Potentiometric acid-base titrations in molten salts—IV. Basic character of some oxide-ion donors in molten KNO3: their reaction with NaPO3 and K2Cr2O7

Abstract

The basic character of electrogenerated O2−, OH−, O22−, CO32−, HCO3−, HCOO−, (COO)22− and CH3COO− in fused KNO3 at 350°C was studied by forward and backward potentiometric neutralization experiments with the two acids NaPO3 and K2Cr2O7. The anions fall into two distinct groups. To the first, the “oxide” group, belong O2−, OH− and O22−, which give rise to O2-electrode potentials varying between −850 and −92O mV, and allow the formation of the basic compounds PO43−·O2− and 2CrO42−·O2−. Cyclic neutralization curves suggest the presence of two phosphate glasses, namely, an acid glass nPO3−·P2O74−, and a basic glass nPO43−·O2−. The other anions, forming the “carbonate’, give rise to O2-electrode potentials of ca −550 to −600 mV, and do not form the basic phosphate or chromate.The thermal decomposition of bicarbonate, oxalate, formate, and acetate in fused KNO3 was studied in detail. Bicarbonate changes into carbonate. Oxalate produces carbonate and not oxide as previously claimed, together with an equivalent quantity of nitrite. The same occurs also with formate and acetate, but in the latter case decomposition follows a different route.