Imagine you've just eaten a heavy, spicy meal. Your stomach works by releasing hydrochloric acid (HCl) to digest food. That acid is strong — strong enough to break down proteins. Normally, your stomach lining is protected. But sometimes, the acid gets too much: you feel a burning sensation in your chest or stomach. That's hyperacidity.
What do you want? Something that will neutralise that extra acid — turn it into harmless substances like water and salt. That's exactly what an antacid does.
Note
The word "antacid" literally means "against acid." An antacid is a base that reacts with stomach acid to raise the pH of the stomach contents, relieving the burning sensation.
The Chemistry in Simple Terms
Stomach acid is mostly hydrochloric acid, HCl. An antacid is typically a weak base — often a metal hydroxide or carbonate. The reaction is a simple acid-base neutralisation:
Acid+Base→Salt+Water
For example, magnesium hydroxide, Mg(OH)X2, reacts with HCl:
Mg(OH)X2+2HClMgClX2+2HX2O
The acid is gone; the burning stops.
Common Antacids and Their Chemistry
Antacid
Chemical Formula
How It Works
Magnesium hydroxide
Mg(OH)X2
Neutralises acid, but can cause a laxative effect
Aluminium hydroxide
Al(OH)X3
Neutralises acid, but can cause constipation
Sodium bicarbonate
NaHCOX3
Neutralises quickly, but produces COX2 gas (burping)
Calcium carbonate
CaCOX3
Also neutralises, produces COX2
Many commercial antacids combine magnesium and aluminium hydroxides to balance the side effects.
Watch out
Sodium bicarbonate reacts violently with acid, producing carbon dioxide gas. This can cause belching and, in rare cases, stomach rupture if taken in excess. It also adds a lot of sodium to your system — not ideal for people with high blood pressure.
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Milk of Magnesia (Mg(OH)2 suspension) is a mild base that neutralises excess stomach HCl; drugs used for this purpose are classed as antacids.
Milk of Magnesia is the common name for an aqueous suspension of magnesium hydroxide. It is a weak, insoluble base, so it reacts slowly and safely with the excess hydrochloric acid secreted in the stomach: Mg(OH)2+2HCl→MgCl2+2H2O, relieving acidity/heartburn. This is exactly the defining action of an antacid (a drug that neutralises excess stomach acid), unlike a t …