Battle of the antacids
Did you know that your stomach produces between 1 L and 2 L of gastric juice daily? The main constituent
in this juice is hydrochloric acid, and the pH of a normal stomach is about 1.5 - acidic enough to dissolve
magnesium metal! The purpose of this very acidic medium is to digest food. But the stomach itself is made
of muscle, so why does it not digest itself? The stomach copes with normal levels of acidity because it
completely replaces its lining every few days. However, if the concentrations of acid in the stomach are too
high, problems can occur. Pain, swelling, inflammation, and bleeding in the stomach’s lining can cause a
condition commonly called “acid indigestion”. One solution to the problem is to take a medication that
contains an antacid - a mild base that can neutralize acid. The typical bases found in common antacids
include sodium bicarbonate (Alka-Seltzer), calcium carbonate (Tums & Rolaids), and magnesium hydroxide
(Maalox).
Liquid Universal Indicator pH Color
4.0 Red
5.0 orange red
5.5 orange
6.0 yellow orange
6.5 yellow
7.0 yellow green
7.5 green
8.0 dark green
8.5 blue green
9.0 blue
9.5 violet
10.0 reddish violet
PREDICTION:
Which over-the-counter antacid is most effective in neutralizing acid?
MATERIALS
safety goggles
large test tube & stopper
100 mL graduated cylinder
balance
mortar & pestle
liquid universal indicator
dilute hydrochloric acid (HCl)
3 different antacid tablets
Microdroppers
PROCEDURE
1. Put on your safety goggles and then gather your equipment.
2. Use a mortar and pestle to crush your antacid tablet. Measure and record the mass (g) of the crushed
tablet.
3. Put the antacid sample in the test tube. Add 10 mL of distilled water and 10 drops of the universal liquid
indicator. Stopper the test tube and then shake it until the antacid is dissolved. What is the pH of the sample
(see chart above)?
4. Remove the stopper and add 1 drop of HCl. Stopper the test tube and shake it. Continue adding 1 drop of
HCl, stoppering and shaking until the color of the liquid indicates a pH of 7.0
5. Record the number of drops of HCl added.
6. Rinse your glassware with water and then repeat steps 2 to 5 for the other antacid sample.
7. When you are finished clean up your lab station, return all your equipment, and wash your hands.
8. Calculate and record the neutralizing ability of each antacid (#drops ÷ mass).
DATA TABLE:
Antacid
Mass of 1 tablet
Starting pH
# of drops of HCl the antacid
was able to neutralize
# drops/ mass
ANALYSIS
1. This experiment required you to be very accurate. What are 2 major sources of error that could have
affected your results? Explain each.
2. Based on your data, which antacid neutralized the stomach acid the best? Explain your answer.
3. What is an antacid? Would you want an antacid to dissolve in your stomach instantly or over a period of
time? Explain.
4. Fish muscle contains bases that give cooked fish their “fishy” odor. Suggest why a squirt of lemon juice
often makes this odor disappear.
5. One way to treat a lake polluted with acid rain is to add calcium hydroxide to it. How does this help? Why
is this only a short-term “fix” to the acid rain problem for the lake?