Distillation of an Organic Product (Oxford AQA International A Level Chemistry)

Required Practical 4: Distillation of a Product

Objective

• To prepare ethanal by the oxidation of ethanol and to distil the ethanal from the reaction mixture

Apparatus

• Distillation apparatus

• Electric heater

• Two measuring cylinders 10 cm³ and 25 cm³

• Pipette

• Anti-bumping granules

• Test tube

• Thermometer

• Acidified potassium dichromate(VI), K₂Cr₂O₇ (aq)

• Ethanol, CH₃CH₂OH (l)

• 0.05 mol dm^-3 silver nitrate solution, AgNO₃ (aq)

• 2 mol dm^-3 ammonia solution, NH₃ (aq)

• 2 mol dm^-3 sodium hydroxide solution, NaOH (aq)

• 1 mol dm^-3 sulfuric acid, H₂SO₄ (aq)

Method

Distillation

1. Using a 25 cm³ measuring cylinder, transfer 12 cm³ of acidified potassium dichromate(VI) to a pear shaped flask

   • Gloves should be work as acidified potassium dichromate(VI) is corrosive

2. Cool the pear shaped flask in a beaker of cold water

3. Measure out 2 cm³ of ethanol using a 10 cm³ measuring cylinder

4. Using a pipette, slowly add the ethanol dropwise to the pear shaped flask

   • The solution must be kept cool

5. Add some anti-bumping granules to the pear shaped flask

6. Attach the pear shaped flask to distillation apparatus, as shown in the diagram

7. Heat gently using an electric heater

8. Collect roughly 5cm³ of distillate for testing

Diagram

Testing the distillate using Tollens' reagent

1. Prepare a fresh sample of Tollens' reagent

   1. Add 5 drops of sodium hydroxide solution to 2 cm³ of silver nitrate solution

   2. Add the minimum amount of ammonia solution required to dissolve the brown precipitate formed

   3. Gently warm a 5 cm³ portion of this reagent in a test tube

2. Add 10 drops of the distillate to the warmed portion of Tollens' reagent

3. Wait for the reaction to complete

   • A positive result for the aldehyde in the distillate is the formation of a silver mirror

Practical Tip

• When testing for the distillate, drip the Tollens' reagent around the inside edge of the test tube to help develop the formation of the silver mirror on the glass

Results

• A silver mirror is seen on the inside of the test tube

Evaluation

• A positive result for the aldehyde in the distillate is the formation of a silver mirror