Back Titration of Antacid Tablets

Measuring the acid-neutralizing capacity of commercial antacids

Titrations Intermediate (High School) 60 min ~$12.00

Objective

Determine the acid-neutralizing capacity of a commercial antacid tablet using a back titration method.

Background

Direct titration of antacid is impractical because the active ingredients dissolve slowly. In a back titration, excess acid is added to the antacid, allowed to react fully, and the remaining unreacted acid is titrated with base. The difference reveals how much acid the antacid neutralized.

Safety Warnings

  • HCl and NaOH are corrosive
  • Wear safety goggles and gloves
  • Use caution with the hot plate

Required PPE

goggles gloves lab_coat

Materials

  • Antacid tablets (2 tablets)
    CaCO₃-based, like Tums
  • Hydrochloric acid (HCl) (200 mL)
    0.5M
  • Sodium hydroxide (NaOH) (100 mL)
    0.5M standardized
  • Phenolphthalein indicator (5 mL)
  • Distilled water (200 mL)

Equipment

50 mL burette Burette stand and clamp 250 mL Erlenmeyer flask 25 mL pipette Mortar and pestle Analytical balance Hot plate

Procedure

1

Weigh the antacid tablet accurately on the analytical balance and record the mass.

3 min
2

Crush the tablet into a fine powder using the mortar and pestle.

3 min
3

Transfer the powder to the Erlenmeyer flask. Add exactly 50.0 mL of 0.5M HCl using the pipette.

3 min Handle HCl carefully
4

Gently heat the mixture on the hot plate for 10 minutes to ensure complete reaction of the antacid.

12 min Do not boil vigorously
5

Allow the solution to cool to room temperature.

5 min
6

Add 2-3 drops of phenolphthalein indicator.

1 min
7

Fill the burette with 0.5M NaOH. Titrate the excess HCl until a persistent pale pink color appears.

10 min
8

Record the volume of NaOH used. Calculate moles of excess HCl, then moles neutralized by the antacid.

5 min

Expected Results

A typical CaCO₃-based antacid tablet (500 mg) should neutralize approximately 10 mmol of HCl. The mass of CaCO₃ calculated should approximate the labeled amount on the package.

Cleanup

Neutralize all waste solutions before disposal. Rinse glassware thoroughly. Clean the mortar and pestle.

Details

Category
Titrations
Difficulty
Intermediate (High School)
Duration
60 min
Est. Cost
$12.00
Steps
8
Materials
5

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Frequently Asked Questions

What is the objective of Back Titration of Antacid Tablets?
Determine the acid-neutralizing capacity of a commercial antacid tablet using a back titration method.
How difficult is Back Titration of Antacid Tablets?
This experiment is rated as Intermediate (High School). It takes approximately 60 minutes to complete.
What safety precautions are needed for Back Titration of Antacid Tablets?
Key safety precautions include: HCl and NaOH are corrosive; Wear safety goggles and gloves; Use caution with the hot plate.
What materials are needed for Back Titration of Antacid Tablets?
The main materials required are: Antacid tablets, Hydrochloric acid (HCl), Sodium hydroxide (NaOH), Phenolphthalein indicator, Distilled water.
What results should I expect from Back Titration of Antacid Tablets?
A typical CaCO₃-based antacid tablet (500 mg) should neutralize approximately 10 mmol of HCl. The mass of CaCO₃ calculated should approximate the labeled amount on the package.