A conjugate acid–base pair refers to two substances that are related to each other by the gain or loss of a proton (H⁺ ion).
Key idea:
- An acid becomes its conjugate base after it donates a proton.
- A base becomes its conjugate acid after it accepts a proton.
Examples in words:
- When hydrochloric acid donates a proton, it turns into chloride ion. Together, they form a conjugate acid–base pair.
- When ammonia accepts a proton, it becomes ammonium ion. Ammonia and ammonium ion form another conjugate pair.
Why it matters:
- Conjugate acid–base pairs help explain how acids and bases behave in reversible reactions.
- They show that every acid has a “partner base” and every base has a “partner acid.”
In short: A conjugate acid–base pair consists of two forms of the same substance, one as an acid (with an extra proton) and the other as a base (without that proton).