Final answer:
Antacids contain bases such as calcium carbonate (CaCO3) to neutralize the hydrochloric acid (HCl) in stomach acid, aiding in the relief of heartburn and acid indigestion.
Step-by-step explanation:
The main ingredient in antacids used to neutralize gastric juices is often a base that reacts with the hydrochloric acid (HCl) present in stomach acid. One of the most common substances used is calcium carbonate (CaCO3), which neutralizes HCl through a simple neutralization reaction:
CaCO3(s) + 2HCl(aq) → CaCl2 (aq) + H2O(l) + CO2(g)
This reaction not only neutralizes stomach acid but also releases CO2 gas, which may lead to a belch. Options that contain alkaline ions or weak bases like sodium bicarbonate (NaHCO3), also known as baking soda, can serve the same purpose. These antacid ingredients effectively reduce the acidity in the stomach, relieving pain and discomfort from heartburn or excess stomach acid.