KINETICS AND MECHANISMS OF THE REDOX REACTIONS OF 2,6-DICHLOROPHENOL INDOPHENOL WITH OXYANIONS, HYDRAZINE AND HYDROGEN PEROXIDE IN AQUEOUS MEDIUM
KINETICS AND MECHANISMS OF THE REDOX REACTIONS OF 2,6-DICHLOROPHENOL INDOPHENOL WITH OXYANIONS, HYDRAZINE AND HYDROGEN PEROXIDE IN AQUEOUS MEDIUM
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Date
2018-02
Authors
ILIYASU, Suleiman Sani
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Abstract
The kinetics of the redox reactions of 2,6-dichlorophenol indophenol (DCPIP) by metabisulphite ions (S2O52-), sulphite ions (SO32-), hydrazine (N2H4) and hydrogen peroxide (H2O2) at 28 ± 1 °C was studied at λmax of 600 nm in aqueous medium under pseudo-first order conditions at I = 0.2 mol dm-3 (NaCl). The stoichiometry of 1:1 was obtained for all the reactions except DCPIP - S2O52- which was 2:1. The reactions were first order in [S2O52-], [N2H4], [H2O2] and zero order with respect to [SO32-]. The reactions conform to the following rate equations:
d[DCPIP]= k2 [DCPIP] [S2O52-]
dt
where k2 = 16.24 ± 0.03 dm3 mol-1 s-1
d[DCPIP]= k1[DCPIP]
dt
where k1 = 1.79 ± 0.02 dm3 mol-1 s-1
d[DCPIP]= k2 [DCPIP] [N2H4]
dt
where k2 = 0.13 ± 0.02 dm3 mol-1 s-1
d[DCPIP]= k2[DCPIP] [H2O2]
dt
where k2 = 3.01 ± 0.02 dm3 mol-1 s-1. The rates of reactions displayed negative salt effect for DCPIP - S2O52- reaction, positive salt effect for DCPIP - N2H4 reaction and zero salt effect for DCPIP - SO32- and DCPIP - H2O2 reactions. Added cations catalysed the reaction of DCPIP - S2O52- but had no significant effect in the reactions of DCPIP - SO32-, DCPIP - N2H4 and DCPIP - H2O2. While added anions had negligible effect for all the reactions except DCPIP - N2H4 reaction. There was no evidence of formation of intermediate complex of significant stability for any of the reactions. Free radicals were not detected in all the reactions. Based on the results obtained in these studies, outer-sphere mechanism was proposed for the reactions of DCPIP with S2O52-, SO32- , H2O2 and inner-sphere mechanism for the reaction of DCPIP with N2H4.
Description
A DISSERTATION SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES,
AHMADU BELLO UNIVERSITY, ZARIA
IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE AWARD OF A
MASTER OF SCIENCE DEGREE IN INORGANIC CHEMSTRY
DEPARTMENT OF CHEMISTRY
FACULTY OF PHYSICAL SCIENCES
AHMADU BELLO UNIVERSITY, ZARIA
NIGERIA.
Keywords
KINETICS,, MECHANISMS,, REDOX REACTIONS,, 2,6-DICHLOROPHENOL INDOPHENOL,, OXYANIONS,, HYDRAZINE,, HYDROGEN PEROXIDE,, AQUEOUS MEDIUM,