Quantitative determination of an aluminate dimer in concentrated alkaline aluminate solutions by Raman spectroscopy

The ultrasonic velocities, densities, viscosities, and electrical conductivities of aqueous solutions of magnesium nitrate and magnesium acetate have been measured as functions of concentration (0.0145 ≤ m/mol·kg-1 ≤ 6.545) and temperature 273.15 ≤ T/K ≤ 323.15. The results are in reasonable agreement with literature data where comparisons are possible. The viscosity and electrical conductivity data are consistent with greater ion association in Mg(OAc)2 solutions

Viscosities and densities of highly concentrated aqueous MOH solutions (M+ = Na+, K+, Li+, Cs+, (CH3)4N+) at 25.0°C

The absolute (dynamic) viscosities (η) and densities (ρ) of carbonate-free aqueous tetramethylammonium and alkali metal hydroxides have been determined up to saturation concentrations ([NaOH] ≤ 19.1 M, [KOH] ≤ 14.1 M, [LiOH] ≤ 4.8 M, [CsOH] ≤ 14.8 M, and [(CH3)4NOH] ≤ 4.2 M) at 25.00°C using a Ubbelohde viscometer and a vibrating tube densitometer, respectively. The viscosities are believed to be precise to within 0.1% and the densities to within 5 × 10-6 g cm-3. Densities of isoplethic MOH solutions increase in the order of (CH3)4N+ < Li+ < Na+ < K+ ≪ Cs+. Viscosities for [MOH] < 4 M solutions increase in the reverse order, but the viscosities of CsOH solutions become extremely large at very high concentrations. The shape of the density vs concentration function of (CH3)4NOH solutions is also quite different when compared with the alkali metal hydroxide solutions. Density data were fitted up to the highest concentrations using the Masson equation. Viscosity vs concentration functions are represented in the form of a fifth-order (empirical) polynomial

A general method for the determination of copper(I) equilibria in aqueous solution

Copper(I) equilibrium constants can, for the first time, be studied routinely in aqueous solution by potentiometric titration using CuI solutions produced by reduction of CuII with an excess of copper and stabilized by chloride

Carbonate removal from concentrated hydroxide solutions

Methods for routinely lowering the carbonate content of concentrated aqueous hydroxide solutions [MOH with M+ = Li+, Na+, K+, Cs+ and (CH3)4N+] to analytically negligible levels (≤ 0.2% of the total alkalinity) are described. No single method was satisfactory for all MOH. Carbonate can be removed from highly concentrated (ca. 50% w/w) NaOH solutions by filtration since Na2CO3 is almost insoluble in this medium. However, for LiOH (ca. 4 M), (CH3)4NOH (ca 4.5 M) and KOH (ca. 14 M) and less concentrated NaOH (< 10 M), treatment with excess solid CaO followed by filtration gave the best results. For CsOH, which may be seriously contaminated with carbonate, the only satisfactory procedure was treatment of very concentrated soultions with excess solid Ba(OH)2. Residual calcium and barium concentrations in the decarbonated solutions were at trace levels

A hydrogen electrode study of concentrated alkaline aluminate solutions

A detailed study of highly concentrated aqueous alkaline aluminate solutions has been made by hydrogen electrode potentiometry in cells with liquid junction at 25°C in 8 M Na(ClO4) media. Measurements were performed over the total concentration ranges 0.1 M < [NaOH]T < 4-0 M and 0.02 M < [AlIII]T < 3.2 M, and at total concentration ratios of 6.92 ≥ [OH-]T/[AlIII]T ≥ 4.3. Nernstian electrode behaviour was observed at [NaOH]T ≤ c. 2 M in pure NaOH/NaClO4 mixtures. At low [AlIII]T the data were consistent with the formation of only the well known Al(OH)4-(aq) species but there is clear evidence of a systematic release of hydroxide as [AlIII]T and [NaOH]T increase. The data are consistent with the formation of polymeric aluminate complexes having a stoichiometry of Alq(OH)3q-rr+= (q = 4-7, q + r = 1 or 2). However, unequivocal identification of these species is difficult on account of strong correlations in the data and the possible effects of ion-pairing

27Al NMR and Raman spectroscopic studies of alkaline aluminate solutions with extremely high caustic content - Does the octahedral species Al(OH)63- exist in solution?

27Al NMR and Raman spectra of alkaline aluminate solutions with 0.005 M ≤ [Al(III)]T ≤ 3 M in various M′OH solutions (M′+ = Na+, K+ and Li+) were recorded and analysed. Caustic concentrations up to 20 M were used to explore whether higher aluminium hydroxo complexes are formed at extremely high concentrations of hydroxide. A single peak was observed on the 27Al NMR spectrum of each solution. The chemical shift of this peak shifts significantly upfield with increasing [M′OH]T in solutions with [Al(III)]T < 0.8 M. This variation shows a strong dependence on the cation of the solution and practically disappears in systems with [Al(III)]T ≥ 0.8 M. For Raman spectra of solutions with [Al(III)]T = 0.8 M and [NaOH]T ≥ 10 M, the peak maximum of the symmetric ν1-AlO4 stretching of Al(OH)4- shifted progressively from ∼620 to ∼625 cm-1 and decreased in intensity with increasing [NaOH]T. In parallel, modes centred at ∼720 and ∼555 cm-1 (cf. ∼705 and ∼535 cm-1 at lower [NaOH]T, ascribed to a dimeric aluminate species appeared, and their intensities increased with increasing [NaOH]T. These variations in the 27Al NMR and Raman spectra can be interpreted in terms of contact ion-pairs formed between the cation of the medium and the well-established Al(OH)4- or the dimeric aluminate species. Assumption of higher aluminium hydroxo complex species (e.g., Al(OH)63-) is not necessary to explain the spectroscopic effects observed

Dielectric relaxation of dilute aqueous NaOH, NaAl(OH)4 and NaB(OH)4

The complex dielectric permittivity of aqueous NaOH (c ≤ 2 M) and of dilute (≤0.6 M) NaAl(OH)4 and NaB(OH)4 solutions in NaOH ([Na] = 1 M) at 25°C has been determined in the frequency range 0.2 ≤ v/GHz ≤ 20. All spectra could be represented by a single Cole-Cole relaxation time distribution attributed to the cooperative relaxation of the solvent. The concentration dependence of the effective hydration number of OH- has been determined. For aluminate and borate solutions the deduced parameters: effective conductivity Ke, static permittivity ε, relaxation time τ, and distribution parameter a suggest a 1:1 replacement of hydroxide by aluminate and borate, accompanied by a release of bound water. The lack of an ion-pair relaxation process despite notable ion association suggests that rapid proton exchange is important not only for the dynamics of OH- but also for Al(OH)4- and B(OH)4-

Thermodynamics of protonation and sodium binding of sulfate in concentrated NaCl and CsCl solutions studied by Raman spectroscopy

The protonation constant (pKa) of SO42-(aq) has been determined at ionic strengths 0.5 M ≤ I ≤ 4.0 M in NaCl and CsCl media at 25°C by using Raman spectroscopy. These data were used to calculate the association constant of the NaSO4- (aq) ion pair in CsCl media. The results are in excellent agreement with previous values obtained by other techniques. The pKa was also measured at I = 4 M in both media at temperatures up to 85°C and the associated enthalpy and entropy changes were calculated. However, reliable thermodynamic data for the ion-pairing reaction could not be obtained at higher temperatures probably because of competition from CsSO4-(aq)

Structure of aqueous sodium aluminate solutions: A solution X-ray diffraction study

A structural analysis of six alkaline sodium aluminate aqueous solutions by the X-ray diffraction method is reported. On average, each Al atom is surrounded by four oxygens, indicative of the predominance of Al(OH)4-(aq) in these solutions. Detailed least-squares fitting indicates that a significant contraction of the Al-O distances occurs with increasing aluminate concentration, from 1.80 Å at 2 M to 1.74 Å at 6 M Al-(OH)3 in 8 M NaOH. The local structure has been described by models that have separate hydrated ions in the most dilute aluminate solution but contact sodium aluminate ion pairs in the most concentrated solution. The hydration number of the sodium ion decreases with increasing concentration, but the overall coordination number appears to be unchanged by the ion pair formation. An extensive rearrangement in the hydrogenbonded network of bulk water also occurs as the aluminum concentration rises, with the appearance of new diffraction distances at 3.3 and 3.9 Å. A gradual appearance and disappearance of shorter hydrogen bonds between first neighboring O atoms is observed. The data are consistent with the occurrence of oligomeric aluminate species but are not conclusive within the limits of the experimental error