Neutron scattering studies on the hydration of phosphate ions in aqueous solutions of K3PO4, K2HPO4 and KH2PO4

Abstract

The difference methods of neutron diffraction and isotopic substitution (NDIS) were applied to the total scattering patterns of H/D substituted solutions containing three types of phosphate anion (H₂PO₄⁻, HPO₄²⁻, PO₄³⁻). The data were used to determine the pairwise structure associated with the hydrogen and oxygen atoms of the solution. The results are consistent with hydrogen bonds between the H₂PO₄⁻, HPO₄²⁻ and PO₄³⁻ anions and water molecules being respectively stronger than, comparable to and weaker than those between the hydrogen bonds of water molecules. It is also deduced that the coordination number for the PO₄³⁻ ion is 15 ± 3, and a similar value is proposed for the other two anions.