High-Temperature Raman Investigation of Concentrated Sulfuric Acid Mixtures:  Measurement of H-Bond ΔH Values between H₃O⁺ or H₅O₂⁺ and HSO₄^-

Abstract

Forty-two mol percent sulfuric acid is a room-temperature molten salt composed of H-bonded ion pairs H 3 O + -HSO 4 -(8.2 M) and H 5 O 2 + -HSO 4 -(5.4 M), the former breaking primarily below ∼360 °C and the latter, mainly between ∼360 °C and the critical point. These ruptures produce H 2 SO 4 and H 2 O. Iterative van't Hoff thermodynamic analysis of Raman spectra to 360 °C employing peak height or component area ratios at ∼905 and ∼1035 cm -1 or at ∼1165 and ∼1035 cm -1 yielded an average ∆H of 3.2 ( 0.2 kcal/mol corresponding to H-bond breakage between H 3 O + and HSO 4 -. A Raman ∆H of 5.9 ( 0.3 kcal/mol was measured for the rupture of H 5 O 2 + -HSO 4 -H-bonds between 360 and 513 °C Versus ∼5.7 kcal/mol calculated. H-bonds exist between species other than the two hydronium-bisulfate ion pairs but are not measured by the Raman H 2 SO 4 /HSO 4intensity ratios. Hydrogen bonding wanes near the critical point, ∼665 °C, at which only neutral species, H 2 SO 4 and H 2 O (plus some SO 3 ), remain. A ∆H of 3.5 ( 0.4 kcal/mol was also measured from the 87 mol % acid, close enough to the 3.2 ( 0.2 kcal/mol value to assign both to H 3 O + -HSO 4and also because H 5 O 2 + cannot form in the 87 mol % solution. The integral heat of solution (42 mol %) calculated using Raman data for the two hydronium-bisulfate ion pairs is consistent with the calorimetric value. Values of the dielectric constant were also estimated from Raman data.

Sulfates on Mars: A systematic Raman spectroscopic study of hydration states of magnesium sulfates

“…The middle three spectra in Fig. 2 (Walrafen and Young, 1960;Young and Walrafen, 1961;Walrafen et al, 2002).…”

Evaluation of time-gated Raman spectroscopy for the determination of nitric, sulfuric and hydrofluoric acid concentrations in pickle liquor

“…11 These findings are in agreement with previous reports. [9][10][11][12] Linear dependence between the intensity of Raman scattering and concentration was observed for both HNO3 and H2SO4. Although the responses seemed linear even when analyzing solutions containing both HNO3 and H2SO4, sulfuric acid produces some Raman scattering (HSO4 -(ν3) and (ν4) modes) at the HNO3 1042 cm -1 wavenumber region.…”

“…Although the responses seemed linear even when analyzing solutions containing both HNO3 and H2SO4, sulfuric acid produces some Raman scattering (HSO4 -(ν3) and (ν4) modes) at the HNO3 1042 cm -1 wavenumber region. 9,10,12,13 Hence a multivariate model might be a more suitable data analysis method in part because of this (discussed more in depth later). Any Raman peaks correlating with sample HF concentration were not observed with the time-gated Raman spectrometer used.…”

Refined electrolyte‐NRTL model: Activity coefficient expressions for application to multi‐electrolyte systems

“…Attempts to model the sulfuric acid system have led to accurate thermodynamic representations of the system, 13-17 but these are deficient in the prediction of speciation. Considering the complexity of the aqueous sulfuric acid system and the large number of proton hydrates that can exist in this solution, 18 it is indeed an intriguing problem to predict the speciation. At low electrolyte concentrations, hydration can be considered of constant extent, but with increasing concentration the decreasing extent of hydration can be the dominating factor in the accuracy of model predictions.…”

“…Because of its high importance the aqueous sulfuric acid solution has been extensively studied experimentally during the last century. These works can be categorized as vapor pressure, osmotic coefficient and activity coefficient measurements, 8,36-41 speciation measurements 8,18,35,39,[42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59] and thermal properties measurements. …”