Isopiestic Studies On Multi-component Unsaturated Aqueous Solution Systems

Isopiestic measurements were known to be one of the most accurate methods in determining thermodynamic properties for aqueous solutions. This method for various multi-component unsaturated solutions could be used directly to check the validity of partial simple solution model.This model contains the partial ideal solution model and the partial dilute solution model. Starting from the Zdanovskii’s rule for mixed electrolyte aqueous solutions and Turkdogan’s linear solubility equation for carbon in ternary alloys, professor Zhi-Chang Wang had presented two general linear concentration rules for the real systems {A+B+C+...+Z} related to their binary subsystems{A+i}(i∈B, C,..., Z) at constant chemical potential of A. One linear concentration rule and the corresponding partial ideal solution model held good for the systems having zero interchange energy among B, C,..., Z, while the other rule and the corresponding partial dilute solution model, for the systems, having nonzero interchange energies among them. That meant pure component A+classically ideal solution{B+C+...+Z}=partial ideal solution{A+B+C+...+Z} and pure component A+classically dilute solution{B+C+...+Z}=partial dilute solution{A+B+C+...+Z}. The two general simple rules were in excellent agreement with a great deal of experimental datas.Isopiestic measurements have been carried out at the temperature298.15K for the mixed Nd(NO3)3, HNO3, and sucrose unsaturated aqueous solution{H2O(A)+Nd(NO3)3(B)+HNO3(C)+sucrose(D)}. It is showed that the experiment results are influenced by HNO3. The experiment error is big. Therefore, it is necessary to adjust the equivalence point of Nd(NO3)3aqueous solution. The titration method was used to measure the equivalence point. Secondary derivative method is used to determine pH value at the point, and the pH=3.18.Isopiestic measurements have been carried out at the temperature298.15K for the mixed rare earth nitrate and sucrose ternary unsaturated aqueous solution{H2O(A)+Nd(NO3)3(B)+sucrose(C)}, taking sodium chloride as the reference solution. The results showed that this unsaturated aqueous solution did not follow the linear concentration rules at constant activity of one component water. The interaction force between Nd(NO3)3and sucrose is shown to exist in the system. Therefore, the ternary unsaturated aqueous solution{H20(A)+Nd(NO3)3(B)+sucrose(C)} fit the partial dilute solution model.