The Colors Inside - Photosynthesis and Paper Chromatography

My education has spanned a larger than average corner of the STEM world.  I have a BS in Biology (from an Engineering School), a MA in Environmental Biology and Ecology (from a Liberal Arts School) and an ME in Biological and Chemical Engineering (from a Science School).  So when I saw this experiment combine plant biology and separations, I got a little excited.  I tried to do the extraction version, where you place torn up leaves in acetone or rubbing alcohol, but it takes 30 minutes to extract plus another 30-90 to separate, and with an hour meeting, that wasn't going to cut it.  Then, I tried rubbing some of the color onto a filter with a coin.  That transfer worked well, but the rubbing alcohol is a horrible solvent!  The acetone (regular nail polish remover concentrations) worked very well.  The Japanese Red Maple was my best leaf, with a red, green and yellow/orange band noticeable even on an unbleached coffee filter.



Links to the full worksheet (which includes two versions of the experiment, based on your time availablity and kids' age range) as well as an additional data sheet over in Google Docs.  But, here's the basic experiment, if you don't want or need the formal downloads.

Materials
Coffee filters cut into 1" wide strips
Tall, skinny glasses (I used mini-pint glasses). NOTE: make sure it's compatible with acetone
Acetone based nail polish remover
Leaves
Coin
Pencil for labeling
Clips or tape

Methods

1. Place a leaf under the coffee filter and rub with a coin about an 1" up from the bottom. You should get a good color transfer onto the paper.  It's ok if you got some leaf pieces, but try not to tear the paper
2.  Pour about 3/4" of acetone into the bottom of the glass
3. Place the paper into the glass so that the bottom of the paper is in the acetone, but the leaf rubbing is above it. Secure the paper to the glass so it doesn't fall in or out
4. Wait about 15-30 minutes

What's happening?

The acetone (the mobile phase) is traveling up the paper (stationary phase) and bringing the dyes along with it.  The dyes have different solubility in the acetone, which is causing them to separate.  Depending on the leaf, you'll see red, yellow and/or orange in addition to the green.  For older kids, measure the distance each color traveled and divide it by the distance the acetone traveled to get the "relative distance" for each color.  Each leaf will have a unique pattern (a chromatogram) and you should be able to determine an "unknown" leaf by it's chromatogram and relative distance of each color. 
When the leaves change colors in the fall, the green pigment (chlorophyll) stops being produced, allowing the yellow and orange (carotenoids), which are present year round, to finally be seen.  Red pigment (anthrocyanin) is created in the leaves when there are warm days and cold nights in the fall.  The tree is still making sugar during the warm day, and the anthrocyanin helps move it out of the leaves to store the food before it falls with the leaf.  Browns are caused by tannins, which is a waste product and can be used for protection against leaf eating insects such as the gypsy moth.

For More Info:
 Kids Discover has a great photosynthesis infographic you can download for free (you need to have a free account)