Paper chromatography

Principles

The following video from Cognito uses animation to show the principles of paper chromatography.

Felt tips 

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 R_F 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 . 

Kitchen chromotography

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 and resources from our Kitchen to classroom 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.