The Temperature Dependence of the Conductivities and Ion-Association Constants of Potassium Nitrate and Potassium Perchlorate in Water

Abstract

Abstract The electric conductivities of potassium nitrate and potassium perchlorate in water have been measured at eleven temperatures from 0 to 50 °C and analyzed in order to obtain the ion-association constants and the limiting molar conductivities of these salts. It was found that the observed ion-association constants have a minimum value at 30 °C for KNO3 and at 36 °C for KClO4. Such a characteristic temperature dependence was considered to be due to the presence of specific short-range interactions within contact ion pairs, although the weak hydration of the ions seemed to help the formation of the contact ion pairs. The experimental standard enthalpies and entropies of ion association were discussed in comparison with the theoretical ones. The limiting molar conductivities of NO3− and ClO4− at each temperature were also evaluated and expressed as cubic equations of the temperature.