Fats and Oils

Unsaturation in fats and oils
Food labels and advertisements often refer to unsaturated fats and oils. A comparison of the amounts of unsaturated fats and oils present in different foodstuffs can be made by titrating solutions of samples with aqueous bromine (bromine water), which reacts with the carbon - carbon double bonds present in such fats and oils.
Read our standard health & safety guidance
Lesson organisation
This is suitable as a class experiment for advanced classes where sufficient fume cupboard space is available, perhaps as part of a circus of experiments if such space is limited. Do not be tempted to do this in an open lab as too much bromine vapour escapes. Two such titrations, comparing two different fats or oils on a semi-quantitative basis, might be done in 45 minutes by students who already have experience of carrying out titrations.
Apparatus and chemicals
Eye protection
Each working group will require:
Conical flask (100 cm3)
Dropping pipette
Measuring cylinder (10 or 25 cm3)
Burette, filled with bromine water (see note 2)
Burette stand, or clamp and stand
White tile
Access to:
A fume cupboard
Bromine water, approx 0.02 mol dm–3 (Harmful), provided in ready-filled burettes (see note 1)
Volasil 244 (Harmful), 5 cm3 needed for each titration (see note 3)
Various vegetable oils, fats, as available (see note 4)
Technical notes
Bromine water (Harmful) Refer to CLEAPSS Hazcard 15B and Recipe card 28
Volasil 244 (Harmful) Refer to CLEAPSS Hazcard 106
1 Bromine water should be freshly prepared in a fume cupboard. 1 dm3 should be sufficient for around 10 working groups carrying out two titrations each. If less is required, reduce quantities pro rata, but any excess can be stored as bromine water for future qualitative use. The experiment is only semi-quantitative – essentially comparing results for different foodstuffs.
2 50 cm3 burettes will not fit in many fume cupboards - 25 cm3 burettes are better, if available. The...