Selenium Isotope Effects in the Reduction of Sodium Selenite and of Sodium Selenate

Selenium isotope effects in the reduction of sodium selenite and of sodium selenate have been studied. Rate constant ratios for the 76 Se and 82 Se species have been determined for the reactions Se iv → Se 0 (1.017), Se vi → Se iv (1.018), and Se 0 → Se iv (1.010) at room temperature. Theoretical predictions of the first two ratios, from the use of models in which the rate-controlling steps are assumed to be Se—O bond cleavages in SeO 3 2− and SeO 4 2− , respectively, lead to predictions in good agreement with experiment.