Acid-Base Speciation of Carboxylate Ions in the Surface Region of Aqueous Solutions in the Presence of Ammonium and Aminium Ions

Abstract

The acid base speciation of surface-active carboxylate ions in the surface region of aqueous solutions was studied with synchrotron-radiation-based photoelectron spectroscopy. The protonated form was found at an extraordinarily large fraction compared to that expected from the bulk pH. When adding salts containing the weak acid NH₄⁺ to the solution, the fraction of the acidic form at the surface increases, and to a Much greatet extent than expected from the bulk pH of the solution. We show that ammonium ions also are overrepresented in the surface region, and propose that the interaction between the surface-active anionic carboxylates and cationic ammonium ions creates a carboxylateammonium bilayer close to the surface, which increases the probability of the protonation of the carboxylae ions. By comparing the situation when a salt of the less volatile amine diethanolatnine is used, We also show that the observed evaporation of ammonia that occurs after such an event only affects the equilibrium marginally.

Published in

Journal of Physical Chemistry B
2015, volume: 119, number: 10, pages: 4033-4040
Publisher: AMER CHEMICAL SOC

SLU Authors

• Werner, Josephina

  • The Department of Chemistry and Biotechnology, Swedish University of Agricultural Sciences
    
  • Uppsala University

UKÄ Subject classification

Physical Chemistry
Atom and Molecular Physics and Optics
Meteorology and Atmospheric Sciences

Publication identifier

• DOI: https://doi.org/10.1021/jp509945g

Permanent link to this page (URI)

https://res.slu.se/id/publ/67458