On a pre-plated, polycrystalline silver rde, the silver electrodeposition process from solutions consisting of 1 x 10(-3) M AgNO3 + x M NaNO3 + 0.025 M Na2S2O3 was studied by means of ac impedance spectroscopy, stationary polarization curves and low frequency electrohydrodynamic (EHD) impedance measurements. The sodium nitrate concentration (x) was varied between 0.05 and 0.6 M in order to investigate its influence on the kinetic parameters in a formerly proposed CE mechanism, A catalytic effect of NaNO3 on both the chemical and charge transfer reaction rates was observed and quantified through the combined use of the different measurements. Thus, a continuous transition was monitored from a clearly noticeable chemical reaction (0.05 M NaNO3) to one hard to detect (0.6 M NaNO3), possibly explained through hydration phenomena. These results highlight the important consequences of adding NaNO3, originally intended to be a supporting electrolyte.