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A True Acid Test

An amazing chemical can be found in red cabbage. This stuff, called cyanidin (sigh-AN-ih-din), can be used to identify two important kinds of chemicals: acids and bases.

Acids are famous for their ability to eat away at rocks and metals. But many acids are not so dangerous. In fact, the acid known as vitamin C can and should be eaten.

A base is the opposite of an acid. When the two are mixed together, they react and cancel out each other’s effects. Many people have seen this kind of reaction when vinegar (an acid) has been mixed with baking soda (a base).

You can use cyanidin to test for acids and bases in your home. Here’s how.

With an adult’s help, mix one cup of shredded red cabbage with two cups of water, then simmer the mixture in a saucepan for about fifteen minutes. The water should now be a dark blue or purple. Remove the pan from the heat and let the liquid cool to room temperature.

Drain the liquid into a glass, bowl, or jar and throw away the cabbage. Push a clean coffee filter or piece of paper towel all the way down into the water. Let the paper soak for at least ten minutes. Then remove it and drape it over a drinking glass or a dish drainer to dry.

When the paper is dry, it should have a blue or purple tint. Use scissors to cut several strips about two inches long and one-quarter inch wide.

These strips can be used to tell whether a liquid contains an acid, a base, or a balance of the two. Lay a strip on a light-colored, washable surface, such as a saucer. A drop of vinegar or any other acid will turn a strip red. A drop of base, such as a mixture of water and baking soda, will turn a strip green. A liquid that is neither an acid nor a base will not change the color.

Use a new strip to test each liquid, and rinse and dry the saucer between tests to make sure you are testing the new liquid and not the previous one.

Start by testing vinegar and baking soda, since you already know how they should affect the test paper. Then try lemon juice, orange juice, and a carbonated drink such as cola.

You might also try some cleaning products—but only with an adult’s help because some of these products can be harmful. Try dishwashing detergent, laundry detergent, and a spray cleaner such as Fantastik or Formula 409.

Now create and test your own chemical reaction. Try to mix small amounts of vinegar and baking soda so that their effects cancel each other. You’ll know you have succeeded when the mixture leaves a test strip its original blue color.

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