High-temperature hydrolysis of molten halides

These reactions were investigated mainly for alkaline halides and their mixtures. Hanf and Sole studied the hydrolysis of solid and molten NaCl in the temperature range 600-950 C by so-called dynamic method which consisted of passing inert gas (Nj) containing water vapor through a layer of solid or fused NaCl. The developed routine determined the equilibrium constant of the following reaction  

The hydrolysis of NaCl occurs to a slight extent, although the rate of HCl evolution exceeded the expected value because of dissolution of NaOH formed in NaCl. 

An evident disadvantage of the above method is assumption that the partial pressure of HCl in the gas phase is equal to the equilibrium pressure. The same method was used to study the high-temperature hydrolysis and oxidation of sodium iodide.According to the estimates, the heats of the reactions  

A simple but unquestionable method has been used to investigate high-temperature hydrolysis of molten KCl-NaCl. A mixture of HCl and H2O obtained by passing an inert gas through aqueous solutions at a definite concentration was passed into the melt. Measurements of the equilibrium O concentration by potentiometric method allowed to calculate the equilibrium constants of [10.4.13] as pK=55.3xl0 T -40.2. At 1000, pK=15.1, it means that equilibrium [10.4.13] in molten KCl-NaCl is displaced to the left. 

A similar method has been used to study the hydrolysis of the eutectic KCl-LiCl at 500 C (pK=9.77+0.4). The hydrolysis of the chloride melt is thermodynamically unfavorable and is completely suppressed in the presence of bases (even at a concentration of 10 mole/kg). 

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Examinations of the interactions of ionic halide melts-solvents with gaseous reagents of acidic or basic character, which include high-temperature hydrolysis of molten alkali-metal halides, their purification from oxygen-containing admixtures, and studies of the dissociation of strong and weak Lux bases (such as COf-, OH-, 0 ) in melts of different acidity. 

Pure oxygenless melts contain no oxide ions in any form, and because of it, pure melts carmot serve as donors of 0 . The melts, which are solvents of the second kind, can affect acid-base interaction in two manners by fixation of oxide ions entering melt and by solvation of conjugated acid or base. These ionic solvents are used in practice for research and applied purposes, however, they contain admixtures of oxide ion donors, which are formed in the melt from initial admixtures of oxoanions such as SO4, CO3, OH . The second way of the appearance of oxide ion admixtures in molten media is characteristic of the melts based on alkali metal halides the process of high-temperature hydrolysis of the halide melts results in formation of hydroxide and, after their dissociation, of oxide ions ... 

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