Tollens’ Test):

AQA A-Level Chemistry Tollens’ reagent silver mirror test confirming presence of an aldehyde such as ethanal

Prepare Tollens’ reagent by combining silver nitrate, NaOH, and dilute ammonia.
Warm 5 cm³ of reagent to 50–60 °C in water bath.
Add 10 drops of distillate. A silver mirror confirms ethanal.

Safety Notes

Wear gloves and use a fume cupboard for both practicals.
Concentrated acids and oxidisers are corrosive – handle with care.
Dispose of Tollens’ reagent thoroughly to avoid explosive residues.