Sodium bicarbonate
Sodium bicarbonate is an antacid. It is sometimes used to relieve acid indigestion, a sickness caused by lots of acid in one's stomach. This was usually done by mixing sodium bicarbonate with water and drinking it.  When there is too much acid, it causes heartburn, an uncomfortable feeling in the stomach. It reacts with acids to produce carbon dioxide gas. It also reacts with bases to reduce their harmful effects.