Practice Assignment 05
Is your green sweet really green?
The experiment should work with any sweets from which the food dyes can be easily extracted. Sugar-coated chocolate beans work well.
The packet may list the food dyes used (by name or by E-number), though probably not which dyes for which colours. Sets of food dyes, including the six mentioned in Standard Procedure SP 0005:2005 are available from:
Sensient Colors UK, Oldmedow Road, Kings Lynn, Norfolk, PE30 4LA
(Contact: Sarah Armstrong, Customer Care Manager, 01553 669444)
Or:
Town End (Leeds) plc, Silver Court, Intercity Way, Stanningley, Leeds, LS13 4LY
(Contact: Dr Adrian Hayes, 0113 256 4251, adrianhayes@dyes.co.uk)
These dyes should be made up as approx. 0.05% solutions.
A supply of hot water would save time in getting water bath up to temperature.
Depending on the thickness and absorbency of the wool, several 10 cm lengths may be needed to absorb the dyes. Teachers are advised to test the wool in advance, to determine a suitable quantity.
Students may require help in concentrating and spotting dyes for the chromatogram.
Health and safety note
Evaporation of the solution evolves ammonia, so must be performed in a fume cupboard.
Apparatus and Reagents
- Standard Procedure:
- SP 0005:2005 Method for identifying food dyes in colour-coated chocolate beans
- 4 boiling tubes
- hot water bath (or 400 cm3 beaker)
- 10 cm3 measuring cylinder
- dropper
- evaporating basin
- stirring rod
- tweezers
- 7 capillary tubes, for spotting the chromatogram
- chromatography vessel (or large beaker with cling-film cover)
- white wool
- chromatography paper
- approx 1 mol dm-3 ethanoic acid
- approx 6 mol dm-3 ammonia solution
- universal indicator paper
- solutions of known food dyes as listed in the sweets’ ingredients list
Test Specimens
- 6 colour-coated chocolate beans (or other sweets) of the same colour