Did you know even though our eyes see a single color, like the color of a marker, you might actually be seeing a combination of colors? Do you think you can separate these colors? Chromatography comes from the Greek words “chroma”, meaning color, and “graph”, meaning to write. In this activity, you will be able to combine several colors to create a tie-dye effect and also solve an ink mystery.
- 2 Coffee Filters
- 3 Cups
- 3 Wet Sponge Pieces
- 3 Washable Markers (1 Red, 1 Blue, 1 Yellow)
- 2 Different Washable Black Markers
1. With the first coffee filter, cut out three strips about 2 inches long.
2. Have a friend dot one of the strips with one of the black markers near the bottom of the strip. Make sure you don’t know which marker made the dot.
3. Using a pencil, mark one of the
unmarked coffee filter strips with and ‘X’ and the other with an ‘O’ at the top. You must use a pencil so the label will stay in place!
4. Now, at the bottom of the strip marked 'X', make a dot with one if the black markers. At the bottom of the strip marked 'O', make a dot with the other black marker. Remember which marker made which dot.
5. In each cup, place a damp sponge. The sponge should fit
flat at the bottom of the cup.
6. Carefully place the coffee filter strips in each cup with only the bottom edge touching the sponge.
7. Watch as the water is sucked up by the coffee filter. What colors do you see? Do both black markers look the same as the color moves up the strip?
8. Once the water has traveled almost to the top of the strips, take them out of the cups and compare.
9. Which marker do you think made the mystery dot? ‘X’ or ‘O’?
10. With the second coffee filter, cut out a T-shirt shape.
11. Use any combination of red, blue, and yellow markers to design your T-shirt. The best results happen when you use short lines and/or dots. Don’t color in the T-shirt completely!
12. Crumple up the T-shirt and place in a cup with a damp sponge and then place another damp sponge on top. Make sure it is making good contact with both without being squashed. Watch and observe how the water is absorbed and spreads through the filter. Lay out or hang the T-shirt to dry!
How did the ink move and spread? Washable markers use inks that are made of colored pigments and water, which means they are water soluble, or able to dissolve in water well. That’s why they’re easy to wash off your hands!
In the activities we conducted, the water is soaked through the filter paper. Molecules in ink and other mixtures have different characteristics which allows them to travel at different speeds. The ink molecules of each color will go faster if they are more attracted to the water (mobile phase)than the coffee filter (stationary phase). Other ink molecules will go slower if they are attracted more to the filter than the water. The solvent, or the water in our experiment, moves using capillary action when the attraction of the solvent to the paper, or adhesive force, and the attraction of the solvent to itself, or cohesive force, work together to pull the solvent up.
You have probably seen capillary action happening without even knowing it! How about a straw left in a cup of water? The cohesive force binds the water molecules together, creating strong surface tensions, and the adhesive force pulls the water towards the inner straw walls as well. This combined effort is a little stronger than gravity, so the water will rise inside the straw a little higher than the rest of the water.