Kinetics and Mechanisms of Catalysed and Uncatalysed Oxidation of Organic Dyes by Inorganic Species and Indicator Reaction for Determination of Cations
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Date
1998
Authors
Ngugi, Sironik Stephen
Journal Title
Journal ISSN
Volume Title
Publisher
Kenyatta University
Abstract
The rate of oxidation of both the uncatalysed and Vanadium
(V) catalysed reaction between indigo carmine (IC) and
Chromium (VI) as well as the uncatalysed and Ruthenium (III)
catalysed reaction between methylene blue (MB) and cerium
(IV) have been studied. Both reactions were performed in
sulphuric acid media by monitoring the absorbances of IC and
MB at 610 nm and 665 nm respectively at 25°C. The kinetics
and the probable mechanisms of these reactions have been
elucidated. For the former reaction, the order with respect
to IC, H+ and Cr(VI) were 1, 2 and 1.5 respectively and 1
for V(V) in the case of catalyzed reaction while for the
latter reaction the partial orders with respect to MB,
Ce(IV) and H+ were 2, 1 and 0 respectively and 1 for Ru(III)
in the case for the catalysed. The mechanism for the ICCr(
VI) reaction involves an initial two electron process
which is confirmed by the limiting induction factor of 0.5
from the iodide ion induction reaction. Further the presence
of V(V) ion in the reaction mix!ure caused an increase in
the rate of the oxidation of IC that was affected by traces
of Ru(III) and Mo(VI). The interfering effects of the
Ru(III) and Mo(VI) were effectively masked by traces of
thiourea and thiocyanate respectively without any
appreciable effect on the rate of the uncatalysed reaction.
The uncatalyzed and RU(III)-catalyzed reaction between MB
and cerium (IV) sulphate in acidic media occurred by means
of a chain reaction. The presence of free radicals in the
reaction media were established by means of introducing
acrylamide which formed a co-polymer with MB whose rate of
formation was drastically reduced using 1,4-benzoquinone. In
addition a high stoichiometry of MB:Ce(IV) 1:40 was observed
for both the catalyzed and uncatalyzed reactions. The
presence of Mo(VI), W(VI) and Co(III) ions was found to
interfere with the rate of the indicator reaction. The
interfering effect of W(VI) and Co(III) were masked by
ammonium hydrogen phosphate and sodium fluoride respectively
while that of Mo(VI) could be effected by extraction using
2-Methylpropanol followed by ethylacetate prior to
oxidation.
Further, a fixed time method is described for the
determination of V(V) and Ru(III), based on their ability
to catalyze the oxidation of IC by Cr(VI) and MB by ceric
sulphate respectively and the interference of other cations
on their determination studied using synthetic mixtures.
Description
A Thesis Submitted in Partial Fulfilment for the Requirement of Master of Science Degree of Kenyatta University, 1998. QD 281 .O9N58