Thermodynamic Study of the Activity of Cadmium Chloride in Aqueous Solutions at Various Temperatures

The thermodynamic properties of cadmium chloride in aqueous solutions were investigated by the hygrometric method and thermodynamic modeling at different temperatures. The water activities were measured in the molality range from 0.10 mol·kg –1 up to m max = (6.60 to 7.65) mol·kg –1 at temperatures from 298.15 to 353.15 K, respectively. From the newly measured data, the osmotic coefficients of water were deduced. The cadmium chloride aqueous solutions contain some additional complexes such as CdCl 2 (aq), Cd 2+ (aq), CdCl + (aq), CdCl 3 – (aq), and CdCl 4 2– (aq). Based on emf data of the literature for CdCl 2 (aq) at 298.15 K, the consistency of the activity coefficient was evaluated using an adequate model. The parametrizations were developed by the ion interaction models, and the Filippov–Charykov–Rumyantsev model is the only one that gives a better representation of the experimental results with excellent prediction of the activity coefficients. This procedure is extended to obtain the recommended activity coefficients at various temperatures. The water activities, activity coefficients, and molalities of the saturated points were used to calculate the solubility product and the Gibbs energy of dissolution at different temperatures. The calculated Δ G diss ° was compared with that existing in the literature at 298.15 K, and good agreement is obtained.