- In this investigation, you will mix an antacid tablet with water and a colored chemical called an indicator. The indicator changes color depending on whether an acid or a base is present. Then you will add acid to the solution to determine how much acid can be neutralized by the antacid tablet. You should test several different types of antacids to compare the effectiveness of various products.
MATERIALS
safety goggles 
100-mL beaker antacid tablet graduated cylinder distilled water 250-mL Erlenmeyer flask 50 mL 1 M hydrochloric acid medicine dropper neutral red indicator 2 large metal spoons PROCEDURE
1. Put on safety goggles.
2. Obtain an antacid tablet. In the DATA TABLE, record the brand name and active ingredient(s) listed on the label.
3. Put 100 mL of distilled water in a clean, dry Erlenmeyer flask. Dissolve the tablet in the water. If you are using a chewable tablet, crush it between two large spoons before dissolving it. (Some tablets may not dissolve completely.)
4. Put a sheet of white paper under the flask. Add enough neutral red indicator to the solution to produce a noticeable color. This should be about 10 drops.
5. Carefully put 50 mL of 1 M hydrochloric acid in a beaker. REMEMBER, if you get any hydrochloric acid on your skin or clothing, wash with plenty of water. Wipe up any spills with paper towels.
Read steps 6 - 8 before continuing with them.
6. Use a medicine dropper to add the 1 M hydrochloric acid to the flask. Remember; in science, a medicine dropper is a transfer pipette. Always hold it straight up and down, never at an angle. This lets gravity take the drop off the dropper, and makes each drop the same volume. Add five drops at a time, then swirl the contents of the flask.
7. Keep track of the number of drops of 1 M hydrochloric acid that you add to the flask. At some point, adding drops of hydrochloric acid will cause red swirls of color to form in the yellow solution. This means the antacid tablet can neutralize only a little more acid. At that point, add only one drop of acid at a time. Swirl the flask after each drop.
8. Stop adding acid when the solution stays red and does not return to yellow. At this point, the antacid tablet cannot neutralize any more acid.
9. Record in the DATA TABLE the number of drops of acid you added.
10. Repeat steps 1 through 9, with one or more different brands of antacid.
DATA TABLE Antacid Active Ingredient(s) Drops of Hydrochloric Acid Added
QUESTIONS
1. What active ingredients are in the brands tested?
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2. Do some antacids contain inactive ingredients? If so, what are they?
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3. Which antacid tablet neutralized the most acid? What active ingredient(s) does it contain?
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4. Which antacid tablet neutralized the least acid? What active ingredient(s) does it contain?
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CONCLUSION
What factors could account for any differences you observed in the acid-neutralizing capacities of the antacids tested?
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COMPARING THE EFFECTIVENESS
OF
SEVERAL ANTACIDS
INTRODUCTION