The Science of Color

Paper Chromatography

This week at CHA, the 7th grade students experimented with the chemistry technique known as chromatography.  Variations of this technique are used in labs to separate and purify DNA, proteins, and other molecules for a wide range of experiments.  We used paper chromatography to separate out the various colored dyes and pigments found in several different colors of markers.  First we talked about chemical mixtures and solutions, and then learned that inks are actually solutions of different pigments and dyes.

If an ink is hydrophilic, or “water-loving”, it’s pigments and dyes will dissolve in water or in other solvents that are polar like water is, while hydrophobic inks “water fearing” will dissolve in nonpolar solvents.   The solvent used in class was rubbing alcohol (a moderately nonpolar solvent, which also dissolves the inks used in permanent markers like Sharpies).

We found that there are different mixtures used by different companies  (Crayola and Rose Art) to produce “black” markers.   It is very interesting to see the different color separations from the markers, particularly the differences between different brands or types of the same color marker!

This is actually a great experiment to continue at home; all you need are markers, filter paper (coffee filters or paper towels work just fine), a solvent (rubbing alcohol or water), and a way to hang the paper so that just one end dips into the solvent. We clipped our papers to a pencil using small binder clips and then hung them on a container with a bit of rubbing alcohol in the bottom. Or try it with different colored leaves!

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