This Week's Experiment - #217 Cabbage Indicator
This week's experiment is a very old classic, but it is still a very
fun one. We will throw in a slightly new twist, to make it easier and
a bit more dramatic. You will need:
a jar of pickled red cabbage from the grocery
vinegar
baking soda
a drinking glass
Traditionally, to do this experiment, you need a fresh, red cabbage.
You grate up the cabbage and then use one of several methods to extract
the juice from it. Instead, we will just open the jar of pickled red
cabbage and drain the juice from that into a glass. You can save the
cabbage to have with your supper. Be sure to at least try a taste, as
many people like it. I know I do.
Pour some of the juice into a saucer. Now comes the fun part.
Sprinkle just a tiny pinch of baking soda into the juice. Watch what
happens. As soon as the white baking soda hits the red cabbage juice,
you get green foam. If you put in much baking soda, you will get a lot
of green foam, so be ready to clean up your mess. Eventually, all of
your red cabbage juice will turn green. It seems that our experiment
is over, but it is not. Now it is time to get out the vinegar. Add a
little vinegar to the green cabbage juice. What do you get? Pink
foam! Again, there is the potential for lots of mess, so either be
careful or have lots of paper towels ready.
Once your cabbage juice is red again, guess what comes next. More
baking soda and more green foam. You can keep going back and forth,
over and over. Why?
The coloring in the cabbage juice is an acid/base indicator. It is a
chemical that changes color. When it is in an acid (such as vinegar),
it turns red. When it is in a base (such as baking soda), it turns
blue-green. There are many other chemicals that do this, and chemists
use them to measure how acid or basic a substance is. You can use it
to find out which substances in your refrigerator are acids and which
are bases. Divide your cabbage juice into two cups. Use a little
vinegar and baking soda, so that the juice in one cup is red and the
other is green. Put one drop of each onto a plate. Add a drop of
lemon juice to each. What happened? The red juice stayed red. The
green juice turned red. That tells us that lemon juice is an acid.
Try the same thing with some of the other things in the refrigerator.
Just be sure to clean up your mess and be sure that no one eats your
experiment.
(Well, I found out that pickled red cabbage is not a worldwide food. If you
can't find it, you can get a fresh, red cabbage and chop some of it into a
blender with a little water. Blend it until the liquid is very red and then
strain it. The liquid will change colors with baking soda and vinegar. You
can also test other red and purple fruits and vegetables, as many of them
will also change colors, although not as dramatically.)
From Robert Krampf's Science Education Company
PO Box 60982
Jacksonville, FL 32236-0982
904-388-6381
krampf@aol.com
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