Upset Stomach Lab

Comparing the neutralizing power of commercial antacids

Why do we need antacids?

• Overindulging with food or drink can lead to excessive secretion of HCl by the stomach lining

• This leads to heartburn the main symptom of gastroesophageal reflux disease

• Antacids neutralize the excessive HCl relieving the heartburn

How Antacids Work

• Antacids are weak bases that can neutralize the acid to make a salt and water

acid + base salt + water

• The type of base depends on the antacid

Type of Antacids

Type of AntacidsSome antacids (milk of magnesia) are hydroxides

Mg(OH)2 + 2HCl MgCl2 + 2H2O

Some antacids (Rolaids and Mylanta) are bicarbonates

NaHCO3 + HCl NaCl + H2O + CO2

Some antacids (Tums) are carbonates

MgCO3 + 2HCl MgCl2 + H2O + CO2

Notice that milk of magnesia and Tums neutralizes twice as much HCl per mole than Rolaids

Measuring the Neutralizing Power• Use a burette to measure 30 mL of 0.50M HCl into a 250 mL

Erlenmeyer flask• Crush an antacid tablet in a mortar with a pestle and weigh the

crushed tablet in a weighing boat M• Transfer the crushed tablet into the Erlenmeyer flask• Add 2 drops of phenolphthalein as an indicator• Repeat with other flasks and antacids• Fill the other burette with 0.50 M NaOH and record the initial

volume Vi (to 2 decimal places)• Titrate the acid in the Erlenmeyer with the NaOH• Titrate to the endpoint (solution goes pink for about 10 secs and

then clears – one more drop and the solution goes permanently light pink) record the final volume Vf(to 2 decimal places)

Titration Set-Up

When phenolphthalein stays pink for 10 s or so and clears the acid is neutralized