The influence of P-3 on the passive behaviour of copper was analysed in the potential region -0.32 to 0.70 V vs RHE in borax solutions (pH 9.2) through voltammetric techniques and ellipsometry. Oxide formation can be explained as a sequence of Cu2O growth, Cu(II) chemisorption, and dissolution precipitation steps similar to those corresponding to copper electrodes in deaerated solutions. The role of Cu(II) chemisorption is discussed in this paper. The progressive accumulation of hydrated layers hinders the reaction between O-3 and the metal. O-2 and O-3 promote growth and dissolution processes (both at open circuit and in controlled potential experiments) but O-3 has a stronger effect.