Hydrochloric acid (HCl) is one of the substances found in gastric juices secreted by the lining of the stomach. HCl is needed by the enzyme pepsin to catalyze the digestion of proteins in the food we eat. Heartburn is a symptom that results when the stomach produces too much acid (hyperacidity).
Antacids are bases used to neutralize the acid that causes heartburn. Despite the many commercial brand, almost all antacids act on excess stomach acid by neutralizing it with weak bases. The most common of these bases are hydroxides, carbonates, or bicarbonates. The following table contains a list of the active ingredients found in several common commercial antacids, and the reactions by which these antacids neutralize the HCl in stomach acid. Compound Chemical Formula Chemical Reaction Aluminum hydroxide Al(OH)3 Al(OH)3(s) + 3 HCl(aq) -----> AlCl3(aq) + 3 H2O(l) Calcium carbonate CaCO3 CaCO3(s) + 2 HCl(aq) -----> CaCl2(aq) + H2O(l) + CO2(g) Magnesium carbonate MgCO3 MgCO3(s) + 2 HCl(aq) -----> MgCl2(aq) + H2O(l) + CO2(g) Magnesium hydroxide Mg(OH)2 Mg(OH)2(s) + 2 HCl(aq) -----> MgCl2(aq) + 2 H2O(l) Sodium bicarbonate NaHCO3 NaHCO3(aq) + HCl(aq) -----> NaCl(aq) + H2O(l) + CO2(g) In this experiment, several brands of antacids will be analyzed to determine the number of moles of acid neutralized per tablet and the cost analysis of each tablet. The analytical procedure used is known as back titration. In this procedure, a known amount of HCl, which is in excess, will be reacted with a weighed portion of a ground antacid tablet. The HCl remaining after the antacid neutralization reaction occurs will be determined by titration with a standardized NaOH solution to a phenolphthalein endpoint. The number of moles of HCl neutralized by the antacid (HClneutralized) is the difference between the moles of HCl initially present in the excess (HClinitial) and the moles of HCl titrated by the NaOH (HCltitrated).