A SIMPLE THEORETICAL-MODEL FOR THE SELF-ENHANCEMENT OF THE CATHODIC VOLTAMMETRIC WAVES OF WEAK ACIDS

Weak acids dissociate negligibly, but their reduction wave heights, in the absence of supporting electrolyte, are higher by a factor of 2 co mpared to the excess electrolyte case. A simple theoretical model pres ented in this work supports the experimental findings, The model is ba sed on solving the set of equations which include the transport equati on (diffusion and migration), the Nernst-Planck equation, the electron eutrality principle, and the dissociation equilibrium of the acid unde r consideration. It was found that the concentration profiles of H+ an d A(-) in the absence of supporting electrolyte are substantially diff erent from those obtained for excess supporting electrolyte. Regarding the electroactive species, the gradient and the concentration of the hydrogen ion are apparently higher in the absence of supporting electr olyte and are responsible for the enhancement of the waves of weak aci ds by a factor of 2.