mixed-electrolyte systems were investigated by the potentiometric method. The experimental data were modeled by connecting the Nernst equation with the Pitzer or Harned model. The mean ionic activity coefficients of CsF, γ ±A , and CsBr or CsNO 3 , γ ±B , were calculated. Moreover, other properties, such as mean ionic activity coefficients in pure and trace quantities (γ 0 and γ tr ), osmotic coefficients, Φ, excess Gibbs energies, G E , and the change in excess Gibbs energy of the mixture, ΔG m ex , were obtained and discussed.