Conductometric Study of Ion Association of Hexaamminecobalt(III) Complexes in Ethanol + Water

Abstract

The conductivities of the chloride, bromide, iodide, nitrate, and perchlorate of the hexaamminecobalt(III) complex were measured in (10−70) mass % ethanol + water at temperatures between (10 and 50) °C. The ion association constants (KA) were determined by analyzing the conductivity data in terms of the Robinson−Stokes equations. Ion association constants calculated for all complex salts in ethanol + water increased, dependent on the amount of ethanol. This was equivalent to the ion association constants increasing with a decrease in the relative permittivity of the mixed solvents. While KA values increased with increasing temperature for the chloride and bromide, the iodide of [Co(NH3)6]3+ indicated some disorder. It was observed that these values decreased dependent on the temperature for oxoacid ions. The ion association constants of the complex ion with the anions had minimum values (Kmin) at temperatures (tmin) characteristic of the salts. The values of tmin increased in the order Cl- < Br- < I- < NO3- < ClO4-. The standard entropy and enthalpy changes of ion association in ethanol + water were calculated from an equation by using Kmin and tmin values. The entropy and enthalpy changes were investigated dependent on temperature and amount of ethanol. The limiting molar conductivities of complex ion and monovalent anions in the mixed solvents were estimated from our experimental data using the Kohlraush equation.