Accurate Determination of Ion Polarizabilities in Aqueous Solutions

Abstract

We present a novel method for obtaining salt polarizabilities in aqueous solutions based on our recent theory for the refractive index of salt solutions, which predicts a linear relationship between the refractive index and the salt concentration at low concentrations, with a slope determined by the intrinsic values of the salt polarizability and the density of the solution. Here we apply this theory to determine the polarizabilities of 32 strong electrolyte salts in aqueous solutions from refractive index and density measurements. Setting Li + as the standard ion, we then determine the polarizabilities of seven cations (Na + , K + , Rb + , Cs + , Ca 2+ , Ba 2+ , and Sr 2+ ) and seven anions (F - , Cl - , Br - , I - , ClO 4 - , NO 3 - , and SO 4 2- ), which can be used as important reference data. We investigate the effect of temperature on salt polarizabilities, which decreases slightly with increasing temperature. The ion polarizability is found to be proportional to the cube of bare ionic radius (r bare 3 ) for univalent ions, but the relationship does not hold for multivalent ions. Contrary to findings of Krishnamurti, we find no significant linear relationship between ion polarizability and the square of the atomic number (N 2 ) for smaller ions.