ISSN:
0538-8066
Keywords:
Chemistry
;
Physical Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The reaction between chromium(VI) and L-ascorbic acid has been studied by spectrophotometry in the presence of aqueous citrate buffers in the pH range 5.69-7.21. The reaction is slowed down by an increase of the ionic strength. At constant ionic strength, manganese(II) ion does not exert any appreciable inhibition effect on the reaction rate. The rate law found is \documentclass{article}\pagestyle{empty}\begin{document}$$ r = k_p k_r [Cr({\rm VI})][{\rm L - ascorbic\,acid][H}^{\rm + }]/(1 + k_p [H^ +]) $$\end{document} where Kp is the equilibrium constant for protonation of chromate ion and kr is the rate constant for the redox reaction between the active forms of the oxidant (hydrogenchromate ion) and the reductant (L-hydrogenascorbate ion). The activation parameters associated with rate constant kr are Ea = 20.4 ± 0.9 kJ mol-1, ΔH≠ = 17.9 ± 0.9 kJ mol-1, and ΔS≠=-152 ± 3 J K-1 mol-1. The reaction thermodynamic magnitudes associated with equilibrium constant Kp are ΔH0 = 16.5 ± 1.1 kJ mol-1 and ΔS0 = 167 ± 4 J K-1 mol-1. A mechanism in accordance with the experimental data is proposed for the reaction. © 1993 John Wiley & Sons, Inc.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/kin.550250402
