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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.

In this paper, we present atmospheric pressure liquid densities for binary mixtures of n-methyldiethanolamine + water over the entire composition range at temperatures between 263.15 and 363.15 K. We measure the liquid densities using a vibrating tube densimeter and use them to produce a correlation for excess molar volumes based upon a Redlich-Kister equation. The excess volumes exhibit negative deviations from ideality at all the investigated temperatures and become less negative with increasing temperature.

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Densities and viscosities of (N,N-dimethylformamide + water) have been measured from T = (283.15 to 353.15) K in the entire mole fraction composition. Densities are measured with a vibrating tube densimeter, while two different Cannon-Fenske viscosimeters are used for the viscosity measurements. Excess molar volumes and viscosity deviations from the composition weighted average of the pure component viscosities are calculated from experimental measurements and represented with Redlich–Kister equations. Excess molar volumes present negative deviations from ideality at all investigated temperatures and become more negative with decreasing temperature. Viscosity deviations are positive for all the temperatures and mole fractions considered in this work.