You and Your Students!
Vicki Cobb, Education World Science Editor
Change the color of a mixture by adding different substances.
Setting the Scene (Background)
I've known about the color-changing properties of red cabbage juice for so long that I sometimes forget how exciting and effective it is for a fresh audience. It's like the old magician's "water changing into wine" trick. Most importantly, it gives kids ideas about trying things just for fun to see what happens.
If you remember the "litmus" test from your own school days you have a general idea of what this demonstration will illustrate. Cabbage juice can be used to distinguish between two important kinds of chemicals -- acids and bases
Do this as a demonstration; but explain to students how they can make the cabbage juice in case they want to try it when they get home.
To prepare the red cabbage juice:
Perform the following demonstration for students:
What color does the mixture become with each added ingredient? (Some things will turn the red juice pink, while other things will turn it green)
Ask students to take notes -- to answer these questions as you proceed:
Be sure students do not mix bleach and ammonia. The combination of bleach and ammonia can be very harmful.
Behind the Scenes
The cabbage juice contains a pigment that changes color depending on the chemicals around it.
See if other colored pigments from fruits and vegetables react the way the cabbage juice reacted. Try making extracts of beets, cherries, or blueberries. You might try violets or irises by chopping them up and mashing them in water.
Article By Vicki Cobb
Copyright © 2005 Education World