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

Rabindra N. Roy, Darin R. Gregory, Lakshmi N. Roy, Denis Pierrot, Frank J. Millero

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11 Scopus citations


The emf of the cell Pt, H2 (g, 1 atm) | HCl (mA), GdCl3 (mB) | AgCl, Ag without a liquid junction was used to investigate the HCl + GdCl3 + H2O mixed electrolyte system. The emf of the cell was measured for HCl + GdCl3 + H2O 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°C at 5°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 hydrochloric 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°C were found to be ΘH,Gd = 0.07 ± 0.03 and ΨH,Gd,Cl = 0.14 ± 0.03. These values were determined using literature values of β(0), β(1), and Cφ for GdCl3 at 25°C and estimates of the effect of temperature from 5 to 55°C using enthalpy and heat capacity data.

Original languageEnglish (US)
Pages (from-to)619-631
Number of pages13
JournalJournal of Solution Chemistry
Issue number7
StatePublished - Jul 2000
Externally publishedYes


  • Emf
  • Gadolinium chloride
  • Harned's rule
  • Hydrochloric acid
  • Mixtures of electrolytes
  • Pitzer equations, activity coefficients

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Molecular Biology
  • Physical and Theoretical Chemistry


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