Vapor Pressures and Isopiestic Molalities of the Ternary LiNO3+Urea + H2O System at 298.15 K

Isopiestic vapor-pressure measuremenst were made for LiNO3+Urea + H2O from totalmolality m=0.4 mol kg-1 to m=6.1 mol kg-1 at 298.15 °K. Measurements were made withNaCl(aq) as reference standard for both pure solutions and for the mixed solutions with variousmolality fractions of LiNO3 ( 0.25, 0.50 and 0.75 ). The experimental results were treated by amodified forms of Pitzer and McKay-Perring methods. Isopiestic procedure is actually asecondary method for studying VLE , wherin the vapor pressure values are evaluated based uponsolvent activities. Accordingly the iso-activity rule of Zdanovskii was tested and the resultdemonstrated slight discrepancy fom semi-ideally behavior. Based on the optimized values of theinteraction parameters of modified Pitzer model, osmotic coefficients and activity coefficients ofthe ternary and of the both limiting binary constituents (LiNO3+H2O) and ( CO(NH2)2+H2O)were calculated and compared well with those evaluated by McKay-Perrig method. Lastlyexcess energy of Gibbs was evaluated and the interaction of the dissolved components areindicated by the high, negative GE values [1-4].

Keywords:

Osmotic Coefficients , Activity Coefficients , Vapor Pressure , Isopiestic , Mixed-Electrolyte-Nonelecrolyte , Lithium Nitrate , Urea