The behaviour of several oxoanions dissolved in molten alkali-metal nitrates

Abstract

The behaviour of several oxoanions (HSO₄-, HSO₃-, NO₂-, ClO₄-, ClO₃-, SO₄^2-, SO₃^2-) dissolved in a molten NaNO₃-KNO₃ eutectic at 300°C was studied by means of an oxygen electrode. NaHSO₄ and NaHSO₃ were found to decompose very rapidly to form S₂O₇^2- or S₂O₅^2-, and water. NO₂-, SO₄^2-, and SO₃^2- were found to dissociate to a measurable extent to form O^2- and the equilibrium constants were determined for these dissociations. SO₄^2- and SO₃^2- appear to dissociate according to the equations SO₄^2- ←→ SO₃ + O² And SO₃^2- ←→ SO₂ + O² in which SO₃ and SO₂ remain solvated in the melt under the conditions used. ClO_4- was found to be completely stable in the melt, but ClO_3- appears to form an adduct with O^2-. Tentatively assuming that the reaction is ClO₃- + O^2-←→ ClO₄^3- we have found the equilibrium constant to be 3.57 x 10³.