Thermodynamic properties of alkali halides. IV. Apparent molal volumes,expansibilities, compressibilities,and heat capacities in urea-water mixtures |
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Authors: | Nicole Desrosiers Gérald Perron John G Mathieson Brian E Conway Jacques E Desnoyers |
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Institution: | 1. Department of Chemistry, University of Sherbrooke, Sherbrooke, Quebec, Canada 2. Department of Chemistry, University of Ottawa, Ottawa, Ontario, Canada
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Abstract: | The apparent molal volume φv, expansibility φE, compressibility φK, and heat capacity φc of NaCl were measured in urea-water mixtures, as a function of salt (<1.5m) and urea (<13m) concentrations at 25°C. At a fixed urea concentration, the transfer functions from H2O to 3m urea are linear functions of the NaCl aquamolality. At a fixed salt aquamolality, (0.1m), the sign of the transfer functions is in the direction of a decrease in the structure-breaking effect, and the absolute values of the transfer functions tend to level off at high urea concentrations (13m). The functions φv, φE, φK, φc, and (?φv/?T)p were measured for the sodium halides and alkali, bromides (chlorides in the case of φK) at a fixed salt aquamolality of 0.1m and fixed urea molality of 3m. The corresponding transfer functions from H2O to 3m urea are opposite those from H2O to D2O and similarly are relatively independent of ionic size. This suggests that urea, shows no specific interaction affinity for ions and that the overall number of water molecules influenced by the ions is relatively constant for all alkali halides. The lithium halides are an exception in that Li+ seems to have hardly any structure-breaking effect. |
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