The effects of ions and non-electrolytes on equilibria involving sulphur (IV) oxospecies in solution

Salts of Li, Na, K and Cs are used to demonstrate and explain the effects of solute-solute interactions on the acid dissociation of ‘sulphurous acid’, SO2.H2O, and the conversion of HSO3− to S2O52−. Ion-pair interactions involving the cations and SO32− and S2O52− are identified spectrophotometrically, and are shown to perturb the generally accepted equilibria involving these oxospecies in solution. The effects of ion-pairing are greater in water-non-electrolyte mixtures. SO2-halide ion interactions tend to increase the pK1 of SO2.H2O.