Molten Nal

As for the correctness of the above experiments, it should be mentioned that the positions of some Lux acids in this scale are incorrect this concerns V205, acidic phosphates, sodium meta- and pyro-phosphate, whose dissolution in the melt is accompanied by the evolution of gaseous iodine. In the case of V205 the reason consists in its strong oxidation properties in acidic solutions. As regards the iodine evolution upon dissolution of the various phosphates, in the case of acidic phosphates it is explained by the pyrohydrolysis of the melt by water formed by dehydration of the acidic salts—for example, potassium 

The relative basicity of some Lux bases (OH-, C03-, S04-) in molten Nal at 700 °C was investigated by the potentiometric titration method with weights of sodium pyrophosphate from base to acid [165]. The first of these bases reacted with the acid-titrant in the proportion 2 1, the others were neutralized in the proportion 1 1. Depending on the value of the pO drop at the equivalence points the studied bases were arranged in the sequence OH--C0 --S04- with decreasing basicities. The constants of the acid-base equilibria were not determined. Among the results presented, the most doubtful is the validity of the process of sulfate ion decomposition by the Lux acid. The reason consists in the fact that S03 formed as a result of the acid-base reaction 

Investigations of the oxoacidic properties of boron(III) compounds in molten Nal and KCl-NaCl at 700 °C were reported by Cherginets and 

Banik [166, 167]. The acidic properties of Na2B407 were studied by the potentiometric titration method using NaOH and Na2C03 as base-titrants, and the equilibrium oxide ion molality was detected by the potentiometric cells with the membrane oxygen electrode Pt(02)lYSZ. The process of titration was performed both from the acid to the base and from the base to the acid. The most characteristic potentiometric curves and the dependencies of the ligand number on the titrant molality are presented in Fig. 1.2.13. 

The pO drop at the equivalence point corresponds to the ligand number 1, which confirms the running of the interaction (1.2.91) in molten Nal. This interaction is characterized by a pK value of —5.02 0.6. It should be emphasized that with the excess of the Lux acid the equilibrium is achieved slowly enough. This seems to be caused by the fact that sodium tetraborate is practically completely polymerized, although the polymerizations effects on the titration process are less pronounced than in the case of B203. After the equivalence point, with the pO drop of 3-3.5 pO units, the equilibrium conditions are achieved in a shorter period, since under these conditions all the polymerized particles are destroyed. The excess of the base over that necessary for the formation of B02 results in the fixation of O2- by the formed metaborate, which demonstrates the oxoacidic properties. The dependence of the ligand number on the initial titrant molality allows us to assume that the final product is sodium orthoborate, B03- (equation (1.2.92)), whose pK value is close to 2. All that we have said above shows that the oxoacidic properties of tetraborate ions in molten sodium iodide are stronger 

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Dixon M, Sangster MJL (1975) Simulation of molten Nal including polarization effects. J Phys C Solid State Phys 8(1) L8-L11... 

Molecular Dynamics Calculations of the Raman spectra of Molten Nal. 

Polarization on Some Static and Dynamic Properties of Molten Nal. 

The curves from the direct and reverse potentiometric titration of metavanadate ions with the Lux bases NaOH and Na2C03 are presented in Fig. 1.2.14a. The neutralization process runs in two stages according to the equations (1.2.87) and (1.2.88), to which two small diffuse pO-drops (bends) in the potentiometric curves correspond. Nevertheless, these bends become apparent on the differential potentiometric titration curve, shown in Fig. 1.2.14b. The reverse titration results in two steps of neutralization, also, that confirms the reversibility of the process of the acid-base neutralization of vanadium(V) oxocompounds in molten Nal. Comparison with the corresponding dependencies for the molten equimolar KCl-NaCl... 

Fig. 2.5.9. Dependence of pK of reaction (1.2.3) against the inverse temperature in molten Nal (1), Csl (2), CsCl-KCl-NaCl (3) and KCl-LiCl (4).

It should be noted that iodine evaporation from the strongly acidic solutions was observed by Rybkin and Seredenko in molten caesium iodide at 650 °C (POJ solutions) [63] and by Rybkin and Banik [64] who studied solutions of PO, H2PO4, VO, etc. in molten Nal at 700 °C. 

Rybkin and Banik obtained the empirical acidity scale in molten Nal at 700 C. The basicities of COs and OH" were close which is incorrect since 0.01 mole/kg solutions were used for the scale constructing while equations... 

We have performed a study of aeidie properties of boron (HI) and vanadium (V) oxo-compounds in molten Nal at 700"C (see Table 10.4.1). A eomparative study of strength of Lux bases OH", C03 , S04 was determined " " by potentiometrie titration using sodium pyrophosphate as acid. Two moles of the first base may be neutralized by 1 mole of P407 , while two other moles react with the acid in ratio 1 1. On the base of e.m.f. drop magnitude at the equivalence point, the bases have been arranged in sequence 0H>C03 >S04 of basicity decrease. The equilibrium constants were not estimated. "" " ... 

In any aqueous solution in which electrolysis is to take place, the electrolysis of water is also possible. For example, consider the electrolysis of a sodium iodide solution, as shown in Figure 18.24 t. For the electrolysis of molten Nal, we can readily predict that 1 is oxidized at the anode and that Na is reduced at the cathode. In an aqueous solution, however, two different oxidation half-reactions are possible at the anode, the oxidation of 1 and the oxidation of water ... 

We have performed a study of acidic properties of boron (III) and vanadium (V) 0x0-compotmds in molten Nal at 700°C (see Table 9.2.4). 

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