The Equilibria in Acidic Solutions of Chromium(III) Ion and Thiocyanate Ion

Postmus, C.; King, Edward L.

doi:10.1021/j150534a007

Cited by 84 publications

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“…T-', from which we find AH0 = 9.2, kcal mole-'; this compares favorably with AH0 = 9.4 f 0.4 kcal mole-' reported by Postmus and King (13). It follows that tempera- …”

Section: In Our Experiments [H'supporting

confidence: 85%

“…A precedent for a AVO value of this magnitude for metal-ion hydrolysis can be found in Spiro, Revesz, and Lee's (16) dilatometric value of AVO = + 20.6 cm3 mole-' for reaction 12 at low ionic strength and atmospheric pressure ; combination of this value with AVO = -21.3 cm3 mole-' for the autoprotolysis of water under similar conditions (14) leads to AVO = -0.7 cm3 mole-' for reaction 13, which is closely analogous to reaction 4. The failure of AVO for reactions such as [4] and [13] to correlate with A V0 for the dissociation of simple protonic acids probably originates in the effective spreading of the triple positive charge of the aqueous metal ion over the surface of an unusually large sphere, since the central cation is complexed with aquo (or ammine) ligands. Thus, the reduction of the formal charge of this large species by one unit, together with the creation of a free aqueous proton, niay not result in a significant dissipation of charge density, so that AVcl may be much less positive than predicted on the basis of naive applications of the Drude-Nernst equation.…”

Section: Pressure Dependence Of Kmentioning

confidence: 99%

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The effect of pressure on the hydrolysis equilibria of aqueous metal ions

Swaddle¹,

Kong²

1970

Can. J. Chem.

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The molal acid dissociation ("hydrolysis") constant Km of aqueous hexaaquochromium(II1) ion, at 25.0" and ionic strength 0.5 m, has been determined spectrophotometrically as a function of pressure P up to 3 kbar. K m increases with P (kbar) in accordance with the equationIn K,,, = 0.151 P -9.474The molal volume change is -3.8 + 0.7 cm3 mole-', and the enthalpy and entropy changes at 1 bar are 9.3 kcal mole-' and 12.1 cal deg-I mole-'. Compressions of 0.1, 0.5, and 1.0 M aqueous perchloric acid, lithium perchlorate, and sodium perchlorate up to 4 kbar have also been measured.Canadian Journal of Chemistry, 48, 3223 (1970) Introduction ambient temperature over a convenient period The experimental data relating to the effect of time without complications arising from of pressure on the dissociation of electrically hydrolytic polymerization (reaction 5), which is neutral weak acids (eq. 1) and bases (eq. 2) in essentially a substitution process. aqueous solution have been reviewed by Hamann [51 2Cr(HZ0)50HZ+ = (HZ0)4Cr(OH)zCr(OHz)44+

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“…T-', from which we find AH0 = 9.2, kcal mole-'; this compares favorably with AH0 = 9.4 f 0.4 kcal mole-' reported by Postmus and King (13). It follows that tempera- …”

Section: In Our Experiments [H'supporting

confidence: 85%

Section: Pressure Dependence Of Kmentioning

confidence: 99%

The effect of pressure on the hydrolysis equilibria of aqueous metal ions

Swaddle¹,

Kong²

1970

Can. J. Chem.

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“…Thus, to develop efficient strategies for the removal of chromium from the sludge, it is important to understand the chemical behavior of chromium(III) in alkaline solutions. However, most of the studies on chromium(III) have been conducted in acidic to neutral systems, [2][3][4][5][6][7][8][9][10][11][12][13] while few data exist for alkaline solutions. For example, information is available on the hydrolysis and oligomerization of chromium(III) in acidic to neutral solutions.…”

Section: Introductionmentioning

confidence: 99%

Oligomerization of chromium(iii) and its impact on the oxidation of chromium(iii) by hydrogen peroxide in alkaline solutions

Rao

Zhang

Friese

et al. 2002

J. Chem. Soc., Dalton Trans.

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Kinetic studies on the oxidation of separated/characterized chromium(III) oligomers by hydrogen peroxide indicate that the degree of oligomerization has a significant impact on the rate of oxidation in alkaline solutions. The oxidation rate constant decreases in the order: monomer > dimer > trimer > aged/unseparated chromium(III) solution where higher oligomers dominate. SummaryMonomeric, dimeric and trimeric chromium(III) species in solution were separated by ion exchange and characterized with UV/Vis absorption and Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS). The kinetics of the oxidation of the separated species by hydrogen peroxide in alkaline solutions was studied by conventional and stopped-flow UV/Vis absorption spectroscopy. Results indicate that the intensity of Cr-Cr scattering in the EXAFS spectra (d Cr-Cr ~ 2.99 Å), a measure of the degree of oligomerization, increases as the solution alkalinity is increased. As the oligomerization proceeds, the rate of oxidation by hydrogen peroxide in alkaline solutions decreases in the order: monomer > dimer > trimer > aged/unseparated alkaline chromium(III) solution where higher 1 oligomers dominate. The dominant redox pathway has an inverse order with respect to C NaOH . The data suggest that the rate-determining step involves the weakening of the bridging bonds in the oligomer and a concomitant release of one hydroxyl group from the chromium(III) moiety upon the attack by hydrogen peroxide.

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“…Therefore it is interesting that CrNCS 2+ shows a strong absorption at 270-295 m/z [3], whereas the other complexes do not show this. At 200-250m/z CrC12÷ shows a much stronger absorption than CrF 2+ and Cr 3+ [2].…”

Section: Equation (1) Predicts a Shift Of Elt2 Of 59 MV To More Negatmentioning

confidence: 99%

“…Preparation, stability and rates of homogeneous substitution reactions of a number of these complexes have been described in the literature [1][2][3].…”

Section: Introductionmentioning

confidence: 99%

Reduction of some acidopentaaquochromium(III) complexes at the mercury electrode

Kooy

Gellings

1970

Journal of Inorganic and Nuclear Chemistry

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Abstract-The complexes [CrNCS(H20)5] 2+, [CrCI(H20)s] ~+, [CrF(H20)~, 2+ and [Cr(H20)6] a+ were studied by polarography and cyclic voltammetry in aqueous solution. It is shown that Triton X-100 and gelatine shift the polarographic waves to more negative potentials. In 1M NaCIO4-HCIO4 the half-wave potentials in the absence of maximum suppressor are (in Volts vs. SCE): CrNCS2+: --0.675; CrCI2+: -0.62; CrF~+:-1.105; Cr3+: -0.90 (water omitted in the formula). All reductions are irreversible. Replacement of NaC104 by NaSCN makes the reduction of CrNCS 2+ and CrCI z+ more reversible and shifts E½ 50 mV per log [SCN-I unit to more negative potentials for CrNCS z+ and 66 mV for CrCI 2+. It is suggested that CrNCS 2+ and CrCI 2+ may be reduced via a mecbanism analogous to the inner-sphere mechanism in homogeneous reductions.

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The Equilibria in Acidic Solutions of Chromium(III) Ion and Thiocyanate Ion

Abstract: In this paper, the nomenclature recommended in National Bureau of Standards Letter Circular No. 857 is adopted. The definitions and symbols are included in Table I.

Cited by 84 publications

References 0 publications

The effect of pressure on the hydrolysis equilibria of aqueous metal ions

The effect of pressure on the hydrolysis equilibria of aqueous metal ions

Oligomerization of chromium(iii) and its impact on the oxidation of chromium(iii) by hydrogen peroxide in alkaline solutions

Reduction of some acidopentaaquochromium(III) complexes at the mercury electrode

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