A study of the hydrogen ion concentrations of scandium perchlorate solutions to which sodium hydroxide has been added reveals that the data cannot be explained by assuming a single acid dissociation step. The data can be interpreted in terms of a single acid dissociation followed by dimerization of the base conjugate to the hexaquo ion. In the solvent salt sodium perchlorate at a concentration of one molar, for the first step is equal to , with the for the dimerization equal to . The literature indicates that this may be a general phenomenon.