Coffee Filter Chromatography

What colors are your markers really made of? You can use paper chromatography to find out. Paper chromatography is a technique for separating and identifying mixtures that is colored, especially pigments.

Materials:

  • Colored water based markers – include brown and orange (Mr Sketch Scented Water Color Markers works the best. We’ve tried Crayola washable markers and they just didn’t work).
  • White coffee filter
  • Medium sized glass jar
  • Water

Method:

Step 1:

Cut the filter paper in half and mark circles about 1/2-1 inch from the cut edge (we used light blue, brown and orange.

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Step 2:

Fill your jar about 1/4 inch to a 1/2 inch of water, below the marker dots and place in your coffee filter cut edge down

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Step 3:

Wait for the magic to happen

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Step 4:

Observe the results

We can see pink, brown, greenish yellow, and blue pigments in the brown spot:

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We can see pink and orange in the orange spot.
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What is happening?

The coffee filter is separating out the molecules of pigments in the markers. When the water soluble markers are dipped in water, the water rises up the coffee filter paper via capillary action, (which is similar to but not quite the same as drinking through a straw). When it reaches the water soluble ink, the ink will dissolve in the water and some of the molecules will be carried along with the water molecules. Different pigments in the sample mixture travel at different rates due to differences in solubility in the solvent, and due to differences in their attraction to the fibers in the paper. Basically, some of the molecules will stick to the paper at various points, while others travel farther. There may not be complete separation of colors because they have similar solubilities.

Some markers have only one pigment – like blue, and other colors are mixtures of more than one pigment – like brown and orange.

To download or print a copy of this experiment click the print or download on the image below.

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