الفهرس 
Kinetics of complexation reaction of Cr (III) ion with Nicotinic acid
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Abstract
Kinetic study of formation of 1:2 complex between
chromium (III) and nicotinic acid in weak acid aqueous
solution was investigated spectrophotometrically at
λ=575 nm. The studies indicated that the reaction
between chromium(III) and nicotinic acid in weak acidic
aqueous solutions involves an ion pair is the first product
formed in a very fast step. The nonlinearity of log (A∞ -
At) versus time plots obtained, are indicative of a
complex reaction, not a single process. The
independence of the rate constants of the reaction on
chromium concentration confirmed the assumption of
two consecutive steps. In the first (slow) a bond is
formed between Cr and the oxygen atom of the
carboxylate group (compound A). In the second step, a
bond is formed between the second oxygen atom of the
carboxylate group and Cr forming a four-membered ring
(compound B). The formation of compounds A and B is
the slow step followed by forming chromium nicotinate
complex [Cr(nic)2(H2O)3OH] in a fast step. This is due to
when one molecule of nicotinic acid enters the inner
coordination sphere of the chromium ion and compound
B is formed, the electron density on Cr(III) is increased,
and the remaining water ligands are labilized very easily.
Both steps are followed by pH decrease suggesting that
proton release is taking place. The different factors
affecting the rate of reaction were studied.- The kinetics oxidation of chromium (lII)-dinicotinate
complex by periodate were investigated. The reaction
was first-order in chromium(III)-nicotinate complex,
accelerated with increasing periodate concentration, pH,
temperature and ionic strength of the reaction medium.
The oxidation of chromium (III)-nicotinate complex by
periodate is assigned an inner-sphere mechanism. A
common mechanism for the oxidation of ternary
chromium(III) complexes by periodate is proposed and
is supported by the excellent isokinetic relationship
between ΔH* and ΔS* values for this reaction.
3- The kinetics of substitution of aquo-ligand from
hydroxopentaaquo Ferric (III) by N-Phthaloylglycine in
aqueous medium has been studied
spectrophotometrically. The rate law involving the
formation of ion-pair has been established in the pH 2.8
and 50ºC. The reaction between [Fe(H2O)5 OH]2+ and
Ph-GLy involves outer sphere association between the
two reacting species followed by an associative
interchange process in which both bond-breaking and
bond-making are equally important. The different factors
affecting the rate of reaction were studied.