Activity coefficients in (hydrogen chloride + holmium chloride) (aq) from T = (278.15 to 328.15) K

Abstract

Activity coefficients of HCl in (hydrogen chloride + holmium chloride) (aq) have been calculated from the observed e.m.f.s using the Nernst equation. The temperatures ranged from (278.15 to 328.15) K at 5 K intervals and at constant total ionic strengths of (0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1.0, and 1.5) mol · kg −1. Electromotive-force measurements were made on the cell without liquid junction of the type: Pt | H 2 ( g , p = 101 . 325 kPa ) | HCl ( m A ) , HoCl 3 ( m B ) | AgCl ( s ) , | Ag ( s ) The results of the activity coefficients of HCl for this mixed electrolyte mixture have been interpreted in terms of the simpler Harned’s equations and the ion-interaction model of Pitzer. Results show that the quadratic term is sufficient for the full range of Y B (the ionic strength fraction of the salt) to 0.9 at all the ionic strengths studied. The Pitzer’s mixing parameters S θ H , Ho and Ψ H,Ho,Cl (including higher order electrostatic effects) and θ H,Ho and Ψ H,Ho,Cl (excluding higher order electrostatic effects) have been determined. These values at T = 298.15 K are: S θ H , Ho = 0 . 115 , Ψ H,Ho,Cl = −.071; and θ H,Ho = −.663, Ψ H,Ho,Cl = 0.165. The parameters obtained in this study reproduce the activity coefficients of HCl in the mixtures within 0.015 over the entire range of ionic strengths and within 0.009 for I ⩾ 0.05 mol · kg −1 over the entire temperature range.