Transcript Slide 1

Finding Hidden Colors
in Leaves
4th grade chromatography experiment
Dennis Sparks,[email protected]
University of Kentucky,
Center for Applied Energy Research
2540 Research Park Dr., Lexington, KY 40511
859-257-0274
Overview
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Objective
Materials
Procedure
General Hints & Observations
Conclusion
Experiment Objective
To demonstrate the use of paper
chromatography to separate
some of the chemical compounds
found in tree leaves
Materials Needed
•Whatman #42 filter paper, cut into ~1” x 4”
strips. (Substitution: coffee filters)
•Isopropyl alcohol (91% preferred, 70% is
acceptable)
•A collection of leaves from several different
types of trees
•Small glass bottles with lids, such as baby
food jars
•Medicine droppers or disposable pipettes*
•18 oz disposable plastic cups (not Styrofoam)
•Small paper plates*
*1 per student or group
Procedure
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Cut or shred 1-2 leaves from one type of tree into small pieces.
Place these pieces in a glass jar, half fill the jar with isopropyl
alcohol and replace the cap.
Repeat this for several different types of trees (maple, oak,
pine, etc.)
Let stand for 1-3 days until the alcohol turns green as it
extracts the chlorophyll and other compounds from the leaves.
Lightly crease filter paper strips lengthwise, forming a long
shallow ‘V’.
Use a dropper to dispense a few drops of the colored alcohol
onto filter paper strips about 1” from one end and let it dry.
Pour ½” of alcohol into plastic cup and place the strip into cup.
The drop of leaf extract should be near, but not submerged in
the alcohol.
Cover the plastic cup with a small paper plate (with student’s
name written) and wait 10-20 minutes.
Remove and examine the filter paper strips for bands of slightly
different colors.
General Observations and
Helpful Hints
As the alcohol wicks up the filter paper strip, it passes the drop of
extract and begins to carry the chemical compounds with it as it
continues to move upward. Certain compounds interact more
strongly with the filter media, retarding the rate at which they
move. This causes the compounds to separate from one another.
This can be seen as slightly different bands of color on the
filter paper.
You can use either 91% or 70% isopropyl alcohol, but the higher
concentration is preferred. The rest is water, which wets the
filter paper and retards the wicking action of the alcohol.
Bending the filter paper strip into a shallow ‘V’ will help to stiffen it
so that it doesn’t curl and sink into the cup. Covering the cup
with a paper plate reduces the evaporation rate, increasing the
alcohol vapor in the cup, thus quickening the rate at which the
liquid alcohol in the bottom of the cup will climb the filter paper.
Have students write their names on the plates, along with the
type of leaf.
Observations, cont.
Since this experiment’s timeframe is very short, the
resulting color bands are not very strong. The most
you’ll usually obtain is a smearing of the green that
is the chlorophyll, with tinges of brown tannin.
You can substitute food coloring for the leaf extract.
Green food coloring will readily separate into blue
and yellow. Mixing red and blue food coloring will
produce purple, which can be re-separated with this
method. Both of these will produce vivid bands of
color and illustrate the concept of chromatography.