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The first ionization constants of phosphoric acid and acetic acid have been measured in H2O and D2O from T = 373 K to T = 573 K and p = 11.5 and 20 MPa to yield accurate values of the deuterium isotope effect. Sequential conductivity measurements using a unique high-precision flow-through AC conductance instrument were made on dilute (m ≤ 10–2 mol·kg−1) aqueous solutions of phosphoric acid, acetic acid, potassium dihydrogenphosphate, sodium acetate, potassium hydroxide, sodium hydroxide, hydrochloric acid, potassium chloride and sodium chloride in light and heavy water under the same experimental conditions (temperature, pressure, flow-rate), so that systematic experimental errors between the two solvents would cancel. The experimental molar conductivities of potassium dihydrogenphosphate, sodium acetate, hydrochloric acid, and the corresponding chloride salts were used to calculate the molar conductivities for the fully dissociated acids [λ(D+), λ(D2PO4−) and λ(CH3COO−)]. Together with the molar conductivities measured for partially ionized acids, Λ(D3PO4) and Λ(CH3COOD), these yielded values for the degree of dissociation, α, and the ionization constants, pKa1. The iterative process was repeated at each temperature in both H2O and D2O where the Fuoss-Hsia-Fernández-Prini ("FHFP") and the Quint-Viallard ("QV") equations were used to correct for ionic strength. The resulting values of pKa1 for phosphoric acid in H2O agree with those reported from conductivity studies by previous works over the entire temperature range and with low temperature potentiometric studies to within the combined experimental uncertainties. The results for pKa1 above 298.15 K in D2O are the first to be reported in the literature. The new values for pKa(CH3COOD) yield more accurate values for the deuterium isotope effect on the ionization constant of acetic acid than those reported in our previous work (Erickson et al. in J. Phys. Chem. B. 123:9503–9506, 2019). The single-ion limiting conductivities for dihydrogenphosphate and acetate in D2O, λ(D2PO4−) and λ(CH3COO−), were found to be the same as those in H2O once corrected for viscosity effects, confirming previous observations for other ions. [ABSTRACT FROM AUTHOR]

Raman spectra of aqueous sodium borate solutions, with and without excess NaOH, NaCl, and LiCl, have been obtained from perpendicular and parallel polarization measurements acquired using a custom-built sapphire flow cell over the temperature range 25 to 300 °C at 20 MPa. The solvent-corrected reduced isotropic spectra include a large well-defined band at 865 cm−1 which overlaps with the boric acid B(OH)3 band at 879 cm−1, and becomes increasingly intense at elevated temperatures. This band does not correspond to the spectrum of any other previously reported aqueous polyborate ions, all of which have symmetric stretching bands at frequencies below that of borate, [B(OH)4]−, at 745 cm−1. Based on the classic high-temperature potentiometric titration study by R. E. Mesmer, C. F. Baes and F. H. Sweeton, Acidity measurements at elevated temperatures. VI. Boric acid equilibriums, Inorg. Chem., 1972, 11, 537–543, the new band was postulated to arise from a diborate ion, [B2(OH)7]− or [B2O(OH)5]−. Ab initio density functional theory (DFT), together with chemical modelling studies, suggest that it is most likely [B2(OH)7]−. Thermodynamic formation quotients derived from the peak areas showed variations with ionic strength as well as charge-balance discrepancies, which suggest one or more unidentified minor equilibrium species may also be present. The most likely candidate is the divalent diborate species [B2O2(OH)4]2− which is also predicted to have a band near 865 cm−1 and is postulated to be present as a sodium ion pair. These are the first quantitative Raman spectra ever reported for borate-rich solutions under such conditions and provide the first spectroscopic evidence of a diborate species at PWR reactor coolant temperatures. [ABSTRACT FROM AUTHOR]

Maricite, NaFeIIPO4, is an important iron(II) corrosion product in high-pressure steam generators operating under phosphate pH control. Experimental solubilities of maricite, in equilibrium with a large excess of magnetite and a known partial pressure of hydrogen, have been determined in a stirred Hastelloy C pressure vessel at temperatures from 220 to 300 °C. Equilibrium constants have been determined for the solubility reaction, Fe 3 O 4 s + 3 Na + aq + 3 HPO 4 2 - aq + H 2 aq ⇌ 3 NaFePO 4 s + 3 OH - aq + H 2 O(1) The resulting molar Gibbs energy of formation of maricite at 250 °C, has been combined with previously reported molar heat capacities and the enthalpy of formation at 25 °C to calculate the Gibbs energy of formation under standard conditions ΔfG°298(NaFePO4,s) = −1453.81 ± 2.76 kJ·mol−1. A thermodynamic model for the solubility of maricite over the experimental temperature range is reported. These values are combined with previously reported data for iron (III) compounds to provide a self consistent database for the reactions of magnetite protective films in high pressure steam generators operating under sodium phosphate chemistry control. [ABSTRACT FROM AUTHOR]

High-temperature tracer diffusion coefficients for H3O+ and OH− are important parameters in the modeling of diffusion-controlled reaction kinetics and mass transport processes under hydrothermal conditions, and these tracer diffusion coefficients are directly related to the ionic electrical conductivities in the limit of infinite dilution through the Nernst–Einstein relationship. The limiting conductivity of H3O+ and OH− in water is controlled by two separate mechanisms of ionic movement: (i) the bulk ionic diffusion and (ii) proton hopping, also known as "Grotthuss" mechanism and/or "prototropic transfer." This work reports a critical assessment of the limiting electrical conductivity data (Λ°) for aqueous HCl, KOH, and NaOH measured above room temperature. The initial assessed dataset included temperatures from 273.15 K up to 873.15 K and water densities from 1000 kg m−3 down to 270 kg m−3 and was reduced down to a final critically evaluated dataset spanning temperatures between 273.15 and 678.15 K and densities between 346 and 1006 kg m−3. The results were used to derive values for the excess conductivity due to prototropic transfer, λ E ° , of H3O+ and OH− using correlations previously reported for aqueous KCl. Simple empirical correlations of water viscosity and density were derived for Λ°(HCl), Λ°(KOH), Λ°(NaOH), λ E ° (H3O+), and λ E ° (OH−). Tests using the λ E ° (OH−) correlation and a previously reported function for Λ°(NaCl) show that the NaOH data can be accurately reproduced to within the estimated uncertainties. The reported correlations provide a means to model more accurately the tracer diffusion coefficients for H3O+ and OH− to supercritical conditions. [ABSTRACT FROM AUTHOR]

A custom-built flow-through AC conductivity instrument was used to measure the deuterium isotope effect on the ionization quotient of bisulfate from 150 to 300 °C, at p = 11.5 MPa. Standardized solutions of KCl, HCl, KOH, KHSO4, K2SO4, and H2SO4 were prepared in light and heavy waters and their conductivities were measured and fitted with the Quint–Viallard conductivity model to obtain single ion conductivities at infinite dilution for K+, Cl−, H+, OH−, HSO4−, and SO42−. These are the first conductivities of DSO4− and SO42− measured in heavy water at any temperature, and the first ionization constants for bisulfate reported in heavy water above 225 °C. The deuterium isotope effect on the chemical equilibrium constant, ΔpK2a = pK2a,D − pK2a,H, was found to increase with temperature, in contrast to the behaviour seen for other simple oxyacids. [ABSTRACT FROM AUTHOR]

Apparent molar volumes were determined using a high-pressure vibrating-tube densimeter for aqueous solutions of glycolic acid (HGly = HOCH(sub 2)COOH) and tartaric acid (H(sub 2)Tar = HOOCCH(OH)CH(OH)COOH) at temperatures from 25 degree C to 350 degree C and pressure as 20 MPa. It was suggested that the Krichevskii parameter, A(sub kr) = lim(x(sub 2) -> )) (deltap/deltax(sub 2))(super c)(sub t,v), which describes the discontinuities in standard partial molar properties at the critical point of water, is negative and almost all aqueous nonelectrolytes are characterized by Krichevskii parameters.

Apparent molar heat capacities [C.sub.p,[Phi]] and apparent molar volumes [V.sub.[Phi]] for aqueous diethanolamine[(HO[C.sub.2][H.sub.4]).sub.2]NH, diethanolammonium chloride [(HO[C.sub.2][H.sub.4]).sub.2]N[H.sub.2]Cl, N,N'-dimethylethanolamine (HO[C.sub.2][H.sub.4])[(C[H.sub.3]).sub.2]N, and N,N'-dimethylethanolammonium chloride (HO[C.sub.2][H.sub.4])[(C[H.sub.3]).sub.2]NHCl were determined from 283.15 to 328.15 K with a Picker flow microcalorimeter and vibrating tube densimeter. The experimental results have been analyzed in terms of Young's Rule with the Guggenheim form of the extended Debye--Huckel equation and appropriate corrections for chemical relaxation effects. These calculations lead to standard partial molar heat capacities and volumes for the neutral amines, [(HO[C.sub.2][H.sub.4]).sub.2]NH(aq) and (HO[C.sub.2][H.sub.4])[(C[H.sub.3]).sub.2]N(aq), and the ions [(HO[C.sub.2][H.sub.4].sub.2]N[H.sub.2][sup.+](aq) and (HO[C.sub.2][H.sub.4])[(C[H.sub.3]).sub.2]N[H.sup.+](aq) over the experimental temperature range. Key words: standard partial molar volumes, standard partial molar heat capacities, diethanolamine, dimethyethanolamine, aqueous alkanolamine ionization.

A custom-built titanium-sapphire flow cell has been used with a confocal Raman microscope to collect solvent-corrected reduced isotropic spectra of sodium and potassium phosphate solutions in light and heavy water from 75 to 300 °C at 20.4 ± 0.4 MPa over a wide range of concentrations. The symmetric vibrational modes of PO43− and HPO42−/DPO42− in both solvents broadened and moved to lower wavenumbers with increasing temperature, suggesting that oxyanion–water hydrogen bond strengths increase at elevated temperatures. Raman scattering coefficients, measured relative to the trifluoromethanesulfonate ion, were used to determine thermodynamic equilibrium quotients for the reaction PO43− + H2O HPO42− + OH− and its deuterium counterpart. Standard-state acid ionization constants were calculated using a modified Pitzer model and fitted as a function of temperature and solvent molar volume over the range of 25 to 300 °C from psat to 20 MPa. The deuterium isotope effect on the chemical equilibrium constant, ΔpK3a,m = pK3a,D,m − pK3a,H,m, was found to decrease from 1.045 ± 0.046 at 25 °C to 0.898 ± 0.073 at 250 °C. This behaviour is consistent with a model in which zero-point energy effects dominate at low temperatures and long-range solvent polarization becomes increasingly important as the temperature increases towards the critical point of D2O. These are the first experimental ionization constants to be reported in the literature for this reaction in light water above 50 °C and in heavy water at any temperature. [ABSTRACT FROM AUTHOR]