Plant Chromatography for Kids

 - by KitchenPantryScientist

What started out as a food science experiment turned into a seasonal one this morning, and we ended up outside pulling leaves off our Maple tree to see how the pigments from a red leaf would compare to those from a green one. Liquid chromatography allows you to separate the pigments (molecules that give plants color) using paper as a solid medium for the molecules to travel up, and alcohol as the solvent that separates and carries the pigments up the paper at different speeds, depending on how large they are.

To do this experiment, you’ll need a green leaf, and one or more that has turned color (we found a red and green one from the same tree!)  In addition, you’ll need a coin, a jar, a pencil, paper towels or coffee filters and rubbing alcohol. Young children MUST be supervised during this experiment since rubbing alcohol is a toxic substance if ingested!

Balance the pencil on the lip of the jar and cut a strip of paper towel or coffee filter long enough to hang (folded in half) over your pencil and dangle with both ends just above the bottom.

Draw a pencil line about half an inch above the bottom of the strip on one side.  Wrap a leaf around the coin (dimes work well) and press it down against the line on the left side, hard enough to rub color onto the line. (See photo above!) Do the same thing with the other leaf. Get as much color as possible onto each spot and let dry for a few minutes, or dry with a blow dryer.

Fill the jar with just enough rubbing alcohol so that the bottom of the strip will touch it, but the spots of color will not.  Hang your paper strip over the pencil with the bottom touching the alcohol. (You can have it doubled or have one half hanging outside the jar. Both worked for us.) Try to make sure that the strip is hanging evenly so the color will travel straight up.

Watch as the colors travel up the strip and take the strip out of the alcohol before they reach the top.  Let it dry and observe. The colors may be faint, but you should be able to make them out.

What do you see?  Green leaves contain a pigment called chlorophyll, which helps plants do photosynthesis (get energy from sunlight, water and carbon dioxide.)  In the fall, many trees stop making this pigment, which is why the other colors in the leaves become visible. Are your results consistent with this?

We tried the same experiment to compare spinach leaves that were fresh or had been microwaved in a ziplock (blanched). Although I read that the pigments change when vegetables are cooked or stored, we didn’t see much difference, except a brown smear near the very bottom.  What other veggies could you try this experiment with?

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