First dissociation constant of sulfurous acid, as pKa.
SO₂·H₂O ⇌ HSO₃⁻ + H⁺, pKa 1.81 at cellar temperature (Boulton, Singleton,
Bisson & Kunkee). This is why a sulfite dose depends on pH: only the
undissociated molecular SO₂ is antimicrobial, and the fraction of free SO₂
that's molecular falls by a factor of ten for every unit of pH.
First dissociation constant of sulfurous acid, as pKa.
SO₂·H₂O ⇌ HSO₃⁻ + H⁺, pKa 1.81 at cellar temperature (Boulton, Singleton, Bisson & Kunkee). This is why a sulfite dose depends on pH: only the undissociated molecular SO₂ is antimicrobial, and the fraction of free SO₂ that's molecular falls by a factor of ten for every unit of pH.