# How do you conjugate acid and base?

The conjugate base of an acid, is the formula of the starting acid, $H A$, less a proton, ${H}^{+}$ to give ${A}^{-}$. That is the conjugate base of $H A$ is ${A}^{-}$.
And the conjugate acid of a base is the starting base, ${A}^{-}$, plus a proton, ${H}^{+}$, to give $H A$.
As in any chemical reaction, both MASS and CHARGE are conserved. Thus taking sulfuric acid, ${H}_{2} S {O}_{4}$, as the exemplar, its conjugate base is $H S {O}_{4}^{-}$, and in turn the conjugate base of this bisulfate anion is $S {O}_{4}^{2 -}$.
What are the conjugate bases of $H F$ and ${H}_{3} P {O}_{4}$? What is the conjugate acid of $H P {O}_{4}^{2 -}$? And what is the conjugate acid/base of water, $O {H}_{2}$?