Chemistry

Make a Red Cabbage Indicator



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You don't have to be a rocket scientist to enjoy making a red cabbage pH indicator to use for testing for acids and bases. It is easy and educational. The kids will just think it is fun!

The study of acids and bases is expressed in terms of pH balance. The acids, which have a low pH, are sour, corrosive to metal, change litmus to red and becomes less acidic when it is mixed with a base. Bases, which have a high pH, feel slippery and change the litmus to blue. If you do not have litmus paper and you want to know about the pH balance of a substance, you can create your own pH indicator with regular red cabbage sold at the grocery store. 

Place your red cabbage on a cutting board and chop it up into one inch squares. Measure out two cups and place it in a food processor. Add one cup of distilled water to the mixture and blend it, chopping the cabbage into small, uniform pieces. Heat the cabbage and water in a pan until the color is released into the water. Pour the mixture through cheesecloth and into a glass jar. Eat or throw out the cabbage but keep the liquid to use as a pH indicator.

Test your indicator on two substances that you know to be either an acid or a base. For example, choose vinegar, which is a known acid and ammonia, which is a known base. Add one teaspoon of the red cabbage juice to one-half cup of both the vinegar and the ammonia. Stir them with separate stir sticks. Observe the color that forms in each container. Now you know what to look for as you test other substances.

Run a battery of tests on different foods. Set up several clean test tubes to use in the experiments. Add cabbage juice to foods that you know are supposed to be bases. Then, test some that you know are supposed to be acidic, like lemon juice or orange juice, but also test foods that you are unfamiliar with, perhaps baking soda. Look for the shades of color created  by the vinegar and ammonia experiments or check the pH chart located here. Keep a chart, listing your test results.

Repeat the experiments using household cleaners and other chemicals. Predict, then experiment to determine the validity of your hypothesis. Look for common factors in food that will help you determine your hypothesis, then check your answers with your indicator. 

Use your red cabbage indicator to test a little of everything you eat. The fun never has to end. If your supply runs low, refer back to the beginning of this article and make more. It is easy, fun, inexpensive and educational!

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