What are conjugate acid-base pairs?

Apr 14, 2014

All acids have a conjugate base. All bases have a conjugate acid. Acids "donate" ${H}^{+}$ when they react. This is most easily seen when they dissociate in water:

${H}_{2} S {O}_{4}$ + ${H}_{2} O$ => $H S {O}_{4}^{-}$ + ${H}_{3} {O}^{+}$

In this example, sulfuric acid (${H}_{2} S {O}_{4}$) is an acid because it "donates" ${H}^{+}$ to the water. It becomes the hydrogen sulfite ion ($H S {O}_{4}^{-}$) which is the conjugate base of sulfuric acid.

The same idea applies to a base:

$N {H}_{3}$ + ${H}_{2} O$ <=> $N {H}_{4}^{+}$ + $O {H}^{-}$

Ammonia ($N {H}_{3}$) is a base because is "accepts ${H}^{+}$ from water to come its conjugate acid, the ammonium ion ($N {H}_{4}^{+}$).

This video gives an overview of acids and bases; the second half is about conjugate pairs:

Simple, easy to understand can be on this site http://www.chemteam.info/AcidBase/Conjugate-Pairs.html