Lakshmi N. Roy

Thermodynamics of the dissociation of boric acid in seawater at S = 35 from 0 to 55°C

The stoichiometric dissociation constants of boric acid in seawater at S = 35 have been determined from 0 to 55°C. The constants were determined from electromotive force measurements made with the cell, Pt|H2 (g, 1 atm)|;borax in synthetic seawater|;AgCl, Ag. The results are discussed in terms of “total” hydrogen ion scale. Our results are in excellent agreement (±0.0004 in ln K∗) with the measurements of Dickson (1990a). This study demonstrates that the measurements made by Dickson (1990a) are more reliable than the earlier measurements (Buch, 1933; Lyman, 1956; Hansson, 1973b) and should be used in all future studies of the carbonate system in seawater.

The standard potential for the hydrogen-silver, silver chloride electrode in synthetic seawater

The characterization of acid-base equilibria in seawater requires the measurement of the pH using buffers that have been calibrated using the H 2 , Pt|Ag, AgCl electrode system. The calculation of the pH of these buffers and the dissociation constants of acids in seawater requires a knowledge of the standard potential for seawater with added HCl. In this study we present measurements of the standard potential for the AgCl(s)+1/2 H 2 (g)↔Ag(s)+HCl(aq) cell reaction in synthetic seawater from 0 to 55 o C and at salinities from 5 to 45. The measurements were made at various concentrations of HCl and the results extrapolated to the pure medium. The extrapolations were made by using the total proton scale, m * (H + )=m(H + )+m(HSO 4 - )

The Thermodynamics of Aqueous Borate Solutions. II. Mixtures of Boric Acid with Calcium or Magnesium Borate and Chloride

AbstractPotentials for the cell without liquid junction

Second dissociation constants of 4-[N-morpholino]butanesulfonic acid and N-[2-hydroxyethyl]piperazine-N'-4-butanesulfonic acid from 5 to 55°C

H_2 ,Pt\backslash B(OH)_3 (m_1 ), MB(OH)_4 (m_2 ), MCl(m_3 )\backslash AgClAg

Buffers for the physiological pH range: Thermodynamic constants of substituted aminopropanesulfonic acids from 5 to 55°C

where M is sodium or potassium are reported over a range of ionic strength to I=3 mol-kg−1 at 5 to 55°C. Total boron concentration in the solutions was restricted to low levels to minimize formation of polynuclear boron species. Cell potentials are treated with the Pitzer ion interaction treatment for mixed electrolytes, with linear ionic strength dependence assumed for the activity coefficient of undissociated boric acid. Trace activity coefficients of sodium and potassium borates in chloride media are calculated at various temperatures.

Activity coefficients in (hydrogen bromide + magnesium bromide)(aq) at several temperatures. Application of Pitzer's equations☆

The second dissociation constant pK2 of 3-(N-morpholino)propanesulfonic acid (MOPS) has been determined at eight temperatures from 5 to 55°C by measurements of the emf of cells without liquid junction, utilizing hydrogen electrodes and silver–silver chloride electrodes. The pK2 has a value of 7.18 ± 0.001 at 25°C and 7.044 ± 0.002 at 37°C. The thermodynamic quantities ΔG°, ΔH°, ΔS°, and ΔCpo have been derived from the temperature coefficients of the pK2. This buffer at ionic strength I = 0.16 mol-kg−1 close to that of blood serum, has been recommended as a useful secondary pH standard for measurements of physiological fluids. Five buffer solutions with the following compositions were prepared: (a) equimolal mixture of MOPS (0.05 mol-kg−1) + NaMOPS, (0.05 mol-kg−1); (b( MOPS (0.05 mol-kg−1) + NaMOPS (0.05 mol-kg−1) + NaCl (0.05 mol-kg−1); (c) MOPS (0.05 mol-kg−1) + NaMOPS (0.05 mol-kg−1); + NaCl (0.11mol-kg−1); (d) MOPS (0.08 mol-kg−1) + NaMOPS (0.08 mol-kg−1); and (e)MOPS (0.08 mol-kg−1) + NaMOPS (0.08 mol-kg−1) + NaCl (0.08 mol-kg−1).The pH values obtained by using the pH meter + glass electrode assembly are compared with those measured from a flow–junction calomel cell saturated with KCl (cell B), as well as those obtained from cell (A) without liquid junction at 25 and 37°C. The conventional values of the liquid junction potentials Ej have been obtained at 25 and 37°C for the physiological phosphate reference solution as well as for the MOPS buffers (d) and (e) mentioned above.

Activity coefficients for (hydrogen bromide + calcium bromide + water) at various temperatures. Application of Pitzer's equations

The values of the second dissociation constant, pK2, for the dissociation of the NH+ charge center of the zwitterionic buffer compounds 4-(N-morpholino)butanesulfonic acid (MOBS), and N-(2-hydroxyethyl)piperazine-N′-4-butanesulfonic acid (HEPBS) have been determined from 5 to 55°C, including, 37°C at intervals of 5°C. The electromotive-force (emf) measurements have been made utilizing hydrogen electrodes and silver–silver chloride electrodes. The value of pK2 for MOBS was found to be 7.702 ± 0.0005, and 8.284 ± 0.0004 for HEPBS, at 25°C, respectively. The related thermodynamic quantities, Δ Go, Δ Ho, Δ So, and Δ Cpo for the dissociation processes of MOBS and HEPBS have been derived from the temperature coefficients of pK2. Both the MOBS and HEPBS buffer materials are useful as primary pH standards for the control of pH 7.3 to 8.6 in the region close to that of physiological fluids.

Buffers for the Physiological pH Range: Thermodynamics of the Second Dissociation of N-(2-Hydroxyethyl)piperazine-N′-2-hydroxypropanesulfonic Acid From 5 to 55°C

A comprehensive array of electrochemical cell measurements for the system HCl +SmCl3 + H2O was made from 5 to 55°C using a cell without liquid junction ofthe type:Pt; H2(g, 1 atm)|HCl (mA) + SmCl3 (mB)|AgCl, Ag (A)The present study, unlike previous studies of trivalent ions, are not complicatedby hydrolysis reactions. Measurements of the emf were performed for solutionsat constant total ionic strengths of 0.025, 0.05, 0.1, 0.25, 0.5, 1.0, 1.5, 2.0, 2.5,and 3.0 mol-kg−1. The mean activity coefficients of HCl (γHCl) in the mixtureswere calculated using the Nernst equation. All the experimental emf measurements(about 850) were first treated in terms of the simpler Harneds rule. Harnedinteraction coefficients (αAB and βAB) were calculated. The linear form of Harnedsrule is valid for most ionic strengths, but quadratic terms are needed at I = 1.5and 3 mol-kg−1. The Pitzer model was used to evaluate the activity coefficientsusing literature values, β(0), β(1), and Cφ, for HCl from 0 to 50°C and 25°C forSmCl3. The effect of temperature on the parameters for SmCl3 has been estimatedusing enthalpy and heat-capacity data. The mixing parameter ΘH,Sm wasdetermined at 25°C. The addition of the ΨH,Sm,Cl coefficient did not improve the fitsignificantly and no temperature dependence was found to be significant. Thevalue of ΘH,Sm = 0.2 ± 0.01 represented the values of γHCl with a standarddeviation of σ = 0.009 over the entire range of temperatures and ionic strength.The use of higher-order electrostatic effects (EΘH,Sm, EΘH,Sm) was included as itgave a better fit of the activity coefficients of HCl.