Lux, definition

It should be noted that there are some curious interpretations in the literature concerning oxoacidity, which distort to a greater or lesser degree the original definition. For example, Delimarskii and Barchuk [3] give as the Lux definition where a base is a donor of oxide or halide ions. Moreover, at least in the Russian translation of a book [21], the Lux-Flood definition is where an acid is a donor of oxide ions and a base is an acceptor of O2-. Certainly, these definitions are erroneous, as may be seen by reading the original Lux paper [17]. 

The data on the solubility of CaO and ZnO in the chloride melts allow us to trace the effect of the acidic properties of the melt-constituent cation on the metal-oxide solubilities the ratio of the solubilities in K+, Na+ and Li+-based melts is 1 1.5 15. However, these are the total solubilities, and the data are distorted by the contribution of an appreciable concentration of non-dissociated oxide, which is not sensitive to changes in the melt-acidity. It should be emphasized that since we do not know the ratios of the ionized fraction to the non-dissociated one in all the melts studied, we cannot estimate quantitatively the oxoacidic properties of all the melts in question. This neglect of the metal-oxide s dissociation is because the said work was published in 1923, whereas the Lux definition was formulated only in 1939. Therefore, the authors of Ref. [327] did not take into account the dissociation of the oxides in the molten salts, which from our point of view, reduced the significance of this investigation. 

Since Arrhenius, definitions have extended the scope of what we mean by acids and bases. These theories include the proton transfer definition of Bronsted-Lowry (Bronsted, 1923 Lowry, 1923a,b), the solvent system concept (Day Selbin, 1969), the Lux-Flood theory for oxide melts, the electron pair donor and acceptor definition of Lewis (1923, 1938) and the broad theory of Usanovich (1939). These theories are described in more detail below. 

The various acid-base definitions are summarized in the Venn diagram (Fig. 2.1). From this it can be seen that the Usanovich definition subsumes the Lewis definition, which in turn subsumes all other definitions (i.e. Arrhenius, Bronsted-Lowry, Germann-Cady-Elsey, Lux-Flood). 

In silicate melts and other nonprotonated solvents, the Bronsted-Lowry equation is not applicable and is conveniently replaced by the Lux-Flood acid-base definition (Lux, 1939 Flood and Forland, 1947), according to which free oxygen 0 replaces A basic oxide is one capable of furnishing oxygen ions, and an acidic oxide is one that associates oxygen ions ... 

Hie base (GaO) is an oxide donor and (be add (SiO,) is an oxide acceptor The usefulness of the Lux-Flood definition is mostly limited lo systems such as molten oxides. 

Lux—Flood Definition In contrast to the BrpnstedLowry theory, which emphasizes the proton as the principal species in acid-base reactions, the definition proposed by Lux and extended by Flood describes add-base behavior in terms of the oxide ion. This add-base concept was advanced to treat non protonic systems which were not amenable to the Bipnsted-Lowry definition. For example, in high-temperature inorganic melts, reactions such as the following take place ... 

Use the Lewis definition of acids and truces to explain the examples given tor the Br0nsted-Lowry, Lux-Flood, and solvent system definitions (Eqs 9.1-9.4, 9.S-9.8, 9 9-9.361. 

Molten carbonates display variable acid-base behavior according to the Lux-Flood modification of the Lewis definition of acidity,... 

Lux—Flood Definition In contrast to the Brpnsted-Lowiy theory, which emphasizes the proton as the... 

Use the generalized deHnilion of acids and buses to explum the examples given for the Br0nsicd-Lowry, Lux-Flood, solvent system, and Lewis definitions (Eqs. 9.I-9.4. 9 5-9 8. 9.9-9 36 9.37-9.40). 

This brings us to another definition put forward by Lux, which goes back to Berzelius who wrote... 

Effects of Additives. Selected additives to molten nitrate systems offer possibilities of specific acid-base reactions or formation of specific complexes with the various chemical species. Acids and bases are conveniently denoted in oxyanionic molten salt systems by the Lux-Flood definition (18, 19). Acids are defined as compounds capable of removing oxide ions from the melt, while bases are defined as compounds capable of donating oxide ions to the melt. Examples of various acidic and basic species may be found in the general review articles (14, 15,... 

The preconditions of another approach to the treatment of acid-base concepts can be found in the classic solvosystem concept described above. Careful reading of this concept shows that the acid-base definition connects the terms acid and base only with the process of autodissociation of a molecular solvent or of one capable of ionization. Nevertheless, it is obvious that acid-base interactions can occur in those solvents, which are not able to form acid and base owing to a dissociation process. Aprotic solvents may serve as a typical example of solvents of such a kind another case of solvents incapable of the acid-base autodissociation takes place if we consider the Lux acid-base equilibria in molten oxygen-free media. Therefore, in relation to any given acid or base there exist two kinds of solvents of differing auto-dissociation ability with the formation of the said acid or base [36, 37, 44, 45]. 

Quantitative investigations of the reactions of oxide ions and oxo-compounds in high-temperature ionic solvents are, therefore, of considerable scientific and applied importance. The interactions of such kinds are referred to as acid-base ones, according to Lewis. Since 1939, when Lux proposed a definition of acids as oxide ion acceptors and bases as donors of O2-, such acid-base interactions came to be called oxoacidity . The most general scheme of a Lux acid-base interaction is presented by the following equation ... 

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