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 Experiemnts 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.
This actvity sheet is available as a PDF file. You will need to download Acrobat Reader to be able to read this file.
Our Secondary School editors work hard to distill all the JCE materials to produce a fraction of particular interest to high school teachers. We call it CLIC.
In recent years we have worked hard to better match our advertisers with our readers. When shopping for chemistry education materials, visit our advertisers' WWW sites first.
Take JCE along on your outreach missions. Copies of the Journal, guest access to JCE Online, our publications catalog, and more are available for your participants.