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Thermodynamic Study of Cadmium Chloride in Aqueous Mixtures of 2-Butanol from Potential Difference Measurements

The standard molal potential differences Eo have been determined for the cell: CdHgx (two phase) ; CdCl2(m), H2O(1-w), 2-butanol(w) ; AgCl ; Ag(s) in aqueous mixtures of low mass fraction of 2-butanol (w2-butanol = 0.05, 0.10, and 0.15) by using the literature data for the stability constants of the chlorocadmium complexes and the present potentiometric data for this cell at five temperatures from (293.15 to 313.15)K and at 10 molalities of CdCl2 from (0.002 to 0.02) mol-kg– 1. The resulting values of Eo have been used to calculate the standard thermodynamic quantities for the cell reaction, the stoichiometric mean molal activity coefficients of CdCl2, and the standard thermodynamic functions for CdCl2 transfer from water to the examined aqueous mixtures of 2-butanol. The values obtained have been compared with the analogous literature data for aqueous mixtures of 2-butanone ; standard thermodynamic quantities for transfer of CdCl2 and HBr from water to mixtures containing the same mass fraction of 2-butanol have also been compared. For both electrolytes, these quantities show analogous trends with the alcohol content. This transfer process is nonspontaneous and endothermic. Enthalpy and entropy are evidently influenced by structural changes.

activity coefficients; aqueous mixtures of 2-butanol; cadmium chloride; potentiometry; thermodynamic quantities

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