# What is the conjugate base of H2O?

If I remove ${H}^{+}$ from ${H}_{2} O$, clearly I get the hydroxide ion, $O {H}^{-}$. Mass and charge have been conserved. If I remove a proton from sulfuric acid, I get bisulfate anion, $H S {O}_{4}^{-}$; thus bisulfate is the conjugate base of sulfuric acid. What is the conjugate base of bisulfate ion? What is the conjugate base of $O {H}^{-}$?
The conjugate base of ammonia, $N {H}_{3}$, does not exist in water, but it does exist in liquid ammonia. What is it?