The Laliberté–Cooper density model: Self-consistency and a new method of parameterization

The recently published Laliberté–Cooper model predicts the density of multi-component aqueous electrolyte solutions as a function of composition using coefficients derived from single electrolyte solutions. In this model, an individual electrolyte is a cation and anion pair, and it has not been clear if the model results depend on the user's choice of how the cations and anions are paired together in multi-ion mixtures. The present paper investigates the self-consistency of the Laliberté–Cooper model when cations and anions are paired in different ways. The densities of a number of mixtures of monovalent cations and anions were modeled. The resulting densities were insensitive to the way the cations and anions were paired up to the 5th significant figure in the density for all but the most concentrated solutions. These results confirm that the Laliberté–Cooper model is self-consistent. This conclusion affords the opportunity to derive model coefficients for unmeasured electrolytes when coefficients for other electrolytes are available that contain the cation and anion in the electrolyte of interest. An example was performed where it was shown that the model coefficients for KAl(OH)4 could be calculated solely from the coefficients for NaAl(OH)4, NaOH, and KOH without directly fitting the model to experimental data. The results were confirmed by comparing the calculated densities to published experimental data. The model was able to accurately predict experimentally determined densities (R2 > 0.99) using model coefficients derived without using any experimental data from solutions containing KAl(OH)4.