kinetics of the Formation of the Blue Complex CrO(O_2)_2 Formed by Dichromate and H_2O_2 in Acid Solutins. A Stopped-Flow Investigation Using Rapid-Scan UV-VIS Detection

摘要

The kinetics of the CrO(O_2)_2 formation by H_2O_2 and Cr_2O_7~(2-) in aqueous acidic media was measured at 293 (+-) 2 K in a pH range between 2.5 and 3.3. Using the stopped-flow method with rapid scan UV-VIS detection, the rate law of the formation of CrO(O_2)_2 was determined. For the media HClO_3, HNO_3 and CH_3COOH, the reaction order in the Cr_2O_7~(2-) concentration was found to be 0.5. For [H_2O_2] as well as for [H~+], the reaction was first order in all acids used. In HCl and H_2SO_4 media the reaction was first order in Cr_2O_7~(2-). At T=293 (+-) 2 K the rate constant for the formation of CrO(O_2)_2 was determined. For the media HClO_4, HNO_3 and CH_3COOH, the reaction order in the Cr_2O_7~(2-) concentration was found to be 0.5. For [H_2O_2] as well as for [H~+], the reaction was first order in all acids used. In HCl and H_2SO_4 media the reation was first order in Cr_2O_7~(2-). At T=293(+-) 2 K the rate constant for the formation of Cr(O)(O_2)_2 was found to be (7.3(+-)1.9) centre dot 10~2 M~(-3/2) s~(-1) in HClO_4.