In contrast, the cyanide ion, CN-, is a strong B-L base.
It has a great attraction for protons, and the reaction
is heavily shifted to the right. As a result, HCN is a very weak
In the examples discussed so far, the acidic species has been electrically
neutral and the basic species charged. This need not always be so.
Ammonia is a B-L base, and the ammonium ion is a B-L acid, capable
of releasing a proton:
We can write an acid-dissociation equilibrium espression in the
This is related to the base-dissociation constant seen previously,
This is the value of Ka for the ammonium ion that is
given in the table on Page 8. You can either think of NH3
as a moderately strong base with a Kb of 1.76 x 10-5,
or NH4+ as a very weak acid with a Ka
of 5.68 x 10-10. The results of any calculation involving
this acid-base equilibrium always will be the same whether you use
Ka or Kb, as long as you know what you are
Water can act as both a B-L acid and a B-L base.
We can regard the hydrating water molecules around a proton in
solution as a weak B-L base
The Bronsted-Lowry theory has so influenced chemistry that two
generations of chemists have written H3O+
for the hydrated form of H+ and called it the "hydronium
ion", even though the true hydration state of the proton is
not known, but it is probably more like H+(H2O)4