Arsenic(IV). A Pulse-radiolysis study

Journal Article · Wed Jul 12 00:00:00 EDT 1989 · Inorganic Chemistry; (USA)

DOI:https://doi.org/10.1021/ic00313a007· OSTI ID:5040661

Klaening, U K ^[1]; Bielski, B H.J. ^[2]; Sehested, K ^[3]

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1. Aarhus Univ. (Denmark)
2. Brookhaven National Lab., Upton, NY (USA)
3. Riso National Lab., Roskilde (Denmark)

Four As(IV) species assumed to be As(OH){sub 4} and HAsO{sub 3}{sup {minus}} and the corresponding bases As(OH){sub 3}O{sup {minus}} and AsO{sub 3}{sup 2{minus}} (pK{sub a} = 7.38 and 7.81, respectively) were observed by the radiolysis technique in aqueous arsenious acid, arsenite, and arsenate solutions. As(OH){sub 4} and As(OH){sub 3}O{sup {minus}} were observed in acid and weakly alkaline solution by the reaction of arsenious acid or arsenite with OH. HAsO{sub 3}{sup {minus}} and/or AsO{sub 3}{sup 2{minus}} are formed by the reaction of e{sup {minus}}{sub aq} with H{sub 2}AsO{sub 4}{sup {minus}} and HAsO{sub 4}{sup 2{minus}}; AsO{sub 3}{sup 2{minus}} is formed by the reaction of arsenite with O{sup {minus}} in strongly alkaline solution and by the reaction of arsenite with the carbonate radical anion CO{sub 3}{sup {minus}}. As(OH){sub 4} and As(OH){sub 3}O{sup {minus}} convert into HAsO{sub 3}{sup {minus}} and AsO{sub 3}{sup 2{minus}} by general-base-catalyzed reactions. In acid solution an equilibrium between As(OH){sub 4} and HAsO{sub 3}{sup {minus}} is observed. The kinetics of dehydration of As(OH){sub 4} suggest a slow dehydration step catalyzed by H{sup +} followed by protolysis. The thermodynamic parameters are reported. By comparison with activation parameters of other dehydration-hydration processes, these values are taken to suggest a cyclic transition state containing an extra water molecule. While As(OH){sub 4} and As(OH){sub 3}O{sup {minus}} react with O{sub 2} to yield directly HO{sub 2} and O{sub 2}{sup {minus}}, HAsO{sub 3}{sup {minus}} and AsO{sub 3}{sup 2{minus}} react with O{sub 2} with formation of a relatively stable complex that subsequently decomposes to HO{sub 2} or O{sub 2}{sup {minus}} in reactions catalyzed by H{sup +} and OH{sup {minus}}. The various As(IV) species disappear in second-order reactions. 42 refs., 8 figs., 2 tabs.

• DOE Contract Number: AC02-76CH00016
• OSTI ID: 5040661
• Journal Information: Inorganic Chemistry; (USA), Vol. 28:14; ISSN 0020-1669
• Country of Publication: United States
• Language: English

Related Subjects

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
ARSENIC COMPOUNDS
RADIOLYSIS
AQUEOUS SOLUTIONS
ELECTRONS
EXPERIMENTAL DATA
PULSED IRRADIATION
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTIONS
CHEMISTRY
DATA
DECOMPOSITION
DISPERSIONS
ELEMENTARY PARTICLES
FERMIONS
INFORMATION
IRRADIATION
LEPTONS
MIXTURES
NUMERICAL DATA
RADIATION CHEMISTRY
RADIATION EFFECTS
SOLUTIONS
400600* - Radiation Chemistry