The red colors of leaves in the fall, and the colors of radish skins, beets, and some cabbages result from pigments known as anthocyanins. This activity makes use of the fact that these substances are also acid-base indicators. The earliest definition of acids was given by Robert Boyle, who stated that acids turned plant juices red. In his book Experiments upon Colours, published in 1663, Boyle described a means of making indicator paper from the juices of violets, cornflowers, roses, snowdrops, brazilwood, primroses, cochineal, and litmus. Use of such natural acid-base indicators predates the use of synthetic indicators such as phenolphthalein by over 2000 years.
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The "Chemistry Teacher Connection" (CTC) is especially for high school chemistry teachers. For only $40/year, it offers an online-only subscription to CLIC along with membership in the Division of Chemical Education, normally $65/year. CTC subscribers receive access to all articles and supplements from 1996 through the current issue.
Through special arrangement with the ACS, JCE High School CLIC is now able to provide subscribers with online access to Chemical & Engineering News articles that have been selected specifically for secondary science instructors and their students.
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