The voltammetric contribution of some specifically adsorbed anions (acetate, oxalate, chloride and bromide) is revised for the case of Pt(111) electrodes by means of experiments of displacement by CO in acidic medium. It is found that the usual states correspond to the reversible adsorption/desorption of hydrogen whereas the so-called unusual states would correspond to the adsorption/desorption of anions. This means that the maximum coverage of hydrogen adatoms prior to hydrogen evolution is around two-thirds of a complete monolayer of Pt(111). From the potential dependence of the voltammetric profiles the electrosorption valency of the different anionic species is calculated.