Fick equations for the diffusion of electrolytes in ternary liquid junctions

Abstract

Fick equations for the fluxes of neutral electrolyte components (such as NaCl or NaOH), rather than Nernst–Planck equations for the fluxes of ions, are used to describe diffusion in liquid junctions. The advantages and limitations of this approach are discussed. For purposes of illustration the Taylor dispersion technique is used to measure the ternary interdiffusion coefficients of LiCl–KCl–water, NaCl–NiCl₂–water, NaCl–NaOH–water, NalO₃–HlO₃–water and CuSO₄–H₂SO₄–water at 25 °C. The results are used to predict accurate concentration profiles in the liquid junctions between binary solutions of each electrolyte. Allowance is made for both the interactions between the diffusing electrolytes and the changes in the diffusion coefficients across the junctions.