The electrical conductivity of [Co(NH3)5NO2]SO4 in aqueous solution under high pressure

Abstract

The electrical conductivity of aqueous [Co(NH_3)_5NO_2]SO_4 solution has been measured as a function of pressure up to 3, 000kg/cm^2 for concentrations from 2.0×10^-4 to 1.0×10^-3N at the temperatures of 15, 25 and 40℃. The equivalent conductance at infinite dilution, Λ°, has a maximum against pressure. The pressure of this maximum conductance has been found to be higher than that of the minimum viscosity of water at each temperature. These phenomena may be attributed to the decrease in the effective radii of the hydrated ions with increasing pressure. The hydration numbers of the ions estimated by the Robinson-Stokes method are little changed by pressure and temperature. Both the closest approach distance of the ion-pair, a, calculated by using the theoretical equation of Fuoss and the thermodynamic parameter, ΔV^^-°, calculated from the pressure coefficient of the dissociation constant suggest that this ion-pair, [Co(NH_3)_5NO_2]^2+・SO_4^2-, would be very near to the contact one.