Download separation of the colors in a leaf using paper chromatography

SEPARATION OF THE COLORS IN A LEAF USING PAPER CHROMATOGRAPHY
MATERIALS
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Green leaves from several different trees (Trees with a dramatic color change, like maples, work
best)
Beaker
Rubbing alcohol
Plastic wrap
Chromatography or filter paper (you can use coffee filters)
Pencil
BACKGROUND
We all enjoy the colors of autumn leaves. Did you ever wonder how and why a fall leaf
changes color? Why a maple leaf turns bright red? Where do the yellows and oranges come
from? To answer those questions, we first have to understand what leaves are and what
they do.
Leaves are nature's food factories. Plants take water from the ground through their roots.
They take a gas called carbon dioxide from the air. Plants use sunlight to turn water and
carbon dioxide into glucose. Glucose is a kind of sugar. Plants use glucose as food for
energy and as a building block for growing. The way plants turn water and carbon dioxide
into sugar is called photosynthesis. That means "putting together with light." A chemical
called chlorophyll helps make photosynthesis happen. Chlorophyll is what gives plants their
green color.
As summer ends and autumn comes, the days get shorter and shorter. This is how the trees
"know" to begin getting ready for winter.
During winter, there is not enough light or water for photosynthesis. The trees will rest, and
live off the food they stored during the summer. They begin to shut down their food-making
factories. The green chlorophyll disappears from the leaves. As the bright green fades away,
we begin to see yellow and orange colors. Small amounts of these colors have been in the
leaves all along. We just can't see them in the summer, because they are covered up by the
green chlorophyll.
The bright reds and purples we see in leaves
are made mostly in the fall. In some trees, like maples, glucose is trapped in the leaves after
photosynthesis stops. Sunlight and the cool nights of autumn cause the leaves turn this glucose into a red
color. The brown color of trees like oaks is made from wastes left in the leaves.
It is the combination of all these things that make the beautiful colors we enjoy in the fall.
THEORY
Leaves contain different pigments, which give them their color. Green chlorophyll is the most common
type of pigment, but there are also cartenoids (yellow, orange) and anthocyanins (red). Chlorophyll, which
is essential for photosynthesis, usually hides the other pigments, except when autumn comes along and it
begins to break down. This is why leaves turn different colors in the fall. This project will expose the hidden
colors in a green leaf and predict what color it will be in the fall!
PROCEDURE
Keep leaves from different trees separate and follow the steps below for each set of leaves, so you can
compare results.
1. Tear the leaves into several pieces and place them in a beaker or glass, then add just enough
rubbing alcohol to cover them. Cover the beaker with plastic wrap to keep the alcohol from
evaporating.
2. Put the beaker in a dish of hot tap water for about 30 minutes, until the alcohol turns green as the
pigments from the leaves are absorbed into it.
3. Cut a strip of filter paper about a half inch wide and tape it to a pencil. Suspend the pencil across
the beaker and let the strip just barely touch the alcohol and pigment mixture.
SUMMARY
A bit of the mixture will travel slowly up the paper. After about 30-90 minutes you should be able to see the
"green" color break up into several different colors as the different pigments begin to separate. You'll see
different shades of green, and perhaps other colors as well. Which leaves had the most colorful pigments?
Based on your experiment, which trees' leaves do you think will turn the brightest and least brightest colors
this fall?
1. Can you identify which pigments are present?
2. Do you think the season in which the leaves are picked affect their colors?
Tips:
1. Experiment with other types of chromatography paper.
2. You can substitute other alcohols for the rubbing alcohol, such as ethyl alcohol or methyl alcohol.
3. If your chromatogram is pale, next time use more leaves and/or smaller pieces to yield more
pigment.
REFERENCES
http://www.sciencemadesimple.com/leaves.html, “Why do Fall leaves change color?”, I Can Read: Fall
Leaves, 27 June 2009.
http://www.hometrainingtools.com/article.asp?ai=1548&bhcd2=1246129259, “Leaf Chromatography”, 27
June 2009.
http://chemistry.about.com/cs/howtos/ht/paperchroma.htm, “How To Do Paper Chromatography
With Leaves”, by Anne Marie Helmenstine, Ph.D., 27 June 2009.