Change of liquid water structure under the presence of phosphate anion during changing its kosmotropic character to chaotropic along its deprotonation route

Abstract

Temperature dependence of OH-stretching bands of water and aqueous phosphoric acid solutions were compared to clarify how the presence of ions alters the hydrogen bonded structure of water. Investigations were performed by Raman measurements at different pH considering that the slightly chaotropic character of H2PO4− anion changes to kosmotropic in the cases of the HPO42− and PO43− anions. This property is determined by the number of OH groups (proton donors) versus the lone pairs of oxygen atoms (proton acceptors). The number of molecules assisted to form hydrogen bonds through their oxygen lone pairs decreases at elevated temperature and increased pH.