Occurrence potentiometric titration

Extensive data are given in the Uterature for the potentiometric titration of polymer acids which may be used to study the behaviour of polyelectrolyte systems under different conditions. For poly(a-D) galacturonic acid there are few data of this kind, especially in connection with the occurrence of a conformational transition induced by pH variations, or with the effect brought about by the addition or the exchange of counterions. Since for a polyacid not exhibiting a conformational transition in the course of titration, pK K denoting the apparent dissociation constant) increases monotonously with degree... 

Bipotentiometric titrations, that is potentiometric titrations with a constant imposed passage of current of the order of 5-10 /iA, usually between two platinum electrodes, should also be mentioned here. These are not strictly speaking potentiometric titrations, since /= 0, but they involve a reading of potential. The current flow provokes the occurrence of a half-reaction. Where there is a dominant redox couple before and after the endpoint, the potential difference registered is more or less constant, but in the zone of the equivalence point there is generally a... 

A conaparison of the results of potentiometric titration of preparations of the starting cellulose and of the phosphorylated cellulose has shown that the latter contains acidic hydroxyl grou] It has also been found that all of the reaction products obtained contain methoxyl groups. These rraults, together with data frcan chromatographic studies, show that the phosphorylation erf cellulose with monomethylphosphite involves the simultaneous occurrence of the esterification and transesterification reactions. 

When the reduction potential of the aromatic hydrocarbon is high enough a second electron may be transferred, involving the addition of an electron to the univalent negative ion. This is demonstrated in Fig. 1, which shows the photographic record obtained from the potentiometric titration of a solution of anthracene in tetrahydrofuran. Two successive waves appear, pointing to the occurrence of reactions (1) and (2), respectively. 

The stoichiometry of the proton in Eqs. (10.7) and (10.8) (denoted by j) is a collective term that represents three possible configurations for the M Hy cit +- - (6Z ) complex. The value of j is 1 when Hc iP occurs in the complex, as in MHcif (6Z ). In this instance, a single carboxyl and the hydroxyl are protonated on the citrate molecule. Such complexes are significant only when solution pH values are less than 4. More commonly, j is zero or negative, the latter representing either the occurrence of H iciP in the complex (all citrate moieties ionized) [as in MH icit (ag)], or the occurrence of H ciP and a metal hydrolysis product in the complex [as in MOH(H icit)2 (ag)]. Chemical models derived from potentiometric acid-base titration studies cannot distinguish between the two potential proton sources (citrate hydroxyl or metal-bound water), as titrations... 

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