Coupled mutual diffusion in aqueous paracetamol + sodium hydroxide solutions

Abstract

Ternary mutual diffusion coefficients (Dik) measured by the Taylor dispersion method are reported for aqueous paracetamol + NaOH solutions at 25.00 °C and concentrations up to 0.050 mol dm−3. The coupled diffusion of paracetamol (1) and NaOH (2) is significant, as indicated by the large negative cross-diffusion coefficients. In sodium hydroxide solutions, paracetamol, a weak acid, is partially converted to its sodium salt. To help interpret the results, the measured Dik coefficients are compared with predictions based on Nernst and Nernst-Planck equations for mixed electrolyte solutions. The analysis shows that the diffusion of the paracetamol and sodium hydroxide components is strongly coupled by the electric field (diffusion potential) generated by the ionic concentration gradients.