KINETICS AND MECHANISMS OF THE REDOX REACTIONS OF CRYSTAL VIOLET WITH SOME OXYANIONS IN AQUEOUS ACIDIC MEDIUM BY SAFIYA ABDULSALAM DEPARTMENT OF CHEMISTRY FACULTY OF SCIENCE AHMADU BELLO UNIVERSITY, ZARIA NIGERIA JUNE,
KINETICS AND MECHANISMS OF THE REDOX REACTIONS OF CRYSTAL VIOLET WITH SOME OXYANIONS IN AQUEOUS ACIDIC MEDIUM BY SAFIYA ABDULSALAM DEPARTMENT OF CHEMISTRY FACULTY OF SCIENCE AHMADU BELLO UNIVERSITY, ZARIA NIGERIA JUNE,
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Date
2015-06
Authors
ABDULSALAM, SAFIYA
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Abstract
The kinetics and mechanisms of the redox reaction of crystal violet (hereafter CV+) was studied with some oxyanions (S2O52-, BrO3-, IO4- and ClO-) in aqueous acidic medium. The stoichiometries of the reactions were found to be 1:1 for CV+- S2O52-, 2:3 for CV+- BrO3-, and 1:2 for CV+- IO4- and CV+- ClO- systems. The order of the reactions was one with respect to both oxidant and reductant in CV+- S2O52-, -BrO3- and -ClO- reactions respectively. For the CV+- IO4- system, the order of the reaction was one with respect to the [CV+] and zero with respect to [IO4-]. Studies on the influence of [H+] on the rates of reactions point to two parallel pathways for S2O52-, BrO3-, IO4- reactions and one reaction pathway for ClO- reaction. The reaction conformed to the following rate equations:
(a + b [H+]-1)[CV+][S2O52-]
a = 2.27 dm3 mol-1 s-1 and b = 0.86 s-1
(c + d [H+] 2)[CV+][BrO3-]
c = 9.22 dm3 mol-1 s-1 and d = 1.16 dm9 mol-3 s-1
(e + f [H+])[CV+]
e = 1.49 s-1 and f = 1.8 x 10-3 dm3 mol-1 s-1
(g [H+])[CV+][ClO-]
g = 6.16 dm6 mol-2 s-1
the rate of the reaction displayed positive salt effect for CV+- BrO3- and CV+- IO4- reactions and negative salt effect was observed for CV+- S2O52- reaction. In the case of CV+- ClO- reaction, increase in ionic strength has no effect on the rate of reaction. Added anions inhibited the rate of reactions of CV+- S2O52- and CV+- BrO3- but increased that of CV+- ClO-, while added anions has no effect on the rate of reaction for CV+- IO4-. Added cations had no effect on the rate of reactions of all the systems except for CV+- BrO3- where the rate of the reaction decreased with increase in cation concentration. Spectroscopic investigations and Michaelis-Menten plot showed no evidence of intermediate complex formation in all the reactions except for CV+- IO4- where evidence of intermediate complex was noticed by shift in λmax from 585 to 620 nm. Outersphere mechanism was proposed for all the systems except CV+- IO4- system where the reaction was believed to proceed via innersphere mechanism.
Description
A THESIS SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES,
AHMADU BELLO UNIVERSITY, ZARIA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD OF A
MASTER OF SCIENCE DEGREE IN INORGANIC CHEMISTRY
DEPARTMENT OF CHEMISTRY
FACULTY OF SCIENCE
AHMADU BELLO UNIVERSITY, ZARIA
NIGERIA
Keywords
KINETICS,, MECHANISMS,, REDOX REACTIONS,, CRYSTAL VIOLET,, OXYANIONS,, AQUEOUS,, ACIDIC MEDIUM.