The base-dissociation constant, kb, for pyridine, c5h5n, is 1.4x10-9 the acid-dissociation constant, ka, for the pyridinium ion, (pyridine's conjugate acid, is

We are given the base dissociation constant, Kb, for Pyridine (C5H5N) which is 1.4x10^-9. The acid dissociation constant, Ka for the Pyridium ion or the conjugate acid of Pyridine is to be determined. We know from our chemistry classes that:

Kw = Kb * Ka

where Kw is always equal to 1x10^-14

so, to solve for Ka of Pyridium ion, substitute Kb to the equation together with Kw and solve for Ka:

1x10^-14 = 1.4x10^-9 * Ka
solve for Ka

Ka = 7.14x10^-6 

Therefore, the acid dissociation constant of Pyridinium ion is 7.14x10^-6.