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.
A Common Confusion: Ranitidine
You mentioned ranitidine. Here's the critical distinction: …
An antacid is a mild base that neutralises excess stomach acid, which distinguishes it from an analgesic, an antibiotic or a sulpha drug among the options. …
Antacids are mild bases that neutralise excess hydrochloric acid in the stomach, relieving acidity. Magnesium hydroxide, Mg(OH)2 (milk of magnesia), reacts with HCl to form MgCl2 and water, raising the stomach pH.
Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.
CBSE 2023Set F1 markMCQ
Q.Which of the following is used as an antacid?
(a) Magnesium hydroxide
(b) Phinacetin
(c) Penicillin
(d) Sulphanilamide
›Reveal solutionSolution
Magnesium hydroxide is an antacid — option (A).
Antacids are mild bases that neutralise excess hydrochloric acid in the stomach, relieving acidity. Magnesium hydroxide, Mg(OH)2 (milk of magnesia), reacts with HCl to form MgCl2 and water, raising the stomach pH.
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 …
Antacids are basic substances taken to counteract the excess gastric HCl responsible for acidity/heartburn.
Antacids are chemical substances (generally weak bases) that neutralise the excess hydrochloric acid secreted by the gastric glands of the stomach, providing relief from acidity, indigestion, and heartburn. They act simply by an acid-base neutralisation reaction, e.g.:
Q.Over production of acid in stomach can be controlled by -
(a) Antacid
(b) Analgesic
(c) Antipyretic
(d) Antibiotic
›Reveal solutionSolution
Over-acidity is treated by antacids (mild bases that neutralise HCl).
The stomach secretes hydrochloric acid for digestion. Its overproduction causes acidity/hyperacidity. Antacids (e.g. metal hydroxides like Mg(OH)2, Al(OH)3, or NaHCO3, and drugs like ranitidine/omeprazole) are basic and neutralise or reduce the excess a …