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Learn Burn Tuesday (LBT)

A GCSE science workout on calculating Rf values.

· GCSE Study Tips

Welcome to the first blog on 'Learn Burn Tuesday' (LBT). Every Tuesday I will post a blog on a particular GCSE science topic. This will literally allow you to 'feel the burn' and come away with a better understanding of the topic. The blog will be based on the Evidence Based Teaching theory of P.A.R.:

  • Present
  • Analyse
  • Review

This first blog is on 'Calculating Rf values' when using the technique of chromatography. 



Paper chromatography is used to separate a mixture of two soluble substances. It can be used to distinguish between pure and impure substances. Examples are inks and food dyes.


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For example, in the chromatogram above the Rf value of dye 3 can be calculated as follows:

Rf value = 8 / 10

= 0.8

By knowing the Rf values of substances it is possible for us to identify those that are unknown. If we have a “mystery’ sample, doing chromatography on that sample will allow us to produce a chromatogram that will tell us:

  1. If the sample is pure or impure
  2. The Rf values of the substance
  3. Compare the Rf values with those of known substances to identify what the mystery substance is.



Practise, practise, practise exam questions to self-assess.


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I hope this was useful. Feedback is greatly received. Also, if you have a GCSE science topic that you would like to include in 'Learn Burn Tuesday' (LBT), then contact me a let me know be clicking onto the combiclassroom website.