2.9 - Paper chromatography and phases
You will explain why soluble substances separate on paper using the mobile and stationary phases, then connect that explanation to the baseline, solvent level and solvent front.
What chromatography separates
Paper chromatography is used for mixtures whose substances can dissolve in a suitable solvent. A common GCSE example is a mixture of coloured dyes in ink or food colouring, but the important idea is not the colour: it is that the substances are soluble enough to be carried by the solvent.
Paper chromatography
Paper chromatography is the separation of mixtures of soluble substances by running a solvent through the mixture on paper.
The paper is not just a holder. It is part of the separation. The solvent moves through the paper and carries substances from the original mixture. If every substance in the mixture moved at exactly the same rate, they would stay together and no separation would happen.
In a successful separation, one substance may be carried further up the paper while another substance stays closer to the baseline. The mixture has separated because its substances have moved different distances in the same run.
Why substances move at different rates
Chromatography always involves two phases. A phase is a part of the system that a substance can be in or interact with.
Mobile phase
The mobile phase is the solvent that moves through the mixture and over the paper.
In paper chromatography, the mobile phase is usually a liquid solvent such as water or another suitable solvent. It moves up the paper and can carry dissolved substances with it.
Stationary phase
The stationary phase is the phase contained in the paper; it stays in place while the mobile phase moves through it.
Different substances do not spend the same amount of time being carried by the mobile phase and held by the stationary phase. A substance that is carried more strongly by the mobile phase moves faster and further. A substance that is held more strongly by the stationary phase moves more slowly and stays closer to the baseline.
That difference in movement is the reason paper chromatography separates mixtures.
Continue this lesson.
You’re previewing NovaLearn without an account. Create a free account to read the rest.
Create free account