Surface tension of aqueous electrolyte solutions at high concentrations — representation and prediction

A calculation method was developed for representing and predicting surface tension of aqueous electrolyte solutions over a wide range of concentrations, up to 36 m. Based on the Gibbs dividing surface concept, the Langmuir adsorption equation was adopted for modeling the surface excess of electrolyte(s). The activities of electrolytes in the aqueous solutions were calculated by the Pitzer equation. The surface tensions for 45 aqueous single-electrolyte systems at a single temperature were used to correlate the model parameters, and the correlation yields an overall average absolute percentage deviation (AAPD) of 0.47. Surface tensions for 23 aqueous inorganic electrolyte systems are available at several temperatures. Application of these model parameters to extrapolate surface tensions of these systems to different temperatures yields an overall AAPD of 0.91. The proposed method was successfully applied to predict surface tensions for an aqueous binary electrolyte system containing a free acid (HNO 3) and its salt (KNO 3), which have opposite effects on surface tension with an increase in their concentrations, with an overall AAPD of 1.87. The predicted surface tensions for additional 11 binary and five ternary mixed-electrolyte aqueous systems indicate an overall AAPD of 1.69.