Jump to main content
Jump to site search

Issue 5, 2014
Previous Article Next Article

Thermodynamics of hydronium and hydroxide surface solvation

Author affiliations

Abstract

The concentration of hydronium and hydroxide at the water–air interface has been debated for a long time. Recent evidence from a range of experiments and theoretical calculations strongly suggests the water surface to be somewhat acidic. Using novel polarizable models we have performed potential of mean force calculations of a hydronium ion, a hydroxide ion and a water molecule in a water droplet and a water slab and we were able to rationalize that hydronium, but not hydroxide, is slightly enriched at the surface for two reasons. First, because the hydrogen bond acceptance capacity of hydronium is weaker than water and it is more favorable to have the hydronium oxygen on the surface. Second, hydroxide ions are expelled from the surface of the droplets, due to the entropy being lower when a hydroxide ion is hydrated on the surface. As a result, the water dissociation constant pKw increases slightly near the surface. The results are corroborated by calculations of surface tension of NaOH solutions that are in reasonable agreement with the experiment. The structural and thermodynamic interpretation of hydronium and hydroxide hydration provided by these calculations opens the route to a better understanding of atmospheric and surface chemistry.

Graphical abstract: Thermodynamics of hydronium and hydroxide surface solvation

Back to tab navigation

Supplementary files

Publication details

The article was received on 15 Oct 2013, accepted on 06 Dec 2013 and first published on 09 Dec 2013


Article type: Edge Article
DOI: 10.1039/C3SC52862F
Citation: Chem. Sci., 2014,5, 1745-1749
  •   Request permissions

    Thermodynamics of hydronium and hydroxide surface solvation

    J. S. Hub, M. G. Wolf, C. Caleman, P. J. van Maaren, G. Groenhof and D. van der Spoel, Chem. Sci., 2014, 5, 1745
    DOI: 10.1039/C3SC52862F

Search articles by author

Spotlight

Advertisements