Ionization of moderately strong acids in aqueous solution. Part 2.—Further E.m.f. studies of the dissociation of the bisulphate ion

Abstract

New measurements on the cell: Pt,H₂∣ Na₂SO₄, NaHSO₄, NaCl ∣ AgCl ∣ Ag have failed to substantiate the original measurements made by Hamer forty years ago and subsequently reanalysed many times. The range of values for the dissociation constant of the bisulphate ion (K₂ of sulphuric acid) is substantially in agreement with that obtained from the simpler cell in which sodium chloride was omitted and the mercury-mercury(I) sulphate reference electrode was used. K₂= 0.0113 ± 0.0005 mol kg^–1 at 25°C where the uncertainty arises from a range of reasonable choices for the ion-size parameter.