Equilibrium and structural of silicon(IV) and aluminum(III) in aqueous solution. 21. A potentiometric and sup 27 Al NMR study of the system H sup + -Al sup 3+ -MoO sub 4 sup 2 minus

Journal Article · Wed Sep 20 04:00:00 EDT 1989 · Inorganic Chemistry; (USA)

DOI:https://doi.org/10.1021/ic00318a004· OSTI ID:6985563

Oehman, L O ^[1]

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1. Univ. of Umea (Sweden)

Equilibria in the H{sup +}-Al{sup 3+}-MoO{sub 4}{sup 2{minus}} system have been studied by potentiometry and {sup 27}Al NMR spectroscopy in 0.6 M Na(Cl) medium at 25{degree}C. The total concentration of aluminum, B, and molybdate, C, were varied within the limits 0.9 {le} B/mM {le} 10, 5.5 {le} C/mM {le} 120, and 2 {le} C/B {le} 12 within the range 1.5 {le} -log (H{sup +}) {le} 6.0. All data unambiguously show that one single ternary species, Al(OH){sub 6}Mo{sub 6}O{sub 18}{sup 3{minus}}, is formed. According to potentiometric data, the formation constant for this species (as related to the reaction 6H{sup +} + Al{sup 3+} + 6MoO{sub 4}{sup 2{minus}} {r reversible} Al(OH){sub 6}Mo{sub 6}O{sub 18}{sup 3{minus}}) is log ({beta}{sub 6,1,6} {plus minus} 3{sigma}) = 50.95 {plus minus} 0.04. Independent {sup 27}Al NMR data yielded the value 50.96 {plus minus} 0.06, i.e. in full agreement with emf data. The high thermodynamic stability of the complex was manifested in a model calculation, showing that even at B = 10{sup {minus}5} M, C = 6 {times} 10{sup {minus}5} M, and -log (H{sup +}) = 3.7, 40% of B and C remained bound in this species. In acidic media, equilibration times of approximately 6 h were observed, while in near-neutral solutions the decomposition rate is higher by several orders of magnitude. With -log (H{sup +}) {le} 2, the complex decomposes with the formation of free aluminum ions and isopoly molybdates, while in near-neutral solutions (-log (H{sup +}) {ge} 5) the decomposition yields amorphous aluminum hydroxide and molybdate ions. The solubility product for this phase, defined by the reaction Al{sup 3+} + 3H{sub 2}O {r reversible} Al(OH){sub 3}(s) + 3H{sup +}, was determined to be log (K{sub {minus}3,1,0} {plus minus} 3{sigma}) = {minus}10.49 {plus minus} 0.08. Data were analyzed with the computer programs Letagropvrid and Solgaswater. 20 refs., 8 figs., 1 tab.

• OSTI ID: 6985563
• Journal Information: Inorganic Chemistry; (USA), Journal Name: Inorganic Chemistry; (USA) Vol. 28:19; ISSN 0020-1669; ISSN INOCA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
400202 -- Isotope Effects
Isotope Exchange
& Isotope Separation
ALUMINIUM 27
ALUMINIUM COMPOUNDS
ALUMINIUM ISOTOPES
AQUEOUS SOLUTIONS
CATIONS
CHARGED PARTICLES
CHEMICAL REACTIONS
DATA
DISPERSIONS
EXPERIMENTAL DATA
INFORMATION
IONS
ISOTOPES
LIGHT NUCLEI
MIXTURES
MOLYBDATES
MOLYBDENUM COMPOUNDS
NMR SPECTRA
NUCLEI
NUMERICAL DATA
ODD-EVEN NUCLEI
OXYGEN COMPOUNDS
REFRACTORY METAL COMPOUNDS
SILICON COMPOUNDS
SOLUTIONS
SPECTRA
STABLE ISOTOPES
TRANSITION ELEMENT COMPOUNDS