首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 32 毫秒
1.
The weak association between sodium and carbonate ions has been investigated at 25°C using high-precision sodium ion-selective electrode potentiometry in solutions of ionic strength ranging from 0.5 to 7.0 M in CsCl and in 1.0 M Me4NCl media. The protonation constants of CO 3 2- (aq) were also measured, using a H+-responsive glass electrode in 1.0 M Me4NCl and NaCl. The value of the ion-pair association constant calculated from the difference in the protonation constants in these two media was in excellent agreement with that obtained from the Na+ISE measurements. Evidence is also presented for the formation of extremely weak ion pairs between Na+ and HCO 3 - and between Cs+ and CO 3 2- .  相似文献   

2.
The association constant for the reaction: has been measured at 25°C using magnesium ion-selective electrode (Mg–ISE) potentiometry in aqueous solutions of ionic strength (I) ranging from 0.25 to 6 M in CsCl and in 1 M (Me4NCl). The value of log (MgSO4) = 0.98 ± 0.02 in 1 M (Me4NCl) was significantly higher than that of 0.75 ± 0.01 obtained in 1 M(CsCl). This difference can be explained by a weak association between Cs+and SO 4 2- , with log (CsSO 4 - ) = –0.11 ± 0.03, which is also qualitatively consistent with the absence of an increase in (MgSO4) at high ionic strength in CsCl media. Extrapolation of the results in CsCl media gave an infinite dilution value of log ° (MgSO4) = 2.38 ± 0.03 that was rather dependent on the nature of the extrapolation function. The performance of the Mg–ISE in various media is also briefly described.  相似文献   

3.
Measurements by fluoride ion-selective electrode potentiometry on the very weak monofluoride complexes of the alkali metal ions in aqueous solution at 25°C and an ionic strength of 1M indicate their stability constants lie in the order Li+ > Na+ > K+ > Rb+ ? Cs+. Data at varying ionic strengths and temperatures were used to calculate infinite dilution stability constants and enthalpies and entropies of complexation for LiF and NaF.  相似文献   

4.
Ion-pair formation constants (mol–1 dm3 unit), KMX for a univalent metal salt (MX) and KMLX for its ion-pair complex (ML+X) with a crown ether (L) in water, were determined at various ionic strengths (I) and 25°C by potentiometry with ion-selective electrodes for MX=NaPic, NaMnO4, NaBPh4, KPic, and KMnO4; and MLX=Na(18C6)Pic, K(18C6)Pic, and Na(18C6)BPh4, where Pic and 18C6 denote a picrate ion and 18-crown-6 ether, respectively. Equations for analyzing I-dependence of logKMLX and logKMX were derived and fitted well to the I-dependence using a non-linear regression analysis. The equilibrium constants at I=0 mol dm–3, KMLX° and KMX°, were simultaneously obtained from the analysis. The experimental values of KMLX and KMX were only in agreement with the values calculated from KMLX° and KMX°, respectively, in the ranges of higher I.  相似文献   

5.
A study of the association between copper(II) and sulfate ions in aqueous solution has been made using copper ion-selective electrode potentiometry at constant ionic strengths (I) of 0.05, 0.1, 0.25, 0.5, 1.0, 3.0 and 5.0 mol·L?1 in NaClO4 media at 25 °C. Only one complex was detected, corresponding to the equilibrium: \( {\text{Cu}}^{ 2+ } ({\text{aq}}) + {\text{SO}}_{4}^{2 - } ({\text{aq}}) \rightleftarrows {\text{CuSO}}_{4}^{0} ({\text{aq}}). \) No higher order complexes were detected even at sulfate/copper(II) concentration ratios of up to 1,000. The present potentiometric values of log10 K 1(I) are shown to be consistently higher than those obtained by UV–Vis spectrophotometry because of the failure of the latter technique to detect all of the solvent-separated ion pairs present. Extrapolation of log10 K 1(I) to infinite dilution using an extended Guggenheim equation yielded a standard state value of log10 \( K_{1} \{ {\text{CuSO}}_{4}^{0} ({\text{aq}})\} = 2.32 \pm 0.09 \) , which is in excellent agreement with a recent IUPAC-recommended value.  相似文献   

6.
The acid–base properties of phytic acid [myo-inositol 1,2,3,4,5,6-hexakis(dihydrogen phosphate)] (H12Phy; Phy12–=phytate anion) were studied in aqueous solution by potentiometric measurements ([H+]-glass electrode) in lithium and potassium chloride aqueous media at different ionic strengths (0<I mol L–13) and at t=25 °C. The protonation of phytate proved strongly dependent on both ionic medium and ionic strength. The protonation constants obtained in alkali metal chlorides are considerably lower than the corresponding ones obtained in a previous paper in tetraethylammonium iodide (Et4NI; e.g., at I=0.5 mol L–1, logK3H=11.7, 8.0, 9.1, and 9.1 in Et4NI, LiCl, NaCl and KCl, respectively; the protonation constants in Et4NI and NaCl were already reported), owing to the strong interactions occurring between the phytate and alkaline cations present in the background salt. We explained this in terms of complex formation between phytate and alkali metal ions. Experimental evidence allows us to consider the formation of 13 mixed proton–metal–ligand complexes, MjHiPhy(12–i–j)–, (M+=Li+, Na+, K+), with j7 and i6, in the range 2.5pH10 (some measurements, at low ionic strength, were extended to pH=11). In particular, all the species formed are negatively charged: i+j–12=–5, –6. Very high formation percentages of M+–phytate species are observed in all the pH ranges investigated. The stability of alkali metal complexes follows the trend Li+Na+K+. Some measurements were also performed at constant ionic strength (I=0.5 mol L–1), using different mixtures of Et4NI and alkali metal chlorides, in order to confirm the formation of hypothesized and calculated metal–proton–ligand complex species and to obtain conditional protonation constants in these multi-component ionic media.Presented at SIMEC–02, Santiago de Compostela, 2–6 June 2002  相似文献   

7.
Summary From extraction experiments andg-activity measurements, the extraction constant corresponding to the equilibrium NH(aq)+NaL+(nb)?NH4L+(nb)+Na+(aq) taking place in the two-phase water-nitrobenzene system (L = p-tert-butylcalix[4]arene-tetrakis (N,N-diethylacetamide); aq = aqueous phase, nb = nitrobenzene phase) was evaluated as logKex(NH,NaL+)=-1.8. Further, the stability constant of the p-tert-butylcalix[4]arene-tetrakis (N,N-diethylacetamide)-ammonium complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: logbnb(NH4L+)=6.7.  相似文献   

8.
From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Na+(aq)+HL+(nb)⇆NaL+(nb)+H+(aq) taking place in the two-phase water-nitrobenzene system (L=18-crown-6; aq=aqueous phase, nb=nitrobenzene phase) was evaluated as logK ex (Na+,HL+)=0.1. Further, the stability constant of the 18-crown-6-sodium complex in nitrobenzene saturated with water was calculated: logβ nh(NaL+)=8.0.  相似文献   

9.
The rate of the cerium (IV) oxidation of p-chloromandelic acid has been studied in perchlorate media at an ionic strength of 1.50 mol/dm3 by the stopped-flow technique and in H2SO4? MHSO4 (M+ = Li+, Na+, K+) and H2SO4? MClO4 (M+ = H+, Li+, Na+) mixtures at constant total electrolyte concentrations of 1.00 and 2.00 mol/dm3 using the conventional spectrophotometric method. In perchlorate media the kinetic data indicate the formation of two intermediate complexes between cerium (IV) and the organic substrate, but only one is significantly involved in the intramolecular electron-transfer process. The oxidation rate is markedly lower in sulfate media, where two reaction paths have been found to contribute to the overall redox reaction. The univalent cations examined exhibit negative specific effects upon the overall oxidation rate increasing in the order H+ < Li+ < Na+ < K+. Activation parameters have been also estimated.  相似文献   

10.
In order to obtain insights into relationships between the calix[4]arene structure and the ion selectivity in the electrode system, 20 ionophoric calix[4]arenes were synthesized and their ion selectivity (with Na+ as a standard) estimated. Among these ionophoric calix[4]arenes, 25,26,27,28-tetrakis[(ethoxycarbonyl)methoxy]-p-t-octylcalix[4]arene afforded the highest logK NA,M pot value (–3.1) in the presence of 2-fluorophenyl-2-nitrophenylether (10) as the best of 13 plasticizers. This is the first example in which the Na+/K+ selectivity exceeds a factor of 103 in the electrode system based on the neutral carrier. The high Na+ selectivity is attributed to modification of the upper rim which ostensibly has no relation with the component of the cavity. This paper demonstrates the potential relationships between the unique structure of the calix[4]arene-based ligands and selectivity performance for the design of ion-selective electrodes.  相似文献   

11.
Summary From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Li+(aq)+NaL+(nb) ↔LiL+(nb)+Na+(aq) taking place in the two-phase water-nitrobenzene system (L = valinomycin; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as logKex(Li+,NaL+)=-1.1. Further, the stability constant of the valinomycin-lithium complex species in nitrobenzene saturated with water was calculated: logβnb(LiL+)=6.3.  相似文献   

12.
Conductivities of some tetraalkylammonium halides, viz. tetrapentylammonium chloride (Pen4NCl), tetrahexylammonium chloride (Hex4NCl), tetraheptylammonium chloride (Hep4NCl), and tetraoctylammonium chloride (Oct4NCl) were measured at 298.15 K in THF + CCl4 mixtures with 40, 60 and 80 mass% of THF. A minimum in the conductometric curves (molar conductance, Λ vs. square root of concentration, √c) was observed at concentrations which is dependent both on the salt and the solvent. The observed molar conductivities were explained by the formation of ion-pairs (M+ + X ↔ MX, KP) and triple-ions (2M+ + X ↔ M2X+; M+ + 2X ↔ MX2, KT). A linear relationship between the triple-ion formation constants [log(KT/KP)] and the salt concentrations at the minimum conductivity (log Cmin) was given for all salts in THF + CCl4 mixtures. The formation of triple-ions might be attributed to the ion sizes in solutions in which coulombic interactions and covalent bonding forces act as the main forces between the ions (R4N+X).  相似文献   

13.
The intercalation of cations into layered-structure electrode materials has long been studied in depth for energy storage applications. In particular, Li+-, Na+-, and K+-based cation transport in energy storage devices such as batteries and electrochemical capacitors is closely related to the capacitance behavior. We have exploited different sizes of cations from aqueous salt electrolytes intercalating into a layered Nb2CTx electrode in a supercapacitor for the first time. As a result, we have demonstrated that capacitive performance was dependent on cation intercalation behavior. The interlayer spacing expansion of the electrode material can be observed in Li2SO4, Na2SO4, and K2SO4 electrolytes with d-spacing. Additionally, our results showed that the Nb2CTx electrode exhibited higher electrochemical performance in the presence of Li2SO4 than in that of Na2SO4 and K2SO4. This is partly because the smaller-sized Li+ transports quickly and intercalates between the layers of Nb2CTx easily. Poor ion transport in the Na2SO4 electrolyte limited the electrode capacitance and presented the lowest electrochemical performance, although the cation radius follows Li+>Na+>K+. Our experimental studies provide direct evidence for the intercalation mechanism of Li+, Na+, and K+ on the 2D layered Nb2CTx electrode, which provides a new path for exploring the relationship between intercalated cations and other MXene electrodes.  相似文献   

14.
The protonation of 1,10-phenanthroline has been studied potentiometrically in different aqueous salt media (LiCl, NaCl, KCl, Me4NCl, Et4NI, MgCl2, CaCl2, SrCl2, and BaCl2) in the ionic strength range 0≤1≤1 M. This ligand forms two protonated species, [H(phen)]+ and [H(phen)2]+; the monoligand species shows protonation constants strongly dependent on the medium. Medium effects were explained by the formation of some weak species: [H(phen)Cl]0, [M(phen)]2+ (M=alkaline earth metal cations). Formation thermodynamic parameters are reported.  相似文献   

15.
The gold(III) 1,3-diaminopropane complex [Au(1,3-pn)(1,3-pn-H)]Cl2 has been synthesized. Its dissociation constant has been determined: Au(1,3-pn)23+ = Au(1,3-pn-H)2+ + H+, logK a1 = −7.03 ± 0.05 (I = 0.1 mol/L NaClO4). Considerable spectral changes are observed for strong alkali solutions (pH 11–14) containing the monoamido forms of the gold(III) ethylenediamine, 1,3-diaminopropane, and diethylenetriamine complexes (Au(en)(en-H)2+, Au(1,3-pn)(1,3-pn-H)2+, Au(dien-H)OH+). These changes are attributed to the formation of the diamido species Au(en-H)2+, Au(1,3-pn-H)2+, and Au(dien-2H)OH0. The dissociation constants of the monoamido complexes have been determined: Au(en)(en-H)2+ (logK a2 = −10.9 ± 0.1 at I = 0.001–0.01 mol/L NaCl); Au(1,3-pn)(1,3-pn-H)2+ (logK a2 = −11.3 ± 0.1 at I = 0.1 mol/L NaCl); Au(dien-H)OH+ (logK a2 = −12.4 ± 0.1 at I = 0.1 mol/L NaCl).  相似文献   

16.
When the sodium ion (Na+) concentration is increased above 0.5 mol-dm−3 (M), the concentrations of dissolved silica in aqueous sodium chloride (NaCl) and sodium nitrate (NaNO3) solutions decrease because of the salting out effect. On the other hand, the concentration of the dissolved silica in aqueous sodium sulfate (Na2SO4) solutions increases monotonously as the concentration of Na+ is increased above 0.5 M. The purpose of this study is to determine the reasons why the salting-out effect is not observed in Na2SO4 solutions. FAB-MS (Fast Atom Bombardment Mass Spectrometry) was used to sample directly the silica species dissolved in aqueous Na2SO4, NaCl, and NaNO3 solutions. In the FAB-MS spectra of these solutions, the peak intensity ratios of the linear tetramer to the cyclic tetramer largely increased for Na+ concentrations between (0.1 and 1) M. This shows that some characteristics of the Na2SO4 solutions are similar to those of the NaCl and NaNO3 solutions. In Na2SO4 solutions, however, when the concentration of Na+ is higher than 1 M, the peak intensity of the dimer is much higher than those of the other silicate complexes. In Na2SO4 solutions, the SO42− ion undergoes partial hydrolysis to form HSO4 and OH is produced. In particular, in the range where the concentration of SO42− is high, the pH of the solution increases slightly. This higher pH yields more dimers from the hydrolysis of silicate complexes. This increase in dimer production agrees with the observation that silica dissolves in sodium hydroxide (NaOH) solutions mainly as a dimer when the concentration of NaOH is less than 0.1 M. In Na2SO4 solutions at high concentrations, a salting-out effect is not observed for silica. This is due to the increase in the concentration of OH, which accelerates the hydrolysis of silica and results in dimer formation.  相似文献   

17.
On a mis en évidence un pont Mo-F-Mo dans des oxoperoxomolybdates VI complexes de coordinence sept de formule MI{Mo2O2(O-O)2(dipic)2F}; MI = {(C2H5)4N}+, {(CH3)4N}+, Cs+, Rb+, K+, Na+ -(dipic) = {C7H3NO4}2-. L'ion est mononucléaire pour MI = NH+4 et si le ligand halogéno eset Cl.  相似文献   

18.
The kinetics of the redox reaction between mandelic acid (MA) and ceric sulfate have been studied in aqueous sulfuric acid solutions and in H2SO4? MClO4 (M+ = H+, Li+, Na+) and H2SO4? MHSO4 (M+ = Li+, Na+, K+) mixtures under various experimental conditions of total electrolyte concentration (that is, ionic strength) and temperature. The oxidation reaction has been found to occur via two paths according to the following rate law: rate = k[MA] [Ce(IV)], where k = k1 + k2/(1 + a)2[HSO4?]2 = k1 + k2/(1 + 1/a)2[SO42?]2, a being a constant. The cations considered exhibit negative specific effects upon the overall oxidation rate following the order H+ ? Li+ < Na+ < K+. The observed negative cation effects on the rate constant k1 are in the order Na+ < Li+ < H+, whereas the order is in reverse for k2, namely, H+ ? Li+ < Na+. Lithium and hydrogen ions exhibit similar medium effects only when relatively small amounts of electrolytes are replaced. The type of the cation used does not affect significantly the activation parameters.  相似文献   

19.
Studies of the stoichiometry and kinetics of the reaction between hydroxylamine and iodine, previously studied in media below pH 3, have been extended to pH 5.5. The stoichiometry over the pH range 3.4–5.5 is 2NH2OH + 2I2 = N2O + 4I? + H2O + 4H+. Since the reaction is first-order in [I2] + [I3?], the specific rate law, k0, is k0 = (k1 + k2/[H+]) {[NH3OH+]0/(1 + Kp[H+])} {1/(1 + KI[I?])}, where [NH3OH+]0 is total initial hydroxylamine concentration, and k1, k2, Kp, and KI are (6.5 ± 0.6) × 105 M?1 s?1, (5.0 ± 0.5) s?1, 1 × 106 M?1, and 725 M?1, respectively. A mechanism taking into account unprotonated hydroxylamine (NH2OH) and molecular iodine (I2) as reactive species, with intermediates NH2OI2?, HNO, NH2O, and I2?, is proposed.  相似文献   

20.
From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the equilibrium M +(aq) + 1 · Na+ (nb) ⇄ 1 · M + (nb) + Na+ (aq) taking place in the two-phase water-nitrobenzene system (M + = Li+, H3O+, NH4 +, Ag+, K+, Rb+, Tl+, Cs+; 1 = tetraphenyl p-tert-butylcalix[4]arene tetraketone; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Moreover, the stability constants of the 1 · M + complexes in water saturated nitrobenzene were calculated; they were found to increase in the order Cs+ < Rb+ < Tl+ < K+ < NH4 + < Ag+ < H3O+ < Li+. Correspondence: Emanuel Makrlík, Faculty of Applied Sciences, University of West Bohemia, Pilsen, Czech Republic.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号