Kids, how much do you know about lemons? Here is a very quick and easy test of the power of lemon juice. Have an adult partner make a mug of hot tea for you from a teabag. Use a white or clear mug so that you can easily see the color of the tea. Now take a fresh lemon wedge and squirt in a few drops of the juice. Upon stirring, certain kinds of tea will instantly lighten up considerably, "magically", right before your eyes. In some cases this works so well that you can make a magic trick out of it. Squirt the lemon juice into a spoon first, out of sight, and then stir it in the tea to watch the color change. Try different types of teabags to see which work best. I have found that the best are the so-called "black" teas (see "Chemistry in a Teabag" from this column in October 1998), such as: regular Lipton tea, Superior orange pekoe & pekoe cut black tea, and Pickwick English Blend traditional black tea.
Please note: All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.
What appears to be happening is a type of mild bleaching process. In fact, the vitamin C (ascorbic acid) in lemons is known to be a bleach (see another one of our columns, "Clearly it's Vitamin C" from October 1999). Bleaching is the process of removing the natural color of something (cloth, paper, wood, food, etc.). Chemists call the processes either "oxidizing" or "reducing". Vitamin C is an organic compound, which means that it contains carbon, hydrogen, and oxygen (the formula is actually C6H8O6). It happens to oxidize very easily, which means that it is a good reducing agent. Tannins or other highly colored organic molecules in the tea are reduced when the ascorbic acid is oxidized.
If you were to stain a white cotton rag with some black tea and let it dry, you could try to remove it by spotting with lemon juice and letting it dry in the sun before washing. This might also work if tea were to accidentally stain a t-shirt, tablecloth, or linen napkin.
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Kathleen Carrado Gregar, PhD, Argonne National Labs
[email protected]
May 2002
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Reference: Check http://library.thinkquest.org/27034 for all kinds of bleaching.
