Activity and osmotic coefficients from the Emf of liquid membrane cells. IX: Mn(ClO4)(2) and MnSO4 in water at 25 degrees C

The relative activity coefficients of MnSO4 and Mn(ClO4)(2) were measured d own to about 5 x 10(-5) mol-kg(-1) by means of cells with ion-exchange liqu id membranes. The measurements at high dilution provide an answer to the ag e-old problem of absolute values of the activity coefficients for MnSO4. Th ey also lead to a correction of the activity coefficients for Mn(ClO4)(2), whose literature values are found to be biased by ca. 6.5%. Like other biva lent metal sulfates, MnSO4 does not obey the Debye-Huckel law inasmuch as n egative instead of positive deviations from the limiting law are observed i n the dilute regions. The possibility for this kind of behavior to denote i on association is discussed. The best-fit parameters of Fitter's equation, able to provide accurate values of the activity and osmotic coefficients of the two salts for any concentration, are reported.