Activity Coefficient Determination for the Ternary Systems CsCl in N-Methylformamide or Urea + Water Mixtures at T = 298.15 K

The mean activity coefficients for CsCl in N -methylformamide or urea ( w ) + H 2 O (1 −  w ) systems were determined in this work by potentiometry, using ion-selective electrodes at 298.15 K. The value of mass fraction w was varied between 0.00 and 0.40 in five unit-steps and the molality of CsCl was between 0.0020 and 1.4009 mol·kg −1 . The experimental data have been correlated with the Pitzer, modified Pitzer and the extended Debye–Hückel equations. The resulting values of the mean activity coefficients, the osmotic coefficients and the standard Gibbs energy of transfer, together with the Pitzer ion-interaction parameters ( β (0) , β (1) and C φ ), extended Debye–Hückel parameters ( a , c and d ), and modified Pitzer parameters ( b , B MX , C MX ) are reported for the investigated systems.