Single ion activity coefficients of chloride ions in aqueous sodium chloride and magnesium chloride estimated potentiometrically based on ionic liquid salt bridge at 298 K

Abstract

The single ion activity coefficients of Cl-,γCl-, in aqueous NaCl and MgCl2 solutions have been estimated at 25 °C potentiometrically by use of galvanic cells with ionic liquid salt bridge consisting of tributyl(2-methoxyethyl) phosphonium bis(pentafluoroethanesulfonyl) amide. With increasing the ionic strength, Im, the γCl- decreases monotonously up to ca. 1 and 1.5 mol kg−1 for NaCl and MgCl2 solutions, respectively.The observed monotonous decrease is distinctively different from the leveling-off of the values greater than 0.5, previously reported, and is in agreement with the prediction by the Franekel’s Debye-Hückel-Smaller-ion Shell (DH-SiS) model that shows no minimum in γCl- versus Im curves in both NaCl and MgCl2 solutions. Quantitatively, the measured γCl- values are consistently smaller than those predicted by the DH-SiS model.