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.
Present
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.
![broken image](http://custom-images.strikinglycdn.com/res/hrscywv4p/image/upload/c_limit,fl_lossy,h_9000,w_1200,f_auto,q_60/3842484/655700_592170.gif)
Analyse
![broken image](http://custom-images.strikinglycdn.com/res/hrscywv4p/image/upload/c_limit,fl_lossy,h_9000,w_1200,f_auto,q_auto/3842484/559156_900155.png)
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:
- If the sample is pure or impure
- The Rf values of the substance
- Compare the Rf values with those of known substances to identify what the mystery substance is.
Review
Practise, practise, practise exam questions to self-assess.
![broken image](http://custom-images.strikinglycdn.com/res/hrscywv4p/image/upload/c_limit,fl_lossy,h_9000,w_1200,f_auto,q_auto/3842484/530417_215683.png)
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.