Red Cabbage Tells the Tale
FOOD EXPERIMENT: RED CABBAGE INDICATOR
_____________________________________________________________________________
The following experiment is designed to supplement activities in already
existing food and nutrition projects. First read the section "Caution-Be
Science Wise" and then help 4-H members work through the experiment.
CAUTION - BE SCIENCE WISE!
Before you begin any science experiment, you should always follow these basic
rules:
1. Be sure to read ALL directions before starting the experiments.
2. In many experiments, a "control" is used. The control is the standard
against which you compare the experimental food.
3. When doing the experiments, keep everything the same as the control except
for the one thing the directions say to change. Use the same size pans,
the same type of bowls and the same mixing speeds. Be sure that just ONE
thing changes each time.
4. Be sure to label each food when conducting these experiments. Use a piece
of masking tape, a marking pencil, a crayon or anything that will help you
remember which food is which. In some experiments, you'll have no trouble
telling the foods apart. In others, the foods may look the same.
5. The experimental food is not meant to be perfect. Since you are purposely
doing something wrong, you can't expect it to be perfect! So it's all
right when something turns out "bad." That's what is SUPPOSED to happen.
6. Not all experiments in food science yield products that can be eaten.
NEVER SAMPLE PRODUCTS IN AN EXPERIMENT UNLESS YOUR LEADER SAYS THEY ARE
SAFE TO EAT.
7. Records are an important part of any scientific project. You should write
down what happens in each experiment. Experiments may not turn out exactly
the same every time. Recording your results will help you and others who
may try to repeat your experiment.
RED CABBAGE TELLS THE TALE
In The Red Cabbage Riddle experiment, you discovered that the pigments in red
cabbage change color when an acid or a base is added. This ability to change
color makes red cabbage useful as an indicator. An indicator is a substance
that can show if other foods are acids or bases. The color of an indicator
changes depending on whether a food added to it is an acid or a base.
Here's how you can make an indicator.
INGREDIENTS
1/2 of a red cabbage
1 to 2 cups of water
1/4 teaspoon vinegar
1/4 teaspoon baking soda
And all or some of the following:
1/4 teaspoon cream of tartar
1 teaspoon fruit juice
1 teaspoon cottage cheese
1 orange section
1 teaspoon soft drink
1 slice tomato
1 slice apple
1 egg white
EQUIPMENT
2 large bowls
Grater
Measuring cups - liquid
Strainer
Slotted spoon
Cutting board
Knife
Very clean glass jar
3 white dishes or custard cups
Measuring spoons
Masking tape
Marker
PROCEDURE
1. Cut the cabbage into quarters. Grate it section by section into a bowl.
Be careful!
2. Add between one and two cups of water until the cabbage is covered. Let
the cabbage stand in the water for about 10 minutes. Stir it occasionally
so that all the cabbage is moistened.
3. When the water is a bluish-purple color, remove as much of the grated
cabbage as you can with the slotted spoon. Put the cabbage you removed
into the remaining large bowl.
4. Pour the bluish-purple water through the strainer into the glass jar.
5. Add the drained cabbage from the strainer to the rest of the cabbage you
have removed.
6. Put one tablespoon of the bluish-purple water into a small, white dish.
This bluish-purple water is now the "indicator."
7. Add 1/4 teaspoon of vinegar, which is an acid. Stir well. Indicate on
the chart the color the water turned. Label this sample "Indicator plus
vinegar" and set aside for later comparison.
8. Put one tablespoon of the bluish-purple indicator into a second small
white dish.
9. Add 1/4 teaspoon of baking soda, which is a base. Stir well. Indicate on
the chart the color the water turned. Label this sample "Indicator plus
baking soda" and set aside for later comparison.
10. Use the third white dish to test other foods. (Be sure to wash and dry it
each time you test a new food.) Start with one tablespoon of the bluish-
purple water each time you test a new food. Add the food you are testing
to the bluish-purple water and note the color change on the chart. Decide
whether each food tested reacted as an acid or as a base and check the
proper column on the chart. You may want to compare the foods with your
samples from steps 7 and 9.
11. See if you can answer these questions based on what you observed:
* Do most foods react more like acids or more like bases?
* Why can red cabbage be used to test other foods to see if they are acids
or bases?
______________________________________________________________________________
Indicate One:
Food Color Acid Base
______________________________________________________________________________
Vinegar X
______________________________________________________________________________
Baking soda X
______________________________________________________________________________
Cream of tartar
______________________________________________________________________________
Fruit juice
______________________________________________________________________________
Cottage cheese
______________________________________________________________________________
Orange section
______________________________________________________________________________
Soft drink
______________________________________________________________________________
Tomato
______________________________________________________________________________
Apple
______________________________________________________________________________
Egg white
______________________________________________________________________________
EXPLANATION
Red cabbage can be used to make an indicator solution. This is because the
pigments in red cabbage change color when an acid or base is added. Most
foods will react as an acid when the foods are added to a red cabbage
indicator solution.
SOURCE: Food Mysteries, Michigan State University
Contact for questions
 |
to Jan Scholl's home page |
Updated 8/15/05