Conductometric titrations complex-formation titration

In principle, any type of titration can be carried out conductometrically provided that during the titration a substantial change in conductance takes place before and/or after the equivalence point. This condition can be easily fulfilled in acid-base, precipitation and complex-formation titrations and also the corresponding displacement titrations, e.g., a salt of a weak acid reacting with a strong acid or a metal in a fairly stable complex reacting with an anion to yield a very stable complex. However, for redox titrations such a condition is rarely met. 

Fig. 2.6. Conductometric titration of basic salt, and of chloride with precipitation or complex formation.

In fact, any type of titration can be carried out potentiometrically provided that an indicator electrode is applied whose potential changes markedly at the equivalence point. As the potential is a selective property of both reactants (titrand and titrant), notwithstanding an appreciable influence by the titration medium [aqueous or non-aqueous, with or without an ISA (ionic strength adjuster) or pH buffer, etc.] on that property, potentiometric titration is far more important than conductometric titration. Moreover, the potentiometric method has greater applicability because it is used not only for acid-base, precipitation, complex-formation and displacement titrations, but also for redox titrations. 

HMPA gives, however, poorly conducting solutions 89 In the course of the conductometric titration of FeCl3 with HMPA in nitrobenzene a conductivity maximum is observed at a molar ratio HMPA FeCl3 = 1 2 and [FeCl4 ] ions are present at this composition of the solution. It is likely that the complex cation which is simultaneously produced by autocomplex formation may contain coordinated nitrobenzene molecules ... 

Breaks in the conductometric titration curves for the aqueous ZrOCl2-K3-[MoO(OH)(CN)4] system occur at molar ratio 3 2 with the potassium salt as titrant and at 1 1 and 3 2 with ZrOCl2 as titrant corresponding to the formation of KZrO[MoO(OH)(CN)4] and (ZrO)3[MoO(OH)(CN)4]2.292 The e.p.r. spectra of frozen solutions of Zr and Hf peroxo complexes have been analysed.147 The increase in conductivity with decreasing concentration of solutions ofZr02L2 (L = quinoline N-oxide) has been interpreted293 in terms of the equilibrium ... 

The slope of the conductometric titration curve gives a measure of not only the strength of complexation but also its solvation. If an increase in conductance is observed on complex formation, this may indicate that the anions are highly solvated and therefore less mobile than the complex ion. This behaviour is uncommon but has been previously observed for systems involving lithium and... 

The enhancement in the receptor capacity to host anions has been successfully achieved by the design of double-cavity ligands. This is reflected in the conductometric titration curve (Fig. 4c) for the fluoride anion when titrated with receptor 7. In fact, in A/,A/-dimethylformamide, this receptor takes up two anions per unit of ligand while discriminating against other spherical (chloride, bromide and iodide) and non-spherical (hydrogen sulphate, perchlorate, nitrate and tri-fluoromethane sulphonate) anions except H2POj. With this anion only the formation of a 1 1 complex was observed. 

Giebeler et al. [73] investigated the polyelectrolyte complex formation of triblock copolyampholytes, polystyrene-frZock-poly( 2 or 4)-vinylpyridine)-b/oc/c-poly(methacrylic acid). By potentiometric, conductometric and turbi-dimetric titrations of acidic THF/water solutions the formation of an interpolymer complex at the isoelectric point was found, in which most likely the hydrophobic polystyrene cores are embedded in a mixed corona of the two polyelectrolyte blocks. 

The experimental results may be represented both by the titration curves or property-composition dependences. The extremums or bends on the titration curves indicate the formation of complexes and their composition. Thus, investigating the-possi-bility of complex formation in polyelectrolyte - nonionic polymer systems, one can use the methods of conductometric and potentiometric titration. The formation of interpolymer complexes in these systems, as some authors suggest18,211, is caused by a co-operative formation of hydrogen bonds between carboxy groups of the polyacid and oxygen atoms of nonionic polyvinylpyrrolidone or poly(ethylene glycol) and is therefore accompanied by an increase of pH of the solution. The typical titration curves for the system polyvinylpyrrolidone - copolymer maleic anhydride and acrylic add are shown in Fig. 1. The inflection points of the titration curves indicate the ratio at which the macromolecular components react with each other, i.e. the composition of the formed complexes. 

The complex formation in PAA-PVP-methanol and PMAA-PVP-DMF systems has also been investigated44. The composition of the complexes in these solvents has been determined by conductometric and potentiometric methods. The titration curves in methanol and DMF (Fig. 15) exhibit a typical inflection point termining the molar ratio of the components in the complex. The complex compositions in organic solvents and water are different (Table 2). For comparison the titration curves in Fig. 15 of PAA with PVP in DMSO are illustrated. The solvent (DMSO) strongly competes for hydrogen bonds and it has been already shown48 that the complex is broken down. No inflection point on the titration curves is observed in this case. 

There are a number of other methods, spectroscopic as infra-red (IR), ultraviolet-visible (UV-Vis), which allow the evaluation of the ability of the Ca complex formation. Not all of them are suitable in every case. We have decided to explore the flame photometry and conductometric titration since the NMR changes were too small to perform the correct analysis. 

Several studies including the use of conductometric titration showed that for pyridine and A-methylpyrrole in CH2CI2 complex formation occurs, but for the weaker... 

The formation of mercaptofurfuryl [9] and methyl-3-mercaptopropionate [10] complexes of La, Ce, Pr and Sm(III) have been established on the conductometric titration of alcohol solutions of Ln(N03)3. The complexes were not isolated from the solutions. 

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