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Ever wonder why leaves change colors in the fall?
The colors that we see are created by pigments in the leaves. A pigment is a molecule that is a certain color based on the wavelengths of light it absorbs and reflects.
There are several types of pigments that give plants color but one of the most important is chlorophyll. Chlorophyll is a green pigment that absorbs sunlight and allows plants to create their own food using photosynthesis. Two other important categories of pigments are carotenoids and anthocyanins. Carotenoids appear yellow or orange. They are the pigments that give color to corn and carrots. Anthocyanins are pigments that appear purple, red or blue.
Most of the year, chlorophyll is produced in such high quantities that it masks all other pigments. In the fall, however, chlorophyll production drops in preparation for winter and we are able to see the other pigments present in the leaves.
Different trees produce pigments in different quantities and other factors such as temperature and moisture can influence what color the leaves on a tree turn.
In this experiment we will be using chromatography to separate the different pigments in fall leaves. Chromatography is a scientific technique for separating different components from a mixture.
This activity is best for elementary students. It includes about 30 minutes of preparation and the experiment takes approximately two days.
- Small glass cups or jars
- Isopropyl alcohol (rubbing alcohol)
- Gathered fall leaves separated by color, each group should be from the same tree.
- Paper towels cut or folded into 2-to-3-inch strips
- A muddler, large whisk or wooden spoon
1. Once you have collected and sorted your leaves, tear them up into small pieces and put each group into one of the glasses.
2. Pour enough alcohol into each glass to just cover the leaves. An adult should assist younger learners with this step.
3. Use the back of the whisk or the muddler to crush the leaves into the alcohol.
4. Leave in a dimly lit room for at least 24 hours.
5. Place a paper towel strip into each glass so that the very edge just touches the alcohol. If your glass is too large to rest the paper towel in, tape the towel to a chopstick or pencil and use it to suspend the paper towel over the cup.
6. Leave in a dimly lit room for 24-48 hours.
7. When you return, your paper towel strips will be dyed with the pigments in the leaves. What colors can you see on each strip?
Now that you’ve got the hang of chromatography, experiment with leaves from different trees or different colored leaves from the same tree. Try repeating the experiment later in the season to see how the pigments have changed.