Akiko Okumura

The oxygen exchange reaction of pentaamminechromatocobalt(III) ions with water

Abstract The oxygen exchange reaction of pentaamminechromatocobalt(III) ions with water in the presence of the concurrent hydrolysis of the complex ions has been studied at 0 and 25 °C in the pH-range 6.0–8.0. The results were interpreted by a set of concurrent mechanisms: 1) RHCrO2+4 + RCrO+4 ⇌ RCr2O7R4+ + OH−, 2) RHCrO2+4 + HCrO−4 ⇌ RCr2O+7 + H2O, 3) RCrO+4 + HCrO−4 ⇌ RCr2O−7 + OH−, and 4) RCrO+4 + H2O → ROH2+ + HCrO−4, HCrO−4 + H182O ⇌ HCrO183O− + H2O, ROH2+ + HCrO183O− → RCrO183O+ + H2O (R stands for (NH3)5Co·). The CrO bond is broken in the hydrolysis of the chromato complex at pH 6.7.

The kinetics of the hydrolysis reaction of pentaamminechromatocobalt(III) chloride

Abstract The hydrolysis reaction of pentaamminechromatocobalt(III) complex and the anation of the aqua complex by chromate ions: were studied at 25 °C, and in the pH ranges 6.0–8.5 and 3.5–7.5, respectively. The equilibrium constant of the hydrolysis reaction has a minimum value at pH ∼ 6. The important paths for the reaction (1) are: the rate constants were obtained as: k 1 = 2.2 × 10 −3 s −1 , k −1 = 2.3 M −1 s −1 , k 0 = 151 M −1 s − , and k −0 = 1.7 × 10 5 M −2 s −1 .

Kinetic studies of the catalytic oxygen exchange reaction of chromate ions with water by arsenious acid and the redox reaction between chromate ions and arsenious acid

The oxygen exchange reaction between chromate ions and water is catalyzed by a small amount of arsenious acid. The catalytic oxygen exchange reaction was studied at 25 °C over the pH range of 7–12 ([Cr(VI)] = 0.072 M, [As(III)] = 1.4 × 10−4 M, I = 0.2 M). The catalytic action has been interpreted in terms of the reversible complex formation between various kinds of As(III) and Cr(VI) to form heteropolyanions As(III)·Cr(VI). The redox reaction between arsenic(III) and chromium(VI) was studied over the pH range of 2.5 ∼ 13 under the same conditions as was used in the oxygen exchange except that the concentration of As(III) was chosen to be 1.4 × 10−3 M. The rate of the redox reaction is considerably lower than that of oxygen exchange. The observed results are consistent with the mechanism: On the basis of this mechanism, the kinetic results were analyzed to obtain the values of the rate constants of the complex formation ki and the apparent rate constants of the slow redox process k′i((Kik′ri)).