Stomach Acid

Question: Which antacid works best when you have an upset stomach?

Experiment Overview

Each time you eat something, your stomach produces acid, which helps your body digest the food. Too much acid can cause indigestion, or an upset stomach. In this experiment, you will test different antacids to see which of them neutralize acid the best. You will use an acid-base indicator, made from red cabbage, to test the success of the antacids.

Science Concept

In your stomach, acid is used to break down the food you eat so that it can be digested and converted to energy for your body. However, sometimes your stomach produces too much acid, and it causes a feeling of discomfort.

In addition, that acid can sometimes come up your throat, giving you a burning feeling in your chest commonly known as heartburn. To counteract this acid buildup, people usually take antacids, which are tablets containing ingredients that neutralize the acidity in their stomach.

You will be using carbonated soda to simulate the acid in your stomach and will use the red cabbage indicator to test to see how well each antacid works. The redder the indicator is, the more acidic the material you are testing. As more of the acid is neutralized, the indicator turns first a bluish, and then a greenish color.



  • 1 (2-liter) bottle of carbonated soda

  • Several short drinking glasses

  • Several brands of antacid, available for purchase in a drugstore

  • Baking soda

  • Spoon

  • Jar of canned red cabbage, available for purchase in a grocery store

  • Several small saucers, such as those you would use with coffee cups


  1. Drain the juice from the jar of red cabbage. This will serve as your acid indicator.

  2. Pour a small amount of the indicator into each saucer.

  3. Pour the soda into each of the drinking glasses.

  4. Gently crumble one tablet of each of the antacids you are testing into the drinking glasses containing carbonated soda.

  5. Add one spoonful of baking soda to its own glass of soda.

  6. Use the spoon to stir each antacid into the soda until it is completely dissolved. Rinse the spoon after stirring in each glass.

  7. Add one spoonful of each soda mixture to its own saucer of acid indicator and stir gently to mix. Be sure to rinse the spoon after each mixture.

  8. Observe the final color of the acid indicator and determine which antacid was most effective at neutralizing the acid in the soda.

  9. Questions for the Scientist

    1. Which of the antacids was the best at neutralizing the acid in the soda?

    2. Which foods do you think are most likely to produce heartburn or discomfort in your stomach?

    3. Are all acids dangerous for you? Research foods that contain acid to see which are healthy and which are not.


    Your stomach is an incredible machine. It takes all the food you eat and converts it into the energy you need in order to run, play, laugh, learn, and live. Take care of it and it will last you a lifetime. That means eating well, keeping yourself active, and living a healthy lifestyle.

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