Do some science while taking in the colors of the autumn season! All you need is some filter paper and typical household items.
For a little science lesson on chromatography, check out our other post on flower chromatography here.
Chromatography is a method to separate molecules using a liquid phase (solvent) and a stationary phase (filter paper). You will be able to see the different colors in the leaves separated onto paper. By taking advantage of the difference in solvent solubilities and attraction to the filter paper, the different colored molecules will spread out and dye the paper in a beautiful ombre before your eyes.
Below are some of the compounds responsible for the colors. The yellow (xanthophylls) and orange (carotenoids) are present in the leaf all year long and assist in the transfer of light to chlorophyll. Normally there is so much chlorophyll in leaves that the green color blocks out all the other colors. But when the plant starts to prepare for winter by stopping nutrient delivery to the leaves, the chlorophyll breaks down revealing the oranges and yellows. The red shades (anthocyanins) in most plants are produced during the fall from the sugars leftover in the leaf. Source
Note: I’ve included affiliate links to bring you right to where you can find these supplies.
- Eye protection! (always protect your eyes with goggles or safety glasses when you’re working with solvents)
- Fall leaves with more than one color
- Filter paper (Premium Filter Paper, 15cm, Pack of 100)
- Glass container (like a mason jar or drinking glass)
- Nail polish remover (acetone or ethyl acetate, or both. It’s ok if there are other ingredients, but try not to get one with too much color dye)
- Rubbing alcohol (aka isopropanol) (Swan Isopropyl Alcohol, 99%, Pint, 16 OZ)
- Mortar and pestle (Mortar and Pestle, Porcelain, 2.75-Inch x 1.5-Inch)
- Scissors or knife
- Go pick some beautiful fall leaves and take a picture of each one so you will remember the colors. Try finding two of each leaf so you can compare the results using different solvents.
- Cut your filter paper into strips that will fit into your glass container.
- Pick a leaf to start with.
- If you have a notebook, record the colors of the leaf and your solvent choice for each chromatography run.
- Cut up the leaf into pieces and add them to the mortar.
- Crush and smear the leaf in about 1 tsp of solvent until the solvent has a lot of color in it.
- Take a metal fork or spoon and dip it into your solution, then blot a thin straight line about an inch up from the bottom of your filter paper.
- Once the line is dry, blot another bit of solution right on top of that line.
- Once dry, blot one more time.
- Add 2 tablespoons or so of nail polish remover or rubbing alcohol to the glass container.
- Suspend the blotted filter paper in the solvent in the glass container so that only the very tip of the paper is in the solvent. Make sure the edges of the paper aren’t touching the sides of the glass. Try using tape or a pencil to suspend it in the glass.
- Place something over the top of the container if you can. This will help the smell.
- Wait for the solvent to run up ~90% or so of the filter paper. (different solvents will travel faster than others)
- Repeat this process with other solvents for the same type of leaf and color.
- Repeat this process for other leaves.
If you use different solvents, like acetone vs isopropanol, for some types of leaves the colors will reverse! This is because the molecules responsible for the colors have different solubilities in each of the solvents. The more soluble they are in the that solvent, the further they will travel on the paper since the solvent is “carrying” them along.
The papers on the left are from the red and green leaf below. The left strip was run in acetone and the right strip was run in isopropanol. Do you see how in the left strip, the red color (most likely anthocyanins since it also changed color with pH for us) ran up the paper, but the green (chlorophyll) stayed at the origin line. Conversely, in the right strip with isopropanol, the green ran with the solvent while the red stayed at the origin line. So, we can assume that anthocyanins are more soluble in acetone than chlorophyll (since they traveled further in acetone), while chlorophyll is more soluble in isopropanol than anthocyanins.
This is similar to what we saw with the yellow and red leaves in the right-most picture! Different solvents will give you different separation patterns because of the different solubilities of the molecules are you are separating.
I hope you enjoy doing this little science experiment! Post your results to us on social media! We’d love to see them!