Complex formation in the ternary systems M
n
+
+ dipicolinic acid + amino acids or
N-(2-acetamido)iminodiacetic acid (H2ADA), where
M
n
+ = CuII, ZnII,
NiII, CoII, HgII, CdII,
PbII, UO2
II, YIII, and
CeIII, have
been investigated pH-metrically in aqueous media at 25 °C and at
ionic strength I = 0.10 mol
dm-3
(KNO3). The stability constants of the different
binary and ternary complexes formed in such systems
have been determined and discussed in terms of the nature of both metal
ion and secondary ligand (amino
acids or H2ADA). It was deduced that, except in
the case of dicarboxylic amino acid, the stability of the
ternary complex is lower than that of the corresponding binary
M
n
+ + amino acid or
H2ADA.
The acid dissociation constants of some 2-mercaptobenzazoles in
aqueous-organic solvent mixtures are
determined potentiometrically at (25 ± 0.1) °C and an ionic
strength of I = 0.02 mol dm-3
(KNO3). The
organic solvents are methanol, ethanol, DMF, DMSO, and acetonitrile.
The pK
a values are discussed
in
terms of the proportion and nature of the organic cosolvent. It
was concluded that hydrogen bonding
interactions of the conjugate base with the solvent and the solvent
basicity in addition to the electrostatic
effect contribute the major effects in the ionization process.
Moreover, thermodynamic functions (ΔH,
ΔG, and ΔS) of the ionization process in an
aqueous medium containing 0.1 mole fraction of ethanol are
also determined and discussed.
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