Abstract

In this article, seven relationships that have been widely used to estimate the dependence of apparent partial specific volume (APSV) with concentration are reviewed and compared with each other. Also, 10 methods to evaluate partial molar volume (PMV) were derived and compared with each other. At null concentrations the values of APMV of all relationships meet each other; therefore all of the above relationships at very low concentrations are useful and estimate values near to each other. However, as the concentration increases the differences also increase. The variation of APMV with molality or mole-fraction of solute is not linear, and therefore any line fitted to the data to get the slope and intercept to estimate PMV is visual approximation and hence it is bias. The values of PMV obtained through APMV values follow the same curvature trend as values of APMV with a positive slope. Whereas the values of PMV calculated from the slope of density versus molality fit-in a perfect straight line with negative slope (in the range of concentration studied). The appropriate concentration unit for PMV and partial specific volume (PSV) is molality, and the combined relationship is the most appropriate way to evaluate PMV. However, other concentration units such as mass per volume and weight fraction as concentration unit are also studied. It was demonstrated that when a combined relationship is used, evaluation of PMV and PSV is easier and exact. Also, the values of PMV extrapolated to zero concentration were compared with the molar volumes of solvent and solute.

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