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1.
The stability of the ion pair NaSO4 was determined by measuring the change in sodium activity with medium composition at constant ionic strength, using a sodium-sensitive glass electrode. The stability constants of MgSO4 and MgCl+ were determined indirectly from measurements of the stability of MgF+ in different media. All measurements were performed at 1 atm pressure, 25 ± 0.1 °C and 0.7 M formal ionic strength. The stability constants for NaSO4?, MgSO4, MgF+ and MgCl+ are 1.8 ± 0.1, 6.3 ± 0.1, 22.9 ± 0.1 and 0.34 ± 0.02 M?1, respectively.  相似文献   

2.
The stability constants of the ion pairs NaSO4?, KSO4?, MgSO4?, CaSO4, MgCl+ and CaCl+ were determined at 25°C and 0.7 M formal ionic strength, by measuring the solubility of gypsum (CaSO4 · 2H2O) in different media. The media used contained one or two of the following electrolytes: NaCl, KCl, MgCl2, NaClO4, Mg(ClO4)2, Na2SO4. Values for the stability constants are 1.22, 1.84, 12.3, 30.6, 0.48 and 1.20 M?1, respectively, and the solubility product for gypsum is 2.87 · 10?4M2. The distribution of the main constituents of seawater was calculated using these results and the values of the carbonate and bicarbonate constants given by Dyrssen and Hansson (1972–1973). The solubility of gypsum in seawater as calculated and determined experimentally was 21.43 mM and 21.10 mM, respectively.  相似文献   

3.
The conditional stability constant of HSO4? has been determined at 25°C, 1 atm and a formal ionic strength of 0.7 M in solutions containing sodium, magnesium, chloride and sulphate. This was done spectrophotometrically (UV), using diphenylamine as indicator. The value obtained was 17.0 ± 0.1 (molar scale). Single ion activity coefficients for Na2SO4, K2SO4 and MgSO4 have been calculated according to the Bates et al. (1970) model, assuming that the sulphate ion is not hydrated. It was found that the single ion activity coefficient of sulphate changes very little between Na2SO4, K2SO4 and MgSO4 when the formal ionic strength is kept constant.These results have been used to obtain relations between the stability constants of NaSO4? and MgSO4 valid for seawater.  相似文献   

4.
The formation of the ion pairs MgSO4 and NaSO4? was investigated calorimetrically at 0.75 M ionic strength, 25°C, 1 atm. Simultaneous determinations of enthalpy changes, ΔH10, and stability constants, K1, were not possible, and values of K1 determined independently had to be introduced for the calculation of ΔH10. The values of ΔH10 obtained were 1–3 kJ mol?1 for MgSO4 and 0 kJ mol?1 for NaSO4?.  相似文献   

5.
The sorption of yttrium and the rare earth elements (YREEs) by amorphous ferric hydroxide at low ionic strength (0.01 M ≤ I ≤ 0.09 M) was investigated over a wide range of pH (3.9 ≤ pH ≤ 7.1). YREE distribution coefficients, defined as iKFe = [MSi]T / (MT[Fe3+]S), where [MSi]T is the concentration of YREE sorbed by the precipitate, MT is the total YREE concentration in solution, and [Fe3+]S is the concentration of precipitated iron, are weakly dependent on ionic strength but strongly dependent on pH. For each YREE, the pH dependence of log iKFe is highly linear over the investigated pH range. The slopes of log iKFe versus pH regressions range between 1.43 ± 0.04 for La and 1.55 ± 0.03 for Lu. Distribution coefficients are well described by an equation of the form iKFe = (Sβ1[H+]− 1 + Sβ2[H+]− 2) / (SK1[H+] + 1), where Sβn are stability constants for YREE sorption by surface hydroxyl groups and SK1 is a ferric hydroxide surface protonation constant. Best-fit estimates of Sβn for each YREE were obtained with log SK1 = 4.76. Distribution coefficient predictions, using this two-site surface complexation model, accurately describe the log iKFe patterns obtained in the present study, as well as distribution coefficient patterns obtained in previous studies at near-neutral pH. Modeled log iKFe results were used to predict YREE sorption patterns appropriate to the open ocean by accounting for YREE solution complexation with the major inorganic YREE ligands in seawater. The predicted log iKFe′ pattern for seawater, while distinctly different from log iKFe observations in synthetic solutions at low ionic strength, is in good agreement with results for natural seawater obtained by others.  相似文献   

6.
The activities of most of the major seawater components at 1,001 bars have been estimated, and values for the ions deduced. Equations giving the effect of pressure on the activities of ionic species in seawater (S = 35‰) have been developed. The species covered are: NaSO4?, MgSO40, CaSO40, H+, the free base (NH3), the HCO3?/CO32 activity ratio and the ion activity product of calcium carbonate. Comparison of the latter with the “ideal” solubility of calcite (pure solid in equilibrium with a mixed electrolyte solution) indicates a degree of saturation compatible with the trends indicated by in situ measurements.  相似文献   

7.
合浦珠母贝基质蛋白KRMP-3对二价金属离子选择性的研究   总被引：1，自引：0，他引：1  
用大肠杆菌表达含有GST标签的基质蛋白KRMP-3。利用圆二色谱(Circular Dichroism, CD)研究不同浓度钙离子和镁离子对基质蛋白 KRMP-3二级结构的影响。结果表明,钙离子对其二级结构的变化远大于镁离子;同时,采用荧光淬灭法研究 KRMP-3对钙,镁,锶,钡等二价金属离子的选择性,结果表明, KRMP-3对钙离子有特异性选择性,钙离子与KRMP-3的结合常数K约为103 L/mol,结合位点数 n 近似为1,表明 KRMP-3与钙离子的结合能力适中,推测基质蛋白 KRMP-3对合浦珠母贝( Pinctada fucata)棱柱层形成起到促进作用。  相似文献   

8.
It is shown that the values of pK1C and pK2C for carbonic acid, pKB for boric acid and the ionic product of water, pKw, in sea water may be explained on the basis of their determination in 0.7 Mw sodium chloride and the formation of the following ion-pairs: NaSO4?, MgSO4, CaSO4, MgCO3, CaCO3, MgHCO3+, CaHCO3+, MgOH+, HSO4?, MgB(OH)4+ and CaB(OH)4+. On the whole the calculated stability constants are lower than those given by Garrels and Thompson (1962).  相似文献   

9.
The results of a potentiometric investigation (by ISE-H+, glass electrode) on the speciation of phytate ion (Phy12−) in an ionic medium simulating the major components (Na+, K+, Ca2+, Mg2+, Cl− and SO42−) of natural seawater, at different salinities and t = 25 °C, are reported. The work was particularly aimed at determining the possible formation of mixed Ca2+–Mg2+–phytate ion pairs, and to establish how including the formation of these mixed species would affect the speciation modeling in seawater media. After testing various speciation models, that considering the formation of the MgCaH3Phy5−, MgCaH4Phy4−, Mg2CaH3Phy3− and Mg2CaH4Phy2− species was accepted, and corresponding stability constants were determined at two salinities (S = 5, 10). A discussion is reported both on the choice of the experimental conditions and on the possibility to extend these results to those typical of real seawater. A detailed procedure is also described to demonstrate that the stability of these species is higher than that statistically predicted. As reported in literature, a parameter, namely log X, has been determined in order to quantify this extra stability for the formation of each mixed species at various salinities. For example, at S = 10, log X113 = 2.67 and log X114 = 1.37 for MgCaH3Phy5− and MgCaH4Phy4− (statistical value is log Xstat = 0.60), and log X213 = 6.11 and log X214 = 2.15 for Mg2CaH3Phy3− and Mg2CaH4Phy2− (log Xstat = 1.43), respectively. Results obtained also showed that the formation of these species may occur even in conditions of low salinity (i.e. low concentration of alkaline earth cations) and low pH (i.e., more protonated ligand).  相似文献   

10.
Acid–base equilibrium constants of triethanolamine (TEA) have been determined by potentiometric titrations with a glass electrode, at 25 °C. Ionic strength was kept constant with only one electrolyte (using one of these salts: NaCl, KCl, MgCl2 or CaCl2), with binary mixtures of MgCl2 and CaCl2, and finally, in a solution with a composition approximately similar to that of natural seawater without sulfate. Equilibrium constants have been expressed in function of ionic strength by means of Pitzer equations and interaction parameters proposed in this theory have been obtained. It has been found that acid–base behaviour of TEA depends greatly on the salt used: basicity of TEA is decreased by CaCl2, while it is increased by the other electrolytes used in this work.  相似文献   

11.
The dissociation constants (pK1, pK2 and pK3) for cysteine have been measured in seawater as a function of temperature (5 to 45 °C) and salinity (S = 5 to 35). The seawater values were lower than the values in NaCl at the same ionic strength. In an attempt to understand these differences, we have made measurements of the constants in Na–Mg–Cl solutions at 25 °C. The measured values have been compared to those calculated from the Pitzer ionic interaction model. The lower values of pK3 in the Na–Mg–Cl solutions have been attributed to the formation of Mg2+ complexes with Cys2− anions
Mg2+ + Cys2− = MgCys
The stability constants have been fitted to
after corrections are made for the interaction of Mg2+ with H+.The pK1 seawater measurements indicate that H3Cys+ interacts with SO42−. The Pitzer parameters β0(H3CysSO4), β1(H3CysSO4) and C(H3CysSO4) have been determined for this interaction. The formation of CaCys as well as MgCys are needed to account for the values of pK2 and pK3 in seawater.The consideration of the formation of MgCys and CaCys in seawater yields model calculated values of pK1, pK2 and pK3 that agree with the measured values to within the experimental error of the measurements. This study shows that it is important to consider all of the ionic interactions in natural waters when examining the dissociation of organic acids.  相似文献   

12.
  相似文献   

13.
It is shown that the values of the diffusion coefficient of MgSO40 ion pairs computed by Harned and Hudson (J. Am. Chem. Soc., 73: 5880, 1951) and Katz and Ben-Yaakov (Mar. Chem., 8: 263, 1980) are too high by a factor of 2. The correct value of the ion pair diffusion coefficient at infinite dilution was obtained from the measured mutual diffusion coefficient after applying corrections for incomplete dissociation, the electrophoretic effect, the viscosity of the solution and the effect of chloride ion pairs (in the ionic media used during measurements of the stoichiometric association constant of MgSO40 ion pairs). The MgSO40 diffusion coefficient is calculated to be 0.65 × 10?5 cm28?1. The result is independent of the concentration up to a value of 0.8 mol dm?3.Values were also calculated for the diffusion coefficients of the following ion pairs: NaSO4? (0.81 × 10?5), CaCl+ (0.78 × 10?5), BaCl+ (0.85 × 10?5), NaCl0 (0.86 × 10?5), KCl0 (1.09 × 10?5), NH4Cl0 (1.10 × 10?5) and CaCl0 (1.27 × 10?5). In general, the diffusion coefficients are less than those of the free ions. The results show quantitative agreement with theoretical predictions.  相似文献   

14.
Gross sedimentation rates (GSR) have been measured using sediment traps placed at nine different levels above the bed (0·3, 0·5, 0·8, 1·0, 2·0, 4·0, 6·0, 8·0 and 10·0 m). The sediment traps were deployed for 1·25 years and recovered 28 times during the study period. Low average GSR values of 5·5 g m-2 day-1 were obtained at 10·0 m, and high average GSR values of 114·8 g m-2 day-1 were obtained at 0·3 m. An expression for the eddy diffusion coefficient of suspended particulate matter (Ks), based on the measured GSR is given. The expression has been used for modelling of Ks at the different trap levels above the bed. High values (≈42 cm2 s-1) of Ks were obtained at the upper traps, whereas low values (≈2 cm2 s-1) were obtained near the bed. Comparison between level of turbulent energy in terms of shear stress at the boundaries of the water column, i.e. from the wind and the bed flow, showed that wind energy exceeded that of the bed flow by a factor 16. At 5·0 m Ks was positively correlated (r=0·66) to the eddy diffusion coefficient of momentum (Km) derived from the wind energy transfer to the water, giving an average β of 0·5 for Ks =βKm. The density difference between surface and bottom waters has been designated a parameter of stratification, and is discussed in relation to variations of Ks and Km .  相似文献   

15.
The apparent stability constants for chloride and sulfate ions with Co (II) at ionic strength of 0.67 were determined by the cation exchange method. The value of the stability constant 1 for chloride ion with Co (II) ion was 0.79±0.055. The stability constants 1, 2 and 3 for sulfate ion with Co (II) ion were 12.0±0.27, 91.5±11.4 and l,110±250, respectively. The chemical species of Co (II) in seawater was estimated at the pH of 8.0 to be present as Co2+ (63%), CoCl+ (27%) and CoSO4 0 (8.6%) using the known value of dissociation constant of Co (II), and under the assumption that only major inorganic anions are responsible for the chemical equilibrium of Co (II).  相似文献   

16.
A theoretical evaluation of basic thermodynamic relationships reveals that variation of activity coefficients, ion pairing and electrical interactions must be considered when modelling ionic diffusion in seawater. The contributions of ion-pair formation and change in activity coefficient along the diffusion path were studied experimentally by conducting diffusion experiments in which solutions of KCl, NaCl, MgCl2, Li2SO4, K2SO4, Na2SO4 and MgSO4, at an ionic strength of 0.7, were allowed to diffuse into distilled water. The study reveals that the thermodynamic factor, required to correct for changes in the activity coefficient along the diffusion path, is significant for all the salts studied. Agreement between a simple diffusion model, which does not include ion pairing, and observed data was good for completely dissociated salts, but poor for salts which are known to form ion pairs at the concentration levels studied. The diffusion of MgSO4, 0.425 of which is associated at I = 0.7, was successfully modelled by assuming that the diffusion coefficient of the MgSO40 ion pair is different from the diffusion coefficient of the dissociated salt. The diffusion coefficient of this ion pair is estimated to be 1.9 × 10−5 cm2 s−1 at 30°C, as compared to 0.49 × 10−5 cm2 s−1 for the dissociated salt. It is suggested that the high mobility of this ion pair could cause magnesium enrichment in pore water of sulfate depleted sediments.  相似文献   

17.
Two independent voltammetric techniques, differential pulse cathodic stripping voltammetry (DPCSV) and differential pulse anodic stripping voltammetry (DPASV), determined that 95% of the dissolved zinc is organically complexed at two depths (60 and 150 m) within the surface euphotic zone at an open ocean station in the Northeast Pacific. Average values for the concentrations of the natural zinc-complexing organic ligands (CL) obtained from duplicate determinations at these two depths by DPCSV versus DPASV are in excellent agreement: 1.60 ± 0.01 versus 1.76 ± 0.03 nM at 60 m, and 2.14 (n=1) versus 2.22 ± 0.06 nM at 150 m. Average values for the conditional stability constants (with respect to free Zn2+) of the natural zinc-organic complexes (log K′ZnL) from duplicate determinations at both depths by DPCSV versus DPASV are 10.3 ± 0.2 versus 11.2 ± 0.2. Additional research is required to assess the significance of the difference in the conditional stability constants determined by these two techniques. These results confirm recent observations that strong zinc complexes formed with an organic ligand class existing at nanomolar concentrations dominates zinc speciation in the North Pacific.  相似文献   

18.
The dissociation constants (pK1 and pK2) for methionine have been measured in artificial seawater as a function of salinity (S = 5 to 35) and temperature (5 to 45 °C). The seawater pK2 values were lower than the values in NaCl at the same ionic strength while the pK1 values in seawater were lower only at S = 35. In an attempt to understand these differences, we have made measurements of the constants in Na–Mg–Cl solutions at 25 °C. The measured values have been used to determine the formation of Mg2+ complexes and Pitzer interaction parameters for Mg2+ with methionine. The seawater model with the interaction parameters accounts for the differences between the value of pK1 and pK2 between NaCl and seawater. This study demonstrates that it is important to consider all of the ionic interactions in natural waters when examining the dissociation of organic acids.  相似文献   

19.
The interactions of Fe(II) and Fe(III) with the inorganic anions of natural waters have been examined using the specific interaction and ion pairing models. The specific interaction model as formulated by Pitzer is used to examine the interactions of the major components (Na+, Mg2+, Ca2+, K+, Sr2+, Cl−, SO4−, HCO3−, Br−, CO32−, B(OH)4−, B(OH)3 and CO2) of seawater and the ion pairing model is used to account for the strong interaction of Fe(II) and Fe(III) with major and minor ligands (Cl−, SO42−, OH−, HCO3−, CO32− and HS−) in the waters. The model can be used to estimate the activity and speciation of iron in natural waters as a function of composition (major sea salts) and ionic strength (0 to 3 M). The measured stability constants (KFeX*) of Fe(II) and Fe(III) have been used to estimate the thermodynamic constants (KFeX) and the activity coefficient of iron complexes (γFeX) with a number of inorganic ligands in NaClO4 medium at various ionic strengths: In(KFeX/γFeγX) = InKFeX − In(γFeX) The activity coefficients for free ions (γFe, γx) needed for this extrapolation have been estimated from the Pitzer equations. The activity coefficients of the ion pairs have been used to determine Pitzer parameters (BFeX, BFeX0, CFeXφ) for the iron complexes. These results make it possible to estimate the stability constants for the formation of Fe(II) and Fe(III) complexes over a wide range of ionic strengths and in different media. The model has been used to determine the solubility of Fe(III) in seawater as a function of pH. The results are in good agreement with the measurements of Byrne and Kester and Kuma et al. When the formation of Fe organic complexes is considered, the solubility of Fe(III) in seawater is increased by about 25%.  相似文献   

20.
Four geosim families, with fully available resistance test results, have been re-analyzed to check the possible scale effect on the form factor. The form factor determined by Prohaska's method, with exponent n=4 and ITTC'57 correlation line, increases with the model size in all four cases analyzed. Because of its high correlation coefficient, a linear variation of the form factor with the scale is assumed. It is possible to have a first estimation of the ship's form factor extrapolating for λ=1 in the regression line. Form factor Reynolds number dependency will always be associated with a friction line. Using the ITTC'57 correlation line, the following equation KS−KM=1.91·(λ−1)·10−3 can be used to estimate the scale effect on the form factor. Calculations carried out, for axisymetric bodies, with some CFD codes are in good agreement with the experimental findings.  相似文献   

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