Separate Colors in a Fall Leaf using Chromatography
Fall is a beautiful time of year with all the leaves are changing colors. Children wonder why it happens, so it's a great opportunity to use the power of science to show them the separate leaf colors and to explain how the leaves actually change colors.
What you need:
- Leaves that have changed color
- Small jar (baby food jars are the best)
- Lid for the jar (aluminum foil or plastic wrap if you don't have a lid)
- Rubbing alcohol
- Paper coffee filter
- A shallow pan or tray
- Hot water
- Tape
- A pen
- Plastic knife or spoon
- A timer
What you do:
NOTE: Adult supervision is required for this activity. Please read all instructions completely before starting. Observe all safety precautions.
1. Collect two or three fairly large leaves. Tear or chop them up and put them into a jar.
2. Add rubbing alcohol to the jar so that you completely cover the chopped up leaves. Use the plastic knife or spoon to grind the leaves into the alcohol and break them up.
NOTE: Rubbing alcohol can be dangerous if mishandled or misused. Please read and follow all warnings on the rubbing alcohol bottle.
3. Loosely cover the jar with the lid (aluminum foil or plastic wrap). Fill the shallow pan with about an inch of hot water and carefully place the jar into the pan. Gently swirl the jar every five minutes and replace the hot water as it cools off.
4. Leave the jar in the water for at least half an hour or until the alcohol becomes colored. The deeper the color of the alcohol the better.
5. While you're waiting, cut a long strip of coffee filter paper. When the jar is ready, remove it from the water and uncover it. Put the strip of coffee filter paper into the jar so that one end is in the alcohol and the other end is outside the jar. Secure the dry end with a piece of tape to the outside of the jar.
6. The colored alcohol will travel up the paper. If you leave the paper in the alcohol for about 90 minutes or so, each color of chlorophyll (as well as other "color" chemicals) will travel a different distance up the paper as the alcohol evaporates. You should be able to see different
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shades of green, yellow, orange, red, etc, depending on the color and type of leaves you're using.
7. Remove the strip of paper and let it dry by taping it to a plain piece of paper.
Why the Leaves Change Color
During summer, the leaves of trees are factories producing sugar from carbon dioxide and water by the action of light on chlorophyll. Chlorophyll causes the leaves to appear green. Water and nutrients flow from the roots, through the branches, and into the leaves. The sugars produced by photosynthesis flow from the leaves to other parts of the tree, where some of the chemical energy is used for growth and some is stored.
The shortening days and cool nights of autumn trigger changes in the tree. One of these changes is the growth of a corky membrane between the branch and the leaf stem. This membrane interferes with the flow of nutrients into the leaf. Because the nutrient flow is interrupted, the production of chlorophyll in the leaf declines, and the green color of the leaf fades.
If the leaf contains carotene, as do the leaves of birch and hickory, it will change from green to bright yellow as the chlorophyll disappears.
In some trees, as the concentration of sugar in the leaf increases, the sugar reacts to form anthocyanins. These pigments cause the yellowing leaves to turn red. Red maples, red oaks, and sumac produce anthocyanins in abundance and display the brightest reds and purples in the autumn landscape.
The range and intensity of autumn colors is greatly influenced by the weather. Low temperatures destroy chlorophyll and promote the formation of anthocyanins, if the nights stay above freezing.
Bright sunshine also destroys chlorophyll and enhances anthocyanin production. Dry weather, by increasing sugar concentration in sap, also increases the amount of anthocyanin. So the brightest autumn colors are produced when dry, sunny days are followed by cool, dry nights.
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