Potentiometric studies on association and dissociation equilibria of orthophosphoric acid, in waterKCl 3M medium at 25°C

Ferroni, G.

doi:10.1016/0013-4686(76)80020-5

Cited by 16 publications

(5 citation statements)

References 9 publications

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“…present. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] The first dissociation equilibrium of the phosphoric acid:…”

Section: Introductionmentioning

confidence: 99%

“…12 In the H 3 PO 4 -KCl system, on the other hand, no association could be verified. 28 It has been demonstrated that there is essentially no association between orthophosphates and K + at 25 • C and Lambert and Watters 51 have reported the value of 10 0.80 for the association quotient for the pyrophosphate complex KP 2 O 7 3in 1 M tetramethylammonium bromide at 25 • C but they were unable to detect association of orthophosphate with potassium ions.…”

mentioning

confidence: 99%

“…ref. 20,21,28) has been proposed. However, as a result of a carefully conducted study in 3 M NaC1O 4 at 25 • C 23 it was shown that at concentrations up to 0.02 m H 3 PO 4 it was unnecessary to invoke the existence of any species other than the mononuclear phosphate species.…”

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confidence: 99%

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Raman- and infrared-spectroscopic investigations of dilute aqueous phosphoric acid solutions

Rudolph

2010

Dalton Trans.

107

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Phosphoric acid in water and heavy water has been studied by Raman and infrared spectroscopy over a broad concentration range (0.00873-1.560 mol kg(-1)) at 23 °C. The vibrational modes of the PO(4) skeleton (C(3v) symmetry) of H(3)PO(4)(aq) and D(3)PO(4)(D(2)O) have been assigned. In addition to the P-O stretching modes a deformation mode has been detected, δPO-H(D) at 1250 and 935 cm(-1), respectively. In addition to the modes of the phosphoric acid and heavy phosphoric acid a mode of the dissociation product H(2)PO(4)(-) and D(2)PO(4)(-) has been detected at 1077 cm(-1) and 1084 cm(-1) respectively. H(3)PO(4) and D(3)PO(4) is hydrated in aqueous solution which could be verified by Raman spectroscopy following the νP[double bond, length as m-dash]O and ν(s)P(OH)(3) mode as a function of temperature. These modes show a pronounced temperature dependence inasmuch as νP[double bond, length as m-dash]O shifts to higher wavenumbers with temperature increase and ν(s)P(OH)(3) to lower wavenumbers. In the range between 300-600 cm(-1) the deformation modes have been observed. In very dilute H(3)PO(4) solutions however, the dissociation product is the dominant species. The dissociation degree, α for H(3)PO(4)(aq) and D(3)PO(4)(D(2)O) as a function of dilution has been measured at 23 °C. In these dilute H(3)PO(4)(aq) and D(3)PO(4)(D(2)O) solutions no spectroscopic features for a dimeric species of the formula H(6)P(2)O(8) and D(6)P(2)O(8) could be detected. Quantitative Raman measurements have been carried out to follow the dissociation of H(3)PO(4) and D(3)PO(4) over a very broad concentration range and also as a function of temperature. From the dissociation data, the pK(1) value for H(3)PO(4) has been determined to 2.14(1) and for D(3)PO(4) to 2.42(1) at 23 °C. In the temperature interval from 24.5 to 99.7 °C the pK(1) values for H(3)PO(4)(aq) have been determined and thermodynamic data have been derived.

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“…present. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] The first dissociation equilibrium of the phosphoric acid:…”

Section: Introductionmentioning

confidence: 99%

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confidence: 99%

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Raman- and infrared-spectroscopic investigations of dilute aqueous phosphoric acid solutions

Rudolph

2010

Dalton Trans.

107

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“…There is significant general experimental, − kinetic, and theoretical evidence for the dimerization of dihydrogen phosphate. Interestingly, the dimerization is a feature of dihydrogen phosphate only (monohydrogen phosphate does not form dimers).…”

Section: Resultsmentioning

confidence: 99%

On TAML Catalyst Resting State Lifetimes: Kinetic, Mechanistic, and Theoretical Insight into Phosphate-Induced Demetalation of an Iron(III) Bis(sulfonamido)bis(amido)-TAML Catalyst

et al. 2023

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At ambient temperatures, neutral pH and ultralow concentrations (low nM), the bis(sulfonamido)bis(amido) oxidation catalyst [Fe{4-NO 2 C 6 H 3 -1,2-(NCOCMe 2 NSO 2 ) 2 CHMe}(OH 2 )] − (1) has been shown to catalyze the addition of an oxygen atom to microcystin-LR. This persistent bacterial toxin can contaminate surface waters and render drinking water sources unusable when nutrient concentrations favor cyanobacterial blooms. In mechanistic studies of this oxidation, while the pH was controlled with phosphate buffers, it became apparent that iron ejection from 1 becomes increasingly problematic with increasing [phosphate] (0.3−1.0 M); 1 is not noticeably impacted at low concentrations (0.01 M). At pH < 6.5 and [phosphate] ≥ 1.0 M, 1 decays quickly, losing iron from the macrocycle. Iron ejection is surprisingly mechanistically complex; the pseudo-first-order rate constant k obs has an unusual dependence on the total phosphate concentration ([P t ]), k obs = k 1 [P t ] + k 2 [P t ] 2 , indicating two parallel pathways that are first and second order in [phosphate], respectively. The pH profiles in the 5.5−8.3 range for k 1 and k 2 are different: bellshaped with a maximum of around pH 7 for k 1 and sigmoidal for k 2 with higher values at lower pH. Mechanistic proposals for the k 1 and k 2 pathways are detailed based on both the kinetic data and density functional theory analysis. The major difference between k 1 and k 2 is the involvement of different phosphate species, i.e., HPO 4 2− (k 1 ) and H 2 PO 4 − (k 2 ); HPO 4 2− is less acidic but more nucleophilic, which favors intramolecular rate-limiting Fe−N bond cleavage. Instead, H 2 PO 4 − acts intermolecularly, where the kinetics suggest that [H 4 P 2 O 8 ] 2− drives degradation.

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“…The dissociation constant of phosphoric acid at lower temperatures is well known from emf studies, conductivity work, and ultrasound absorption among others [4][5][6][7][8][9][10][11][12][13][14][15][16][17]. The effect of temperature on the dissociation reaction has been measured by Nims [18] using conductivities, and by Bates [19] using a spectrophotometric technique, and later by Mesmer and Baes [20] who studied the corresponding hydrolysis reaction: H 2 PO − 4 + H 2 O H 3 PO 4 + OH − up to 300°C by a potentiometric method.…”

Section: Introductionmentioning

confidence: 99%

Raman-Spectroscopic Measurements of the First Dissociation Constant of Aqueous Phosphoric Acid Solution from 5 to 301 °C

Rudolph

2012

J Solution Chem

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Dilute aqueous phosphoric acid solutions have been studied by Raman spectroscopy at room temperature and over a broad temperature range from 5 to 301°C. R-normalized spectra (Bose-Einstein correction) have been constructed and used for quantitative analysis. The vibrational modes of H 3 PO 4 (aq) (pseudo C 3v symmetry) have been assigned. The band with the highest intensity, the symmetric stretch ν s {P(OH) 3 }(ν 1 (a 1 )) is strongly polarized while ν 4 (e), the antisymmetric stretch ν as P(OH) 3 ) is depolarized. The stretching mode of the phosphoryl group (-P=O), ν 2 (a 1 ) occurs at 1178 cm −1 and is polarized. In the range between 300 and 600 cm −1 , the deformation modes are observed. The deformation mode, δ{PO-H}, involving the O-H group has been detected at 1250 cm −1 as a very weak and broad mode.In addition to the modes of phosphoric acid, modes of the dissociation product H 2 PO − 4 (aq) have been observed. The mode at 1077 cm −1 has been assigned to ν s {PO 2 }, and the mode at 877 cm −1 to ν s {P(OH) 2 } which is overlapped by ν s {P(OH) 3 } of H 3 PO 4 (aq). The modes of H 2 PO − 4 (aq) have been measured in dilute solution and were assigned and presented as well. H 3 PO 4 is hydrated in aqueous solution, which can be verified with Raman spectroscopy by following the modes ν 2 (a 1 ) and ν 1 (a 1 ) as a function of temperature. These modes show a strong temperature dependency. The mode ν 1 (a 1 ) broadens and shifts to lower wavenumbers. The mode ν 2 (a 1 ) on the other hand, shifts to higher wavenumbers and broadens considerably with increases in temperature. At 301°C the phosphoric acid is almost molecular in nature. In very dilute H 3 PO 4 solutions at room temperature, however, the dissociation product, H 2 PO − 4 (aq) is the dominant species. In these dilute H 3 PO 4 (aq) solutions no spectroscopic features could be detected for a hydrogen bonded dimeric species of the formula H 5 P 2 O − 8 (or the neutral dimeric acid H 6 P 2 O 8 ). Pyrophosphate formation, although favored at high temperatures, could not be detected in dilute solution even at 301°C due to the high water activity. In highly concentrated solutions, however, pyrophosphate formation is observable and in hydrate melts the formation of pyrophosphate is already noticeable at room temperature.

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Potentiometric studies on association and dissociation equilibria of orthophosphoric acid, in waterKCl 3M medium at 25°C

Cited by 16 publications

References 9 publications

Raman- and infrared-spectroscopic investigations of dilute aqueous phosphoric acid solutions

Raman- and infrared-spectroscopic investigations of dilute aqueous phosphoric acid solutions

On TAML Catalyst Resting State Lifetimes: Kinetic, Mechanistic, and Theoretical Insight into Phosphate-Induced Demetalation of an Iron(III) Bis(sulfonamido)bis(amido)-TAML Catalyst

Raman-Spectroscopic Measurements of the First Dissociation Constant of Aqueous Phosphoric Acid Solution from 5 to 301 °C

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