Weird Science: Chalk Chromatography

Things you need:

• Ink, dye, or food coloring

• White chalk

• Rubbing alcohol – Isopropyl alcohol

• Plastic wrap

• Small cup

The Experiment:

Make a band of color with your ink, dye or food coloring around a piece of chalk, about one centimeter from the end. Depending on what results, you'd like, you can either use a single color to see what multiple colors that one color is made of. Or if you'd like more bands of colors, you can put multiple colors in the same place on the chalk. Pour about half a centimeter of rubbing alcohol into the cup so that the level of the alcohol is below the band of color on your chalk. Place your chalk in the cup with the color band side closest to the alcohol (but should not be submerged, or under the liquid). Cover the cup with plastic wrap to keep the alcohol from evaporating. What happens to the color band after a few minutes? What happens if you leave the chalk in for a longer period of time? Please let the chalk dry completely before using it for writing.

So that's how it works…

Matter exists in three states: solid, liquid, and gas. Sometimes it is easy to see the different parts that make up a mixture. For example, in a glass of iced tea, it is easy to separate the ice cubes from the tea. However, sometimes it is very difficult and even impossible to see the different parts of a mixture. Scientists know that the main parts that make up the air we breathe are nitrogen, oxygen, and hydrogen. However, it is impossible for us to see this mixture. Therefore, it is very difficult to separate this mixture into its separate parts.

Scientists have developed ways to separate mixtures into pure substances. Chromatography (literally translated means "color writing") is one way in which mixtures can be separated. The isopropyl alcohol will move up the chalk by surface tension, similar to how water is absorbed into a napkin. As the alcohol moves up the chalk, it picks up the ink pigment as it travels. In this experiment the separation of the colors occurs because the different colors of the ink have different weights and sizes, therefore, some will travel farther up the chalk than others.