Activity coefficients of (hydrogen chloride plus europium chloride) (aq) using Harned's rule and the Pitzer formalism

Activity coefficients of HCl in (hydrogen chloride + europium chloride) hav e been determined at temperatures ranging from 278.15 K to 328.15 K at 5 K intervals and at eight constant total ionic strengths of(0.025, 0.05, 0.1, 0.25, 0.5, 1.0, 1.5, and 2.0) mol kg(-1). Experimental cell potentials were obtained using a cell without liquid junction of the type Pt\H-2(g, p = 10 1.325 kPa)\HCl (m(A)), EuCl3 (m(B))\AgCl(s)\Ag(s). The treatment of Harned has been used to describe the mean molal activity coefficient of hydrochlor ic acid as a function of ionic strength in acid salt mixtures. Results indi cate that the quadratic form is sufficient for the full range of Y-B (the i onic strength fraction of the salt) to 0.9 at all the experimental ionic st rengths. The ion-interaction model of Pitzer has also been used to calculat e Fitter's mixing parameters Theta (H,Eu) and Psi (H,Cl,Eu) for the system H+ + Eu3+ + Cl- + H2O. The values found, Theta (H,Eu) = 0.2 +/- 0.03 and Ps i (H,Cl,Eu) = 0, were similar to those for other trivalent ions studied pre viously. The parameters used in this study reproduce the activity coefficie nts of HCl in the mixtures to within 0.016 over the entire range of ionic s trengths and within 0.009 for I > 0.05 mol kg(-1) over the entire temperatu re range.