Thermodynamics of 1 : 1 electrolyte solutions in water plus N,N-dimethylformamide mixed solvent system at 25 degrees C: Molar excess enthalpy of mixing

摘要

The molar excess enthalpies of mixing for the six possible binary combinations of solutions of NaCl, KCl, NaBr, and KBr as a function of ionic strength fraction have been measured at 25 degrees C. The experiments were performed at constant ionic strengths of 1.000 and 2.000 mol-kg(-1) with an LKB flow microcalorimeter in the mixed solvent water + dimethylformamide. The equations of Friedman's Model were fitted to the results. Our parameters differ appreciably from the corresponding results in water and Young's cross square rule does not apply. While Pitzer's ion-interaction model was able to represent the enthalpy data for common ion mixings, it was unable to model the data of the noncommon ion mixtures. The data suggests that the problem may arise from variations in solvation of the ions and ion clusters including preferential solvation of certain species. [References: 35]