Do Doubly Charged Monatomicanions Exist in Aqueous Solutions?
Journal Title: Archives of Organic and Inorganic Chemical Sciences - Year 2018, Vol 2, Issue 2
Abstract
The chalcogenide atoms (X = oxygen, sulfur, selenium, tellurium, polonium) form doubly charged monatomic anions, X2-, which exist in crystalline salts. The question arises whether, once such salts are dissolved in water, such species persist, or do they hydrolyze completely to form the hydrochalcogenide anion: X2- + H2ODHX-+ OH - (1) It is clear that in the case of oxygen this reaction proceeds to the right to completion: O2- + H2O → 2OH-. Recently it was shown that also in the case of sulfur the anion S2- does not exist in aqueous solutions [1]. In attempts to push reaction (1) backwards by the addition of massive quantities (high concentrations) of hydroxyl ions, the necessarily added cations (say, Na+)associate with the sulfide anion, yielding the ion pairs (NaS(H2O)p-), but not S(H2O) n2-. On the other hand, spectroscopic evidence shows that the corresponding addition of CsOH does not yieldthe hydrated sulfide dianions either. It was concluded that the doubly charged hydrated sulfide anions S(H2O)n2- do not exist. It is therefore of interest to examine whether the reported evidence related to the existence of hydrated selenide Se(H2O) n2- and telluride Te(H2O)n2- anions in aqueous solutions can be reinterpreted in terms that negate their existence. The evidence concerning the aqueous selenide and telluride dianions pertains to calculations of the second dissociation constant of hydrogen selenide and telluride or the dissociation constant of the aqueous hydroselenide and hydrotelluride anions, K2: Lupinepublishers-openaccessjournals-chemical-science The existence of the dianions Se2- and Te2- in aqueous solutions was assumed a priori in earlier publications as a matter of course. In the polarographic study of the anodic oxidation of H2X [2] it was stated that no experimental value of K2 (for dissociation of HSe- and HTe) was available, so a value was assumed (10-14 and 10-11, respectively) in order to fit the half-wave potentials up to pH = 13.9 (1 M NaOH), but no fit was tried with the value K2 = 0. For the telluride anion there was the added complication that the anodic oxidationresulted in the intermediate formation of elemental tellurium that yields theditelluride anion Te22-, which is then further oxidized. In fact, the polarography of the ditelluridedianion was studied in [3] in aqueous 0.01, 0.1 and 1.0 M NaOH (translated to pH = 12, 13, and 14) on the assumption that the disproportionation Te22-DTe + Te2- takes place, but, again, the nature of the reduced telluride species was not established. What was established was that the polarographic electrode reaction corresponded to a two electron change: H2TeDTe + 2H ++ 2e“ .
Authors and Affiliations
Yizhak Marcus
Keywords
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- EP ID EP602967
- DOI 10.32474/AOICS.2018.02.000134
- Views 70
- Downloads 0
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