Cyclic voltammetry is used to investigate the behavior of tin in a 0.1 M Na2H2PO4 (sodium dihydrogen phosphate) solution at pH 5.2. Voltammograms are obtained for different final anodic and cathodic potentials, numbers of cycles, and scan rates. H2PO4 (-) ions are observed to have a specific effect at the beginning of the anodic process. A mixture of tin dioxides, Sn(OH)(2) and Sn(OH)(4), forms on the electrode surface in the tin dissolution stage, then converting to a mixture of more stable hydrous tin(II) and tin(IV) oxides. A passivating film forms from a mixture of tin(IV) compounds with varying electrochemical stabilities.