Oxoacidic properties of phosphates

Shapoval et al. reported an examination of the acidic properties of metaphosphate ions in the molten KCl-NaCl eutectic at 700 °C [141]. This investigation was performed by the potentiometric method with the use of the gas platinum-oxygen electrode as an indicator. The potentiometric titration with weights of a strong base resulted in the neutralization process occurring in two stages, listed below  

The equilibrium constants of these equilibria (in molar fraction scale) were K = 2.88( 1.2) X 103 and 2.5( 1.4) X 101 for the first and the second steps, respectively. 

The formation of the basic phosphates, to which Delimarskii et al. [141] ascribed the composition of PO O2-, took place with excess of the titrant (O2-), whereas the use of a weak base, Na2C03, did not allow this basic 

The constants of the corresponding equilibria were determined, and the solubilities of the polyphosphates were found. 

The results of potentiometric titration of sodium metaphosphate with weights of Na2C03 and NaOH were reported in Ref. [157], The most indicative potentiometric curves are collected in Fig. 1.2.8a, together with the plot of the ligand number n against the initial concentration of the base-titrant. 

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