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 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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