Fall is a great time to jump in a pile of leaves, but what’s the science behind why they change colors and fall off the trees?
Leaves contain chlorophyll, which makes them green and makes photosynthesis possible. Photosynthesis is the process that lets plants use sunlight to make energy. But as the days get shorter and the nights get longer in the fall, trees get less sunlight and less water. They prepare for winter and the next growing season by blocking the flow of chlorophyll to the leaves.
The green chlorophyll and is so dominant that it hides all the other colors in the leaves. But in the fall, the fading green chlorophyll allows the other colors to finally shine through. So we see the beautiful yellows, oranges, reds and purples hidden in the leaves.
To figure out what color a leaf would be without the dominant chlorophyll color, we can see the colors hidden in leaves by doing this science experiment.
2 or 3 green leaves from the same tree
Plastic baggie (or plastic wrap)
Paper coffee filter
Plastic knife or spoon
Small shallow bowl
Hot tap water
1. Tear or chop the leaves into tiny pieces and put them in the jar.
2. Pour rubbing alcohol over the leaves until they are just covered.
3. Use a plastic knife or spoon to mash and stir the leaves into the rubbing alcohol until the alcohol turns slightly green. Really mash it good for the best results. (NOTE: Rubbing alcohol can be harmful. Use in a well-ventilated area, and avoid contact with skin.)
4. Cover the jar with the baggie or plastic wrap and place it in a small bowl and pour about an inch of hot water into the bowl to heat the jar.
5. Keep the jar in the water for at least 30 minutes, swishing the jar about every 5 or 10 minutes to stir the leaves a bit. The alcohol should be a very dark green (leave longer if needed). If you can, wait even 45 minutes or an hour. Replace the hot water if it cools off.
6. Remove the jar from the water bowl and uncover it. Cut a strip in the coffee filter so that one end of the strip can reach the rubbing alcohol. You can tape it to the edge of the jar.
7. After 30-90 minutes the liquid will travel up the coffee filter and the colors will separate as the alcohol evaporates from the coffee filter. Different colors will travel different distances up the paper as the alcohol evaporates. The green leaves may show yellow, orange, and red.
How does it work?
In this science experiment the rubbing alcohol and energy (hot water) separates the colors. That allows you to see the colors hidden in the leaves.