Determination of Thermodynamic Properties of CsBr in 1,2-Butanediol/1,4-Butanediol + Water Mixtures by Potentiometric Measurements at 298.2 K

The thermodynamic properties of electrolyte solutions elucidate the mechanisms of ionic interactions in solution. This study investigates the thermodynamic properties of the ternary systems containing cesium bromide (CsBr), water, and either 1,2-butanediol (1,2-BDO) or 1,4-butanediol (1,4-BDO) at 298.2 K utilizing potentiometric techniques. CsBr molalities were in the approximate range of 0.01 to 1 mol·kg −1 , and the mass fraction of 1,2-BDO/1,4-BDO in 1,2-BDO/1,4-BDO+H 2 O binary mixed solvents were 0, 0.10, 0.20, and 0.30. The Debye-Hückel model, the Pitzer model, along with the Nernst equation were explored to determine the thermodynamic parameters, which included the mean ionic activity coefficients ( γ ± ), osmotic coefficients ( φ ), excess Gibbs free energy ( G E ), standard Gibbs free energy of transference (Δ G 0 t ), and primary hydration number ( n hydr ). The results reveal that the γ ± of CsBr decreases with increasing the molality of CsBr and with increasing the mass fraction of 1,2-BDO and 1,4-BDO in the binary mixture. A positive value for the Δ G 0 t signifies that the transfer of CsBr from pure water to the mixed solvent system is thermodynamically unfavorable and thus non-spontaneous. These findings can provide thermodynamic data to support potential industrial processes.