Diffusion of Electrolytes and Non- Electrolytes in Aqueous Solutions: A Useful Strategy for Structural Interpretation of Chemical Systems

摘要

In the last years, the diffusion Coimbra group, headed by Prof. Lobo, has been particularly dedicated to the study of mutual diffusion behaviour of binary, ternary and quaternary solutions [1-19], involving electrolytes and non-electrolytes, helping to go deeply in the understanding of their structure, aiming at practical applications in fields as diverse as corrosion studies occurring in biological systems or therapeutic uses. In fact, the scarcity of diffusion coefficients data in the scientific literature, due to the difficulty of their accurate experimental measurement and impracticability of their determination by theoretical procedures, allied to their industrial and research need, well justify our efforts in accurate measurements of such transport property. This transport property has been measured in different conditions (several electrolytes, concentrations, temperatures, techniques used), having in mind a contribution to a better understanding of the structure of those solutions, behaviour of electrolytes or non-electrolytes in solution and, last but not least, supplying the scientific and technological communities with data on this important parameter in solution transport processes. Whereas an open ended capillary cell developed by Lobo has been used to obtain mutual diffusion coefficients of a wide variety of electrolytes [1,2], the Taylor technique has been used mainly for ternary and quaternary systems with non-electrolytes (e.g., [11-19]). From comparison between our experimental results and those obtained from different models, e.g., Nernst, Nernst-Hartley, Stokes, Onsager and Fuoss, and Pikal theoretical equations, and from our semi-empirical equations, and Gordon's and Agar's as well, it has been possible to obtain some structural information, such as diffusion coefficient at infinitesimal concentration, ion association, complex formation, hydrolysis, hydration, or estimations of the mean distance of closest approach involving ions as diffusing entities.