Fall Chromatography

By Amy Cowen on November 10, 2009 4:39 PM

Mashing a pile of fall leaves offers a colorful demonstration of "extraction" and sets the stage for paper-towel-based chromatography.

One of the things that I often miss living in the Bay Area is the definitive visual change of seasons. Having spent many years in Appalachia, I grew up with the splendor of Autumn unfolding around me each September, the array of intense reds and golds giving way to barren branches poised to hold ice and snow through the winter months. It's very different when you live where there is never a hard freeze.

Given that things seem to bloom almost year-round here, I often forget about Autumn foliage, about what it looks like to drive a mountain road and see trees dipped in color, about what it means to have to rake a yard and bag up leaves, about the crisp crunch of them underfoot. Drive an hour south, however, and you run right into changing trees, even ornamental trees in parking lots and around industrial buildings are saturated with color. As I pulled into a parking spot last week for a Science Buddies' meeting, I saw the colors of "fall" in trees all around me and got to thinking about the opportunity these leaves present for studying pigmentation and even chromatography with my kids.

A quick search on the Science Buddies' site turned up a great project with which to dig beneath the surface of things and get a better understanding of what's going on within the leaves at this time of year. With a Science Buddies' Difficulty Level rating of 1 and a timeframe of less than a day, the "What Color Are the Leaves Really Turning?" project idea is perfect for even the youngest of classrooms or for a home-based after-school project. The project involves gathering leaves (a nature walk), sorting them by color (math), and then extracting the pigment by mashing (fun) the leaves in alcohol (a solvent). Once the color has been extracted, ordinary heavyweight paper towels cut into strips allow simple chromatographic analysis of the colors in each extract letting you see the range of colors at play.

There's a lot going on in this simple-to-perform experiment!

Expanding these fundamental concepts and procedures a bit, the Make Your Own Markers project uses color extracted from plants and paper chromatography to make homemade markers. This project can also be done with spices, richly colored vegetables, and other plants, but if an abundance of Autumn leaves are nearby, you've got the makings of a nice set of red and orange markers!