Dec. 09, 2010

Tabletop Science: Leaf Chromatography Experiment

by Lynn Brunelle

Video by Lynn Brunelle, Tabletop Science

Even green leaves have more colors than you might think! See the hidden colors lurking in the leaf with this cool chromatography experiment.

What You Need:
• Coffee filter
• Scissors
• Green leaves
• Penny
• Rubbing alcohol
• Jar
• Pencil
• Tape

What You Do
1. Cut a 3-4 inch long/1-inch wide strip out of the coffee filter.
2. Cut one end of the strip to a point.
3. Place the leaf about ¼ to ½ inch up from the point and use edge of the penny to roll over the leaf and grind the juices into the filter paper.
4. Let the paper dry, and repeat the process with three different leaves. You want a good green smear.
5. Pour about 1/2-inch of rubbing alcohol into the jar.
6. Measure so that the tip of the point of the paper will be dipped but NO more and tape the strip to the pencil so that it will dangle. Make sure the green smear doesn’t touch the alcohol.
7. Leave it for an hour or so and check back frequently
8. What colors do you see?

What’s going on?
The alcohol is a solvent—it dissolves stuff. As the solvent moves up the paper, it mingles with the green smear and makes a mixture of molecules. Because leaves have different pigments, there are a bunch of different shaped and sized molecules that begin to separate when the alcohol passes through the paper. The heavier molecules are left at the bottom, while smaller ones get carried further up. You end up with a cool, rainbow-like effect.

The finished paper is called a chromatogram.

Bonus Activity: Ink Chromatography Challenge
Scientists use chromatography all the time to get a kind of color fingerprint of a chemical. Forensic Scientists can often solve crimes using this technique. Gather a few different pens and try to see if you can crack this mystery.

What You Need:
• Coffee filter
• Scissors
• Assortment of 4-5 different pens
• water
• 4-5 Jars
• 4-5 Pencils
• Tape
• Paper
• Stapler

What You Do
First make chromatograms of each pen/ink--You’re going to need a set-up for each pen sample.
1. For each pen, cut a 3-4 inch long/ 1-inch wide strip out of the coffee filter and cut each strip into a point at one end.
2. At the top, flat end, use a pencil to label each strip with the pen you’re testing.
3. Then place a strip of ink from that pen across the bottom, pointed end about ¼ to ½ inch up from the point.
4. Pour about 1/2-inch of water into each jar.
5. Measure so that the tip of the point of the paper will be dipped but NO more and tape the strip to the pencil so that it will dangle. Make sure the ink stripe doesn’t touch the water.
6. Leave it for an hour or so and check back frequently.If the ink you are testing does not spread out, re-test it using rubbing alcohol.
7. Let the strips dry and compare your results
8. Tape them on a sheet of paper as a record of the different pen types.
What colors do you see?

Next- The mystery!
1. Have someone write a secret message on a piece of coffee filter paper with one of the pens you tested. Don’t peek.
2. Cut out several individual letters from the note.
3. Staple each letter to the bottom of a strip of coffee filter.
4. Conduct the chromatography experiment above on all the strips.
5. Use the results from your previous chromatograms to determine which pen was used to write the secret note.

Former science, English, and art teacher, author, illustrator, Emmy Award-winning writer and mother of two experiment-loving boys, Lynn Brunelle lives and writes on an island in the Pacific Northwest.

About Lynn Brunelle

Lynn Brunelle is a four-time Emmy Award-winning writer for the television series Bill Nye the Science Guy. An editor, illustrator, and award-winning author, Lynn has created, developed, and written projects for PBS, NPR, and Disney, among others.

The views expressed are those of the author and are not necessarily those of Science Friday.

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