Monatshefte für Chemie / Chemical Monthly

, Volume 126, Issue 8–9, pp 819–837 | Cite as

The ionic product of water in highly concentrated aqueous electrolyte solutions

  • I. Kron
  • S. L. Marshall
  • P. M. May
  • G. Hefter
  • E. Königsberger
Anorganische Und Physikalische Chemie

Summary

The ionic product of water,\(K_w = [H^ + ][OH^ - ] = 10^{ - pK_w } \), has been determined in aqueous NaCl (0.5–5.0M), KCl (3.0M), NaNO3 (3.0 and 5.0M), and KNO3 (2.5M) at 25 °C from high-precision potentiometric titrations carried out in cells with liquid junction using either glass or hydrogen electrodes. Measurements ofKw provide a set of self-consistent data that can be used in the estimation of activity coefficient changes and liquid junction potentials in the study of extremely concentrated electrolyte solutions. Where comparison is possible, results obtained by hydrogen electrode measurements are in excellent agreement (ca ± 0.005 inpKw) with other reliable experimental values and the predictions of thePitzer activity-coefficient model. The glass electrode results are, as expected, routinely lower (by 0.03–0.05pKw units), owing to interference by Na+ ions. This effect virtually disappears in solutions of potassium salts. Comparison of the experimental results with thePitzer predictions shows that knowledge of the ternary interaction parameters is essential to account for specific ionic effects in the concentration dependence ofpKw.

Keywords

Aqueous electrolyte solutions Glass electrode Hydrogen electrode Ionic product of water Pitzer model Potentiometric titration 

Das Ionenprodukt des Wassers in hochkonzentrierten wäßrigen Elektrolytlösungen

Zusammenfassung

Das Ionenprodukt des Wassers,\(K_w = [H^ + ][OH^ - ] = 10^{ - pK_w } \), wurde in wässerigen Lösungen von NaCl (0.5–5.0M), KCl (3.0M), NaNO3 (3.0 and 5.0M) und KNO3 (2.5M) bei 25 °C gemessen. Dazu wurden potentiometrische Titrationen unter Verwendung von Glas- oder Wasserstoffelektroden in Zellen mit Überführung durchgeführt. Mit diesenpKw-Werten kann man Änderungen der Aktivitätskoeffizienten in hochkonzentrierten Elektrolytlösungen ermitteln sowie Diffusionspotentiale abschätzen. Die mit Wasserstoffelektroden erhaltenenpKw-Werte stimmen mit verläßlichen Literaturdaten innerhalb vonca. ± 0.005 überein. Bei Messungen mit Glaselektroden führt der Na+-Fehler zu um 0.03–0.05 kleinerenpKw-Werten. Dieser Effekt wurde in Kaliumsalzlösungen nicht beobachtet. Der Vergleich der experimentellen Resultate mit Voraussagen desPitzer-Modells unterstreicht die Bedeutung ternärer Wechselwirkungsparameter für die exakte Berechnung des Ionenproduktes.

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Copyright information

© Springer-Verlag 1995

Authors and Affiliations

  • I. Kron
    • 1
  • S. L. Marshall
    • 1
  • P. M. May
    • 1
  • G. Hefter
    • 1
  • E. Königsberger
    • 1
  1. 1.A. J. Parker Cooperative Research Centre for Hydrometallurgy, School of Mathematical and Physical SciencesMurdoch UniversityMurdochAustralia

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