Testing for Organic Functional Groups (Oxford AQA International A Level Chemistry)

Required Practical 5: Functional Group Testing

Objective

To test for the alcohol, aldehyde, alkene, carboxylic acid and halogenoalkane functional groups

Apparatus

• Ethanol

• Small pieces of metallic sodium under petroleum ether

  • A beaker of ethanol should be available for the safe disposal of any excess sodium

• Ethanal / propanal

• Fehling’s A and B solutions

• Cyclohexene

• Bromine water

• Solid sodium hydrogencarbonate

• Dilute ethanoic acid

• 1-bromobutane

• Sodium hydroxide solution

• Dilute nitric acid

• Silver nitrate solution (0.05 mol dm^–3)

• 250 cm³ beaker

• Anti-bumping granules

• Test tubes, boiling tubes and a test-tube holder

• Thermometer (–10 °C to 110 °C)

• Pipettes

Method

• The required practical involves five separate experiments

• The results from each experiment should be presented in an appropriate table

Part 1 – Testing for an alcohol

• Place 1 cm³ of ethanol in a dry test tube

• Add a small piece of metallic sodium

• Record your observations

• Safely dispose of any excess sodium using the beaker of ethanol provided

Part 2 – Testing for an aldehyde

• Place 1 cm³ of sodium carbonate solution in a test tube

• Add some anti-bumping granules

• Mix equal volumes of Fehling's A and Fehling's B into a clean test tube

  • The resulting Fehling's solution should be a clear dark blue colour

• Add 5 drops of the Fehling's solution to the sodium carbonate test tube

• Add 1 cm³ of ethanal (or propanal) to this same test tube

• Warm the test tube gently for approximately 5 minutes in a water bath

• Remove the test tube and allow its to stand for several minutes

• Record your observations

Part 3 – Testing for an alkene

• Place 2 - 3 drops of cyclohexene in a test tube

• Add 1 cm³ of bromine water

• Shake the contents of the tube vigorously

• Record your observations

Part 4 – Testing for a carboxylic acid

• Place one small spatula of solid sodium hydrogencarbonate in a boiling tube

• Add 2 cm³ of dilute ethanoic acid

• Record your observations

Part 5 – Testing for a halogenoalkane

• Place 1 cm³ of sodium hydroxide solution in a test tube

• Add 5 drops of 1-bromobutane

• Warm the contents of the test tube for a few minutes in a water bath at ~60 °C

• Add 2 cm³ of dilute nitric acid to acidify the contents of the test tube

• Add 1 cm³ of silver nitrate solution

• Record your observations

Practical Tip

• The volumes of chemicals do not need to be precise for these experiments because you are looking for a general observation

Results

Evaluation

• Once you have recorded the results from the tests, use them to check that the functional group has given the correct result