Oxoacids of vanadium V

The reference data show that vanadium(V) oxide, V2Os, decomposes at temperatures above 700 °C [121], i.e. its decomposition starts near its melting 

To determine the acidic properties of vanadium oxocompounds, we performed potentiometric titration of V2O5 in an equimolar mixture of molten KCl-NaCl at 700 °C with known weights of Na2C03 and NaOH (see Fig. 1.2.9a) [157]. The addition of initial weights of V205 to the molten 

These stages are characterized by the equilibrium constant values (pK) equal to -6.5 0.2 and -5.23 0.3, respectively. The buffer solutions, whose formation corresponds to the section of the titration curves with h 1 and the neutralization stage (1.2.86), are characterized by the buffer number of -0.03, whereas for the section conforming to the equation (1.2.87) this value is markedly higher (up to — 0.05). 

In the case when NaOH is used as the base-titrant, its addition after the second equivalence point (meta-vanadate/pyro-vanadate) gives rise to the third slightly pronounced pO drop, which corresponds to the formation of ortho-vanadate from pyrovanadate by the following equation  

This reaction is characterized by a pK value of — 2.04 0.4 and the buffer number equal to (3 — 0.12. The equivalence point of this neutralization step can be detected more sharply using the differential potentiometric titration curve. 

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