Excess Partial Molar Enthalpy of 1-Propanol in 1-Propanol−NaCl−H₂O at 25 °C:  The Effect of NaCl on Molecular Organization of H₂O

Abstract

Excess partial molar enthalpies of 1-propanol, H1PE, in 1-propanol−NaCl−H2O were measured directly, accurately, and in small increments in mole fraction of 1-propanol, x1P, at 25 °C in the range xNaCl < 0.04. xNaCl is the mole fraction of NaCl. The enthalpic interaction function, H1P-1PE, between 1-propanol molecules was then evaluated. H1P-1PE is a convenient, model-free measure for the intermolecular interaction in terms of enthalpy. The behavior of these thermodynamic quantities was compared with that of the binary 1-propanol−H2O. Based on the knowledge accumulated in our laboratory on the binary aqueous 1-propanol, the effect of NaCl on H2O became apparent. Our tentative conclusions are that (1) a NaCl molecule “binds” to seven or eight molecules of H2O on dissolving into H2O, and (2) the reminder of bulk H2O away from solute NaCl is not affected and stays almost the same as pure H2O.