Activity Coefficient Measuring and Modeling for a Single and Symmetrical Mixture in a Mixed Solvent and Friedman’s Footprint of a Higher-Order Limiting Law

Abstract

This study is conducted to investigate the HCl + NaCl + H2O + C2H5OH mixed electrolyte systems. The experimental activity coefficients are collected through measuring the electromotive force by using a cell containing pH and silver chloride electrodes in different alcohol mass fractions w(C2H5OH) in H2O (where w = 0.10, 0.20, and 0.50). All the used electrolyte molalities are between 0.01 and 2.5 mol kg–1, at 298.15 ± 0.01 K. Modeling is achieved using mean activity coefficients data for single and mixed HCl and NaCl in mixed solvent. A detailed study of Pitzer’s equations regarding effectiveness of nonionic species is taken into account. The result shows that this approach is a valuable aspect of the Pitzer equation for activity coefficient correlation of pure and mixed electrolytes, in mixed solvent media. The result underlines the importance of including Friedman’s higher-order limiting law (HOLL) regarding fitting the activity coefficient data for symmetric mixture, that is, not only theoretically accurate but also practically important. It seems that this work would be considered as the first experimental observation for the HOLL to correlate the activity coefficient of symmetrical mixture.