1. Upset Stomach Lab Comparing the neutralizing power of commercial antacids

2. 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

3. 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

4. Type of Antacids

5. Some antacids (milk of magnesia) are hydroxides Mg(OH) 2 + 2HCl  MgCl 2 + 2H 2 O Some antacids (Rolaids and Mylanta) are bicarbonates NaHCO 3 + HCl  NaCl + H 2 O + CO 2 Some antacids (Tums) are carbonates MgCO 3 + 2HCl  MgCl 2 + H 2 O + CO 2 Notice that milk of magnesia and Tums neutralizes twice as much HCl per mole than Rolaids

6. 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 V i (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 V f (to 2 decimal places)

7. Titration Set-Up When phenolphthalein stays pink for 10 s or so and clears the acid is neutralized