A chronopotentiometric investigation of the dissociation of sulphate ions in molten equimolar NaCl-KCl at 750°C

Abstract

The Lux—Flood acid—base equilibrium SO 3 + O 2− ⇌ SO 4 2− in molten equimolar NaCl/KCl at 750°C has been investigated using conventional chronopotentiometry. The equilibrium constant for this reaction is shown to be very high ( K > 10 2). Thus the sulphate ion in solution in this melt does not decompose unless a very strong acid such as the metaphosphate ion is added to the melt. This removes oxide ions according to the reaction. 2PO 3 − + SO 4 2− → SO 3 + P 2O 7 4− The pyrophosphate anion is not a sufficiently strong acid to remove oxide from sulphate.