Dissociation Constants Of Phosphoric Acid Research Articles

Third dissociation constant of phosphoric acid in H2O and D2O from 75 to 300 °C at p = 20.4 MPa using Raman spectroscopy and a titanium-sapphire flow cell.

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.

Novel acrylate/organophosphorus-based hydrogels for agricultural applications. New outlook and innovative concept for the use of 2-(methacryloyloxy)ethyl phosphate as a multi-purpose monomer

Novel hydrogels with phosphoric acid-bearing units suitable for agricultural applications have been obtained. Introducing phosphate moieties into acrylate-based hydrogels could result in better swelling properties, especially under acidic conditions as the dissociation constants of phosphoric acid are much lower than that of acrylic acid. The presence of phosphate groups could also increase hydrogels’ biocompatibility and biodegradability, what in the case of agricultural application may be of great advantage. Presented hydrogels, besides acting as a water reservoir, have a potential to be an additional source of phosphorus - preliminary studies confirmed phosphate release as a result of hydrolysis. To obtain novel hydrogels, two organophosphorus compounds were chosen: 2-(methacryloyloxy)ethyl phosphate (MEP) acting as functional monomer and bis[2-(methacryloyloxy)ethyl] phosphate (BMEP) acting as a crosslinking agent. To the best of our knowledge, the use of these monomers in combination with acrylic acid has not been reported earlier in hydrogel synthesis. Hydrogels with nominal BMEP and MEP concentration 0.5–5.0 wt.% and 1.0–4.0 wt.%, respectively and water regain ranging from 105.5 g/g up to 2837.5 g/g were obtained. Swelling properties and response to different stimuli (pH, ionic strength etc.) were determined, indicating that synthesized materials could be successfully applied in agriculture. Moreover, obtained results gave new information about the properties of MEP, BMEP, products of their polymerization and, simultaneously, on their potential applications.

Dissociation constants of phosphoric acid in dimethylformamide-water mixtures at 298.15 K

The dissociation constants of phosphoric acid (pK 1 and pK 2) in water-dimethylformamide (DMFA) mixtures (0–0.65 mole fractions of DMFA) were determined at 298.15 K by potentiometric titration. The extrapolation of these data to pure DMFA and the comparative calculation method were used to estimate the dissociation constants of the acid in DMFA.

Standard Thermodynamic Properties of H3PO4(aq) over a Wide Range of Temperatures and Pressures

The densities and heat capacities of solutions of phosphoric acid, 0.05 to 1 mol kg-1, were measured using flow vibrating tube densitometry and differential Picker-type calorimetry at temperatures up to 623 K and at pressures up to 28 MPa. The standard molar volumes and heat capacities of molecular H3PO4(aq) were obtained, via the apparent molar properties corrected for partial dissociation, by extrapolation to infinite dilution. The data on standard derivative properties were correlated simultaneously with the dissociation constants of phosphoric acid from the literature using the theoretically founded SOCW model. This made it possible to describe the standard thermodynamic properties, particularly the standard chemical potential, of both molecular and ionized phosphoric acid at temperatures up to at least 623 K and at pressures up to 200 MPa. This representation allows one to easily calculate the first-degree dissociation constant of H3PO4(aq). The performance of the SOCW model was compared with the other approaches for calculating the high-temperature dissociation constant of the phosphoric acid. Using the standard derivative properties, sensitively reflecting the interactions between the solute and the solvent, the high-temperature behavior of H3PO4(aq) is compared with that of other weak acids.

Re-evaluation of the Second Stoichiometric Dissociation Constants of Phosphoric Acid at Temperatures from (0 to 60) °C in Aqueous Buffer Solutions with or without NaCl or KCl. 2. Tests and Use of the Resulting Hückel Model Equations

Previously (in Part 1), equations were determined for the calculation of the second stoichiometric (molality scale) dissociation constant (Km2) of phosphoric acid in buffer solutions containing sodium, or potassium, dihydrogen phosphate, hydrogen phosphate, and chloride from the determined thermodynamic values of this dissociation constant (Ka2) and the molalities of the components in the solutions. These equations were based on single-ion activity coefficient equations of the Hückel type. In the present study (Part 2), these equations were further tested with all reliable thermodynamic data found in the literature from this dissociation reaction in NaCl and KCl solutions. In these data were included a considerable amount of literature results from measurements on cells without liquid junction using hydrogen and silver−silver chloride or mercury−mercury(I) chloride electrodes at temperatures from (0 to 95) °C. Also literature data from hydrogen and glass electrode cells containing liquid junctions were included in the present tests. The new model usually applies well to these data. The new model equations were then used to calculate pH values of the two phosphate buffer solutions recommended by IUPAC (in 1985 and 2002) at temperatures from (0 to 70) °C. Values of p(mH), giving the molality of hydrogen ions directly, calculated from these equations are also tabulated for these buffers as well as for the buffer solutions with NaCl or KCl as major component and with KH2PO4 and Na2HPO4 at an equal molality of 0.0025 mol·kg-1 as minor components.

Re-evaluation of the Second Stoichiometric Dissociation Constants of Phosphoric Acid at Temperatures from (0 to 60) °C in Aqueous Buffer Solutions with or without NaCl or KCl. 1. Estimation of the Parameters for the Hückel Model Activity Coefficient Equations

Equations were determined for the calculation of the second stoichiometric (molality scale) dissociation constant (Km2) of phosphoric acid in buffer solutions containing sodium dihydrogen phosphate, sodium hydrogen phosphate, and sodium chloride and the corresponding systems where mixed potassium and sodium salts were used from the determined thermodynamic values of this dissociation constant (Ka2) and the molalities of the components in the solutions. These equations were based on the single-ion activity coefficient equations of the Huckel type. The parameters of the phosphate ions for these equations and the thermodynamic values of the second dissociation constant of this acid at various temperatures were determined from the Harned cell data of Bates and Acree (1943 and 1945), and these data extend at temperatures from (0 to 60) °C up to ionic strengths of about 0.5 mol kg-1. All calculations from these data were completely revised, and all parameters estimated seem to depend in a simple way on the temp...

First Dissociation Constant of Phosphoric Acid in Non-Aqueous Solvents

The first dissociation constant of phosphoric acid and its equivalent conductance at infinite dilution were determined in non-aqueous solvents like methanol, ethanol and acetonitrile. The single ion conductance values of HThe

First and second dissociation constants of phosphoric acid in 1 and 3 m sodium chloride solutions from 268.15 to 318.15 K

The acid dissociation constants of H 3 PO 4 and H 2 PO 4 - in 1 and 3 m NaCl were determined from measurements of the electromotive force (emf) of cells without a liquid junction at intervals of 10 K from 268.15 to 318.15 K. The hydrogen gas electrode and silver-silver chloride reference electrode were used. The dissociation constants pK 1 * and pK 2 * (referred to standard states in pure NaCl solutions) were derived from the corrected emf data by a modified Harned-Ehlers method

Standard potential of the silver chloride/silver electrode and the second dissociation constant of phosphoric acid in 20, 50, and 80 mass % 2-methoxyethanol + water from -10 to +37 .degree.C

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStandard potential of the silver chloride/silver electrode and the second dissociation constant of phosphoric acid in 20, 50, and 80 mass % 2-methoxyethanol + water from -10 to +37 .degree.CCarmen A. Vega, Mabel Barreto, and Roger G. BatesCite this: J. Chem. Eng. Data 1991, 36, 2, 198–202Publication Date (Print):April 1, 1991Publication History Published online1 May 2002Published inissue 1 April 1991https://doi.org/10.1021/je00002a016RIGHTS & PERMISSIONSArticle Views39Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (537 KB) Get e-Alerts Get e-Alerts

Dissociation constants of phosphoric acid at 25�C and the ion pairing of sodium with orthophosphate ligands at 25�C

The first and second acidity constants of phosphoric acid were determined in a 0.70 ionic strength solution of both a sodium and a potassium ion background salt at 25°C. These experimentally determined constants were compared to literature values as well as values calculated from a theoretical model. Assuming negligible ion pairing of the phosphate ligand with the potassium ions, the stability constants of the NaHPO 4 - and NaH2PO 4 0 complexes were determined to be 1.3±0.3 and 0.49±0.07 (mol-L−1), respectively. These constants were used to model the speciation of orthophosphate in a background of a sodium salt from pH 3 to 10.

Performance testing of pH electrodes suitable for low ionic strength solutions

Performance tests using dilute acid were carried out on 16 glass-reference electrode pairs. Recently marketed electrodes designed for use in dilute solutions and having high leakage rates at the reference junction performed well, but were no better than some others with low leakage rates. The determination of the second dissociation constant of phosphoric acid by potentiometric titration was a more demanding test of electrode performance: satisfactory results were only obtained using a renewable free diffusion junction. There are various indications that the Henderson equation may be inappropriate for calculating liquid junction potentials for dilute acids, but there is a lack of precise experimental work in dilute solutions. Consequently there is uncertainty regarding the errors involved in equating the measured pH of dilute acids to the calculated activity of the hydrogen ion.

Intracellular pH determination by a 31P-NMR technique. The second dissociation constant of phosphoric acid in a biological system

To evaluate the accuracy of pH determination by 31P-NMR, factors which influence the pK value of phosphate were appraised on the basis of the titration of 1 mM phosphate buffer solution. When the method is used for the determination of cytoplasmic pH, ionic strength is the major factor causing shifts of apparent pK (pK') value, and the magnitude of the shift can be predicted from the ionic strength calculated by means of the Debye-Huckel equation. Ions (Na+, K+, Mg2+, and Ca2+) and salivary protein affected the pK' value by 0.1 to 0.3 units in solution with a given ionic strength depending on the species of ion. The form of the titration curve varied with temperature. Based on these results, the value of 6.75 was obtained with the uncertainty of 0.12 for the intracellular pK' of frog muscle at 24 degrees C.

Intracellular pH determination by a 31P-NMR technique. The second dissociation constant of phosphoric acid in a biological system.

To evaluate the accuracy of pH determination by 31P-NMR, factors which influence the pK value of phosphate were appraised on the basis of the titration of 1 mM phosphate buffer solution. When the method is used for the determination of cytoplasmic pH, ionic strength is the major factor causing shifts of apparent pK (pK') value, and the magnitude of the shift can be predicted from the ionic strength calculated by means of the Debye-Hückel equation. Ions (Na+, K+, Mg2+, and Ca2+) and salivary protein affected the pK' value by 0.1 to 0.3 units in solution with a given ionic strength depending on the species of ion. The form of the titration curve varied with temperature. Based on these results, the value of 6.75 was obtained with the uncertainty of 0.12 for the intracellular pK' of frog muscle at 24 degrees C.

Conductometric studies on the dissociation constants of phosphoric acid in methanol-water mixtures

The dissociation constants of phosphoric acid have been determined in methanol-water mixtures (8.0–87% by weight of methanol) by the method suggested by Gelb. The results have been verified by Fuoss—Kraus method. Δ 0 values of HClO 4, KClO 4 and KH 2PO 4 (and hence of H 3PO 4) in mixed solvents have been determined in the usual way. The role of solvents on the dissociation constants has been discussed.

The estimation of acid dissociation constants in sea-water media from potentiometric titrations with strong base. II. The dissociation of phosphoric acid

Abstract The three dissociation constants of phosphoric acid have been determined in seawater media over the temperature and ionic strength ranges 5–30°C and 0.3-0.9 m. The results obtained fitted the equations (concentrations in mol per kg of solution): pK 1P = -75 T +2.16-0.35I 1 2 ( rmsdeviation 0.034 ) pK 2P = 737.6 T ++4.176-0.851I 1 2 ( rmsdeviation 0.015 ) pK 3P = 2404 T +1.31-0.87I 1 2 ( rmsdeviation 0.17 ) The results are only in moderate agreement with those of Kester and Pytkowicz (1967). The reason for this lies partly in differences between the pH scales adopted and partly in the poor precision inherent in their method.

DETERMINATION OF THE APPARENT DISSOCIATION CONSTANTS OF PHOSPHORIC ACID IN SEAWATER1

A method was developed for determining the apparent dissociation constants of a tribasic acid in complex concentrated ionic solutions using potentiometric pH measurements and acid‐base titrations. The apparent dissociation constants of phosphoric acid were determined in artificial seawater over the ranges of temperature and salinity normally encountered in the ocean. These apparent dissociation constants were also measured in 0.68 m NaCl, which has the same ionic strength as seawater of 33‰ salinity. It was estimated that 99.6% of the PO43− species and 44% of the HPO42− species are complexed by cations in seawater other than Na+. The values of the apparent dissociation constants reveal that in seawater of 33‰ salinity at 20C at pH 8.0, 87% of the inorganic phosphate exists as HPO42−, 12% as PO43−, and 1% as H2PO4− .

The Apparent Dissociation Constants of Phosphoric Acid at 38° at Ionic Strengths from 0.1 to 0.5

The Apparent Dissociation Constants of Phosphoric Acid at 38° at Ionic Strengths from 0.1 to 0.5

First dissociation constant of phosphoric acid from 0-degrees-C to 60-degrees-C; Limitations of the electromotive force method for moderately strong acids

First dissociation constant of phosphoric acid from 0-degrees-C to 60-degrees-C; Limitations of the electromotive force method for moderately strong acids

PH values of certain phosphate-chloride mixtures, and the second dissociation constant of phosphoric acid from 0 degrees to 60 degrees C

pH values of certain phosphate-chloride mixtures, and the second dissociation constant of phosphoric acid from 0 degrees to 60 degrees C

ON THE NUMERICAL VALUE OF THE SECOND DISSOCIATION EXPONENT OF PHOSPHORIC ACID AND FACTORS INFLUENCING UPON IT

ON THE NUMERICAL VALUE OF THE SECOND DISSOCIATION EXPONENT OF PHOSPHORIC ACID AND FACTORS INFLUENCING UPON IT: I. Experimental studies on the dissociation constant of phosphoric acid Get access KWANICHI SHIMA KWANICHI SHIMA 1st Division of the Institute of Physiology, Kyoto Imperial University Search for other works by this author on: Oxford Academic PubMed Google Scholar The Journal of Biochemistry, Volume 29, Issue 1, January 1939, Pages 121–145, https://doi.org/10.1093/oxfordjournals.jbchem.a125783 Published: 01 January 1939 Article history Received: 10 August 1938 Published: 01 January 1939