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 - , γ Cl - , 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, I m , the γ Cl - 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-Huckel-Smaller-ion Shell (DH-SiS) model that shows no minimum in γ Cl - versus I m curves in both NaCl and MgCl2 solutions. Quantitatively, the measured γ Cl - values are consistently smaller than those predicted by the DH-SiS model.