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Conductometric analysis of the second acid dissociation constant of H2S in highly concentrated aqueous media

1991; Elsevier BV; Volume: 318; Issue: 1-2 Linguagem: Inglês

10.1016/0022-0728(91)85298-4

2590-2954

Stuart Licht, Kevin Longo, Dharmasena Peramunage, Fardad Forouzan,

Industrial Gas Emission Control

Discrepancies by a factor of 105 have been reported for the fundamental S2− aqueous acid equilibrium constant which acts as a cornerstone for the foundation of aqueous metal sulphide thermochemistry. We report the conductometric determination of the Gibbs free energy and the acid equilibrium constant for S2−aq,K2: Uncertainty in K2 directly affects solubility, thermodynamic and redox potential values of each of the metal sulphides. Unlike previous investigations, the conductometric measurements determine the extent of free OH− in solution directly. This study is performed in unusually concentrated media, and makes conventional use of the anomalously high equivalent conductance of hydroxide compared with other anions. The differential conductometric measurements and conductometric titrations reported here demonstrate that hydroxide resists dehydrolysis in solutions containing less than 3 M hydrosulphide and hydroxide, and the equilibrium: A solution containing 6.4 M KHS and 6.4 M KOH, a solution with a pH of approximately 17, is shown (i) to contain comparable concentrations of free S2−, HS− and OH− species, (ii) to have an ionic conductance for free sulphide of λ 12s2−= 0.87 λHS−, and (iii) to affirm that aqueous sulphide salt thermodynamics, solubilities and rest potentials are limited by HS− and not S2− chemistry.