Electric conductivities of 1:1 electrolytes in liquid methanol along the liquid-vapor coexistence curve up to the critical temperature.I.NaCI,KCI,and CsCI solutions

摘要

The molar conductivities A of NaCl,KCl,and CsCl in liquid methanol were measured in the concentration range of(0.3-2.0)X10~-3 mol dm~-3 and the temperature range of 60-240 deg C along the liquid-vapor coexistence curve.The temperature range corresponds to the solvent density range of(2.78-1.55)rho,where rho_c=0.2756 g cm~-3 is the critical density of methanol.The concentration dependence of A at each temperature and density(pressure)has been analyzed by the Fuoss-Chen-Justice equation to obtain the limiting molar conductivity LAMBDA~0 and the molar association constant K_A.For all the electrolytes studied,LAMBDA~0 increased almost linearly with decreasing density at densities above 2.0_rho_c,while the opposite tendency was observed at lower densities.The relative contribution of the nonhydrodynamic effect on the translational friction coefficient zeta was estimated in terms of LAMBDA zeta/zeta,where the residual friction coefficient LAMBDA zeta is the difference between zeta and the Stokes friction coefficient zeta.At densities above 2.0_rho_c,LAMBDA zeta/zeta increased with decreasing density though zeta and LAMBDA zeta decrease,and the tendencies are common for all the ions studied.The density dependences of zeta and LAMBDA zeta/zeta were explained well by the Hubbard-Onsager(HO)dielectric friction theory based on the sphere-in-continuum model.At densities below 2.0_rho-c,however,the experimental results cannot be explained by the HO theory.