- 3 leaves of red cabbage
- a blender and permission from an adult to use it
- hot water
- a sieve
- a large glass or glass bowl
- powdered soap or detergent
What to do:
- Your first task is to turn the cabbage leaves into mush. Start by tearing the leaves into scraps about the size of a penny.
- Put the scraps in the blender and cover them with hot water. Cover the blender and purée the scraps.
- Hold the sieve over the glass and pour that cabbage mash through it to fill the glass with the juice. Throw out the mush.
- Add 15 milliliters (1 tablespoon) of powdered soap to the glass and stir. Does the color of the juice change?
What's happening?
Cabbage juice is an acid-base indicator. It turns more red when it's mixed with an acid and more blue when mixed with a base. Since soap makes the cabbage juice turn bluish purple, soap must be a base.
Strong bases, like lye, can hurt your skin. Soap is only a mild base, but it still irritates the tender nerves around your eyes. That's why your eyes sting until you rinse the soap out. Soap in your mouth is no fun either—all bases taste bitter.
From Soap Science: A Science Book Bubbling with 36 Experiments by J.L. Bell. Published by Addison-Wesley. Text copyright © 1993 by J.L. Bell. For additional information, contact the author at JnoLBell@earthlink.net.
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