1,721,121 research outputs found
Protonation of anionic indicators in the presence of cationic micelles
No full textThe protonation equilibria of two sulfonephthalein indicators (BCG and BPB) and one sulfonated azo dye
(T-azo-R) in the presence of a cationic surfactant (alkylbenzyldimethylammonium chloride) at a concentration
higher than its critical micellar concentration (c.m.c.) have been investigated. In particular the effect of the ionic
composition of the solution was studied, with the purpose of testing a model which regards the micelles as a true
microphase behaving like a strong base anion-exchange resin. The potential difference at the micelle/aqueous
solution interface accounts for the distribution equilibria of charged species, which are set up according to the
Gibbs-Donnan equation. Thus the ion-exchange constants are expected to be equal to one, while the ion-exchange
coefficients depend on the activity coefficients of the charged species partitioned between the micellar and solution
phases. According to the model a simple relation is derived between the apparent protonation constants in the
presence of micelles, and those in aqueous solution, which has been verified for the systems considered, for other
previously studied organic reagents and in the case of interaction of T-azo-R with albumin in acidic solution
Spectrophotometric investigation on the complexation of Hg(II) with some sulfonated azo-dyes in 0.1 mol dm^-3 NaClO4 aqueous solution
No full textPotentiometric determination of the standard potential of the As(V)/As(III) couple
No full textThe potential of the couple As(V)/As(III) was measured at 25 degrees cent. with a glass electrode as reference electrode in order to eliminate the liquid junction potential. The presence of iodide is required in order to increase the rate of the electron exchange between arsenic at the two oxidation states. A standard potential of 573 mV was determined for the reduction of the hydroxylated specie
Potentiometric study of the complexation of Arsenic(III) by chloride ions
No full textThe reactions between As(OH)3 and chloride ions are studied in different ionic media, at 25 degrees centigrades, by a standard potentiometric technique, based on the measurement of the potential of the redox couple As(V)/As(III) against a glass electrode. Low iodide concentrations were added to the test solution to obtain a rapid and reproducible potential. The formation of hydroxylated complexes was proved
Sorption of Copper, Nickel and Lanthanum on a strong base anion exchange resin containing Chromotrope 2B.
No full textThe sorption of a number of metal ions on the strong-base resin AG 1 X 8 containing the azo-dye Chromotrope 2B has been studied using conventional analytical methods. While lead, cadmium, zinc and magnesium are not sorbed, copper, lanthanum and nickel are. The sorption of nickel was unexpected because complexation in water is negligible. In the resin phase a 1:2 complex was found. For copper both the 1:1 and 1:2 complexes are formed depending on the ligand concentration in the resin. Evidently, the high ligand concentration in the resin promotes the formation of the 1:2 complex. For lanthanum also 1:1 and 1:2 complexes are formed. The experimentally determined extraction coefficients can be related to the intrinsic formation constants with the aid of the Donnan equilibrium. A good agreement is found for the 1:1 complexes of copper and lanthanum, but not for the 1:2 complex of lanthanum, probably due to large differences in the activity coefficient
Simultaneous determination of total and free metal ion concentration in solution of unknown composition by sorption on iminodiacetic resin
No full textA method for determining the total concentration of a
metal ion originally present in a solution, ctot, and the ratio
of total to free metal ion, ZM, is proposed. It consists of
putting different aliquots of the sample (V) in contact with
the resin (w) in batch, by keeping the acidity constant,
and determining the concentration of the sorbed metal ion
c. Then 1/c is plotted against V/w, and ctot and ZM are
calculated from the straight line obtained. The chemical
model that allows evaluation of the ratio of total to free
metal ion is illustrated and discussed. Some synthetic
systems are examined to demonstrate the validity of the
procedure
Determination of the complexing properties of drinking waters towards copper(II) and aluminium(III) by ligand titration
Full text linkThe complexing capacity of some drinking waters for aluminium(III) and copper(II) is
determined by a ligand titration with metal ions based on the use of complexing resins. The resins used
in the titration are the iminodiacetic resin Chelex 100, the carboxylic resin Amberlite CG50 and the
anionic exchange resin AG1X8. They allow the detection of ligands forming complexes of di erent
stability with the metal ions used for the titration, since they have di erent sorbing properties. After
equilibration with the resin, the concentration of the free metal ion in solution is evaluated from the
concentration of sorbed metal ion and from the quantity K, which is the ratio of the concentration of
the metal ion sorbed on the resin to the free metal ion in solution. It strongly depends on the
conditions, but it can be evaluated, at the considered conditions, from the sorption equilibria of the
metal ion on the resin. The concentration of the ligands in solution and the conditional stability
constant are obtained from the Ruzik linearization procedure. Very strong ligands of copper(II) and
aluminium(III) were detected in a tap water sample at concentrations ranging from 10ÿ7 to 10ÿ6 mol
kgÿ1, and forming complexes having conditional complexation constants KcI 2:3 1017 (pH=6.77)
and 4.5 1016 (pH=6.24), respectively, for copper(II) and aluminium(III). Weaker ligands were
detected using the less strongly sorbing resins Amberlite CG50 and AG1X8, but at a concentration
equal to that of the strong ligands. This was ascribed to the presence of competing metals in solution,
not sorbed by the weak resins. Two other drinking waters had completely di erent complexing
properties both towards copper(II) and aluminium(III), containing much weaker ligands
Sorption of divalent metal ions on an iminodiacetic resin from artificial seawater
No full textThe sorption of some bivalent metal ions on the iminodiacetic resin Chelex 100 was examined in artificial seawater as an
example of a complex matrix, and in the presence of an organic chelating substance in the aqueous phase. The curves
reporting the fraction of sorbed metal ions in function of the solution pH were determined experimentally under different
conditions and the exchange coefficients were calculated. The intrinsic complexation constants, which are independent of the
conditions, were evaluated on the basis of the Gibbs-Donnan model for the resin and agree with those previously obtained in
the case of the sorption of the same metals on Chelex 100 from solutions of simpler composition. In some instances the
intrinsic complexation constants were similar to the corresponding complexation constants in aqueous solution, while in other
cases they were different, depending on the activity coefficient ratio of the species inside the resin. It has been demonstrated
that the method derived from the Gibbs-Donnan model can be used for describing and predicting the sorption equilibria also
from complex solutions, if all the equilibria set up in the considered system are known
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