"Conjugate acid/conjugate base pairs" are simply defined by proton exchange, i.e. addition or subtraction of H^+. As with any chemical reaction, charge and mass are conserved:
underbrace(NH_4^+)_("conjugate acid") rarrunderbrace(NH_3)_("conjugate base") + H^+
Ammonia is a good example for the "conjugate acid/conjugate base relationship" because it shows how acid/base chemistry can be extended beyond aqueous solution, and in liquid ammonia the following equilibrium operates:
2NH_3(l) rightleftharpoons underbrace(NH_4^(+))_("conjugate acid of ammonia") + underbrace(NH_2^(-))_("conjugate base of ammonia")
K_"eq" for this ammonolysis reaction is much smaller than for K_"eq" in the water solvent.
NH_2^(-) is the so-called "amide ion"; and is itself the conjugate acid of NH^(2-), "imide ion", which is itself the conjugate acid of N^(3-), "azide ion". These nitrogen bases are not encountered outside of liquid ammonia, a water-like solvent.
The take home message is that "conjugate acid/conjugate base" pairs are defined by proton exchange, i.e. H^+. All (?) you have to do is balance mass and charge.
In liquid HF, (an actual solvent), what is the conjugate acid and what is the conjugate base? Use the same procedure as before.
