KINETICS AND MECHANISMS OF THE REDOX REACTIONS OF CRYSTAL VIOLET WITH SOME OXY-ANIONS AND HYDRAZINE DIHYDROCHLORIDE IN AQUEOUS MEDIUM
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
Authors
OMOTOSHO, MARGARET KEMI
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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:
-d[CV+]/dt = k (a [H+]-1) [CV+] [S2O42-] and
-d[CV+]/dt = k (b + c [H+]) [CV+] [MnO4-] respectively.
Increase in ionic strength of the reaction medium decreased the rate of the reaction for all the systems except for CV+–N2H4.2HCl system, where increase in ionic strength of the reaction medium did not affect the reaction rate.
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Added cationscatalysed the rate of the reaction of CV+ – S2O42- and CV+ – MnO4-systems, inhibited the rate of the reaction of CV+– S2O82-system, while added anions inhibited the rate of the reaction of CV+– S2O82-, CV+ – S2O42- and CV+ – MnO4- systems.However, added ions had no effect on the rate of reaction for CV+– N2H4.2HCl system. Polymerisation test suggested the presence of free radicals for the CV+ –S2O82- and CV+ – S2O42- systems and free radicals ions found to be absent inCV+ – MnO4- and CV+ – N2H4.2HCl systems. Michaelis – Menten plots and spectroscopic studiesgave no evidence of intermediate complex formation for all the systems. The results obtained for all the systems investigated are in favour of the outer –sphere mechanism.
Description
A DISSERTATION SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES, AHMADU BELLO UNIVERSITY, ZARIA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD OF MASTER OF SCIENCE IN INORGANIC CHEMISTRY
DEPARTMENT OF CHEMISTRY,
FACULTY OF PHYSICAL SCIENCE,
AHMADU BELLO UNIVERSITY,
ZARIA, NIGERIA
Keywords
KINETICS,, MECHANISMS,, REDOX REACTIONS,, CRYSTAL VIOLET,, OXY-ANIONS,, HYDRAZINE DIHYDROCHLORIDE,, AQUEOUS MEDIUM,