Ionic solvents based on alkali metal nitrates

3 IONIC SOLVENTS BASED ON ALKALI METAL NITRATES 

Since there are many publications devoted to different aspects of oxo-compounds and oxide ion chemistry in melts based on alkali metal nitrates, these melts are traditionally said to be the most studied. This is mainly because the relatively low melting points of both individual alkali-metal nitrates and their mixtures allows one to use very simple experimental techniques, e.g. to 

The known investigations of oxoacidity in nitrate melts are devoted to the determination of the constants of acid-base equilibria using the above-described kinetic and potentiometric methods. 

Duke and Yamamoto determined the rate and equilibrium constants for the reaction of K2S207 with the KN03-NaN03 eutectic mixture [79, 80] by the kinetic method whose features are described in detail above. The rate constants were found to be 0.038 at 235 °C, and 0.096 at 275 °C, the corresponding values of the equilibrium constants (1.2.11) were 2.6 X 10-2 and 3.8 X 10-2. The activation energy of the direct reaction (1.2.11) was estimated to be 54 kJ mol-1. Besides the parameters of acid-base processes, the solubility of Na2SC 4 in the said melt was found it was equal to (mol kg-1) 2.5 X 10-1 at 235 °C, 2.82 X 10-1 at 250 °C, 3.42 X 10-1 at 275 °C, and 4.21 X 10-1 at 300 °C. The errors of solubility determination were less than 1 X 10-2 mol kg-1. 

The same authors studied the interaction of dichromate ions with the molten KN03-NaN03 eutectic [79] 

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Ionic solvents based on alkali metal nitrates... 

The described levelling of the acidic properties in molten nitrates makes them unavailable for the determination of the constants of Lux acid-base equilibria where the strongest acids take part. The melts based on molten alkali metal halides are the most convenient solvents for this purpose. Since the most essential physico-chemical properties of ionic melts (density, charges and ionic radii) are close,1 application of the data obtained in molten chlorides for the description of acid-base equilibria in molten nitrates is more correct than is the use of a similar approach to room-temperature molecular solvents, since the properties determining their acid-base properties are numerous (e.g. dielectric constants, donor-acceptor properties). 

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