KINETICS AND MECHANISMS OF THE REDOX REACTIONS OF CRYSTAL VIOLET WITH SOME OXY-ANIONS AND HYDRAZINE DIHYDROCHLORIDE IN AQUEOUS MEDIUM
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Date
2016-12-14
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Publisher
Ahmadu Bello University Zaria
Abstract
The kinetics of the redox reactions of crystal violet (CV+) with some oxy-anions (S2O82-,
S2O42-, MnO4-) and hydrazine dihydrochloride (N2H4.2HCl) have been studied
spectrophotometrically in aqueous hydrochloric acid medium for CV+–S2O82- and CV+–
S2O42- systems and aqueous tetraoxosulphate(VI) acid medium for CV+– MnO4- system,
while CV+– N2H4.2HCl was not studied in acidic medium. The reactions were carried out at
[H+] =1.0 × 10-3mol dm-3 (HCl) and I = 0.50 mol dm-3 (NaCl), for S2O82- and S2O42-, [H+] = 5
× 10-2mol dm-3 (H2SO4) and I = 0.50mol dm-3 (Na2SO4) for MnO4-,T = 36 ± 1ºC for S2O82-, T
= 30 ± 1oC for S2O42-, T= 29 ± 1ºC for MnO4-, T = 29±2ºC for N2H4.2HCl, I = 0.50 moldm-3
(NaCl) for N2H4.2HCl and λmax = 585nm The stoichiometric studies showed that one mole of
CV+ consumed one mole of peroxydisulphate ion, dithionite ion, permanganate ion and
hydrazine dihydrochlorideto yield the products. The reactions were found to be first order
with respect to the concentrations of crystal violet, oxy-anions and hydrazine
dihydrochloride. Hydrogen ion concentration had no effect on the CV+– S2O82- system, while
increase in hydrogen ion concentration of the reaction medium decreased the rate of the
reaction for CV+– S2O42- system and increased the rate of the reaction for CV+– MnO4-
system. First orders were obtained with respect to [H+] for both CV+– S2O42- and CV+ –
MnO4- systems having the rate: