Thermodynamics of electrolyte solutions: activity coefficients of NaCl in the NaCl–NiCl2–H2O system at 25, 35, and 45 °C

The activity coefficients of NaCl in the NaCl–NiCl2–H2O system were estimated at 25, 35, and 45 °C and total ionic strengths of 0.5, 1.0, 2.0, and 3.0 m by an EMF method using a Na-ion selective electrode and a silver–silver chloride reference electrode. The Harned coefficients were calculated at all the temperatures studied. At 25 °C the data were analysed using the Pitzer formalism. The osmotic coefficients and the excess free energies of mixing were also calculated at 25 °C. Keywords: activity coefficients, sodium chloride, nickel chloride, Pitzer equations, thermodynamics.

A theoretical treatment of cation exchangers - II. Equilibria between an ion exchanger and an aqueous solution with a common cation

The treatment of an ion exchanger as a concentrated aqueous poly-electrolyte is extended to cover the case of an exchanger saturated with a single cation which is in equilibrium with a solution containing a salt of the same cation. For this purpose equations are derived for the activity and osmotic coefficients of mixtures of 1:1 electrolytes with resinates giving only one mobile ion per equivalent. Applying these equations to experimental data, values of the 'Harned' coefficients α 12 and α 21 are calculated. From these the absolute value of the activity coefficient of the H-resinate (using infinite dilution as the standard state) is deduced, which, taken in conjunction with the osmotic data of part I, enable the activity coefficient curve to be obtained, up to very high concentrations. This curve shows that at high concentrations there is less ion-pair formation for ‘resinates’ of the sulphonated polystyrene type than is shown in aqueous solutions of the corresponding nitrates at the same ionic strength.