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1.
Dissociation Constants for Citric Acid in NaCl and KCl Solutions and their Mixtures at 25 °C 总被引:1,自引:0,他引:1
The constants for the dissociation of citric acid (H3C) have been determined from potentiometric titrations in aqueous NaCl and KCl solutions and their mixtures as a function of ionic strength (0.05–4.5 mol-dm–3) at 25 °C. The stoichiometric dissociation constants (Ki*)
were used to determine Pitzer parameters for citric acid (H3C), and the anions, H2C–, HC2–, and C3–. The thermodynamic constants (Ki) needed for these calculations were taken from the work of R. G. Bates and G. D. Pinching (J. Amer. Chem. Soc. 71, 1274; 1949) to fit to the equations (T/K):
The values of Pitzer interaction parameters for Na+ and K+ with H3C, H2C–, HC2–, and C3– have been determined from the measured pK values. These parameters represent the values of pK1*, pK2*, and pK3*, respectively, with standard errors of = 0.003–0.006, 0.015–0.016, and 0.019–0.023 for the first, second, and third dissociation constants. A simple mixing of the pK* values for the pure salts in dilute solutions yield values for the mixtures that are in good agreement with the measured values. The full Pitzer equations are necessary to estimate the values of pKi* in the mixtures at high ionic strengths. The interaction parameters found for the mixtures are Na-K – H2C = – 0.00823 ± 0.0009; Na-K – HC = – 0.0233 ± 0.0009, and Na-K – C = 0.0299 ± 0.0055 with standard errors of (pK1) = 0.011, (pK2) = 0.011, and (pK3) = 0.055. 相似文献
2.
The graphical representation of equilibrium for the isothermal and isobaric reactions of ideal gases
The equilibrium for the isothermal and isobaric reactions of ideal gases is investigated in virtue of the intuitionistic figure. The curve
is similar to the curve of tangential function which has one inflection and two vertical asymptotes. The equation
only has one root ξ e and it is suitable to find ξ e by dichotomy. For non-inert substance, when
or
x_i^0 $$" align="middle" border="0">
, to increase substance i will make an equilibrium shift in the direction to deplete substance i; when
{\nu_i} \mathord{\left/ {\vphantom {{\nu_i} {\sum_i {\nu _i}}}}
\right. \kern-\nulldelimiterspace} {\sum _i {\nu _i}}> 0$$" align="middle" border="0">
, to increase substance i will make an equilibrium shift in the direction to produce more substance i. 相似文献
3.
M. A. Ryashentseva Kh. M. Minachev V. V. Fomichev V. A. Bardin 《Russian Chemical Bulletin》1986,35(6):1120-1122
Conclusions Rhenium oxides with perovskite structure of the general formula
where BIII=Y and Sm, and Ba3LaZnReWO12 containing Re(VII), exhibit catalytic activity in hydrogenation of ethyl acetate.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1236–1238, June, 1986. 相似文献
4.
A high pressure UV-visible spectrophotometer was used to determine the dissociation constant of boric acid using an indicator technique. The measurements were made at 25°C and at ionic strengths of 0.1 and 1.0m over a pressure range of 1 to 2000 atm. Extrapolation to I=0 gave a thermodynamic dissociation constant of 5.16×10–10 at 1 atm. The pressure dependence yielded a partial molal volume change of –28.9 and –31.8 cm3-mol–1 and a compressibility change of –3.1 and –4.8×10–3 cm3-mol–1-atm–1 for the dissociation at I=0.1 and 1.0m, respectively. The association constant for the formation of the sodium borate ion pair was determined by comparing the acid constants in tetramethylammonium chloride to those in sodium chloride solutions. Extrapolation to I=0 yielded a KA for [NaB(OH)4] of 0.64 at 1 atm. The pressure dependence of KA gave
and
for the formation of the ion pair. 相似文献
5.
Ze-sheng Li Xin-wu Ba Chia-chung Sun Au-chin Tang 《Macromolecular theory and simulations》1992,1(2):91-97
For a polycondensation reaction with identical structural units AaBb (i.e. each unit has a functional groups of type A and b of type B) the kth radius of gyration $ \begin{array}{*{20}c} {\left\langle {R^2 } \right\rangle _k = \sum\limits_n {n^k \cdot \left\langle {R_n^2 } \right\rangle P_n } } & {({\rm sum over all }n{\rm - mers; see Eqs}{\rm . (11) and (17))}{\rm }} \\ \end{array} $ is investigated. By means of a differential method, a recursion formula that holds true for both the pre-gel and the post-gel state is obtained for the evaluation of the kth radius. 相似文献
6.
S. D. L'vova V. M. Kozhukhovskaya M. N. Averin R. P. Evstigneeva 《Chemistry of Natural Compounds》1973,7(4):443-444
Summary The synthesis of the hydrobromide of the tetradecapeptide HBr·H-L-
-L-Pro-L-Asp-L-Asp-L-
-L-Ser-L-Lys-'L-Ile-L-Thr-L-Lys-L-Pro-L-Ser-L-Glu-L-Ser-OH corresponding to sequence 80–93 of cytochrome B5 isolated from the microsomes of calf thymus has been synthesized by the solid-phase method.M. V. Lomonosov Moscow Institute of Fine Chemical Technology. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 466–468, July–August, 1971. 相似文献
7.
George J. Reclos Tijen Tanyalcin Kenneth A. Pass 《Accreditation and quality assurance》2006,11(6):308-312
Models based on biological variation provide a well-accepted database with reliable information for clinical laboratories for all purposes including screening, diagnosis and follow-up. Newborn screening laboratories use a blood spotted paper matrix to measure the analytes. This matrix medium is certainly different than body fluid matrix medium. After long-term monitoring of the performance of the Glucose-6-Phosphate Dehydrogenase Kit (R&D Diagnostics OSMMR 2000-D G6PD), the results obtained from the variation analysis were statistically evaluated. Analytical coefficient of variation, CV
A, was found to be 5.41%. The CV
A derived from between run assays was 5.32%, while within-subject biological coefficient of variation, CV
I, was 7.26%. Since minimum performance is defined as CV
A< 0.750 CV
I
, CV
A should be lower than 5.44%. The analytical bias in calculation of total error was chosen to evaluate the performance of this assay. In this aspect, CV
G, between-subject biological coefficient of variation, was found to be equal to 10.35%. B
A was found to be 4.12%, which is lower than 4.74%, which means that it is acceptable. Therefore, the minimum quality specification for total error allowable is
. When the relevant results obtained in this study were substituted in this formula, TE
a was found to be 13.7% for G6PD measurement in dried blood spots on paper filter matrix. It is expected that this figure will be helpful for the performance evaluation of newborn screening laboratories performing G6PD screening. We have been using error grid graphs for the evaluation of our external quality assurance survey results for the last two years, only because there was no data for assays employing filter matrix. Even the TE
a already reported for EDTA whole blood samples used in G6PD assays has been remarkably high, which can easily create the wrong impression that G6PD is not a reliable test to perform from blood spot cards. The present study shows that this assay is adequately reliable even when performed from dried blood spot matrix. However, we believe that the combination of total allowable error, error grid graphs with a well-defined cut off is the best approach to obtain an accurate performance evaluation for this test.Presented at the 10th Conference Quality in the Spotlight, March 2005, Antwerp, Belgium. 相似文献
8.
The oxidation of H2NOH is first-order both in [NH3OH+] and [AuCl4
–]. The rate is increased by the increase in [Cl–] and decreased with increase in [H+]. The stoichiometry ratio, [NH3OH+]/[AuCl4
–], is 1. The mechanism consists of the following reactions.
The rate law deduced from the reactions (i)–(iv) is given by Equation (v) considering that [H+] K
a.
The reaction (iii) is a combination of the following reactions:
The activation parameters for the reactions (ii) and (iii) are consistent with an outer-sphere electron transfer mechanism. 相似文献
9.
The solubility of boric acid [B] in LiCl, NaCl, KCl, RbCl, and CsCl was determined as a function of ionic strength (0–6 mol ⋅ kg−1) at 25 ∘C. The results were examined using the Pitzer equation
where [B]0 is the concentration of boric acid in water and [B] in solution, γB is the activity coefficient, νi is the number of ions (i), λBc, λBa are parameters related to the interaction of boric acid with cation c and anion a, ζB-a−c is related to the interaction of boric acid with both cation and anion and m is the salt molality. The literature values for the solubility of boric acid in a number of other electrolytes were also examined using the same equation. The results for the 2νcλBc+2νaλBa term (equal to the salting coefficient k
S) were examined in terms of the ionic interactions in the solutions. The solubility of boric acid in LiCl, NaCl, and KCl solutions is not a strong function of temperature and the results can be used over a limited temperature range (5–35 ∘C). Boric acid is soluble in the order SO4 > NO3 and F > Cl > Br > I in common cation solutions. In common anion salt solutions, the order is Cs > Rb > K > Na > Li > H and Ba > Sr > Ca > Mg. The results were examined using correlations of k
S with the volume properties of the ions. When direct measurements were not available, k
S and ζB-c−a were estimated from known values of λBc and λBa.The values of λBc, λBa, and ζB-a−c can be used to estimate the boric acid activity coefficients γB and solubility [B] in natural mixed electrolyte solutions (seawater and brines) using the more general Pitzer equation
相似文献
10.
Summary The oxidation of H2O2 by [W(CN)8]3– has been studied in aqueous media between pH 7.87 and 12.10 using both conventional and stopped-flow spectrophotometry. The reaction proceeds without generation of free radicals. The experimental overall rate law,
, strongly suggests two types of mechanisms. The first pathway, characterized by the pH-dependent rate constant k
s, given by
, involves the formation of [W(CN)8· H2O2]3–, [W(CN)8· H2O2·W(CN)8]6– and [W(CN)8· HO]3– intermediates in rapid pre-equilibria steps, and is followed by a one-electron transfer step involving [W(CN)8·HO]3– (k
a) and its conjugate base [W(CN)8·O]4– (k
b). At 25 °C, I = 0.20 m (NaCl), the rate constant
with H
a
=40±6kJmol–1 and S
a
=–151±22JK–1mol–1; the rate constant
with H
b
=36±1kJmol–1 and S
b
=–136±2JK–1mol–1 at 25 °C, I = 0.20 m (NaCl); the acid dissociation constant of [W(CN)8·HO]3–, K
5
=(5.9±1.7)×10–10
m, with
and
is the first acid dissociation constant of H2O2. The second pathway, with rate constant, k
f, involves the formation of [W(CN)8· HO2]4– and is followed by a formal two-electron redox process with [W(CN)8]3–. The pH-dependent rate constant, k
f, is given by
. The rate constant k
7
=23±6m
–1
s
–1 with
and
at 25°C, I = 0.20 m (NaCl). 相似文献
11.
Enrico Borgarello Jean Desilvestro Michael Grtzel Ezio Pelizzetti 《Helvetica chimica acta》1983,66(6):1827-1834
Conduction band electrons produced by band gap excitation of TiO2-particles reduce efficiently thiosulfate to sulfide and sulfite. \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm 2e}_{{\rm cb}}^ - ({\rm TiO}_{\rm 2}) + {\rm S}_{\rm 2} {\rm O}_3^{2 - } \longrightarrow {\rm S}^{2 - } + {\rm SO}_3^{2 - } $\end{document} This reaction is confirmed by electrochemical investigations with polycrystalline TiO2-electrodes. The valence band process in alkaline TiO2-dispersions involves oxidation of S2O to tetrathionate which quantitatively dismutates into sulfite and thiosulfate, the net reaction being: \documentclass{article}\pagestyle{empty}\begin{document}$ 2{\rm h}^{\rm + } ({\rm TiO}_{\rm 2}) + 0.5{\rm S}_{\rm 2} {\rm O}_{\rm 3}^{{\rm 2} - } + 1.5{\rm H}_{\rm 2} {\rm O} \longrightarrow {\rm SO}_3^{2 - } + 3{\rm H}^{\rm + } $\end{document} This photodriven disproportionation of thiosulfate into sulfide and sulfite: \documentclass{article}\pagestyle{empty}\begin{document}$ 1.5{\rm H}_{\rm 2} {\rm O } + 1.5{\rm S}_{\rm 2} {\rm O}_{\rm 3}^{{\rm 2} - } \mathop \to \limits^{h\nu} 2{\rm SO}_3^{2 - } + {\rm S}^{{\rm 2} - } + 3{\rm H}^{\rm + } $\end{document} should be of great interest for systems that photochemically split hydrogen sulfide into hydrogen and sulfur. 相似文献
12.
The enthalpies and entropies of evaporation of Al(CH3)3–Sn(CH3)4and Ga(CH3)3–Sn(CH3)4solutions were determined. It was established that solvates are formed in these systems and that the dissociation energies of specific interactions in them change in the following order:
(10.3) >
>
>
(4.08 kJ mol–1),
(6.52) >
(5.14) >
>
(4.08 kJ mol–1). 相似文献
13.
Kinetics and equilibria for the formation of a 1:1 complex between palladium(II) and chloroacetate were studied by spectrophotometric measurements in 1.00 mol HClO4 at 298.2 K. The equilibrium constant, K, of the reaction
was determined from multi-wavelength absorbance measurements of equilibrated solutions at variable temperatures as log 0.006 with and , and spectra of individual species were calculated. Variable-temperature kinetic measurements gave rate constants for the forward and backward reactions at 298.2 K and ionic strength 1.00 mol as and , with activation parameters and , respectively. From the kinetics of the forward and reverse processes, and were derived in good agreement with the results of the equilibrium measurements. Specific Ion Interaction Theory was employed for determination of thermodynamic equilibrium constants for the protonation of chloroacetate () and formation of the PdL+ complex (). Specific ion interaction coefficients were derived. 相似文献
14.
Solubility of Oxygen in Some 1-1, 2-1, 1-2, and 2-2 Electrolytes as a Function of Concentration at 25°C 总被引:1,自引:0,他引:1
The solubility of oxygen has been measured in a number of electrolytes [(LiCl, KCl, RbCl, CsCl, NaF, NaBr, NaI, NaNO3, KBr, KI, KNO3, CaCl2, SrCl2, BaCl2, Li2SO4, K2SO4, Mn(NO3)3)] as a function of concentration at 25°C. The solubilities, mol (kg-H2O)–1, have been fitted to a function of the molality m (standard deviation < 3mol-kg–1)
where A and B are adjustable parameters and the activity coefficient of oxygen )O2) = [O2]0/[O2]. The limiting salting coefficient, k
S = (ln / m)m=0 = A, was determined for all salts. The salting coefficients for the chlorides and sodium salts showed a near linear correlation with the crystal molar volume V
cryst = 2.52 r
3. The salting coefficients determined from the Scaled Particle Theory were in reasonable agreement with the measured values. The activity coefficients of oxygen in the solutions have been interpreted using the Pitzer equation
where
is a parameter that accounts for the interaction of O2 with cations (c) and anions (a) with molalities m
a and m
c, and
accounts for interactions for O2 with the cation and anion pair (c-a). The
and
coefficients determined for the most of the ions are in reasonable agreement with the tabulations of Clegg and Brimblecombe. The values of
for most of the ions are a linear function of the electrostriction molar volume (Velect = V0 – V
cryst). 相似文献
15.
16.
The integral equation method was used to study structure formation in concentrated aqueous solutions of lithium chloride in the near-critical region (P = 20 MPa, T = 298-623 K). It is found that when the LiCl–H2O system passes from a concentrated state to a melt-like one (
), some of its structural characteristics change oppositely depending on temperature, leading to anomalous structural properties of the most concentrated solution. Analyzing the temperature dependence of coordination numbers we established the temperature range and the steps of structural changes in the LiCl–H2O system. 相似文献
17.
Molecular structures and vibrational spectra of ScF3, YF3, and LaF3 were studied by the Hartree–Fock– Roothaan method in terms of second-order Möller–Plesset perturbation theory and by the configuration interaction method including all singly and doubly excited configurations and Davidson's correction for quartic excitations (CISD+Q). The atomic core orbitals are defined in terms of the effective relativistic potentials suggested by Stevens et al. The equilibrium nuclear configuration is shown to be planar (D
3h
symmetry) for ScF3 and YF3 and pyramidal (C
3v
) for LaF3 with a bond angle
. The inversion barrier of LaF3 is very low: h = E(D
3h
)- E(C
3v
) = 38 cm
–1
(CISD+Q). The vibrational spectra were calculated by the variational method using the vibrational Hamiltonian describing the nonrigidity of a molecule with respect to out-of-plane deformation. The calculation results are compared with the previously published experimental data. The IR band assignments for matrix-isolated molecular conformations in a vapor over yttrium trifluoride were corrected. 相似文献
18.
The kinetics and mechanism of the reduction of enneamolybdonickelate(IV) by iodide in acid aqueous solution was studied by spectrophotometry. The reaction rate increases, as the concentration of H+ increases and with temperature. It shows that the reaction rate law is
The reaction rate constants and activation parameters of the rate-determining steps were evaluated. A mechanism related to the reaction is proposed. 相似文献
19.
Jan H. van Driel Wigger Heerma Johan K. Terlouw Herman Halim Helmut Schwarz 《Journal of mass spectrometry : JMS》1985,20(11):665-673
Evidence is presented for the gas phase generation of at least eight stable isomeric [C2H7O2]+ ions. These include energy-rich protonated peroxides (ions \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH}_2 {\rm O}\mathop {\rm O}\limits^{\rm + } {\rm H}_{\rm 2} $\end{document} (e), \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH}_{\rm 2} \mathop {\rm O}\limits^{\rm + } {\rm (H)OH} $\end{document} (f) and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm O}\mathop {\rm O}\limits^{\rm + } {\rm (H)CH}_{\rm 3} {\rm (g)),} $\end{document} (g)), proton-bound dimers (ions \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH = O} \cdot \cdot \cdot \mathop {\rm H}\limits^{\rm 3} \cdot \cdot \cdot {\rm OH}_{\rm 2} $\end{document} (h) and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH2 = O} \cdot \cdot \cdot \mathop {\rm H}\limits^{\rm + } \cdot \cdot \cdot {\rm HOCH}_{\rm 3} $\end{document} (i)) and hydroxy-protonated species (ions \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 2} {\rm (OH)CH}_{\rm 2} \mathop {\rm O}\limits^{\rm + } {\rm H}_{\rm 2} (a), $\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH(OH)}\mathop {\rm O}\limits^{\rm + } {\rm H}_{\rm 2} $\end{document} (b) and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm OCH}_{\rm 2} \mathop {\rm O}\limits^{\rm + } {\rm H}_{\rm 2} $\end{document} (c)). The important points of the present study are (i) that these ions are prevented by high barriers from facile interconversion and (ii) that both electron-impact- and proton-induced gas phase decompositions seem to proceed via multistep reactions, some of which eventually result in the formation of proton-bound dimers. 相似文献
20.
G. Wiese und B. Thiele 《Fresenius' Journal of Analytical Chemistry》1978,289(4):272-274
Zusammenfassung Die für eine Verwendung in wäß-rigem Medium erarbeitete Schnellmethode wird auf organische Lösungsmittel (Methanol) übertragen. Mit Hilfe statistischer Prüfmethoden wird gezeigt, daß für die Reaktion des Typs: Z–NH2+HCl Z–NH3
++Cl– (Z–NH2: Propylamin, Anilin, Piperidin) unter den Verfahrensbedingungen der Schnellmethode in methanolischer Lösung eine Äquivalenzpunktbestimmung mit hinreichender Genauigkeit möglich ist [Prozentualer Fehler von
] und daß zwischen Langzeit- und Schnellmethode kein signifikanter Genauigkeitsunterschied besteht.Wir danken dem Fonds der Chemischen Industrie für die finanzielle Unterstützung dieser Arbeit. 相似文献