| 1. |
- Bodor, A., et al.
(författare)
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F-19 NMR study of the equilibria and dynamics of the Al3+/F- system
- 2000
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 39:12, s. 2530-2537
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Tidskriftsartikel (refereegranskat)abstract
- A careful reinvestigation by high-field F-19 NMR (470 MHz) spectroscopy has been made of the Al3+/F- system in aqueous solution under carefully controlled conditions of pH, concentration, ionic strength (I), and temperature. The F-19 NMR spectra show five distinct signals at 278 K and I = 0.6 M (TMACl) which have been attributed to the complexes AlFi(3-i)+(aq) with i less than or equal to 5. There was no need to invoke AlFi(OH)(j)((3-i-j)+) mixed complexes in the model under our experimental conditions (pH less than or equal to 6.5), nor was any evidence obtained for the formation of AlF63-(aq) at very high ratios of F-/Al3+. The stepwise equilibrium constants obtained for the complexes by integration of the F-19 signals are in good agreement with literature data given the differences in medium and temperature. In I = 0.6 M TMACl at 278 K and in I = 3 M KCl at 298 K the log K-i values are 6.42, 5.31, 3.99, 2.50, and 0.84 (for species i = 1-5) and 6.35, 5.25, and 4.11 (for species i = 1-3), respectively. Disappearance of the F-19 NMR signals under certain conditions was shown to be due to precipitation. Certain 19F NMR signals exhibit temperature- and concentration-dependent exchange broadening. Detailed line shape analysis of the spectra and magnetization transfer measurements indicate that the kinetics are dominated by F- exchange rather than complex formation. The detected reactions and their rate constants are AlF22+ + *F- reversible arrow AIF*F2+ + F- (k(02) = (1.8 +/- 0.3) x 10(6) M-1 s(-1)), AlF30 + *F- reversible arrow (AlF2F0)-F-* + F- (k(03) = (3.9 +/- 0.9) x 10(6) M-1 s(-1)), and AlF30 + H*F reversible arrow AlF2*F-0 + HF (k(03)(H) = (6.6 +/- 0.5) x 10(4) M-1 s(-1)). The rates of these exchange reactions increase markedly with increasing F- substitution. Thus, the reactions of AlF2+(aq) were too inert to be detected even on the T-1 NMR time scale, while some of the reactions of AlF30(aq) were fast, causing large line broadening. The ligand exchange appears to follow an associative interchange mechanism. The cis-trans isomerization of AlF2+(aq), consistent with octahedral geometry for that complex, is slowed sufficiently to be observed at temperatures around 270 R. Difference between the Al3+/F- system and the much studied Al3+/OH- system are briefly commented on.
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| 2. |
- Powell, KJ, et al.
(författare)
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Chemical speciation of Hg(II) with environmental inorganic ligands
- 2004
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Ingår i: AUSTRALIAN JOURNAL OF CHEMISTRY. - 0004-9425. ; 57:10, s. 993-1000
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Tidskriftsartikel (refereegranskat)abstract
- Complex formation between Hg(II) and the common environmental ligands Cl-, OH-, CO32-, SO42-, and PO43- can have profound effects on Hg(II) speciation in naturalwaters with low concentrations of organic matter. Hg(II) is labile, so its distribution among these inorganic ligands can be estimated by numerical modelling if reliable values for the relevant stability constants are available. A summary of critically reviewed constants and related thermodynamic data is presented. Recommended values of log(10) beta(p,q,r)(o) and the associated reaction enthalpies, Delta(r)H(m)(o), valid at I-m = 0 mol kg(-1) and 25degreesC, along with the equations and specific ion interaction coefficients required to calculate log(10) beta(p,q,r) values at higher ionic strengths and other temperatures are also presented. Under typical environmental conditions Hg(II) speciation is dominated by the reactions Hg2+ + 2Cl(-) reversible arrow HgCl2(aq) (log(10) beta(2)(o) = 14.00 +/- 0.07), Hg2+ + Cl- + H2O reversible arrow Hg(OH) Cl(aq) + H+ (log(10) beta(o) = 4.27 +/- 0.35), and Hg2+ + 2H(2)O reversible arrow Hg(OH)(2(aq)) + 2H(+) (log(10)* beta(2)(o) =- 5.98 +/- 0.06).
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| 3. |
- Vielma, T., et al.
(författare)
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A Volumetric Pitzer Model for Aqueous Solutions of Zinc Sulfate up to Near-Saturation Concentrations at Temperatures from 293.15 to 393.15 K and Pressures up to 10 MPa
- 2021
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Ingår i: Journal of Chemical and Engineering Data. - : American Chemical Society. - 0021-9568 .- 1520-5134. ; 66:1, s. 58-64
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Tidskriftsartikel (refereegranskat)abstract
- Literature data for the volumetric properties of aqueous solutions of zinc sulfate have been compiled and compared with extensive recently available measurements. A semi-empirical Pitzer model has been derived from these data that reproduces the apparent molar volumes and compressibilities of zinc sulfate solutions with good accuracy to near-saturation concentrations (m 3.0 mol·kg-1) over the temperature range 293.15 ≤ T/K ≤ 393.15 and at pressures up to 10 MPa, using standard volumes, V°, obtained by additivity of ionic values from the literature. By including the dependence of V° on the compressibility of pure water, the model was able to predict apparent molar volumes with good accuracy even up to 100 MPa at 298 K. Of potential use for engineering applications, imposition of the inequality (-2Vφ/-T2)p,m < 0 to the Pitzer model has created the possibility of physically reasonable extrapolations to temperatures well beyond the parameterization range. © 2020 American Chemical Society.
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