Chromatography can be used to identify substances. You can use paper chromatography to identify different substances in a mixture. It uses the fact that different substances wash through wet filter paper at different rates.
1) Put spots of each mixture being tested on a pencil baseline on filter paper.
2) Roll up the paper and put it in a beaker containing a solvent, such as ethanol or water. The baseline must be kept above the level of the solvent.
3) The solvent seeps up the paper, taking the samples with it.
4) The different chemicals in the sample form separate spots on the paper.
5) The result of chromatography analysis is called a chromatogram. A chromatogram with four spots means there are atleast four different substances in the sample mixture.
Real Life Application🤯
One use for chromatography is to separate out the mixture of colouring agents in food. To identify which agents are present, run samples of known mixtures alongside the unknown mixtures and compare where the spots end up.
In I/GCSE Chemistry, you may be asked to calculate the Rf value for each chemical...
An Rf value is the ratio between the distance travelled by the dissolved substance and the distance travelled by the solvent.
Rf = distance travelled by the substance / distance travelled by the solvent.
Rf values are used in the food industry and in forensic science. Scientists keep tables of these values and refer to them to identify substances like food additives and drugs.
Drafted by Catrina (Chemistry)