Chalk Chromatography

Separate Pigments Using Chalk Chromatography

By Anne Marie Helmenstine, Ph.D., About.com Guide

See More About:

• chromatography
• pigments
• chalk
• separations
• color chemistry

These chalk chromatogaphy examples were made using chalk with ink and food coloring.

Anne Helmenstine

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Chromatography is a technique used to separate components of a mixture. There are many different types of chromatography. While some forms of chromatography require expensive lab equipment, others can be performed using common household materials. For example, you can use chalk and alcohol to perfom chromatography to separate the pigments in food colorings or inks. It's a safe project and also a very quick project, since you can see bands of color forming within minutes. After you've finished making your chromatogram, you'll have colored chalk. Unless you use a lot of ink or dye, the chalk won't be colored all the way through, but it will still have an interesting appearance.

Chalk Chromatography Materials

• chalk
• alcohol (isopropyl alcohol or rubbing alcohol seems to work best)
• ink, dye, or food coloring
• small jar or cup
• plastic wrap

1. Apply your ink, dye or food coloring to a piece of chalk about 1 cm from the end of the chalk. You can place a dot of color or stripe a band of color all the way around the chalk. If you are mainly interested in getting bands of pretty colors rather than separating individual pigments in the dye, then feel free to dot multiple colors, all in the same place.

2. Pour enough rubbing alcohol into the bottom of a far or cup so that the liquid level is about half a centimeter. You want the liquid level to be below the dot or line on your piece of chalk.

3. Place the chalk in the cup so that the dot or line is about half a centimeter higher than the liquid line.

4. Seal the jar or put a piece of plastic wrap over the cup to prevent evaporation. You can probably get away with not-covering the container.

5. You should be able to observe the color rising up the chalk within a few minutes. You can remove the chalk whenever you are satisfied with your chromatogram.

6. Let the chalk dry before using it for writing.