Diffusion studies. Part III. Tracer diffusion coefficients of lanthanum(III) in concentrated solutions of HCl and HClO4 at 25 °C

Abstract

Tracer diffusion coefficients of La^III, D_La, were measured in HCl (1·0M–10·0M) and HClO₄(1·1M–9·76M). D_La in HCl decreased slowly as the HCl concentration increased; at 10M-HCl D_La is still ca. 65% of D°_La(0·62 × 10^–5 cm² s^–1). In HClO₄, D_La remains nearly constant at 0·6 × 10^–5 cm² s^–1 from 1·1M to ca. 3·5M-acid and then decreases rapidly to 0·2 × 10^–5 cm² s^–1 in 9·76M-acid.

For the highest concentrations of acid (ca. 10M) studied, D_La in HClO₄ is about half the value in HCl. However, the product of the relative diffusion coefficient and the relative viscosity has the same value in both systems when the activities of water are equal.