Rabindra N. Roy

The dissociation constants of carbonic acid in seawater at salinities 5 to 45 and temperatures 0 to 45°C

The pK1∗ and pK2∗ for the dissociation of carbonic acid in seawater have been determined from 0 to 45°C and S = 5 to 45. The values of pK1∗ have been determined from emf measurements for the cell: Pt](1 − X)H2 + XCO2|NaHCO3, CO2 in synthetic seawater|AgC1; Ag where X is the mole fraction of CO2 in the gas. The values of pK2∗ have been determined from emf measurements on the cell: Pt, H2(g, 1 atm)|Na2CO3, NaHCO3 in synthethic seawater|AgC1; Ag The results have been fitted to the equations: lnK∗1 = 2.83655 − 2307.1266/T − 1.5529413 lnT + (−0.20760841 − 4.0484/T)S0.5 + 0.08468345S − 0.00654208S1 InK∗2 = −9.226508 − 3351.6106/T− 0.2005743 lnT + (−0.106901773 − 23.9722/T)S0.5 + 0.1130822S − 0.00846934S1.5 where T is the temperature in K, S is the salinity, and the standard deviations of the fits are σ = 0.0048 in lnK1∗ and σ = 0.0070 in lnK2∗. Our new results are in good agreement at S = 35 (±0.002 in pK1∗and ±0.005 in pK2∗) from 0 to 45°C with the earlier results of Goyet and Poisson (1989). Since our measurements are more precise than the earlier measurements due to the use of the Pt, H2|AgCl, Ag electrode system, we feel that our equations should be used to calculate the components of the carbonate system in seawater.

Thermodynamics of aqueous carbonate solutions including mixtures of sodium carbonate, bicarbonate, and chloride

Abstract Recently the authors examined electrochemical-cell data leading to values of the activity coefficient for aqueous sodium bicarbonate. Since that preliminary analysis, new experimental measurements have been published which contribute significantly to the overall thermodynamic understanding of (sodium carbonate + sodium bicarbonate + carbonic acid). In this more extensive examination we consider a wide variety of measurements leading to activity coefficients of Na 2 CO 3 and NaHCO 3 from 273 to 323 K and to relative molar enthalpies and heat capacities at 298.15 K. Tables of thermodynamic quantities at selected temperatures are included.

The use of buffers to measure the pH of seawater

The pH of seawater can be measured in the field using potentiometric and spectrophotometric methods. The use of pH standards or buffers is an important aspect of the calibration of both methods in a laboratory on a common concentration scale. The buffers can also be used to monitor the performance of pH meter and spectrophotometer during a cruise. A procedure is described for the determination of the pH of seawater, where the proton concentration is expressed as moles kg-H2O−1 using seawater buffers. The buffers are prepared in synthetic seawater in the laboratory by the methods outlined by Bates and coworkers. We have prepared four buffers (Bis, Tris, Morpholine and 2-Aminopyridine) that cover a pH range from 6.8 to 8.8. The emf values of the buffers were measured with a H2, Pt/AgCl, Ag electrode system after their preparation and bottling for use at sea. The measured emf values were found to be in good agreement (±0.05 mV) with the original measurements of Bates and coworkers from 0 to 45°C. The measured pH of these buffers are in good agreement (±0.001 pH units) with the values calculated from the equations of Dickson on the total pH scale based on Bates et al. Studies are underway to access the long term stability of these buffers. We have also used these buffers to calibrate systems used to make potentiometric and spectrophotometric measurements of pH on seawater relative to the H2, Pt/Ag, AgCl electrode from 5 to 45°C.

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

Activity coefficients for the system HCl + CaCl2+ H2O at various temperatures. Applications of pitzer's equations

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.