KINETICS AND MECHANISMS OF THE REDOX REACTIONS OF MALACHITE GREEN WITH SOME OXY-ANIONS IN AQUEOUS ACIDIC MEDIUM

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dc.contributor.authorIMAM, MADINA
dc.date.accessioned2017-11-17T07:21:09Z
dc.date.available2017-11-17T07:21:09Z
dc.date.issued2016-10
dc.descriptionA DISSERTATION 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, NIGERIAen_US
dc.description.abstractThe kinetics of the redox reactions of malachite green, MG+ with these oxy-anions: Bromate (BrO3‾), Metabisulphite (S2O5²⁻), Sulphite (SO₃²⁻) and Chlorite (ClO₂‾) in aqueous acidic medium were studied under the following experimental conditions: i. [H⁺] = 1.0 10⁻² mol dm⁻³ (H₂SO₄), I = 0.5 mol dm⁻³ (Na₂SO4) and T = 28 ± 1°C for MG+ - BrO₃‾ system. ii. [H+] = 5.0 10⁻³ mol dm⁻³ (HCl), I = 0.5 mol dm⁻³ (NaCl) and T = 28 ± 1°C for MG+ - S₂O₅²⁻ system iii. [H+] = 5.0 10⁻³ mol dm⁻³ (HCl), I = 0.1 mol dm⁻³ (NaCl) and T = 27 ± 1°C for MG+ - SO₃²⁻ system iv. [H⁺] = 1.0 10⁻² mol dm⁻³ (H₂SO₄), I = 0.3 mol dm⁻³ (Na₂SO4) and T = 26 ± 1°C for MG+ - ClO2‾ system The stoichiometries of the reactions were found to be 2:1 for MG+ - BrO3‾ system, 1:1 for MG+ - S2O52⁻, MG+ - SO3²⁻ and MG+ - ClO₂‾ systems. The order of the reaction was one with respect to both oxidant and reductant in all the systems. Increase in reaction rate with increasing acid concentration [H+] was observed for MG+ - BrO3‾ and MG+ - ClO₂‾ systems while a converse effect was observed for MG+ - S2O52⁻ system and the rate of reaction for MG+ - SO3²⁻ system was independent on [H+]. The influence of [H+] on the rates of reactions showed two parallel pathways for S2O52- and ClO2‾ systems, one pathway for BrO3‾ system and no pathway was available for the SO3²⁻ system. The reactions conformed to the following rate equations: (a [H+]2)[MG+][BrO3‾] where a = 3.32 10-1 dm9 mol-3 s-1 (b + c [H+]-1)[MG+][S2O52-] where b = 9.80 10-2 dm3 mol-1 s-1 and c = 1.38 10-3 s-1 [H+]0 [MG+][SO32-] and where d = 0.11 dm3 mol-1 s-1 and e = 8.40 10-2 s-1 Increase in ionic strength increased the rate of reaction for all the systems except for the MG+-ClO₂‾ system where the reaction rate was not affected by changes in ionic strength of reaction medium. Added ions inhibited the rate of reactions for BrO3‾ and S2O52- systems and had no effect on the rate of reaction for the ClO2‾ system. The rate of reaction for the SO32- system was catalysed by added anions. Polymerisation test suggested the absence of free radicals in the ClO2‾ system only. Spectroscopic investigations and Michaelis-Menten plot showed no evidence of intermediate complex formation in all the reactions except for MG+ - ClO2‾ an evidence of intermediate complex formation was noticed by a shift in λmax from 620-600 nm. Outer-sphere mechanism is proposed for all the systems except MG+ - ClO2‾ system where the reaction is believed to proceed via inner-sphere mechanism.en_US
dc.identifier.urihttp://hdl.handle.net/123456789/9431
dc.language.isoenen_US
dc.subjectKINETICS,en_US
dc.subjectMECHANISMS,en_US
dc.subjectREDOX REACTIONS,en_US
dc.subjectMALACHITE GREEN,en_US
dc.subjectOXY-ANIONS,en_US
dc.subjectAQUEOUS ACIDIC MEDIUM,en_US
dc.titleKINETICS AND MECHANISMS OF THE REDOX REACTIONS OF MALACHITE GREEN WITH SOME OXY-ANIONS IN AQUEOUS ACIDIC MEDIUMen_US
dc.typeThesisen_US
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