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Selenous acid

 
Sci-Tech Dictionary: selenous acid
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(sə′lē·nəs ′as·əd)

(inorganic chemistry) H2SeO3 Colorless, transparent crystals; soluble in water and alcohol, insoluble in ammonia; decomposes when heated; used as an analytical reagent. Also spelled selenious acid.

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Wikipedia: Selenous acid
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Selenous acid[1]
Structural formula
Ball-and-stick model
IUPAC name
Identifiers
CAS number 7783-00-8 Yes check.svgY
Properties
Molecular formula H2SeO3
Molar mass 128.97 g/mol
Appearance white hygroscopic crystals
Density 3.0 g/cm3
Melting point

decomposes at 70°C
Solubility in water very soluble
Solubility soluble in ethanol
Related compounds
Related compounds sulfurous acid
tellurous acid
polonous acid
 Yes check.svgY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Selenous acid (or selenious acid) is the chemical compound with the formula H2SeO3. Structurally, it is more accurately described by (HO)2SeO. It is the principal oxoacid of selenium; the other being selenic acid.

Contents

Formation and properties

Selenous acid is analogous to sulfurous acid, but it is more readily isolated. Selenous acid is easily formed upon the addition of selenium dioxide to water. As a crystalline solid, the compound can be seen as pyramidal molecules that are interconnected with hydrogen bonds. In solution it is a diprotic acid:[2]

H2SeO3 is in equilibrium with H+ + HSeO−3 (pKa = 2.62)
HSeO−3 is in equilibrium with H+ + SeO2−3 (pKa = 8.32)

It is moderately oxidizing in nature, but kinetically slow. In 1 M H+:

H2SeO3 + 4 H+ + 4 e− is in equilibrium with Se + 3 H2O (Eo = +0.74 V)

In 1 M OH−:

SeO2−3 + 4 e− + 3 H2O is in equilibrium with Se + 6 OH− (Eo = −0.37 V)

It is used in organic synthesis for the synthesis of 1,2-diketones (e.g. glyoxal).[3]

Uses

One use for selenious acid is the chemical darkening and patination of copper, brass and bronze, producing a rich dark brown color that can be further enhanced with mechanical abrasion.[citation needed]

Health effects

Like many selenium compounds, selenous acid is highly toxic, and ingestion of any significant quantity of selenous acid is usually fatal. Symptoms of selenium poisoning can occur several hours after exposure, and may include stupor, nausea, severe hypotension and death.[4]

References

  1. ^ Lide, David R. (1998), Handbook of Chemistry and Physics (87 ed.), Boca Raton, FL: CRC Press, pp. 4–81, ISBN 0849305942 
  2. ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
  3. ^ “Glyoxal Bisulfite”, Organic Syntheses, Collected Volume 3, p.438 (1955).
  4. ^ MSDS for "Reagent for Special Opiates (Codeine, Heroin, & Morphine)", Sirchie Finger Print Laboratories, Inc. May 12, 2006. (The page cannot be found)


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