The estimation of the pK∗HA of acids in seawater using the Pitzer equations (original) (raw)
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The ionization of sulfurous acid in Na−Mg−Cl solutions at 25°C
Journal of Solution Chemistry, 1991
The stoichiometric pK 1* and pK 2* for the ionization of sulfurous acid has been determined from emf measurements in NaCl solutions with varying concentrations of added MgCl2 (m=0.1, 0.2 and 0.3) from I=0.5 to 6.0 molal at 25°C. These experimental results have been treated using both the ion pairing and Pitzer's specific ion-interaction models. The Pitzer parameters for the interaction of Mg2+ with SO2 and HSO 3− yielded λ=0.085±0.004, β(0) = 0.35±0.02, β(1) = 1.2±0.04, and Cφ = −0.072±0.007. The Pitzer parameters β(0) = −2.8±0.4, β(1) = 12.9±2.9 and β(2) = −2071±57 have been determined for the interactions of Mg2+ with SO 32−. The calculated values of pK 1* and pK 2* using Pitzer's equations reproduce the measured values to within ±0.04 pK units. The ion pairing model with log KMgSO3=2.36±0.02 and logγMgSO3 = 0.1021, reproduces the experimental values of pK 2* to ±0.01. These results demonstrate that treating the data by considering the formation of MgSO3 yields a better fit of the experimental measurements with fewer adjustable parameters. With these derived coefficients obtained from the Pitzer equations and the ion pairing model, it is possible to make reliable estimates of the activity coefficients of HSO 3− and SO 32− in seawater, brines and marine aerosols containing Mg2+ ions.
The pK1* for the dissociation of H2S in various ionic media
Geochimica et Cosmochimica Acta, 1988
The stoichiometric pK: for the dissociation of H2S has been determined from emf measurements in NaCl from 0.1 m to saturation at 5,25 and 45°C and in KCl solutions at 5 and 25°C. The values of pKf' were also measured in NaCl with small amounts of added M&l, and CaCl, to I = 6.0 m at 25°C. The results were used to determine Pitzer coefficients for the interactions of HS-ions with Na+, K+, Mg'+ and Ca '+ Values of the pKt , estimated using .
The pK∗ of TRISH+ in Na-K-Mg-Ca-Cl-SO4 brines—pH scales
Geochimica et Cosmochimica Acta, 1987
The stoichiometric dissociation constant, pK* of TRlSH+ has been determined in NaCl, KCl, MgC12 and CaClz solutions to an ionic strength of 6 molal. The results have been used to derive Pitzer coefficients for the interactions of TRIS with Na+, K+, Me and Ca*' ions. These results can be used to determine the pK* of TRlSH+ in mixed brines which can be used to calibrate pH electrodes. Measurements of pK* of TRlSH+ in mixtures of NaCl-M&l*, NaCl-CaC12, NaCl-Na2S04, KCl-MgC12 and KCl-CaC12, artificial seawater and Dead Sea waters were made to determine the reliability of the Pitzer coefficients. The estimated values were found to be in good agreement with the measured values provided corrections were made for the interactions of H+ with Sa-. It now is possible to use dilute solutions of TRlS and TRISH+ to make buffers that can be used to make reproducible pH measurements in brines.
The protonation constants of glycine in artificial seawater at 25 °C
Marine Chemistry, 1995
The ionization constants of glycine in artificial seawater containing NaCl, KCl, CaCl,, MgCl, and Na,SO, were potentiometrically determined at 2.5" C by using a commercial glass electrode. Measurements were carried out at different salinities, and thus ionic strengths, to simulate seawater and estuarine waters. The experimental data were fitted using different equations as functions of the salinity based on Miller0 (1979). Comparisons were made between the parameters obtained by changing the variables and also the parameters yielded by the Pitzer interaction model, which was previously applied by Miller0 to seawater systems. After considering all the proposed models we found the function in Sli2 to give the best fit and the smallest standard deviation of the parameters, although the extrapolated pK is not as good as the one obtained by the use of Pitzer's model. Some of the models we used yielded extrapolated pKs closer to the values in the literature (2.36 and 9.78) but higher standard deviations in the parameters.
Geochimica et Cosmochimica Acta, 1975
The apparent molal volume, t#+, of boric acid, B(OH),, and sodium borate, NaB(OH),, have been determined in 35x, salinity seawater and 0.725molal NaCl solutions at 0 and 25°C from precise density measurements. Similar to the behavior of nonelectrolytes and electrolytes in pure water, the ~5" of B(OH), is a linear function of added molality and the 4" of NaB(OH), is a linear function of the square root of added molarity in seawater and NaCl solutions. The partial molal volumes, B*, of B(OH), and NaB(OH), in seawater and NaCl were determined from the &'s by extmpolating to infinite dilution in the medium. The P* of B(OH), is larger in NaCl and seawater than pure water apparently due to the ability of electrolytes to dehydrate the nonelectrolyte B(OH),. The Y* of NaB(OH), in itself, NaCl and seawater is larger than the expected value at 0725 molal ionic strength due to ion pair formation [Na+ + B(OH)i -+ NaB(OH)$The volume change for the formation of Na~OH)~ in itself and NaCl was found to be equat to 29.4 ml mol-' at 2S"C and 0.725 molal ionic strength. These large AV*'s indicate that at least one water molecule is released when the ion pair is formed [Na' + R(OH); -+ H,O + NaOB(OH)zJ. The observed V* in seawater and the AV* INaB") in water and NaCl were used to estimate AV* (MaB'? = AT* (C!aB*) = 38.4ml mol-' for the formation of MgB' and CaB+. The volume change' fo; the ion&&m of 'B(OH), in NaCl and seawater was determined from the mofal volume data. Values of AV* = -29.2 and -25.9 ml moi-' were found in seawater, and Ati* = -21.6 and -26.4 in NaCl, respectively, at 0 and 25°C. The effect of pressure on the ionization of B(OH), in NaCl and seawater at 0 and 25°C determined from the volume change is in excellent agreement with direct measurements in artificial seawater (CULBERSON and PYTKOWICZ. 1968: DETECHE and DISTECHE, 1967) and natural seawater (CULBERWN and PYTKOWICZ, 1968).
Journal of Solution Chemistry, 2014
The Pitzer equations have been shown to be very useful in estimating the physical chemical properties of mixed electrolyte solutions like seawater. The equations account for all the ionic interactions occurring in a mixed electrolyte solution. In this paper, the Pitzer equations have been used to estimate the partial molar volumes of ions in 0.725 molÁkg -1 NaCl, which is a near equivalent for average seawater of absolute salinity S A = 35.165 gÁkg -1 . The calculated results at 25°C for a number of cations and anions are in good agreement with the measured values in 0.725 molÁkg -1 NaCl. The estimates in seawater are limited, due to the scarcity of volume data for metal sulfate and bicarbonate salts. The model can now be used to make reasonable estimates of the effect of pressure on equilibria in the oceans and other mixed electrolyte solutions over a wide range of composition, at 25°C, and for some of the major sea salts and the rare earth cations from 0 to 100°C.
Water Research, 2000
AbstractÐOrganic acid anion concentrations (R À ) represent an important part of the anion pool in colored surface waters. When the estimation of R À is based on a charge balance approach, R À cannot be used for the ionic balance control of the correctness of the analyses. We provide here another simple approach for R À estimation, which is independent of the charge balance. In this approach, R À was estimated using the concentration of ionizable carboxylic groups per mass of DOC (X I ), DOC concentration and pH. The X I value was estimated as the dierence between the average total concentration of carboxylic groups per 1 mg of DOC of natural fulvic and humic acids (10 meq mg À1 ) and the concentration of metal-complexed carboxylic groups. The latter concentration was assumed to be equal to organically-bound Al and Fe. When applied to the Bohemian Forest stream waters, the average (2standard deviation) X I was 6.2 2 0.8 meq mg À1 , R À varied from 2 to 146 meq l À1 , and the average percent dierence between the sums of cations and anions was 0.7%. The R À values, obtained using the charge balance approach, were strictly comparable (P < 0.001) to the values estimated from the proposed approach. 7