Solvent isotope effects in the H2O--D2O--NaCl system: enthalpies and free energies of solution

The solvent isotope effects in sodium chloride solutions of normal (H2O) and heavy (D2O) water (especially at low concentration) were investigated. Freezing point depressions in normal and heavy water are reported from approximately 0.01 to approximately 2 m. A new value of the heat of fusion of D2O (-1507 +- 3 cal mole-1) was determined. Values of the partial molal enthalpies are derived from differential heats of solution of sodium chloride in both isotopic waters from 0.01 to 4 m and from 5 to 400. The freezing point data are used to obtain osmotic coefficients at the freezing points of the solutions (H2O and D2O), and the enthalpy data allow calculation of the osmotic coefficient at temperatures up to 400. The present data establish the sodium chloride--D2O system as an isopiestic reference for future measurements on solutions using D2O as solvent. The isotope effect on the relative partial molal enthalpy of the sodium chloride and on the osmotic coefficient shows a √m concentration dependence within experimental error. (Diss. Abstr. Int., B)