Osmotic and activity coefficients of dilute aqueous solutions of the series Me4NI to MeBu3NI at 298.15 K

Osmotic coefficients of dilute aqueous solutions of Me4NI, Me3BuNI, Me2Bu2NI and MeBu3NI were determined by the isopiestic method at 298.15 K. A gravimetric isopiestic vapor pressure technique was used. The osmotic coefficients of tetra-alkyl-ammonium solutions were analyzed with the Debye–Hückel limiting law. The results show that the osmotic coefficient varies in the following way: Me4NI > MeBu3NI > Me2Bu2NI > Me3BuNI. The negative deviation of activity coefficients values from the Debye–Hückel limiting law was interpreted in terms of ion-pair formation. The set of Pitzer parameters b = 1.2 and α1 = 2.0 was used. The results were fitted to the Pitzer model and the parameters β0, β1 and Cϕ were calculated. β0 and β1 were analyzed in terms of ion–ion interactions and ion–solvent interactions.