Dissociation constants of anhydrous ammonium sulphite and ammonium pyrosulphite prepared by gas-phase reactions

Abstract

The products formed by gas-phase reactions between NH₃, SO₂, and water vapour diluted with air have been identified by chemical analysis and i.r. spectroscopy as (NH₄)₂SO₃ and (NH₄)₂S₂O₅. The dissociation constants of these compounds have been determined for the temperature range 273–298 K by a transpiration method. The results for complete dissociation fit the following Arrhenius equations for the sulphite and pyrosulphite respectively: log (K_p/m^–8 N⁴)=(53·29 ± 0·01)–(14,171 ± 33)/T and log (K_p/m^–10 N⁵)=(66·92 ± 0·02)–(17,705 ± 183)/T. The relevance of these reactions to air pollution problems is discussed.