Activity coefficients of HCl+GdCl3+H2O system from 5 to 55 degrees C. Application of Pitzer formalism

The emf of the cell Pt, H-2 (g, 1 atm) \ HCl (m(A)), GdCl3 (m(B)) \ AgCl, Ag without a liquid junction was used to investigate the HCl + GdCl3 + H2O mix ed electrolyte system. The emf of the cell was measured for HCl + GdCl3 + H 2O solutions at ionic strengths of 0.025, 0.05, 0.1, 0.5, 1.0, 1.5, and 2.0 mol-kg(-1) and at eleven temperatures ranging from 5 to 55 degrees C at 5 degrees C intervals. The mean activity coefficients for HCl in the mixtures were determined using the Nernst equation. About 793 experimental emf data points were treated by the Harned equations. Results show that hydrochlori c acid follows Harned's rule at all ionic strengths, but the quadratic term is needed for I = 1.5 mol-kg(-1). The ion-interaction treatment of Pitzer was used to evaluate the results. The binary and ternary mixing parameters at 25 degrees C were found to be Theta(H,Gd) = 0.07 +/- 0.03 and psi(H,Gd,C l) = 0.14 +/- 0.03. These values were determined using literature values of beta((0)), beta((1)). and C-phi for GdCl3 at 25 degrees C and estimates of the effect of temperature from 5 to 55 degrees C using enthalpy and heat c apacity data.