The electronic, structural and morphological characteristics of passive layers formed anodically on tin in the 7-14 pH range were studied. Photocurrent spectroscopy measurements showed that Sn passive films behave as highly disordered n-type semiconductors. The measured band gap values, E-g, diminish as the formation pH is increased. Fourier transform infrared reflection-absorption spectroscopy results indicate that the ratio between Sn-OH and Sn-O-Sn bonds in the passive films increases with increasing formation pH. At pH > 12.5 the films contained appreciable amounts of lattice water. A correlation between E-g and the hydroxylation degree of the films was proposed.