Titration Lab #4
Analysis of Antacids
Purpose: The purpose of this lab is to determine the cost effectiveness of several
commercial antacids.
Introduction: The human stomach produces hydrochloric acid to aid in the digestion of
food components such as proteins. Stomach acid is approximately 0.1mol/L hydrochloric
acid. Excessive secretion of stomach acid causes the acidity of the contents of the
stomach to increase dramatically; the pH then falls below pH 3.0. When excessive acid is
produced, heart burn and/or acid reflux occur. These may result in short term discomfort
and potentially long term damage to the lining of the upper digestive tract.
Antacids such as Tums, Rolaids, etc. consist of compounds that neutralize excess
stomach acid and help return the pH of the stomach to 3.0. Some, but not all, of these
antacids contain calcium and may have the added benefit of contributing this essential
nutrient to the body.
In this experiment, 0.100 mol/L hydrochloric acid is used to simulate stomach acid. A
crushed antacid tablet is added to the acid and allowed to react. The antacid can be
expected to neutralize some of the acid. The ability of the commercial antacid to
effectively neutralize acid will be measured by titration. In this titration the acid
remaining after the antacid has finished reacting is measured. This is achieved by titrating
the unreacted hydrochloric acid with a sodium hydroxide solution of known
concentration (that is, a standardized solution of NaOH). Note that the larger the initial
quantity of hydrochloric acid neutralized by the antacid, the smaller the quantity of
sodium hydroxide required to titrate the remaining acid.
Procedure:
1. Pipet 25.00 mL of an HCl solution of known concentration into a 250 mL
Erlenmeyer flask. Record the concentration of the HCl solution in the data table.
2. Obtain ½ of an antacid tablet. Record the brand used, the mass of a tablet, and the
cost and number of tablets (grams) in the bottle.
3. Crush the tablet, record the weight and add to the Erlenmeyer flask.
4. Swirl the flask to dissolve the antacid and allow it to react with the HCl solution.
(Some inert ingredients in the tablet will not dissolve causing the solution to be
cloudy. This is not adversely effect the analysis.)
5. Add 4-5 drops of phenolphthalein indicator.
6. Rinse and prepare a burette with your 0.3 M NaOH solution in it. Record initial
volume.
7. Titrate the contents of the Erlenmeyer to the endpoint and record final volume of
NaOH in the data table.
8. Perform 3 trials for this brand of antacid.
9. Select a second brand of antacid and perform 3 trials to determine its ability to
neutralize stomach acid.
10. Calculate the cost of the antacid per gram
11. Report the number of moles of acid neutralized per dollar ($1.00) of the antacid
and recommend which brand is the best buy.
Data Table for: _______________________
Trial 1
Molarity of HCl used
Volume of HCl used
Molarity of NaOH used
Initial volume of NaOH
Final volume of NaOH
Total volume of NaOH used
Moles of NaOH used
Moles HCl present
Moles HCl neutralized by
NaOH
Moles of HCl neutralized by
antacid
Mass of antacid used
Moles of acid neutralized per
gram of antacid
Cost of antacid per gram
Moles of acid neutralized per
dollar ($) of antacid
Trial 2
Trial 3