The stomach produces hydrochloric acid to begin the chemical breakdown [digestion] of the food that you eat. Although this acid is quite strong, (about 2 M), the stomach has a thick mucus lining that protects the stomach tissue itself from being digested by the acid. When the stomach is too full or when you have swallowed air, the acid will be forced up out of the stomach into the unprotected esophagus. The acid will react with the unprotected tissue and cause a burning sensation commonly known as "heart burn".
There are a number of over-the-counter medications called "antacids". These are not chemical bases. If they were bases and you used them regularly or took them in large doses, they would raise the pH of your blood. This condition, called alkalosis, would result in kidney damage. The brands of antacids sold in the drug store contain insoluble compounds that acids will react with, resulting in the acid being consumed in the reaction. The most common ingredient used is calcium carbonate [CaCO3], also known as limestone. This limestone is ground to a powder, mixed with a starch paste, and formed into a tablet. Often flavoring and coloring is added to make the tablet more attractive. Other tablets contain insoluble hydroxides that will react with hydrochloric acid.
There are also newer types of antacids that are taken before eating. These consist of a hormone [chemical messenger] that reduces the amount of acid produced by the stomach.
This is not the type of antacid that we will evaluate in this lab.
OBJECTIVE
To determine the amount of acid neutralized by each brand of antacid tablet.
CHEMICALS/EQUIPMENT:
Beaker [100 or 250 ml]
Buret ring stand test tube clamp stirring rod mortar & pestle
0.5 M HCl congo red indicator several brands of antacid tablets such as TUMS, Alka-Seltzer, MAALOX etc.
PROCEDURE
1. Record the names and amounts of the active ingredients contained in each brand of antacid. This information is found on the container.
2. The instructor will have already clamped the buret to the ring stand. Put some water in the buret and make sure that it does not leak. Then drain all of the water out of the buret.
3. Fill the buret with 0.5 M hydrochloric acid to the "zero" line.

4. Crush one antacid tablet using a DRY mortar and pestle.
5. Place the crushed tablet in a clean beaker and add about 50 ml of distilled water. Then add 3-4 drops of congo red indicator. Set up the pH meter inside the container so that the probe is immersed one inch in the water. Take the pH value of the solution and record it on your data table.
6. Place the beaker under the buret. The acid should be added drop wise and stirred until the color changes to blue. Since the antacid is not water soluble, the first blue color is not necessary the end point of this titration. Record the pH level for every 2 mL aliquots.
7. Continue stirring until the blue color remains for five minutes after the last drop of acid was added. This is the end point.
8. Record the amount of acid used by this tablet in mL.
9. Repeat this procedure for each brand of antacid tablet.
SAMPLE DATA
Maalox Tums Alka-Seltzer
Color solution before adding tablet pH before adding tablet
Mass tablet in grams
Do not write
SAMPLE DATA
On
TABLE ONLY
This Page!
Color after dissolved & pH
Ingredients
Amount of HCl used pH
Volume 2 4 6 8 10 12 14 16 18 20 22 24

Results & Calculations (continued):
1. Calculate the pH differences for each tablet using the pH as measured by the Universal
Indicator. (Beginning pH - Final pH)
2. Calculate the pH unit change per gram of tablet - A pH/gram - then rank in order the relative ability to neutralize the acid in the beaker, using #1 for the best neutralizer, #3 for the worst.
SHOW YOUR WORK - NEATLY (Example: pH change of 25, tablet mass of 5 grams = 25 pH/5g = 5 pH change per gram. The biggest pH change per gram would be the BEST acid reducer!)
3. Graphs: a. Graph your results using the CLASS DATA. Y axis = A pH/gram; X axis = bars of each tablet type. Don't forget the title, and a brief conclusion statement explaining the graph.
Make a Box & Whiskers of the 3 tablets compared to one another. (See example on board.) b. Graph a volume/pH curve. X axis = volume (ev ery 2 mL’s); Y axis = pH value. Don't forget the title, and a brief conclusion statement explaining the graph.
4. Do a cost analysis of the price of each antacid per gram, or per tablet. [Get the cost information from your teacher.] Include this data in your analysis.
Analysis:
Write several paragraphs and discuss the results of this lab. Relate your specific results back to your hypothesis.

Did you support your hypothesis or revise it?

What sources of error may have existed that affected your data collection?

How do antacids work?
 What would you now advise friends or family about use of these tablets?
Resources:
 http://serendip.brynmawr.edu/sci_edu/farber/pdf/antacid.pdf

Leslie Hays, Helix Charter HS