Activity coefficients in electrolyte mixtures: HCl + ThCl₄ + H₂O for 5-55 °C

The emf of the cell without liquid junction (A) was used to study the HCl + ThCl₄ + H₂O mixed electrolyte system. The Pt, H₂(g,1 atm)|HCl(m_A), ThCl₄(m_B)|AgCl,Ag (A) emf was measured for solutions at constant total ionic strengths of 0.006, 0.008, 0.01, 0.05, 0.1, 0.25, 0.5, 1.0, 2.0, and 3.0 mol·kg^-1 and at temperatures ranging from 5 to 55°C. The mean activity coefficients of HCl in the mixtures were calculated using the Nernst equation. Two detailed treatments are given of the data for 25°C. In the first, the Harned equations were fitted to the activity coefficient data using least-squares regression techniques. Results show that the quadratic equation is adequate for the full range of Y_B to 0.9 for I ≤ 2.0 mol·kg^-1 but only for smaller Y_B at I = 3.0. Second, an ion-interaction (Pitzer) equation treatment is given in which experimental isopiestic measurements, solubility, and the activity coefficient data are analyzed and the necessary parameters developed for the H⁺-Th⁴⁺-Cl^--H₂O system.