Spectrophotometric investigation of the protonation of monomeric molybdic acid in sodium perchlorate medium

Cruywagen, J. J.; Heyns, J. B. B.; Rohwer, E.F.C.H.

doi:10.1016/0022-1902(76)80463-0

Cited by 38 publications

(11 citation statements)

References 4 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The converged averages ⟨Δ E ⟩ λ and Helmholtz energy changes Δ dp A calculated by the three-point formula (eq ) are given in Table . Also listed are the calculated acidity constants for the first and second protonations of molybdic acid and, for comparison, the experimental p K a values. , These values show that the p K a estimates for the previously assumed −OH protonations are much higher than the experimental values. The difference of ∼10 p K a units is well outside the uncertainty of the present methodology (∼2 p K a units).…”

Section: Resultsmentioning

confidence: 92%

“…In strongly acidic solutions, W(VI) undergoes condensation reactions to form polyoxoanions even when the total W(VI) concentration, [W(VI)] t , is <10 –6 M. − In stark contrast, at pH ≲2.5 and [Mo(VI)] t ≲10 –4 M, uncharged molybdic acid, MoO 2 (OH) 2 (OH 2 ) 2 0 (often written as “H 2 MoO 4 0 ”), undergoes two protonations, forming successively two cations with stoichiometries H 3 MoO 4 + and H 4 MoO 4 2+ (the molybdenyl cation). − Separation of Mo(VI) and W(VI) can then be achieved easily using an appropriate ion-exchange resin. − However, optimization of this process requires a detailed and unambiguous understanding of the extraction mechanism. This, in turn, demands precise knowledge of the composition and structure of the dominant Mo(VI) species in strongly acidic solutions.…”

Section: Introductionmentioning

confidence: 99%

“…Numerous investigations of the protonation equilibria of molybdic acid have been made over the last 60 years, using a variety of techniques such as UV–Vis spectrophotometry, ,, enthalpimetric titrimetry, and electrophoresis . These studies are in broad agreement and indicate that uncharged molybdic acid undergoes two protonations, with acidity constants p K a2 (H 3 MoO 4 + ) ≈ 0.85 to 1.06 and p K a1 (H 4 MoO 4 2+ ) ≈ −2.13.…”

Section: Introductionmentioning

confidence: 99%

“…Calculated Helmholtz Energies (in eV) and pK a Values for Various Protonated Mo(VI) Species in Strongly Acidic Solutions at 300 K a indicates the hydrogen atom that was treated quantum mechanically in the protonated state (H) and as a dummy atom in the deprotonated state (d). b Literature values 11,14. …”

mentioning

confidence: 99%

See 3 more Smart Citations

Nature of Monomeric Molybdenum(VI) Cations in Acid Solutions Using Theoretical Calculations and Raman Spectroscopy

et al. 2019

View full text Add to dashboard Cite

The composition and structures of the two protonated species formed from uncharged molybdic acid, MoO2(OH)2(OH2)2 0, in strongly acidic solutions have been investigated using a combination of density functional theory calculations, first-principles molecular dynamics simulations, and Raman spectroscopy. The calculations show that both protonated species maintain the original octahedral structure of molybdic acid. Computed pK a values indicated that the O moieties are the proton acceptor sites and, therefore, that MoO(OH)3(OH2)2 + and Mo(OH)4(OH2)2 2+ are the probable protonated forms of Mo(VI) in strong acid solutions, rather than the previously accepted MoO2(OH)2–x (OH2)2+x x+ (x = 1, 2) species. This finding is shown to be broadly consistent with the observed Raman spectra. Structural details of MoO(OH)3(OH2)2 + and Mo(OH)4(OH2)2 2+ are reported.

show abstract

Section: Resultsmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

See 2 more Smart Citations

Nature of Monomeric Molybdenum(VI) Cations in Acid Solutions Using Theoretical Calculations and Raman Spectroscopy

et al. 2019

View full text Add to dashboard Cite

show abstract

“…However, molybdic acid will begin to protonate and dimerise when Z > 2 (Eqs. (7)e(9)) [8,11,16,17,24,25], which is undesirable for 12-MPA formation.…”

Section: Mo(vi) Speciation and 12-mpa Formationmentioning

confidence: 98%

The molybdenum blue reaction for the determination of orthophosphate revisited: Opening the black box

Nagul

McKelvie

Worsfold

et al. 2015

Analytica Chimica Acta

325

247

View full text Add to dashboard Cite

The molybdenum blue reaction, used predominantly for the determination of orthophosphate in environmental waters, has been perpetually modified and re-optimised over the years, but this important reaction in analytical chemistry is usually treated as something of a 'black box' in the analytical literature. A large number of papers describe a wide variety of reaction conditions and apparently different products (as determined by UV-visible spectroscopy) but a discussion of the chemistry underlying this behaviour is often addressed superficially or not at all. This review aims to rationalise the findings of the many 'optimised' molybdenum blue methods in the literature, mainly for environmental waters, in terms of the underlying polyoxometallate chemistry and offers suggestions for the further enhancement of this time-honoured analytical reaction.

show abstract

Molybdenum Oxygen Chemistry: Oxides, Oxo Complexes, and Polyoxoanions

Pope

1991

Progress in Inorganic Chemistry

View full text Add to dashboard Cite

Spectrophotometric investigation of the protonation of monomeric molybdic acid in sodium perchlorate medium

Cited by 38 publications

References 4 publications

Nature of Monomeric Molybdenum(VI) Cations in Acid Solutions Using Theoretical Calculations and Raman Spectroscopy

Nature of Monomeric Molybdenum(VI) Cations in Acid Solutions Using Theoretical Calculations and Raman Spectroscopy

The molybdenum blue reaction for the determination of orthophosphate revisited: Opening the black box

Molybdenum Oxygen Chemistry: Oxides, Oxo Complexes, and Polyoxoanions

Contact Info

Product

Resources

About