Antacid Lab
Lab Overview
Your stomach produces hydrochloric acid to aid in the digestion of your food. The strength of
this acid allows the food to break down in your stomach but is harmful to other body tissues.
Fortunately, your stomach is coated with a thick lining of mucus that protects it from this strong acid
concentration (2M) and certain digestive mechanisms prevent this acid from moving to other organs
and tissues. Occasionally this stomach acid can leak out and enter your esophagus where the tissue is
not protected. When the acid comes in contact with this unprotected tissue, you feel a burning
commonly called “heart burn.”
“Antacid” are over-the-counter medications to relieve this heart burn. The chemical compounds
in the medication are NOT bases but react with acids. When these compounds react with your stomach
acid, this excess acid is consumed and your heart burn symptoms are relieved. These medications are
often insoluble and often composed of calcium carbonate (CaCO3) as one ingredient. Calcium carbonate
is also known as “limestone.” Other common ingredients include artificial flavoring and coloring. Some
antacids contain insoluble hydroxides, which also react with stomach acid.
Objective
The objective of this lab is to determine the amount of acid that can be neutralized by each type
of antacid tablet.
Materials
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250ml Erlenmeyer flask
Stirring rod
Mortar and pestle
100 ml graduated cylinder
Congo Red indicator
Antacid tablets—one of each type
Distilled water
0.5M HCl in a medicine bottle
Procedure
1. Obtain the names and amounts of the active ingredients found in each antacid brand. You can find
this information by looking on the container for the appropriate tablet. (1 person)
2. Obtain ONE type of antacid and crush it using a DRY mortar and pestle. (1 person)
3. Place the crushed tablet into the 250ml Erlenmeyer flask and add approximately 50ml of distilled
water to the beaker. Measure the distilled water using a graduated cylinder.
4. Add 3-4 drops of congo red indicator. The color of the solution should change to blue when the end
point of the titration is reached.
5. Using a medicine dropper, add 0.5M HCl solution to the antacid solution in the beaker until the color
changes to blue. Stir the solution as you add the 0.5M HCl.
6. Continue to add the 0.5M HCl to the antacid solution and stir the solution until a blue color remains in
the antacid solution for 5 minutes. After the blue color persists for 5 minutes, you have reached the end
point for this titration.
7. Record the amount of acid (in milliliters) used by the antacid tablet.
8. Clean your glassware and lab station.
Data
Antacid Brand Tested
Ingredients
ml of HCl reacted
Post-Lab Questions
1. List the active ingredients in the antacid tablets. Are these ingredients acids or bases? (You may have
to get information about each tablet from another lab group.)
2. Why was it necessary to stir for five minutes in order to be sure that the end point had been
obtained?
3. What is the difference between the end point and the equivalence point in a titration?
4. Which antacid tablet worked the best? Which tablet was the worst at neutralizing acid? (You may
have to discuss this question with other lab groups)
5. Based on the lab and your knowledge, what tablet brand would you recommend. Explain your
reasoning for this recommendation based on your lab data and your knowledge of acids and bases.