Fajan determination

The Fajans determination of chloride involves a direct titration, while the Volhard approach requires two standard solutions and a filtration step to eliminate AgCl. 

It remains to be determined to what extent the dye adsorption technique is applicable to other substrates. No evidence was obtained for Pseudocyanine adsorption to Mn02, Fe2Os or to pure silver surfaces, although this dye can be bound to mica, lead halides, and mercury salts with formation of a /-band (61). Not only cyanines but other dye classes can yield surface spectra which may be similarly analyzed. This is specifically the case with the phthalein and azine dyes which were recommended by Fajans and by Kolthoff as adsorption indicators in potentio-metric titrations (15, 30). The techniques described are also convenient for determining rates and heats of adsorption and surface concentrations of dyes they have already found application in studies of luminescence (18) and electrophoresis (68) of silver halides as a function of dye coverage. 

The actual calorimetric measurement that is made in determining the heat of hydration of the ions of a salt is not the heat of hydration itself, but the heat of its dissolution of the salt in water or another solvent (Fajans and Johnson, 1942). Let this be Then one can use the first law of thermodynamics to obtain the property... 

Fajans (1962) was the first scientist to put these thoughts into practice. One finds that the determined heats of solvation are reiativeiy small and endothermic (+) for some salts but exothermic (-) for others. However, lattice energies are known to be in the region of several hundreds of kilojoules mor, so that, in rough terms [Eq. (2.3)], heats of solvation should not be more than a dozen kilojoules moF (numerically) different from lattice energies. In Table 2.4 a compilation is given of the quantities mentioned earlier in the case of the alkali haUdes. Now, the method described here gives the sum of the heat of hydration of the ions of a salt. The question of how to divide this sum up into individual contributions from each of the ions of a salt requires more than the thermodynamic approach that has been used so far. The way this is done is described in later sections (e.g., in Section 2.6.2 or 2.15.9). 

By statistical tests of over 60 compounds it was demonstrated (22) that the empirical slopes, which represent the incremental increase in refractivity per mole of alkali fluoride in such complexes, are in fact adequately represented by the sum of Fajans aqueous refractivity values for a given alkali metal ion and fluoride ion (140). Since the slope is known, a single point would determine the line for a series of unknown complexes. The predictive value, and use for determining composition by simple methods are obvious. For example, the empirical refractivity per mole of KF is 5 cm which is such a large fraction of typical refractivity values (about 30 cm3) that even a crude refractive index determination can usually fix the formula within 0.1 to 0.2 mol. 

Now consider FeO and Fe203. In this case, the ionic character cannot be easily assessed by looking at the electronegativities of the elements. Even though the iron in FeO is the Fe " ion, whereas in Fe203 it is the Fe " ion, there is no easy way to determine the electronegativity of an ion. A model that is particularly convenient for this situation, and in many other bonding problems, was proposed by Kazimierz Fajans, a Polish-American chemist. 

A very useful treatment of the kinetics of enzymatic resolution, describing the dependency of the conversion (c) and the enantiomeric excess of substrate (e.e.s) product (e.e.p), was developed by C.J. Sih in 1982 [40] on a theoretical basis described by K.B. Sharpless [41] and K. Fajans [42]. The parameter describing the selectivity of a resolution was introduced as the dimensionless enantiomeric ratio ( ), which remains constant throughout the reaction and is only determined by the environment of the system [43-46]." E corresponds to the ratio of the relative second-order rate constants (va, vb) of the individual substrate enantiomers (A, B) and is related to the cat values of enantiomers A and B according to Michaelis-Menten kinetics as follows (for the thermodynamic background see Fig. 1.7) ... 

Pauling determined the constant of Eq. 11.40 and calculated ionic refractions. The systems of Fajans and Pauling are similar, being based on the same experimental data, namely, the refractions of rare gases. 

Type of charge on a particle could be determined by the measurement of Zeta potential [9] or a titration curve. According to Fajan s rule [10], the ions forming a crystalline phase should be adsorbed prior to other ions. For the system studied in this paper, the sol particles produced must carry positive charge to make it stably adsorb the cationic surfactant. In order to elucidate the effect... 

Like Mohr s method, Fajans method is a direct titration method. It is based on the use of adsorption indicators. A small volume of an acetic acid solution and an adsorption indicator are added to the solution containing the halide to be determined. Then a silver nitrate solution is added. At the equivalence point, the precipitate suddenly turns colored and separates completely from the solution. 

Mittenberger and Gross " determined chlorine in PVC by fusion with sodium peroxide followed by silver nitrate titration of the chloride produced. Tanaka and Morikawa described a semimicro technique for the determination of total chlorine in PVC using a semimicro method based on the Schoniger oxygen flask and Fajans method. 

It seemed worth while, therefore, to apply to the important generalization of Fajans, Russell, Fleck and Soddy a more searching test carrying the fractionation further, and using as a criterion of success not only the measurement of radioactivity but also the determination of atomic wei t. 

The Born-Fajans-Haber cycle uses thermodynamic cycles to determine lattice energy. An alternative to the Born-Fajans-Haber method is one based on fundamental principles. Because the dominant interactions in an ionic crystal are Coulomb interactions, we can use the theory of electrostatics to calculate the lattice energy. Kapustinskii used these ideas and proposed the following equation ... 

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