The kinetics of anodic dissolution and corrosion of zinc are investigated by electrochemical impedance spectroscopy in sulfate medium for various surface preparation conditions and different experimental procedures. A new version of the reaction model, which was established previously, accounts well for the experimental results. It implies several parallel paths of dissolution and three adsorbed intermediates: Zn+ad, Zn2+ad and ZnOHad. From the simulation of impedance data are deduced the values of quantities such as the partial current intensities of each parallel paths or the surface coverages by three adsorbates. It is shown that the surface preparation conditions may affect the balance between the competitive dissolution paths. When zinc is immersed in the electrolyte, a protective layer is formed, which inhibits the direct dissolution of the metal, but which tends to be eliminated by a potential activation. These phenomena are time dependent and may be affected by the slow formation of a corrosion product layer.