Electric conductivities of 1:1 electrolytes in liquid methanol along the liquid-vapor coexistence curve up to the critical temperature. II. KBr and KI solutions

The molar conductivities Λ of KBr and KI in dilute methanol solutions were measured along the liquid-vapor coexistence curve up to the critical temperature (240 °C). The concentration dependence of Λ in each condition was analyzed by the Fuoss–Chen–Justice equation to obtain the limiting molar conductivities and the molar association constants. Using the present data together with the literature ones, the validity of the Hubbard–Onsager (HO) dielectric friction theory based on the sphere-in-continuum model was examined for the translational friction coefficients ζ of the halide ions (the Cl−, Br−, and I− ions) in methanol in the density range of 2.989ρc⩾ρ⩾1.506ρc, where ρc=0.2756 g cm−3 is the critical density of methanol. For all the halide ions studied, the friction coefficient decreased with decreasing density at ρ>2.0ρc, while the nonviscous contribution Δζ/ζ increased; Δζ was defined as the difference between ζ and the friction coefficient estimated by the Stokes law. The density dependence of ζ and Δζ/ζ were well reproduced by the HO theory at ρ>2.0ρc. The HO theory also explained the ion-size dependence of Δζ/ζ which decreased with ion-size at ρ>2.0ρc. At ρ<2.0ρc, on the other hand, the HO theory could not explain the density and the ion-size dependences of ζ and Δζ/ζ. These results indicated that the application limit of the HO theory lied about ρ=2.0ρc which is the same as the application limit observed for the alkali metal ions. The present results were also compared with the results in subcritical aqueous solutions.