A model was established for the impedance response associated with convective diffusion to a disk electrode subjected to a submerged impinging jet. The model accounted for a finite Schmidt number by employing a series expansion in terms of Sc-1.3. The model was incorporated into a quantitative analysis of impedance data for the corrosion of a steel disk in brine saturated with CO2 This work showed that the impedance response was influenced by diffusion through a stagnant layer as well as through a convective region. The Schmidt number obtained was very large, suggesting that the thick layer, observed by in situ video microscopy, is a colloidal gel.