Dependence of the mobility of tracer ions in aqueous perchlorate solutions on the hydrogen ion concentration

摘要

The dependence of the absolute individual ion mobility (AIIM) of the carrier-free radioactive ions [Cs-137] Cs+, [Tl-201]Tl+ and [Co-57]Co2+ on the hydrogen ion concentration in aqueous perchlorate electrolyte mixtures was studied by means of the electromigration technique. The AIIM of the radioactive ions was found to decrease as the hydrogen ion concentration of the electrolyte mixture increases. Above pH > 4 there is a fairly good agreement between experimental and calculated values. Below pH 4 the experimentally observed decrease of the AIIM is not explained by the extended Debye-Huckel-Onsager limiting law. The effect can possibly be explained by a change of the dynamical properties of electrolyte bulk water due to the increasing presence of an excess of hydrated protons in the bulk solution. From the variation of the rotational reorientation time of bulk water molecules in HClO4 electrolytes with the proton concentration, a value of 0.69 ps(-1) is derived for the rate constant for proton transfer between the hydronium ions and the acceptor water molecules. For the proton hopping length a value of 2.46 Angstrom was found. These two values are in good agreement with the literature values. Finally, we propose a relation for mobility of tracer ions in HClO4 electrolytes involving the proton hopping time and length. [References: 53]