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What You Need:
- Paper Towel or Coffee Filter
- Several different kinds of black markers
Cut strips from the paper towel about 1 inch wide – one for each type of marker. Scribble across the bottom of one of the paper towel strips with each kind of marker. Scribble about one inch from one end of the paper towel strip. Tape the OTHER end of the strip to the maker you used to scribble on that strip. That will help you remember which marker goes with each paper towel strip.
Now hang the paper towel strips above the bowl of water so that only a little bit of the scribble end is in the water. Do not submerge the pen scribbles! Check on the paper towels in an hour. What has happened to the pen marks?
What you see happening on the paper towel strips is called chromatography. The color of the ink in markers is made by mixing different pigments together. A pigment is a substance that makes color, like ink or dye. To make black, several pigments are mixed together. When the end of the paper towel strip is submerged in water the water soaks up through the paper towel. When the water passes through the black ink marks it takes the pigment colors with it. Different colors of pigments travel with the water at different rates because the molecules of some pigments stick to the paper more strongly than others. So, as the water travels it separates the colors. This is called chromatography – separating the parts of a mixture so that you can see them one at a time. It looks like there is more than one way to make black!
Here are websites and books that will help you understand solutions and experiment with chromatography:
- Exploratorium Chromatography Activity Sheet
- ZOOM: Paper Towel Chromatography
- Yes Mag: Paper Chromatography
- Candy Chromatography
Mixtures and Solutions Chromatography (pages 34-38)
Words to Know:
Chromatography - A process that separates a mixture by passing it through something that will separate its parts.
Mixture – A substance made by mixing two or more substances together. The molecules of the substances don’t join together so the substances can be easily separated.
Homogeneous Mixture – A type of mixture that is the same throughout. Salt water and ink are good examples.
Pigment - A substance used for coloring; ink, dye, etc.