The study of activity coefficients of (hydrogen bromide + strontium bromide) (aq) using Pitzer's formalism

Electromotive-force measurements were made on the cell:Pt|H 2 (g,p = 101.325 k Pa)|HBr(m A ), SrBr 2 (m B )|AgBr(s)|Ag(s). Activity coefficients of HBr in (hydrogen bromide + strontium bromide)(aq) were determined from electromotive-force measurements at temperatures ranging from 278.15 K to 318.15 K at 10 K intervals and at constant total ionic strengths of (0.1, 0.25, 0.5, 1.0, 2.0, and 3.0) mol · kg −1 . The results have been interpreted using Harned's empirical equations and also the comprehensive treatment of Pitzer. Activity coefficients for HBr in the salt mixture follow Harned's rule only at I = 0.1 mol · kg −1 . At higher ionic strengths, the eperimental results are best described by a non-linear equation. The Pitzer mixing parameters S Θ H.Sr and Ψ H.Sr.Br (including higher-order electrostatic effects) and Θ H.Sr and Ψ H.Sr.Br (excluding higher-order effects) as well as the temperature derivatives of the mixing coefficients have been determined and compared with the results for similar mixtures. The activity coefficients and excess enthalpies for HBr and SrBr 2 have also been calculated at the experimental temperatures and compared with the results of other investigators.