This simple paper chromatography experiment is a great way to learn about this particular method of separating mixtures.
WHAT IS CHROMATOGRAPHY?
Chromatography is a technique used to separate mixtures. Information from a chromatography investigation can also be used to identify different substances.
In chromatography the mixture is passed through another substance, in this case filter paper. The different colour ink particles travel at different speeds through the filter paper allowing you to see the constituent colours of the pen ink.
All types of chromatography have two phases. A mobile phase where the molecules can move and a stationary phase where the molecules can’t move. In the case of paper chromatography the stationary phase is the filer paper and the mobile phase is the solvent ( water ).
The more soluble the ink molecules the further they are carried up the paper.
The video below shows chromatography in action.
Paper Chromatography Experiment
Filter paper or paper towel
Felt tip pens – not washable or permenent
A container – glass, jar or plate
Pour a small amount of water onto a plate or into the bottom of a jar.
Find a way to suspend the filter paper over the water so just the very bottom is touching the water. If you do the experiment in a jar the easiest way to do this is to wrap the top of the filter paper around a pencil, clip it in place and suspend it over the top of the jar.
Our LEGO holder worked well too!
Use the felt tip pens to draw a small circle about 1cm from the bottom of the filter paper with each colour pen you want to test.
Suspend the filter paper in the water and watch as the ink moves up the filter paper.
You should end up with something like this! We call the finished filter paper, a chromatogram.
What happens if you use washable pens?
If the colours are washable they tend to just contain one type of ink and so you don’t see any separation of colour.
You can see below that only a couple of the inks have separated out, compared to the non washable pens above.
Why does chromatography work?
When the filter paper containing the ink spots is placed in the solvent ( in this case water ) the dyes travel through the paper.
Different dyes in ink travel through the chromatography filter paper at different speeds. The most soluble colours dissolve and travel further and faster than less soluble dyes which stick to the paper more.
Experiment with different types and colours of pens, dependng on the typ of ink used, some will work better than others.
Steamstational also has a great leaf chromatography investigation.
More separation experiments
Clean up water by making your own filter.
Separate water and sand by evaporation.
Make colourful salt crystals by separating salt and water.
Separate liquid mixtures with a bicycle centrifuge.