Activity coefficients of rubidium chloride and cesium chloride in methanol–water mixtures and a comparative study of Pitzer and Pitzer–Simonson–Clegg models (298.15 K)

Activity coefficients of rubidium chloride and cesium chloride in methanol–water mixed solvent systems were determined by electromotive force (EMF) measurements at 298.15 K, in the range 0–40% (wt.%) methanol. For our work, the cells:Rb-ISE | RbCl (m), methanol (Y), water (1 − Y) | Cl-ISE;  Cs-ISE | CsCl (m), methanol (Y), water (1 − Y) | Cl-ISEwere used to obtain the emf data. The rubidium and cesium ion-selective electrodes were prepared by ourselves, and they exhibited reasonably good Nernst response. Then the experimental data were calculated by both Pitzer and Pitzer–Simonson–Clegg models. We got the corresponding parameters of two models, the standard potentials and the activity coefficients of rubidium chloride and cesium chloride. Moreover, the standard Gibbs free energies of transference of RbCl or CsCl from water to methanol–water mixtures had been discussed as well. After the comparative study, it was found that the Pitzer–Simonson–Clegg model was superior in this work.