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

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.