The Molar Volumes of Ions in Solution, Part 7. Electrostriction and Hydration Numbers of Aqueous Polyatomic Anions at 25 °C

The standard partial molar volumes of 16 polyatomic more-or-less globular anions in aqueous solutions at 25 degrees C were calculated as the sum of the intrinsic and (negative) electrostrictive volumes and compared with the experimental values. The intrinsic volumes used an empirical additive to the bare ionic radius to account for void spaces near the ions. The volume shrinkage due electrostriction was calculated according to the shell-by-shell electrostatic method. Agreement for many of the anions was achieved, but in some cases, notably the trivalent phosphate and arsenate ones, the calculated values failed to reproduce the experimental ones within reasonable uncertainties of the sizes of the anions.