Abstract
The interaction of hexaaquochromium(III) with salicylic acid was studied in the pH range 2.5-4.2. The composition of the complex formed was one mole of salicylic acid to one mole of hexaaquochromium(III). The variation of pseudo first order rate constant with pH, ionic strength and ligand concentrations indicated a mechanism based on ion-pair formation. The rate equation derived on the basis of this mechanism is:
k
obs=
k
anK
1K
a[salicylic]
T
[H
++K
a+K
1K
a[salicylic]
T
An associative interchange mechanism is suggested for the reaction. The activation parameters calculated by Eyring equation are
ΔH
∗ = 74.48
(±0.33) kJ mol
−1;
ΔS
∗ = −60.49
(±1.11) JK
−1 mol
−1 for anation and
ΔH = −9.00 (±0.43) kJ mol
−1;
ΔS = −13.60(±1.42) KJ
−1 mol
−1 for ion-pairing.