99
arbitrary as there are few guidelines by which to estimate
them. However, it is the effects of varying the back
ground electrolyte which is of principal concern here.
So, as long as the values of d for the species involved
in the equilibrium are held constant, relative effects
of changing the medium can be estimated though absolute
constants may be incorrect. After calculating activity
coefficients for reactants and products, the correction
factor, £ was computed from equation (2-17) where £=
^Dun/(^u^ ) Table 33 lists the correction factors for
oriJr rJn p
the surface binding along with logarithms of the corrected
association constants, log Ks, in the presence of varying
concentrations of the electrolytes. For any given initial
molarity of alkali metal electrolyte, only minor variations
in E are observed for the differing types of cations.
These small differences are reflections of the minor
effect d has on the correction factor. For instance,
values for 0.10M LiH2PO^ and 0.10M CsH-^PO^ are 4.28 and
4.20, respectively, where d is 8 x 10 8 and 2.5 x 10 8 for
the respective cations. Below about 0.010M electrolyte
the correction factor is independent of the character of
the monovalent cation. For ionic strengths greater than
I
about 0.01(M), the order of increasing log Ks is the same
as for log Ks, namely: (CH3)4N+>Rb+>K+>Na+>(Cs+)>Li+.
(Cesium's position is not the same, but data pertaining
to it are probably not reliable, vide supra.) The parallel
order for the corrected values with those based on molar