Kids, did you know that you can draw pictures with fruits and vegetables, and that their colors can be changed using chemistry? 

Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

To do this activity you will need an assortment of foods such as a radish, red cabbage, a carrot, grape juice, and spinach leaves. You will also need a sheet of white construction paper, vinegar, a 50/50 solution of baking soda in water, and cotton swabs. Rub the skins of the foods onto the paper, making three circles of color for each food, and label them. Use a swab for the grape juice. Again using a swab, rub the vinegar onto one circle of each food and the baking soda solution onto the second circle. Leave the third circle alone as a control. What do you observe?

Among other things, there are chemical compounds called "anthocyanins" in some plants. These compounds have different colors depending upon the strength of an acidic or basic solution. The vinegar (acetic acid) is a weak acid and the baking soda (sodium bicarbonate) solution is a weak base. Because of their ability to change colors, anthocyanins are one kind of indicator for determining the strength of an acid or base. Your results should have showed you that radishes, red cabbage, and grape juice all contain anthocyanins. They are also present in the petals of red roses. The major pigment in many green plants is chlorophyll, while that in carrots is called carotene; these compounds do not act as indicators. Try other fruits, vegetables, or plants with your new chemical testing system!  

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Kathleen Carrado Gregar, PhD, Argonne National Labs 
[email protected]
June 1993

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Reference: Ann Benbow of ACS, Coordinator of Pre-High School Science Office, who presented this at the CHEERS/PACTS Workshop on 4/17/93 at W. Aurora H.S.