Conjugate acids and bases

In chemistry, specifically Brønsted–Lowry acid–base theory, an acid and base are conjugates if they can change into each other by adding or removing a hydrogen ion.

An acid-base reaction is a reaction where an acid and a base are converted into their conjugate base and conjugate acid: deprotonation of the acid and protonation of the base.

 Example 
A common example of acid-base reaction is the reaction between sodium hydroxide and hydrochloric acid to make sodium chloride (salt) and water:

In Brønsted–Lowry theory, the reaction is written as

because the sodium ion doesn't change (it is a spectator ion).

Since  loses hydrogen to become , chloride is the conjugate base of hydrochloric acid. Since  gains hydrogen to become , water is the conjugate acid of hydroxide.

Category:Chemistry