Chemical Engineering @ChemengFiles.Com

An electrodynamic balance has been used to measure the water activity as a function of solute concentration at 20 [...]C for eleven single-electrolyte aqueous solutions[...] and three mixed-electrolyte aqueous solutions [...]. The measurements were performed by levitating single, charged, 20-micron diameter droplets of these solutions within the balance and measuring the mass of the particles as a function of the surrounding relative humidity. The deliquescence behavior of the particles was also observed.

Heterogeneous nucleation was inhibited due to the absence of container walls and because the small droplets were less likely than a bulk sample to contain foreign particles. Thus, this technique allowed the thermodynamics of highly concentrated solutions to be studied. For most of the solutions, water activity measurements were made to higher solute concentrations than have previously been reported. At low concentrations, the results were consistent with previously published data. Nucleation theory was used to estimate the surface excess free energy and critical nucleus size from the measured supersaturation at which nucleation occurred.

For the single-electrolyte solutions, the dependence of the solute activity coefficient on concentration was calculated, and the features of this dependence are discussed in relationship to ionic hydration and association. Several semi-empirical electrolyte solution models were tested against the data, and it was found that salt-specific model parameters estimated from low concentration data could not be reliably used to predict the solution behavior at high concentrations. However, with estimated parameters based on the full range of the data, the models were able to represent the experimental data for single-electrolyte solutions to within the uncertainty in the measurements.

Three models of mixed-electrolyte solutions — the Zdanovskii-StokesRobinson, Reilly-Wood-Robinson and Pitzer methods — agreed well with the experimental data for the[...] and [...] systems over the range of concentration that the models could be applied. The mixing rules' predictions were consistent with the experimental observations for the [...] particles assuming a small amount of water was retained in the dry state.

Download Ebook Studies of concentrated electrolyte solutions using the electrodynamic balance