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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.
[
\textTp\textMe2 {\text{Tp}}^{{{\text{Me}}_{2} }} ]M (M = K, Tl) reacts with “GaI” to give a series of compounds that feature Ga–Ga bonds, namely [
\textTp\textMe2 {\text{Tp}}^{{{\text{Me}}_{2} }} ]Ga→GaI3, [
\textTp\textMe2 {\text{Tp}}^{{{\text{Me}}_{2} }} ]GaGaI2GaI2(
\textHpz\textMe2 {\text{Hpz}}^{{{\text{Me}}_{2} }} ) and [
\textTp\textMe2 {\text{Tp}}^{{{\text{Me}}_{2} }} ]Ga(GaI2)2Ga[
\textTp\textMe2 {\text{Tp}}^{{{\text{Me}}_{2} }} ], in addition to the cationic, mononuclear Ga(III) complex {[
\textTp\textMe2 {\text{Tp}}^{{{\text{Me}}_{2} }} ]2Ga}+. Likewise, [
\textTp\textMe2 {\text{Tp}}^{{{\text{Me}}_{2} }} ]M (M = K, Tl) reacts with (HGaCl2)
2
and Ga[GaCl4] to give [
\textTp\textMe2 {\text{Tp}}^{{{\text{Me}}_{2} }} ]Ga→GaCl3, {[
\textTp\textMe2 {\text{Tp}}^{{{\text{Me}}_{2} }} ]2Ga}[GaCl4], and {[
\textTp\textMe2 {\text{Tp}}^{{{\text{Me}}_{2} }} ]GaGa[
\textTp\textMe2 {\text{Tp}}^{{{\text{Me}}_{2} }} ]}[GaCl4]2. The adduct [
\textTp\textMe2 {\text{Tp}}^{{{\text{Me}}_{2} }} ]Ga→B(C6F5)3 may be obtained via treatment of [
\textTp\textMe2 {\text{Tp}}^{{{\text{Me}}_{2} }} ]K with “GaI” followed by addition of B(C6F5)3. Comparison of the deviation from planarity of the GaY3 ligands in [
\textTp\textMe2 {\text{Tp}}^{{{\text{Me}}_{2} }} ]Ga→GaY3 (Y = Cl, I) and [
\textTm\textBu\textt {\text{Tm}}^{{{\text{Bu}}^{\text{t}} }} ]Ga→GaY3, as evaluated by the sum of the Y–Ga–Y bond angles, Σ(Y–Ga–Y), indicates that the [
\textTm\textBu\textt {\text{Tm}}^{{{\text{Bu}}^{\text{t}} }} ]Ga moiety is a marginally better donor than [
\textTp\textMe2 {\text{Tp}}^{{{\text{Me}}_{2} }} ]Ga. In contrast, the displacement from planarity for the B(C6F5)3 ligand of [
\textTp\textMe2 {\text{Tp}}^{{{\text{Me}}_{2} }} ]Ga→B(C6F5)3 is greater than that of [
\textTm\textBu\textt {\text{Tm}}^{{{\text{Bu}}^{\text{t}} }} ]Ga→B(C6F5)3, an observation that is interpreted in terms of interligand steric interactions in the former complex compressing the C–B–C
bond angles. 相似文献
3.
Jerry Ray Dias 《Journal of mathematical chemistry》2010,48(2):313-329
The systematics of fluoranthenoid/fluorenoid and indacenoid hydrocarbons is studied. Successive circumscribing a set of isomeric
structures that result in a constant number of isomers at each circumscribing step gives what is called a constant-isomer
series. Constant-isomer series have a repetitive isomer number pattern in which those series with the same isomer number have
a one-to-one matching in topology among their membership. The general formulas of the matching constant-isomer sets of indacenoids
are reproduced by C4p2+1H4p+1{{\rm C}_{{{4p}^{2}}{+1}}{\rm H}_{4p+1}} and C4p2+4p+3H4p+3{{\rm C}_{{{4p}^{2}}{+4p+3}}{\rm H}_{4p+3}}, respectively, by successively inputting p = 1, 2, 3, . . ., and the general formula for the unique indacenoid constant-isomers is reproduced by Cp2+3p+4H2p+4{{\rm C}_{{p^{2}}{+3p+4}}{\rm H}_{2p+4}}. Similar general formulas for the fluoranthenoid/fluorenoid hydrocarbon constant-isomer series are also presented. 相似文献
4.
Nikos G. Tsierkezos Athanassios I. Philippopoulos Uwe Ritter 《Journal of solution chemistry》2009,38(12):1536-1557
The molar conductivities (Λ) of solutions of bis(2,2′-bipyridine)bis(thiocyanate)chromium(III) triiodide [CrIII(bipy)2(SCN)2]I3 (where bipy denotes 2,2′-bipyridine, C10H8N2), [
_3^-\mathrm{A}^{+}\mathrm{I}_{3}^{-}
], were measured in acetonitrile (ACN) at the temperatures 294.15, 299.15, and 305.15 K. In addition, cyclic voltammograms
(CVs) of [
A+I3-\mathrm{A}^{+}\mathrm{I}_{3}^{-}
] were recorded on platinum, gold, and glassy carbon working electrodes in ACN, using n-tetrabutylammonium hexafluorophosphate (NBu4PF6) as the supporting electrolyte, at scan rates (v) ranging from 0.05 to 0.12 V⋅s−1. Furthermore, electrochemical impedance spectroscopic (EIS) measurements were carried out in the frequency range 50 Hz<f<50 kHz using these three working electrodes. The measured molar conductivities (Λ) demonstrate that [
A+I3-\mathrm{A}^{+}\mathrm{I}_{3}^{-}
] behaves as uni-univalent electrolyte in ACN over the investigated temperature range. The Λ values were analyzed by means of the Lee-Wheaton conductivity equation in order to estimate the limiting molar conductivities (Λ
o), as well as the thermodynamic association constants (K
A), at each experimental temperature for formation of [A+
I3-\mathrm{I}_{3}^{-}
] ion-pairs. The limiting ionic conductivities (
l±o\lambda_{\pm}^{\mathrm{o}}
), the diffusion coefficients at infinite dilution (D
±), as well as the Stokes’ radii (r
St) were determined for both A+ and
I3-\mathrm{I}_{3}^{-}
ions. The thermodynamic parameters for the ionic association process, i.e. the Gibbs energy (
DGAo\Delta G_{\mathrm{A}}^{\mathrm{o}}
), enthalpy (
DHAo\Delta H_{\mathrm{A}}^{\mathrm{o}}
), and entropy (
DSAo\Delta S_{\mathrm{A}}^{\mathrm{o}}
), were also determined. The mobility and diffusivity of the A+ ion increase linearly with increasing temperature because the solvent medium becomes less viscous as the temperature increases.
The K
A values indicate that significant ion association occurs that is not influenced by temperature changes. The ion-pair formation
process is exothermic (
DHAo < 0\Delta H_{\mathrm{A}}^{\mathrm{o}}<0
), leading to the generation of additional entropy (
$\Delta S_{\mathrm{A}}^{\mathrm{o}}>0$\Delta S_{\mathrm{A}}^{\mathrm{o}}>0
). As a result, the Gibbs energy
DGAo\Delta G_{\mathrm{A}}^{\mathrm{o}}
is negative (
DGAo < 0\Delta G_{\mathrm{A}}^{\mathrm{o}}<0
) and the formation of
[A+I3-][\mathrm{A}^{+}\mathrm{I}_{3}^{-}]
becomes favorable. CV studies on
[A+I3-][\mathrm{A}^{+}\mathrm{I}_{3}^{-}]
solutions indicated that the redox pair Cr3+/2+ appears to be quasi-reversible on a glassy carbon electrode but is completely irreversible on platinum and gold electrodes.
EIS experiments confirm that, among these three electrodes, the glassy carbon working electrode has the smallest resistance
to electron transfer. 相似文献
5.
Sargunam Caleb Noble Chandar Kannappan Santhakumar Mahadevimangalam Narayanasamy Arumugham 《Transition Metal Chemistry》2009,34(8):841-848
Twelve surfactant Schiff base ligands were synthesized from salicylaldehyde and its chloro-, bromo- and methoxy- derivatives
by condensation with long-chain aliphatic primary amines, and a number of mixed ligand cobalt(III) surfactant Schiff base
coordination complexes of the type [Co(trien)A]2+ were synthesized from the corresponding dihalogeno complexes by ligand substitution. The Schiff bases and their complexes
were characterized by physico-chemical and spectroscopic methods. The complexes form foams in aqueous solution upon shaking.
The critical micelle concentration (CMC) values of the complexes in aqueous solution were obtained from conductance measurements.
Specific conductivity data (at 303–323 K) served for the evaluation of the thermodynamics of micellization (
\Updelta G\textm0 \Updelta G_{\text{m}}^{0} ,
\Updelta H\textm0 \Updelta H_{\text{m}}^{0} ,
\Updelta S\textm0 \Updelta S_{\text{m}}^{0} ). The complexes were tested for its antimicrobial activity. 相似文献
6.
Paola Antoniotti Claudio Carra Andrea Maranzana Glauco Tonachini 《Theoretical chemistry accounts》2007,118(1):253-264
In two stable structures have a trigonal bipyramidal arrangement around Ge, with the extra electron in equatorial (tbp eq) or
axial (tbp ax) position. In only tbp ax is found, while a second structure with a tetrahedral germyl group has the extra electron on the conjugated π
system. C−Ge bond cleavage yields allyl/ pentadienyl radicals plus germide. Both dissociation reactions require 4–6 kcal mol−1, less than the analogous C and Si systems (ca. 30 and 14 kcal mol−1, respectively). Fragmentation is dramatically activated with respect to homolysis in the corresponding neutrals. The wavefunction
is dominated by one single configuration at all distances, in contrast to homolytic cleavage, in which two configurations
are important. C−Ge bond dissociation is at variance also with heterolysis, due to spin recoupling of one of the C−Ge bond
electrons with the originally unpaired electron.
Contribution to the Fernando Bernardi Memorial Issue. 相似文献
7.
Water Oxidation Catalysis by Synthetic Manganese Oxides with Different Structural Motifs: A Comparative Study 下载免费PDF全文
Carolin E. Frey Prof. Dr. Philipp Kurz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(42):14958-14968
Manganese oxides are considered to be very promising materials for water oxidation catalysis (WOC), but the structural parameters influencing their catalytic activity have so far not been clearly identified. For this study, a dozen manganese oxides (MnOx) with various solid‐state structures were synthesised and carefully characterised by various physical and chemical methods. WOC by the different MnOx was then investigated with Ce4+ as chemical oxidant. Oxides with layered structures (birnessites) and those containing large tunnels (todorokites) clearly gave the best results with reaction rates exceeding 1250 ${{\rm{mmol}}_{{\rm{O}}_{\rm{2}} } }$ ${{\rm{mol}}_{{\rm{Mn}}}^{ - 1} }$ h?1 or about 50 μmolO2 m?2 h?1. In comparison, catalytic rates per mole of Mn of oxides characterised by well‐defined 3D networks were rather low (e.g., ca. 90 ${{\rm{mmol}}_{{\rm{O}}_{\rm{2}} } }$ ${{\rm{mol}}_{{\rm{Mn}}}^{ - 1} }$ h?1 for bixbyite, Mn2O3), but impressive if normalised per unit surface area (>100 ${{\rm{{\rm \mu} mol}}_{{\rm{O}}_{\rm{2}} } }$ m?2 h?1 for marokite, CaMn2O4). Thus, two groups of MnOx emerge from this screening as hot candidates for manganese‐based WOC materials: 1) amorphous oxides with tunnelled structures and the well‐established layered oxides; 2) crystalline MnIII oxides. However, synthetic methods to increase surface areas must be developed for the latter to obtain good catalysis rates per mole of Mn or per unit catalyst mass. 相似文献
8.
The molar enthalpies of solution of 2-aminopyridine at various molalities were measured at T=298.15 K in double-distilled water by means of an isoperibol solution-reaction calorimeter. According to Pitzer’s theory,
the molar enthalpy of solution of the title compound at infinite dilution was calculated to be DsolHm¥ = 14.34 kJ·mol-1\Delta_{\mathrm{sol}}H_{\mathrm{m}}^{\infty} = 14.34~\mbox{kJ}\cdot\mbox{mol}^{-1}, and Pitzer’s ion interaction parameters bMX(0)L, bMX(1)L\beta_{\mathrm{MX}}^{(0)L}, \beta_{\mathrm{MX}}^{(1)L}, and CMXfLC_{\mathrm{MX}}^{\phi L} were obtained. Values of the relative apparent molar enthalpies (
φ
L) and relative partial molar enthalpies of the compound ([`(L)]2)\bar{L}_{2}) were derived from the experimental enthalpies of solution of the compound. The standard molar enthalpy of formation of the
cation C5H7N2 +\mathrm{C}_{5}\mathrm{H}_{7}\mathrm{N}_{2}^{ +} in aqueous solution was calculated to be DfHmo(C5H7N2+,aq)=-(2.096±0.801) kJ·mol-1\Delta_{\mathrm{f}}H_{\mathrm{m}}^{\mathrm{o}}(\mathrm{C}_{5}\mathrm{H}_{7}\mathrm{N}_{2}^{+},\mbox{aq})=-(2.096\pm 0.801)~\mbox{kJ}\cdot\mbox{mol}^{-1}. 相似文献
9.
The molality dependence of specific conductivity of pentadecyl bromide, cetylpyridinium bromide and cetylpiridinium chloride
in aqueous solutions has been studied in the temperature range of 30–45 °C. The critical micelle concentration (cmc) and ionization
degree of the micelles, β, were determined directly from the experimental data. Thermal parameters, such as standard Gibbs free energy
\Updelta Gm0 , \Updelta G_{m}^{0} , enthalpy
\Updelta Hm0 \Updelta H_{m}^{0} and entropy
\Updelta Sm0 , \Updelta S_{m}^{0} , of micellization were estimated by assuming that the system conforms to the pseudo-phase separation model. The change in
heat capacity on micellization
\Updelta Cp , \Updelta C_{p} , was estimated from the temperature dependence of
\Updelta Hm0 . \Updelta H_{m}^{0} . An enthalpy–entropy compensation phenomenon for the studied system has been found. 相似文献
10.
Ponnusamy Sami Kandasamy Venkateshwari Natarajan Mariselvi Arunachalam Sarathi Kasi Rajasekaran 《Transition Metal Chemistry》2010,35(2):137-142
l-cysteine undergoes facile electron transfer with heteropoly 10-tungstodivanadophosphate,
[ \textPV\textV \textV\textV \textW 1 0 \textO 4 0 ]5 - , \left[ {{\text{PV}}^{\text{V}} {\text{V}}^{\text{V}} {\text{W}}_{ 1 0} {\text{O}}_{ 4 0} } \right]^{5 - } , at ambient temperature in aqueous acid medium. The stoichiometric ratio of [cysteine]/[oxidant] is 2.0. The products of the
reaction are cystine and two electron-reduced heteropoly blue, [PVIVVIVW10O40]7−. The rates of the electron transfer reaction were measured spectrophotometrically in acetate–acetic acid buffers at 25 °C.
The orders of the reaction with respect to both [cysteine] and [oxidant] are unity, and the reaction exhibits simple second-order
kinetics at constant pH. The pH-rate profile indicates the participation of deprotonated cysteine in the reaction. The reaction
proceeds through an outer-sphere mechanism. For the dianion −SCH2CH(NH3
+)COO−, the rate constant for the cross electron transfer reaction is 96 M−1s−1 at 25 °C. The self-exchange rate constant for the
- \textSCH2 \textCH( \textNH3 + )\textCOO - \mathord