Diffusive motion in aqueous solutions

857-861The interest in diffusion phenomena arises from both applied and fundamental points of view and in recent years, there has been some spectacular development in this study both theoretically and experimentally. Inelastic neutron scattering, NMR, optical and above all radioactive tracer techniques have accumulated important information about the migration of ions, or molecules through a maze of molecules. The difficulty in the study of liquids lies in the fact that, kinetic energy and potential energy of the constituent particles in a liquid are comparable and both must be taken into account to calculate any property, which is to be compared with observed results. In general, by employing techniques which increase the thermal motion of the constituent particles or by varying the composition of the binary and ternary systems, much information can be gathered about liquids and, in this respect, diffusion study in liquids is an important tool. It is very interesting and very important to observe the change in diffusion coefficient in some aqueous solution with the introduction of known amounts of some other salts or acids. This study of coupled flow has been undertaken by several groups of workers. A sliding cell method based on radioactive tracer technique has been developed in the laboratory of the author and it has been used to measure diffusion coefficient in H3PO4-H2O system containing different amount of salts of this weak acid. Different radioactive isotopes like Na-22, Na-24, Hg-203, Ga-72, Cs-134, Cs-137, TI-204, P-32 etc., have been used in the laboratory for diffusion measurements in different systems. Irreversible thermodynamical principles have been applied to explain the observed results. Both H2O and D2O have been employed as solvents and the breaking of their structures with the introduction of salts have been explained.