Question

What are conjugate acid-base pairs?

Answer 1

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_2SO_4` + `H_2O` => `HSO_4^-` + `H_3O^+`

In this example, sulfuric acid (`H_2SO_4`) is an acid because it "donates" `H^+` to the water. It becomes the hydrogen sulfite ion (`HSO_4^-`) which is the conjugate base of sulfuric acid.

The same idea applies to a base:

`NH_3` + `H_2O` <=> `NH_4^+` + `OH^-`

Ammonia (`NH_3`) is a base because is "accepts `H^+` from water to come its conjugate acid, the ammonium ion (`NH_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