title: pH and the surface tension of water.
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.
authors.affiliation: School of Chemistry, University of Sydney, NSW 2006, Australia. Electronic address: james.beattie@sydney.edu.au.
authors.forename: James K
authors.initials: JK
authors.lastname: Beattie
authors.affiliation: School of Chemistry, University of Sydney, NSW 2006, Australia.
authors.forename: Alex M
authors.initials: AM
authors.lastname: Djerdjev
authors.affiliation: School of Chemistry, University of Melbourne, Victoria 3000, Australia. Electronic address: angusg@unimelb.edu.au.
authors.forename: Angus
authors.initials: A
authors.lastname: Gray-Weale
authors.affiliation: Department of Chemistry, Faculty of Science, University of Zagreb, Horvatovac 102a, HR-10000 Zagreb, Croatia.
authors.forename: Nikola
authors.initials: N
authors.lastname: Kallay
authors.affiliation: Institut für Nukleare Entsorgung, Karlsruher Institut für Technologie (KIT), Herrmann-von-Helmholtz-Platz 1, 76433 Eggenstein-Leopoldshafen, Germany. Electronic address: johannes.luetzenkirchen@kit.edu.
authors.forename: Johannes
authors.initials: J
authors.lastname: Lützenkirchen
authors.affiliation: Department of Chemistry, Faculty of Science, University of Zagreb, Horvatovac 102a, HR-10000 Zagreb, Croatia.
authors.forename: Tajana
authors.initials: T
authors.lastname: Preočanin
authors.affiliation: Department of Chemistry, Faculty of Science, University of Zagreb, Horvatovac 102a, HR-10000 Zagreb, Croatia.
authors.forename: Atiđa
authors.initials: A
authors.lastname: Selmani
keywords: Air/water interface; Gibbs isotherm; Salt effect; Surface tension; pH