Finding Hidden Colors in Leaves

1. Finding Hidden Colors in Leaves 4th grade chromatography experiment Dennis Sparks,sparks@caer.uky.edu University of Kentucky, Center for Applied Energy Research 2540 Research Park Dr., Lexington, KY 40511 859-257-0274

2. Overview • Objective • Materials • Procedure • General Hints & Observations • Conclusion

3. Experiment Objective To demonstrate the use of paper chromatography to separate some of the chemical compounds found in tree leaves

4. 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

5. Procedure 1. Cut or shred 1-2 leaves from one type of tree into small pieces. 2. Place these pieces in a glass jar, half fill the jar with isopropyl alcohol and replace the cap. 3. 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. 5. Lightly crease filter paper strips lengthwise, forming a long shallow ‘V’. 6. 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. 7. 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. 8. Cover the plastic cup with a small paper plate (with student’s name written) and wait 10-20 minutes. 9. Remove and examine the filter paper strips for bands of slightly different colors.

6. 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.

7. 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.