Learn how to separate mixtures, produce a paper chromatogram and calculate RF values from the results
The following video from Cognito uses animation to show the principles of paper chromatography.
This video from Mr Jansen Tan demonstrates paper chromatography of several different water-soluble felt tip pens. It also shows what happens when common mistakes are made, including drawing the base line in ink and filling the solvent above the base line.
Food colourings, and calculating Rf
The required practical video from Malmesbury Education demonstrates an alternative investigation where food colourings are separated using the paper chromatography method. The resulting chromatogram is not as clear as the one produced in the video by Mr Jansen Tan. The demonstration shows how to calculate the RF value using a printed representation of a chromatogram, similar to those learners will recognise from exam-style questions. In the explanation Mrs Peers-Dent implies that the dyes have a preference to be in the stationary or the mobile phase. Although this is a popular analogy it can be a barrier to deeper understanding, therefore anthropomorphism should be applied carefully. Students should be encouraged to review such analogies critically to identify limitations.
Extension: stationary phases and additional analytical techniques
This Royal Society of Chemistry resource is aimed at students 16+. It demonstrates the method on a different stationary phase and additional analytical techniques to view the spots of the separated substances, including using dyes and UV light. This is a useful extension for learners to show how methods may be adapted and improved for use in other real-life scenarios. You can find animations and supporting resources for this video here .
Learners can also be encouraged to try out this separation technique at home using common cupboard essentials such as kitchen roll or coffee filter paper. This video from the #ChemistryInYourCupboard series explains the methods and equipment needed. Learners could be asked to compare the method used in this video with those used in the other videos above, and to suggest improvements to produce better results.
Also check out
- Chromatography fights food fraud – link chromatography to the real world with this feature and accompanying resources.
- Practical chromatography – this CPD article includes ideas for enhancing practical chromatography and a curriculum overview.
- Chromatography of leaves – a class practical investigating the pigments in leaves, with the Nuffield Foundation.
- Chromatography of sweets – a class practical to investigate the different colours in food dyes, with the Nuffield Foundation.
We have collated these videos of key practical experiments to support remote teaching as part of our response to Covid-19. Teachers requested resources to help them deliver practical content without access to laboratories or equipment. We are developing further resources and welcome feedback to help us produce those you most need. Please email us or use the comment section below.
Practical videos | 14–16 students
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