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Issue 7, 2015
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Structure and ionization of sulfuric acid in water

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Abstract

Newly recorded Raman spectra of aqueous sulfuric acid provide scattering shifts of very high sensitivity hence signal-to-noise ratios, at a broad concentration range, up to 17 M. I interpret the spectra as (a) providing no evidence for incomplete H2SO4 ionization at low concentration, (b) reflecting only one dissociation event below ∼5 M, (c) indicating a gradual ion association at ∼5–12.5 M, and (d) exhibiting further structural changes of the sulfate above 12.5 M. The analysis of the Raman shifts supports the postulated presence in solution of the para-bisulfate anion HSO53− as a sole sulfate ion up to ∼5 M, as concluded before (D. Fraenkel, J. Phys. Chem. B, 2012, 116, 11662; D. Fraenkel, J. Phys. Chem. B, 2012, 116, 11678; D. Fraenkel, J. Chem. Thermodyn., 2014, 78, 215), an ion association producing para-sulfuric acid, H4SO5 between 5 and 12.5 M, and a dehydration of H4SO5 to H2SO4 above 12.5 M. These conclusions are rationalized and corroborated by (1) a correlation of the Raman spectra with well-known physicochemical properties of aqueous sulfuric acid, and (2) structural analogies between the proposed para-sulfates and related compounds and anions.

Graphical abstract: Structure and ionization of sulfuric acid in water

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Article information


Submitted
23 Jan 2015
Accepted
24 Mar 2015
First published
25 Mar 2015

New J. Chem., 2015,39, 5124-5136
Article type
Paper
Author version available

Structure and ionization of sulfuric acid in water

D. Fraenkel, New J. Chem., 2015, 39, 5124
DOI: 10.1039/C5NJ00167F

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