pH and the surface tension of water

James K Beattie; Alex M Djerdjev; Angus Gray-Weale; Nikola Kallay; Johannes Lützenkirchen; Tajana Preočanin; Atiđa Selmani

doi:10.1016/j.jcis.2014.02.003

pH and the surface tension of water

J Colloid Interface Sci. 2014 May 15:422:54-7. doi: 10.1016/j.jcis.2014.02.003. Epub 2014 Feb 22.

Authors

James K Beattie¹, Alex M Djerdjev², Angus Gray-Weale³, Nikola Kallay⁴, Johannes Lützenkirchen⁵, Tajana Preočanin⁴, Atiđa Selmani⁴

Affiliations

¹ School of Chemistry, University of Sydney, NSW 2006, Australia. Electronic address: james.beattie@sydney.edu.au.
² School of Chemistry, University of Sydney, NSW 2006, Australia.
³ School of Chemistry, University of Melbourne, Victoria 3000, Australia. Electronic address: angusg@unimelb.edu.au.
⁴ Department of Chemistry, Faculty of Science, University of Zagreb, Horvatovac 102a, HR-10000 Zagreb, Croatia.
⁵ Institut für Nukleare Entsorgung, Karlsruher Institut für Technologie (KIT), Herrmann-von-Helmholtz-Platz 1, 76433 Eggenstein-Leopoldshafen, Germany. Electronic address: johannes.luetzenkirchen@kit.edu.

PMID: 24655828
DOI: 10.1016/j.jcis.2014.02.003

Abstract

Despite the strong adsorption of hydroxide ions, the surface tension of water is almost independent of pH between pH 1 and 13 when the pH is adjusted by addition of HCl or NaOH. This is consistent with the Gibbs adsorption isotherm which measures the surface excess of all species in the double layer, if hydronium ions and hydroxide ions are adsorbed and sodium and chloride ions are not. The surface tension becomes pH dependent around pH 7 in millimolar NaCl or KCl solutions, for now sodium ions can replace hydronium ions as counterions to the adsorbed hydroxide ions.

Keywords: Air/water interface; Gibbs isotherm; Salt effect; Surface tension; pH.