Individual Ionic Surface Tension Increments in Aqueous Solutions

Surface tension increments by aqueous electrolytes, k(E) = [gamma(c(E)) - [gamma(W)]/c(E), can be split into the ionic values, k(i) (k(E) = Sigma nu(i)k(i)), on an arbitrary but plausible manner, notwithstanding the effects of counterions on the behavior of specific ions. Values for 41 ions, mono- and polyatomic and uni- and multivalent, are presented in conjunction with some other ionic properties. The surface potential increments of electrolytes, Delta Delta chi = Delta chi(E) (at c(E) = 1 M) - Delta chi(w), depend linearly on the k(E) values for four anion series with common cations and on the differences between cation and anion k(i), values. The k(i); (normalized to unit charge number) are correlated linearly with the ionic radii r(i) the excess ionic molar refractivity over that of water, R-Di - R-DW, the ionic softness parameters (modified by adding +0.5 to anion and -0.5 to cation values), sigma(+/- 0.5), and to the geometrical factor of water structure making/breaking, Delta(HB)G. No correlation takes place with the ionic polarization corrected for that of water, alpha(i)* = alpha(i) - alpha(w)(r(i)/r(w))(3), nor with the molar Gibbs energy or enthalpy of hydration. The latter fact implies that ion dehydration does not play a major role in the sorption/desorption of ions at the surface. The correlations that were found are discussed in a qualitative manner and compared with theoretical arguments in the literature.