Chemistry / Science GCSE: Investigate the separation of substances using paper chromatography
A demonstration of the key points of the required practical to investigate the separation of substances using paper chromatography for GCSE chemistry and combined science.
This short film begins by introducing some of the key terminology linked with chromatography to support understanding of the science behind the process. It also demonstrates how to avoid common mistakes with this investigation and how to calculate Rf values.
Students are likely to have carried out chromatography at KS3 but may not have calculated Rf values.
The practical allows development of Apparatus & Techniques Chemistry 4 (DfE GCSE subject content guidance, Appendix 4).
It is likely that students will have carried out chromatography at KS3 and possibly even at KS2.
This short film could be used before students’ own investigations to help to support understanding of the science behind the practical and to highlight the key terminology linked with the process.
Alternatively, it could be used after an investigation to revisit and check understanding of the science behind the practical.
As the film highlights some common mistakes made when carrying out chromatography, it could be used to ensure that students are aware of the common pitfalls and, more importantly, why these mistakes affect the validity of results.
Points for discussion:
Even where the process of chromatography is familiar to students and they can recall the method, questions linked with the science behind the practical are often challenging.
The terminology linked with chromatography - for example solution, solvent, solute, soluble, mobile phase, and stationary phase - can be confusing to students and these are highlighted in the film.
There is a focus on the common mistakes made when carrying out chromatography and how to avoid them.
Finally, the film also demonstrates how to calculate Rf values, another aspect of chromatography that students can find challenging.
If students are struggling to identify and articulate the issues linked with the common mistakes, it may be beneficial to allow them to make those mistakes in their own investigation and explore how that affects results.
Students should practice calculating Rf values. Calculating the Rf value of the same substance in a different solvent will help to reinforce the idea that the Rf varies dependent on the solvent used.
Suitable for teaching chemistry and combined science at Key Stage 4 and GCSE in England, Wales and Northern Ireland, and at National 4 and 5 in Scotland.