We have correlated simultaneously experimental data for osmotic and activity coefficients of strong electrolyte solutions using the Pitzer equation and a modification of it. The optimal value for the Pitzer b parameter is different from the traditional value of 1.2 when using higher concentrations in its determination. An analysis of the equation shows that it is possible to reduce the model to a three-parameter form that represents the coefficients at molalities as high as 25 with better accuracy than the model as proposed by Pitzer.

We have established the temperature dependence for a modified Pitzer model. This model adequately correlates osmotic and activity coefficient data together with the dilution enthalpy for single-electrolyte solutions. For multisalt aqueous solutions, the modified model can successfully predict the behavior of the osmotic coefficient and the enthalpy at different temperatures. For the new model, the total average percentage error in the osmotic and activity coefficients is 3.1%.

We present densities, viscosities, and speed of sound of pure and binary mixtures of three ionic liquids, triethylsulfonium bis­(trifluoromethylsulfonyl)­imide, [Et3S]­[TFSI], 1-allyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide, [Amim]­[TFSI], and 1,3-dihydroxyimidazolium bis­(trifluoromethylsulfonyl)­imide, [(OH)2Im]­[TFSI], with 1-propanol from (293.15 to 343.15) K at 0.1 MPa. We also include densities, viscosities, and speed of sound of pure ionic liquid 1-butyl-1-methylpyrrolidinium bis­(trifluoromethylsulfonyl)­imide for validation. Densities and speed of sound are measured using a vibrating tube densimeter while viscosities are from a pellet microviscometer. The density and viscosity of pure ionic liquids are correlated by means of the Gardas and Coutinho and Vogel–Tammann–Fulcher equations, respectively. From the speed of sound measurements, we obtain isentropic compressibility, speed of sound deviation, and isentropic compressibility deviation for mixtures of ionic liquids and 1- propanol. Excess molar volumes and viscosity deviations are calculated from the experimental data. The excess molar volumes for the binary mixtures with [Et3S]­[TFSI] and [Amim]­[TFSI] present positive and negative deviations from ideality while those for the binary mixture with [(OH)2Im]­[TFSI] exhibit only negative deviations. Viscosity deviations for [Et3S]­[TFSI] + 1-propanol, [Amim]­[TFSI] + 1-propanol, and [(OH)2Im]­[TFSI] + 1-propanol are negative over the entire temperature range. The speed of sound deviations are positive and negative for the binary mixtures of 1-propanol with [Et3S]­[TFSI] and [Amim]­[TFSI], whereas those for the mixture with [(OH)2Im]­[TFSI] are negative.

In this work three Pitzer-type models were compared: the original one, the Archer model (an extended Pitzer model) with ionic strength dependence in the third virial coefficient, and the PIH model that uses as an adjusting parameter the closest approach constant. The performance of these models in correlating the osmotic and activity coefficient of 1:1, 1:2, 1:3, 1:4, 2:1, 2:2, 3:1, 3:2, and 4:1 aqueous electrolyte solutions was tested using experimental data sets for 245 single electrolyte aqueous solutions. The absolute average percentage deviations were 0.78, 1.18, and 3.56% for the Archer, PIH, and Pitzer models, respectively. data R 1 2.0/1.4 b 2.0 c /1.4 not required R 2 12 a 12À32Aϕ not required R 3 not required 0.4À2.5 c not required β MX (0)

Activity coefficients of NaCl in water + methanol + ethanol solutions have been determined from electromotive force (emf) measurements at 298.15 K. We have used a cell [ISE Na + |NaCl, H 2 O, MeOH, EtOH|ISE Cl -] to obtain the emf of eight mixture series containing 10 to 40 (w/w) of methanol + ethanol at molalities up to 2.0 of NaCl. A modified Pitzer equation is used together with the Nernst equation to obtain the mean activity coefficient.