Date __________
Lab Time ______
Name ___________________________
Antacid Analysis
Objective
To determine the effective neutralizing strength of commercial antacids by utilizing acidbase titration techniques.
Background
Overindulgence of food or drink can lead to acid indigestion, a discomforting ailment that
results from the excess excretion of hydrochloric acid, HCl, by the stomach wall lining. An
immediate remedy is an over-the-counter antacid, which consists of a base that effectively
neutralizes the acid. Television commercials stress the competition among various brands of
antacids to see which has the greatest neutralization capacity. However, if the pH rises too
high (above pH = 4), the entire digestive process may be hindered. Therefore, the antacid
should only neutralize an amount of HCl in excess of what the body of healthy individual
normally secretes following a meal.
To determine which commercial antacid has the greatest neutralizing strength, a tablet will be
added to 35 mL of HCl, a “simulated stomach”. Not all of the acid, however, will be
neutralized. The neutralization process will be completed by adding enough sodium
hydroxide (NaOH), a base, to convert the excess HCl to salt and water. By keeping track of
exactly how much NaOH is needed to complete the neutralization process, the amount of
HCl originally neutralized by the antacid can be calculated. An indicator (methyl purple)
will be used to determine the point at which neutralization is complete. In the presence of
methyl purple, an acid solution is pink, a basic solution is green, and a neutral solution is
gray or tan. Several antacids will be tested and the relative strengths of each will be
compared.
Materials needed
50.00-mL buret (2)
ring stand and buret clamp
stirring rods
250-mL Erlenmeyer flask (2)
balance
mortar and pestle
weigh boats
______________
Antacid Analysis
0.50 M hydrochloric acid (HCl) (100 mL)
0.50 M sodium hydroxide (NaOH) (100 mL)
methyl purple indicator (dropper bottle)
universal pH paper
antacids: Rolaids, Tums, Alka-Seltzer, etc.
Distilled Water Squirt Bottle
1
Date __________
Lab Time ______
Name ___________________________
Procedure
Prep 1:
1.
Fill the buret labeled “acid” with at least 40 mL of 0.50 M HCl. Record the initial reading (to the nearest
0.01 mL) of HCl in the buret by accurately reading the liquid level from the bottom of the meniscus.
2.
Fill the buret labeled “base” with at least 30 mL of 0.50 M NaOH. Record the initial reading (to the nearest
0.01 mL) of NaOH in the buret.
3.
Deliver ~35.00 mL HCl into a clean 250-mL Erlenmeyer flask. This flask represents a stomach with acid
indigestion. CAUTION: Do not pull downward on the stopcock or the solution in the buret will spill.
4.
Using universal pH paper, measure and record the pH of the HCl solution by dipping a stirring rod in to the
flask and then transferring a small drop to the pH paper. DO NOT PUT THE PAPER DIRECTLY
INTO THE SOLUTION.
5.
Add approximately 3 drops of methyl purple indicator to this flask.
Prep 2:
6.
Grind a single antacid tablet with a mortar and pestle. Fold a small piece of paper and place the crushed
powder in the middle. Measure the mass of the crushed powder and paper.
7.
After Step 8, measure the mass of the empty piece of paper. Determine the mass of just the added crushed
powder and record.
Neutralizing:
8.
Once both preps have been completed, use the folded piece of paper to transfer as much of the powder into
the flask containing the HCl as possible. Swirl the flask for a few minutes to facilitate the dissolving
process. Note your observations on the report sheet.
9.
Using universal pH paper, measure and record the pH of the solution after adding the antacid.
At this point, some of the original acid has been neutralized, but not all.
10. Carefully add base in small increments to the flask containing the partially neutralized solution.
** Initially, you might see a change in color that fades away upon swirling. As you get closer to the point of complete
neutralization (called the endpoint), the new color will persist for longer periods of time. Add the NaOH more slowly
as you approach the endpoint. If you overshoot the endpoint, add a few more drops of HCl to the solution.
11. After you have neutralized the acid in the flask, record the final buret readings of HCl & NaOH and
calculate the actual volumes delivered (added) to the flask (to the nearest 0.01 mL).
12. Using universal pH paper, measure and record the pH of the neutral solution.
13. Determine the number of milliliters of acid that the antacid tablet did neutralize. Calculate the number of
milliliters of acid the antacid neutralized per gram of tablet.
[ Because the concentration of the NaOH is the same as the original stomach acid (0.50 M), the volume of NaOH
used to neutralize the HCl is equal to the volume of HCl that was NOT neutralized by the antacid. ]
14. Repeat Steps 1-13 for one other antacid tablet that has a different set of active ingredients.
Disposal Procedure
** Carefully pour all remaining fluids down the drain in the sink
** Flush all containers with water from the hose in the sink.
______________
Antacid Analysis
2
Date __________
Lab Time ______
Name ___________________________
Report Sheet – Data Analysis
Antacid: _____________________
Active Ingredient: ________________________
Mass of crushed antacid: ________ g
Initial reading of acid: ________ mL
Initial pH:
pH after antacid addition:
Final Reading of acid: ________ mL
Final pH:
________
________
________
*Total volume of acid: ________ mL
Observations:
Initial reading of base:
________ mL
Final reading of base:
________ mL
+
Total volume of base:
________ mL
Calculations:
*Total volume of acid
________ mL
+
________ mL
Total volume of base
Volume neutralized by antacid ________ mL
Volume neutralized per gram
Antacid: _____________________
Active Ingredient: ________________________
Mass of crushed antacid: ________ g
Initial reading of acid: ________ mL
________ mL/g
Initial pH:
pH after antacid addition:
Final Reading of acid: ________ mL
Final pH:
________
________
________
*Total volume of acid: ________ mL
Observations:
Initial reading of base:
________ mL
*Total volume of acid
________ mL
Final reading of base:
________ mL
+
________ mL
+
________ mL
Volume neutralized by antacid ________ mL
Total volume of base:
Calculations:
______________
Antacid Analysis
Total volume of base
Volume neutralized per gram
________ mL/g
3
Date __________
Lab Time ______
Name ___________________________
Post-lab questions:
1. Compare the antacids you analyzed based upon the number of milliliters of acid they
neutralized per gram and list them in order of increasing neutralizing strength.
2. The neutralizing strength is not the only factor for determining which antacid provides
the most relief for acid indigestion. What other factors should be considered?
3. If the entire crushed antacid tablet had not been transferred from the paper to the flask
containing the acid, how would the final results have changed, if any?
______________
Antacid Analysis
4
Date __________
Lab Time ______
Name ___________________________
Summary/Conclusions:
______________
Antacid Analysis
5