共查询到20条相似文献,搜索用时 15 毫秒
1.
Preeti A. Tomar Rahul R. Kolhapurkar Dilip H. Dagade Kesharsingh J. Patil 《Journal of solution chemistry》2007,36(2):193-209
Osmotic vapor pressure and density measurements have been carried out for binary aqueous and ternary aqueous solutions containing
a fixed concentration of 18-crown-6 (0.2 mol⋅kg−1) and ammonium chloride or ammonium bromide at 298.15 K. The concentration of the ammonium salts was varied between 0.02 to
0.5 mol⋅kg−1. The measured water activities were used to obtain the activity coefficient of water and the mean molal activity coefficient
of the ions in binary as well as ternary solutions. Using the method developed by Patil and Dagade reported earlier in this
journal and the McMillan-Meyer pair and triplet Gibbs energy interaction parameters, the thermodynamic equilibrium constant
(K) for the 18-crown-6:NH4
+ complexes were determined. It is observed that the nature and polarizability of anions play important roles in imparting
stability to the complexed species. The log10
K values for the 18-crown-6:NH4
+ complexed species are lower than for the complexes involving alkali metal ions such as K+. The volume of complexation for the studied systems obtained from the apparent molar volumes of ammonium halides in ternary
solutions are positive and of smaller magnitude than those reported for complexation with alkali ions. The results are further
discussed in terms of water structural effects, complex formation, the role of counter anions and hydrophobic interactions. 相似文献
2.
Lakshmi N. Roy Rabindra N. Roy Cole E. Denton Sean R. LeNoue Curtis A. Himes Sarah J. Richards Ashley N. Simon Chandra N. Roy Vikram S. Somal 《Journal of solution chemistry》2006,35(4):551-566
The values of the second dissociation constant, pK
2, and related thermodynamic quantities of N-[tris(hydroxymethyl)methyl-3-amino]propanesulfonic acid (TAPS) have already been reported at 12 temperatures over the temperature range 5–55 ∘C, including 37 ∘C. This paper reports the results for the pH of five equimolal buffer solutions with compositions: (a) TAPS (0.03 mol⋅kg−1) + NaTAPS (0.03 mol⋅kg−1); (b) TAPS (0.04 mol⋅ kg−1) + NaTAPS (0.04 mol⋅kg−1); (c) TAPS (0.05 mol⋅kg−1) + NaTAPS (0.05 mol⋅kg−1); (d) TAPS (0.06 mol⋅kg−1) + NaTAPS (0.06 mol⋅kg−1); and (d) TAPS (0.08 mol⋅kg−1) + NaTAPS (0.08 mol⋅kg−1). The remaining eight buffer solutions consist of saline media of the ionic strength I = 0.16 mol⋅kg−1, matching closely to that of the physiological sample. The compositions are: (f) TAPS (0.04 mol-kg−1) + NaTAPS (0.02 mol-kg−1) + NaCl (0.14 mol⋅kg−1); (g) TAPS (0.05 mol⋅kg−1) + NaTAPS (0.04 mol⋅kg−1) + NaCl (0.12 mol⋅kg−1); (h) TAPS (0.6 mol⋅kg−1) + NaTAPS (0.04 mol⋅kg−1) + NaCl (0.12 mol⋅kg−1); (i) TAPS (0.08 mol⋅kg−1) + NaTAPS (0.06 mol⋅kg−1) + NaCl (0.10 mol⋅kg−1); (j) TAPS (0.04 mol⋅ kg−1) + NaTAPS (0.04 mol⋅kg−1) + NaCl (0.12 mol⋅kg−1); (k) TAPS (0.05 mol⋅kg−1) + NaTAPS (0.05 mol⋅kg−1) + NaCl (0.11 mol⋅kg−1); (l) TAPS (0.06 mol⋅kg−1) + NaTAPS (0.06 mol⋅kg−1) + NaCl (0.10 mol⋅kg−1); and (m) TAPS (0.08 mol⋅kg−1) + NaTAPS (0.08 mol⋅kg−1) + NaCl (0.08 mol⋅kg−1). These buffers are recommended as a pH standard for clinical measurements in the range of physiological application. Conventional pH values, designated as pH(s), for all 13 buffer solutions from 5 to 55 ∘C have been calculated. The operational pH values with liquid junction corrections, at 25 and 37 ∘C for buffer solutions, designated above as (b), (c), (d), (e), (j), (l), and (m); have been determined based on the difference in the values of the liquid junction potentials between the accepted phosphate standard and the buffer solutions under investigation. 相似文献
3.
Rabindra N. Roy Lakshmi N. Roy Shahaf Ashkenazi Joshua T. Wollen Craig D. Dunseth Michael S. Fuge Jared L. Durden Chandra N. Roy Hannah M. Hughes Brett T. Morris Kevin L. Cline 《Journal of solution chemistry》2009,38(4):449-458
The values of the second dissociation constant, pK
2, of N-(2-hydroxyethyl) piperazine-N′-2-ethanesulfonic acid (HEPES) have been reported at twelve temperatures over the temperature range 5 to 55 °C, including
37 °C. This paper reports the results for the pa
H of eight isotonic saline buffer solutions with an I=0.16 mol⋅kg−1 including compositions: (a) HEPES (0.01 mol⋅kg−1) + NaHEPES (0.01 mol⋅kg−1) + NaCl (0.15 mol⋅kg−1); (b) HEPES (0.02 mol⋅kg−1) + NaHEPES (0.02 mol⋅kg−1) + NaCl (0.14 mol⋅kg−1); (c) HEPES (0.03 mol⋅kg−1) + NaHEPES (0.03 mol⋅kg−1) + NaCl (0.13 mol⋅kg−1); (d) HEPES (0.04 mol⋅kg−1) + NaHEPES (0.04 mol⋅kg−1) + NaCl (0.12 mol⋅kg−1); (e) HEPES (0.05 mol⋅kg−1) + NaHEPES (0.05 mol⋅kg−1) + NaCl (0.11 mol⋅kg−1); (f) HEPES (0.06 mol⋅kg−1) + NaHEPES (0.06 mol⋅kg−1) + NaCl (0.10 mol⋅kg−1); (g) HEPES (0.07 mol⋅kg−1) + NaHEPES (0.07 mol⋅kg−1) + NaCl (0.09 mol⋅kg−1); and (h) HEPES (0.08 mol⋅kg−1) + NaHEPES (0.08 mol⋅kg−1) + NaCl (0.08 mol⋅kg−1). Conventional pa
H values, for all eight buffer solutions from 5 to 55 °C, have been calculated. The operational pH values with liquid junction
corrections, at 25 and 37 °C have been determined based on the NBS/NIST standard between the physiological phosphate standard
and four buffer solutions. These are recommended as pH standards for physiological fluids in the range of pH = 7.3 to 7.5
at I=0.16 mol⋅kg−1. 相似文献
4.
From vapor pressure osmometry data, the activity of water, osmotic coefficients and mean ionic activity coefficients of glycine
(m=0.006−3.2 mol⋅kg−1), L-histidine (m=0.005−0.23 mol⋅kg−1), L-histidine monohydrochloride (m=0.008−0.63 mol⋅kg−1), glutamic acid (m=0.004−0.05 mol⋅kg−1), sodium L-glutamate (m=0.007−0.6 mol⋅kg−1), and calcium L-glutamate (m=0.008−0.6 mol⋅kg−1) have been obtained in aqueous solutions at 298.15 and 310.15 K. The Pitzer equations and the mean spherical approximation
(MSA) are used for theoretical modeling. The results are supplied as reference thermodynamic material for the characterization
of more complex molecules such as proteins. 相似文献
5.
Yizhak Marcus 《Journal of solution chemistry》2009,38(5):513-516
In concentrated salt solutions the average distances between the ions, d
av=1.1844⋅(∑ν
i
c
i
)−1/3 nm, are commensurate with the sizes of the solvated ions, so that no ‘bulk solvent’ remains. This is illustrated with two
saturated aqueous solutions, where 16.67 mol⋅dm−3 CsF at 75 °C has d
av(Cs–F)=0.368 nm and 14.54 mol⋅dm−3 LiI at 80 °C has d
av(Li–I)=0.385 nm. The minimal distance required for the bare ions (sum of their radii) are 0.303 nm for CsF and 0.289 nm for
LiI. Hence no water molecule, diameter 0.276 nm, can be fitted between the ions to form linear or slightly bent hydrogen bonds.
Some recent work ignoring such constraints, even in 3–6 mol⋅dm−3 solutions, is criticized on this account. 相似文献
6.
Ahmed E. Fazary Erzalina Hernowo Artik Elisa Angkawijaya Tse-Chuan Chou Chih Hung Lin Mohamed Taha Yi-Hsu Ju 《Journal of solution chemistry》2011,40(12):1965-1986
The complexation equilibria of L-norleucine and gallic acid were studied in aqueous solutions at 25.00 °C and ionic strength
0.15 mol⋅dm−3 (NaNO3), by means of potentiometry and spectrophotometry. The ferric (FeIII), chromium (CrIII), and cupric (CuII) complexing abilities of L-norleucine and gallic acid, along with their overall stability constants, were obtained with the
HYPERQUAD 2008 program from the potentiometric data. The concentration distributions of the various complex species in solution
were evaluated and discussed. UV–visible spectroscopic measurements were carried out to give qualitative information about
the composition of the complexes formed in these solutions. The cytotoxic activities of the binary and ternary metal complexes
of L-norleucine and gallic acid were tested and evaluated against HEp-2 (human laryngeal carcinoma), Daoy (human medulloblastoma),
MCF-7 (human breast adenocarcinoma), and WiDr (human colon adenocarcinoma) tumor cell lines. Also, their antioxidant activities
were examined by free radical scavenging assay. 相似文献
7.
Enthalpies of dilution of N,N′-hexamethylenebisacetamide in water and aqueous alkali halide solutions at the concentration
of 0.150 mol⋅kg−1 (approximately the concentration of physiological saline) have been determined by isothermal titration microcalorimetry at
298.15 K. The enthalpic interaction coefficients in the solutions have been calculated according to the excess enthalpy concept
based on the calorimetric data. The values of enthalpic pair-wise interaction coefficients (h
2) of the solute in aqueous solutions of different salts were discussed in terms of the different alkali salt ions and weak
interactions of the diluted component with coexistent species as well as the change in solvent structure caused by ions. 相似文献
8.
Ternary complex species formed by the V3+ cation with the picolinic acid (Hpic, HL) and dipicolinic acid (H2dipic, H2L) ligands in aqueous solutions have been studied potentiometrically (25 °C, I=3.0 mol⋅dm−3 KCl ionic medium) and by spectrophotometric measurements. Application of the least-squares computer program LETAGROP to the
experimental emf (H) data, taking into account the hydrolytic V(III) species and the binary V3+–picolinic acid and V3+–dipicolinic acid complexes, shows that under the investigated conditions the following ternary complexes are formed: [V(dipic)(pic)],
[V(dipic)(pic)(OH)]− and [V(dipic)(pic)2]−. The stability constants of the ternary complexes were determined by potentiometric measurements whereas the spectrophotometric
measurements were done in order to obtain a qualitative characterization of the complexes formed in aqueous solution. 相似文献
9.
A. M. Radalla 《Journal of solution chemistry》2010,39(9):1394-1407
The binary and ternary complexes of Cu2+, Ni2+, Co2+ and Zn2+ metal ions with resorcinol (R) as primary ligand and some biologically important aliphatic dicarboxylic acids (adipic, succinic,
malic, malonic, maleic, tartaric and oxalic acids) as secondary ligands were studied in aqueous solution at 25 °C and I=0.1 mol⋅dm−3 NaNO3 using the potentiometric technique. The formation of different 1:1 and 1:2 binary complexes and 1:1:1 ternary complexes is
inferred from the corresponding potentiometric pH-titration curves. The ternary complex formation was found to take place
in a stepwise manner. The protonation constants of the ligands were determined and used for determining the stability constants
of the different complexes formed in aqueous solutions. The lower stability of the 1:2 binary complexes compared to the corresponding
1:1 systems of all ligands studied were in accordance with statistical considerations. The order of stability of the complexes
formed in solution was investigated in terms of the nature of the resorcinol, carboxylic acid, and metal ion used. The values
of Δlog 10
K, percentage of relative stabilization (% R.S.), and log 10
X for mixed-ligand complexes studied have been evaluated and discussed. The concentration distribution of the various species
formed in solution was evaluated. The mode of chelation of the ternary complexes was ascertained by conductivity measurements. 相似文献
10.
This work is concerned with the acidic properties of the uranyl ion, UO22+, at 75 and 100 °C in 3.6 mol⋅kg−1 LiClO4 aqueous medium. The investigation was carried out with a coulometric-potentiometric technique. Direct and reverse acid-base
titrations were carried out in order to check whether equilibrium had been reached. Moreover, in order to determine whether
or not the solutions were oversaturated, a further check was carried out with fresh saturated hydrolyzed solutions. 相似文献
11.
Solution equilibria of the systems Cu(II)-adenine (A)-amino acids (L) have been studied pH-metrically. The formation constants
of the resulting mixed ligand complexes have been calculated at 25 °C and ionic strength 0.1 mol⋅dm−3 NaNO3. Ternary complexes are formed by simultaneous reactions. The relative stability of each ternary complex was compared with
that of the corresponding binary complexes in terms of Δlog 10
K values. The concentration distribution of the complexes in solution was evaluated. 相似文献
12.
Clemente Bretti Francesco Crea Ottavia Giuffrè Silvio Sammartano 《Journal of solution chemistry》2008,37(2):183-201
Acid-base properties of some open-chain polyamines (ethylenediamine, diethylenetriamine, triethylenetetramine, spermine, tetraethylenepentamine
and pentaethylenehexamine) were studied at different ionic strengths in different aqueous ionic media at 25 °C. Measured were:
(i) the protonation constants of triethylenetetramine, tetraethylenepentamine and pentaethylenehexamine from potentiometric
measurements [0 ≤I≤2.5 mol⋅L−1 in NaCl and (CH3)4NCl)]; and (ii) protonation enthalpies of ethylenediamine, diethylenetriamine, and spermine from calorimetric measurements
[NaCl: 0≤I≤1 mol⋅kg−1 for ethylenediamine, diethylenetriamine, 0 ≤I≤2 mol⋅kg−1 for spermine; (C2H5)4NI: 0≤I≤1 mol⋅kg−1; (CH3)4NCl: 0 ≤I≤2.5 mol⋅kg−1 only for diethylenetriamine]. Previously published protonation data for these polyamines in aqueous NaCl, (CH3)4NCl and (C2H5)4NI, were also examined. The general trends for the Gibbs energy and entropic contributions are, for ΔG: NaCl>(CH3)4NCl>(C2H5)4NI, and for TΔS: (C2H5)4NI>(CH3)4NCl>NaCl. This trend is more pronounced for the first protonation step. The dependences of these quantities on ionic strength
were modeled with the SIT (Specific ion Interaction Theory) equations, and differences found among the different media were
interpreted in terms of weak complex formation. 相似文献
13.
Densities, partial molar volumes, and viscosities of aqueous solutions of betaine have been measured at 5, 10, 15, 20, 25,
30, 37, and 45 °C over the concentration range 0.05 to 5.0 mol⋅L−1. The partial molar volumes show that betaine exists partly as a monohydrate and partly in its anhydrous form. The proportion
of the anhydrous form increases with increasing temperature. Also, an associated form of betaine appears in concentrated betaine
solutions, possibly with water as a bridging group. The significance of the viscosity B-coefficient is discussed. The signs of B
st, the increment of the viscosity B-coefficients arising from structural changes of water, are negative and the signs of dB/dT, the temperature derivative of B, are positive. These results show that betaine is a water structure breaker especially at lower temperatures, and this effect
decreases to insignificance at higher temperatures. The ionization equilibria of betaine were investigated in aqueous 0.5 mol⋅L−1 and 1.0 mol⋅L−1 NaNO3 at 5, 15, 25, and 37 °C by a potentiometric method. Using the least-square computer program SUPERQUAD, the complex forms
are deduced to be betanium BH, bis(betanium) BHB, and bis(betaine) B2 or bis(betaine)hydrate BH2OB. 相似文献
14.
The complexation of As(V) in aqueous solutions in the presence of iron(III) was investigated spectrophotometrically with both
variable and constant ionic strengths. The determined thermodynamic and stoichiometric formation constants of the FeHAsO4+ species are log10∘β = 9.21± 0.01 and log10Iβ (1.0mol⋅dm−3 NaClO4) = 7.78 ± 0.01, respectively. The numerical treatment of the obtained spectral data was performed with the SPECA program. The analysis required the consideration
of the hydrolysis of Fe(III) and the protonation of As(V) in the pH range studied. No significant hydrolysis was observed
because of the low pH values (pH < 2.5) involved. The stabilities of the solid Fe(III) arsenates was established by solubility
experiments. All of the solubility experiments were performed in aqueous NaClO4 solutions at constant ionic strength (1.0mol⋅dm−3) and at 25∘C. The experimental data were consistent with FeAsO4⋅2H2O being the solid phase (log10 ∘ Kso = −24.30± 0.08). The corresponding thermodynamic constants were computed by means of the Modified Bromley's Methodology (MBM)
that describes the variation of the activity coefficients of all of the ions involved in the complexation and precipitation
equilibria with the medium and ionic strength. Finally, the solid phase obtained in this work was also characterized by FT-IR
and FT-Raman spectroscopies, and the hydration of the solid iron arsenate was confirmed by X-ray diffraction data. 相似文献
15.
Clemente Bretti Concetta De Stefano Claudia Foti Silvio Sammartano 《Journal of solution chemistry》2006,35(9):1227-1244
The protonation constants of phthalate were determined in aqueous NaCl (0.1 ≤ I ≤ 5,mol⋅L−1) and in aqueous Me4NCl (0.1 mol⋅L−1 ≤ I ≤ 3,mol⋅L−1) at t = 25,∘C. Experimental data were employed in conjunction with literature data from studies in different ionic media (Et4NI: 0 ≤ I ≤ 1,mol⋅L−1; NaClO4: 0.05 mol⋅L−1 ≤ I ≤ 2,mol⋅L−1)to study the dependence on ionic strength using different models, such as the SIT and Pitzer equations, and an Extended Debye-Hückel type equation. Experimental calorimetric data in NaCl and protonation constants at different temperatures in Et4NI (5 ≤ t ≤ 45∘C) and in NaClO4 (15 ≤ t ≤ 35 ∘C) were also used to study their dependence on temperature. Recommended equilibrium data are reported together with a short discussion of a prospective protocol for drawing these data. 相似文献
16.
Jelena Miladinović Rozalija Ninković Milica Todorović Joseph A. Rard 《Journal of solution chemistry》2008,37(3):307-329
Isopiestic vapor-pressure measurements were made for {yMgCl2+(1−y)MgSO4}(aq) solutions with MgCl2 ionic strength fractions of y=(0,0.1997,0.3989,0.5992,0.8008, and 1) at the temperature 298.15 K, using KCl(aq) as the reference standard. These measurements
for the mixtures cover the ionic strength range I=0.9794 to 9.4318 mol⋅kg−1. In addition, isopiestic measurements were made with NaCl(aq) as reference standard for mixtures of {xNa2SO4+(1−x)MgSO4}(aq) with the molality fraction x=0.5000 that correspond to solutions of the evaporite mineral bloedite (astrakanite), Na2Mg(SO4)2⋅4H2O(cr). The total molalities, m
T=m(Na2SO4)+m(MgSO4), range from m
T=1.4479 to 4.4312 mol⋅kg−1 (I=5.0677 to 15.509 mol⋅kg−1), where the uppermost concentration is the highest oversaturation molality that could be achieved by isothermal evaporation
of the solvent at 298.15 K. The parameters of an extended ion-interaction (Pitzer) model for MgCl2(aq) at 298.15 K, which were required for an analysis of the {yMgCl2+(1−y)MgSO4}(aq) mixture results, were evaluated up to I=12.075 mol⋅kg−1 from published isopiestic data together with the six new osmotic coefficients obtained in this study. Osmotic coefficients
of {yMgCl2+(1−y)MgSO4}(aq) solutions from the present study, along with critically-assessed values from previous studies, were used to evaluate
the mixing parameters of the extended ion-interaction model. 相似文献
17.
The formation constant of the mononitratouranyl complex was studied spectrophotometrically at temperatures of 25, 40, 55,
70, 100 and 150 °C (298, 313, 328, 343, 373 and 423 K). The uranyl ion concentration was fixed at approximately 0.008 mol⋅kg−1 and the ligand concentration was varied from 0.05 to 3.14 mol⋅kg−1. The uranyl nitrate complex, UO2NO3+, is weak at 298 K but its equilibrium constant (at zero ionic strength) increases with temperature from log 10
β
1=−0.19±0.02 (298 K) to 0.78±0.04 (423 K). 相似文献
18.
The heat transport purification system of CANDU nuclear reactors is used to remove particulates and dissolved impurities from
the heat transport coolant. Zirconium dioxide shows some potential as a high-temperature ion-exchange medium for cationic
and anionic impurities found in the CANDU heat transport system (HTS). Zirconium in the reactor core can be neutron activated,
and potentially can be dissolved and transported to out-of-core locations in the HTS. However, the solubility of zirconium
dioxide in high-temperature aqueous solutions has rarely been reported. This paper reports the solubility of zirconium dioxide
in 10−4 mol⋅kg−1 LiOH solution, determined between 298 and 573 K, using a static autoclave. Over this temperature range, the measured solubility
of zirconium dioxide is between 0.9 and 12×10−8 mol⋅kg−1, with a minimum solubility around 523 K. This low solubility suggests that its use as a high-temperature ion-exchanger would
not introduce significant concentrations of contaminants into the system. A thermodynamic analysis of the solubility data
suggests that Zr(OH)40 likely is the dominant species over a wide pH region at elevated temperatures. The calculated Gibbs energies of formation
of Zr(OH)40(aq) and Zr(OH)4(am) at 298.15 K are −1472.6 kJ⋅mol−1 and −1514.2 kJ⋅mol−1, respectively. The enthalpy of formation of Zr(OH)40 has a value of −1695±11 kJ⋅mol−1 at 298.15 K. 相似文献
19.
Deepti N. Kurhe Dilip H. Dagade Jyoti P. Jadhav Sanjay P. Govindwar Kesharsingh J. Patil 《Journal of solution chemistry》2011,40(9):1596-1617
As proteins and other biomolecules consisting of amino acid residues require external additives for their dissolution and
recrystallization, it is important to have information about how such additives interact with amino acids. Therefore we have
studied the interactions of simple model amino acids with the additives urea and guanidine hydrochloride in aqueous solutions
at 298.15 K, using vapor pressure osmometry. During the measurements, the concentration of urea was fixed as ∼2 mol⋅kg−1 and that of guanidine hydrochloride was fixed as ∼1 mol⋅kg−1 whereas the concentrations of amino acids were varied. The experimental water activity data were processed to get the individual
activity coefficients of all the three components in the ternary mixture. Further, the activity coefficients were used to
get the excess Gibbs energies of solutions and Gibbs energies for transfer of either amino acids from water to aqueous denaturant
solutions or denaturant from water to aqueous amino acid solutions. An application of the McMillan-Mayer theory of solutions
through virial expansion of transfer Gibbs energies was made to get pair and triplet interaction parameter whose sign and
magnitude yielded information about amino acid–denaturant interactions, relative to their interactions with water. The pair
interaction parameters have been further used to obtain salting constants and in turn the thermodynamic equilibrium constant
values for the amino acid–denaturant mixing process in aqueous solutions at 298.15 K. The results have been explained in terms
of hydrophobic hydration, hydrophobic interactions and amino acid–denaturant binding. 相似文献
20.
Jaakko I. Partanen Pekka M. Juusola Arthur K. Covington 《Journal of solution chemistry》2009,38(11):1385-1416
Equations were developed for the calculation of the first stoichiometric (molality scale) dissociation constant (K
m1) of oxalic acid in buffer solutions containing oxalic acid, potassium hydrogen oxalate, and potassium chloride from the determined
thermodynamic values of this dissociation constant (K
a1) and the molalities of the components in the solutions. Similar equations were also developed for the second stoichiometric
dissociation constant (K
m2) of this acid in buffer solutions containing sodium or potassium hydrogen oxalate, oxalate and chloride. These equations
apply at temperatures from 0 to 60 °C up to ionic strengths of 1.0 mol⋅kg−1 and they have been based on single-ion activity coefficient equations of the Hückel type. For the equations for K
m1, the activity parameters of oxalate species and the K
a1 values were determined at various temperatures from the Harned cell data of a recent tetroxalate buffer paper (Juusola et
al., J. Chem. Eng. Data 52:973–976, 2007). By using the resulting equations for K
m1, the activity parameters of oxalate species for K
m2 and the K
a2 values were then determined from the new Harned cell data and from those of Pinching and Bates (J. Res. Natl. Bur. Stand.
(U.S.) 40:405–416, 1948) for solutions of sodium or potassium oxalates with NaCl or KCl. The resulting simple equations for calculation of K
m1 and K
m2 for oxalic acid were tested with all important thermodynamic data available in the literature for this purpose. The equations
for ln (K
a1) and ln (K
a2) are of the form ln (K
a)=a+b(t/°C)+c(t/°C)2. The coefficients for ln (K
a1) are the following: a=−2.8737, b=0.000159, and c=−0.00009. The corresponding coefficients for ln (K
a2) are −9.6563, −0.003059, and −0.000125, respectively. The new activity coefficient equations were used to evaluate the pH
values of the tetroxalate buffer solution (i.e., of the 0.05 mol⋅kg−1 KH3C4O8 solution) for comparison with the pH values recommended by IUPAC at temperatures from 0 to 60 °C and to develop a new two-component
oxalate pH buffer of 0.01 mol⋅kg−1 KHC2O4+0.05 mol⋅kg−1 Na2C2O4 for which pH values are given from 0 to 60 °C. Values of p(m
H) calculated from these equations are tabulated for these buffers as well as for buffer solutions with KCl and KH3C4O8 as the major component and minor component, respectively. Tables of p(m
H) are also presented for 0.001 mol⋅kg−1 KHC2O4+0.005 mol⋅kg−1 Na2C2O4 solutions in which KCl is the supporting electrolyte. 相似文献