Properties of the borate ion in dilute aqueous solutions

Abstract

In this study the viscosity B_η coefficient and the ionic partial molar volume of the borate ion in aqueous solutions have been determined at 25 and 45°C. These properties, together with data reported for the borate mobility, the borate–cation interactions and the formation entropy of the borate ion in aqueous solutions, indicate that B(OH)₄ is a “structure-maker”, but its behaviour resembles neither that of a typical strongly hydrated ion (e.g., Li⁺) nor that of hydrophobic ions.

The partial molar volume and the hydrodynamic radius of the borate ion are close to those corresponding to a rigid sphere having the borate ion crystal radius and bearing a single charge. However, due to its tetrahedrally disposed OH groups it interacts strongly with water molecules but without substantially modifying the bonding pattern present in the solvent.