Selenic acid

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Selenic acid
Structural formula of selenic acid Selenic-acid-2D.png
Structural formula of selenic acid
Space-filling model of selenic acid Selenic-acid-3D-vdW.png
Space-filling model of selenic acid
Selenic acid crystals.png
Names
IUPAC name
Selenic(VI) acid
Other names
Selenic acid
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.029.072 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 231-979-4
KEGG
PubChem CID
RTECS number
  • VS6575000
UNII
UN number 1905
  • InChI=1S/H2O4Se/c1-5(2,3)4/h(H2,1,2,3,4) Yes check.svgY
    Key: QYHFIVBSNOWOCQ-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/H2O4Se/c1-5(2,3)4/h(H2,1,2,3,4)
    Key: QYHFIVBSNOWOCQ-UHFFFAOYAI
  • O[Se+2]([O-])([O-])O
Properties
H2SeO4
Molar mass 144.9734 g/mol
AppearanceColorless deliquescent crystals
Density 2.95 g/cm3, solid
Melting point 58 °C (136 °F; 331 K)
Boiling point 260 °C (500 °F; 533 K) (decomposes)
130 g/(100 mL) (30 °C)
Acidity (pKa)pKa1 = −3
pKa2 = 1.9 [1]
Conjugate base Biselenate
−51.2·10−6 cm3/mol
1.5174 (D-line, 20 °C)
Structure
tetrahedral at Se
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
Corrosive, highly toxic
GHS labelling: [2]
GHS-pictogram-acid.svg GHS-pictogram-skull.svg GHS-pictogram-silhouette.svg GHS-pictogram-pollu.svg
Danger
H301, H315, H318, H331, H373, H410
P260, P261, P264, P270, P271, P273, P280, P301+P310, P302+P352, P304+P340, P305+P351+P338, P310, P311, P314, P321, P330, P332+P313, P362, P391, P403+P233, P405, P501
NFPA 704 (fire diamond)
NFPA 704.svgHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 0: Will not burn. E.g. waterInstability 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazard OX: Oxidizer. E.g. potassium perchlorate
3
0
2
OX
Related compounds
Other anions
selenious acid
hydrogen selenide
Other cations
sodium selenate
potassium selenate
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

Selenic acid is the inorganic compound with the formula H2SeO4. It is an oxoacid of selenium, and its structure is more accurately described as O2Se(OH)2. It is a colorless compound. Although it has few uses, one of its salts, sodium selenate is used in the production of glass and animal feeds. [3]

Contents

Structure and bonding

The molecule is tetrahedral, as predicted by VSEPR theory. The Se–O bond length is 161  pm. [4] In the solid state, it crystallizes in an orthorhombic structure. [5]

Preparation

It is prepared by oxidising selenium compounds in lower oxidation states. One method involves the oxidation of selenium dioxide with hydrogen peroxide:

SeO2 + H2O2 → H2SeO4

Unlike the production sulfuric acid by hydration of sulfur trioxide, the hydration of selenium trioxide is an impractical method. [4] Instead, selenic acid may also be prepared by the oxidation of selenous acid (H2SeO3) with halogens, such as chlorine or bromine, or with potassium permanganate. [6] Using chlorine or bromine as the oxidising agents also produces hydrochloric or hydrobromic acid as a side-product, which needs to be removed from the solution since they can reduce the selenic acid to selenous acid. [7]

To obtain the anhydrous acid as a crystalline solid, the resulting solution is evaporated at temperatures below 140 °C (413 K; 284 °F) in a vacuum. [8]

Reactions

Like sulfuric acid, selenic acid is a strong acid that is hygroscopic and extremely soluble in water. Concentrated solutions are viscous. Crystalline mono- and di-hydrates are known. [6] The monohydrate melts at 26 °C, and the dihydrate melts at −51.7 °C. [4]

Selenic acid is a stronger oxidizer than sulfuric acid, [9] capable of liberating chlorine from chloride ions, being reduced to selenous acid in the process:

H2SeO4 + 2 H+ + 2 Cl− → H2SeO3 + H2O + Cl2

It decomposes above 200 °C, liberating oxygen gas and being reduced to selenous acid: [6]

2 H2SeO4 → 2 H2SeO3 + O2

Selenic acid reacts with barium salts to precipitate solid BaSeO4, analogous to the sulfate. In general, selenate salts resemble sulfate salts, but are more soluble. Many selenate salts have the same crystal structure as the corresponding sulfate salts. [4]

Treatment with fluorosulfuric acid gives selenoyl fluoride: [8]

H2SeO4 + 2 HSO3F → SeO2F2 + 2 H2SO4

Hot, concentrated selenic acid reacts with gold, forming a reddish-yellow solution of gold(III) selenate: [10]

2 Au + 6 H2SeO4 → Au2(SeO4)3 + 3 H2SeO3 + 3 H2O

Applications

Selenic acid is used as a specialized oxidizing agent.

Related Research Articles

<span class="mw-page-title-main">Perchloric acid</span> Chemical compound

Perchloric acid is a mineral acid with the formula HClO4. Usually found as an aqueous solution, this colorless compound is a stronger acid than sulfuric acid, nitric acid and hydrochloric acid. It is a powerful oxidizer when hot, but aqueous solutions up to approximately 70% by weight at room temperature are generally safe, only showing strong acid features and no oxidizing properties. Perchloric acid is useful for preparing perchlorate salts, especially ammonium perchlorate, an important rocket fuel component. Perchloric acid is dangerously corrosive and readily forms potentially explosive mixtures.

Chromic acid is an inorganic acid composed of the elements chromium, oxygen, and hydrogen. It is a dark, purplish red, odorless, sand-like solid powder. When dissolved in water, it is a strong acid. There are 2 types of chromic acid: molecular chromic acid with the formula H
2CrO
4 and dichromic acid with the formula H
2Cr
2O
7.

<span class="mw-page-title-main">Vanadium(V) oxide</span> Precursor to vanadium alloys and industrial catalyst

Vanadium(V) oxide (vanadia) is the inorganic compound with the formula V2O5. Commonly known as vanadium pentoxide, it is a brown/yellow solid, although when freshly precipitated from aqueous solution, its colour is deep orange. Because of its high oxidation state, it is both an amphoteric oxide and an oxidizing agent. From the industrial perspective, it is the most important compound of vanadium, being the principal precursor to alloys of vanadium and is a widely used industrial catalyst.

<span class="mw-page-title-main">Sodium perchlorate</span> Chemical compound

Sodium perchlorate is an inorganic compound with the chemical formula NaClO4. It consists of sodium cations Na+ and perchlorate anions ClO−4. It is a white crystalline, hygroscopic solid that is highly soluble in water and ethanol. It is usually encountered as sodium perchlorate monohydrate NaClO4·H2O. The compound is noteworthy as the most water-soluble of the common perchlorate salts.

<span class="mw-page-title-main">Telluric acid</span> Chemical compound (Te(OH)6)

Telluric acid, or more accurately orthotelluric acid, is a chemical compound with the formula Te(OH)6, often written as H6TeO6. It is a white crystalline solid made up of octahedral Te(OH)6 molecules which persist in aqueous solution. In the solid state, there are two forms, rhombohedral and monoclinic, and both contain octahedral Te(OH)6 molecules, containing one hexavalent tellurium (Te) atom in the +6 oxidation state, attached to six hydroxyl (–OH) groups, thus, it can be called tellurium(VI) hydroxide. Telluric acid is a weak acid which is dibasic, forming tellurate salts with strong bases and hydrogen tellurate salts with weaker bases or upon hydrolysis of tellurates in water. It is used as tellurium-source in the synthesis of oxidation catalysts.

<span class="mw-page-title-main">Selenium dioxide</span> Chemical compound

Selenium dioxide is the chemical compound with the formula SeO2. This colorless solid is one of the most frequently encountered compounds of selenium.

<span class="mw-page-title-main">Selenite (ion)</span> Anion composed of selenium and oxygen

Selenite refers to the anion with the chemical formula SeO2−3. It is the oxyanion of selenium. It is the selenium analog of the sulfite ion, SO2−3. Thus selenite is pyramidal and selenium is assigned oxidation state +4. Selenite also refers to compounds that contains this ion, for example sodium selenite Na2SeO3 which is a common source of selenite. Selenite also refers to the esters of selenous acid, for example dimethyl selenite (CH3)2SeO3.

<span class="mw-page-title-main">Selenous acid</span> Chemical compound

Selenous acid is the chemical compound with the formula H2SeO3. Structurally, it is more accurately described by O=Se(OH)2. It is the principal oxoacid of selenium; the other being selenic acid.

<span class="mw-page-title-main">Perbromic acid</span> Chemical compound

Perbromic acid is the inorganic compound with the formula HBrO4. Perbromic acid is characterized as a colorless liquid which has no characteristic scent. It is an oxoacid of bromine, with an oxidation state of 7+. Perbromic acid is a strong acid and strongly oxidizing, though dilute perbromic acid solutions are slow oxidizing agents. It is the most unstable of the halogen(VII) oxoacids. It decomposes rapidly on standing to bromic acid and oxygen, which releases toxic brown bromine vapors. It can be used in the synthesis of perbromate salts, by reacting with a base.

Selenium trioxide is the inorganic compound with the formula SeO3. It is white, hygroscopic solid. It is also an oxidizing agent and a Lewis acid. It is of academic interest as a precursor to Se(VI) compounds.

<span class="mw-page-title-main">Selenium compounds</span> Chemical compounds containing selenium

Selenium compounds are compounds containing the element selenium (Se). Among these compounds, selenium has various oxidation states, the most common ones being −2, +4, and +6. Selenium compounds exist in nature in the form of various minerals, such as clausthalite, guanajuatite, tiemannite, crookesite etc., and can also coexist with sulfide minerals such as pyrite and chalcopyrite. For many mammals, selenium compounds are essential. For example, selenomethionine and selenocysteine are selenium-containing amino acids present in the human body. Selenomethionine participates in the synthesis of selenoproteins. The reduction potential and pKa (5.47) of selenocysteine are lower than those of cysteine, making some proteins have antioxidant activity. Selenium compounds have important applications in semiconductors, glass and ceramic industries, medicine, metallurgy and other fields.

Bromine compounds are compounds containing the element bromine (Br). These compounds usually form the -1, +1, +3 and +5 oxidation states. Bromine is intermediate in reactivity between chlorine and iodine, and is one of the most reactive elements. Bond energies to bromine tend to be lower than those to chlorine but higher than those to iodine, and bromine is a weaker oxidising agent than chlorine but a stronger one than iodine. This can be seen from the standard electrode potentials of the X2/X− couples (F, +2.866 V; Cl, +1.395 V; Br, +1.087 V; I, +0.615 V; At, approximately +0.3 V). Bromination often leads to higher oxidation states than iodination but lower or equal oxidation states to chlorination. Bromine tends to react with compounds including M–M, M–H, or M–C bonds to form M–Br bonds.

<span class="mw-page-title-main">Sodium selenate</span> Chemical compound

Sodium selenate is the inorganic compound with the formula Na
2SeO
4, not to be confused with sodium selenite. It exists as the anhydrous salt, the heptahydrate, and the decahydrate. These are white, water-soluble solids. The decahydrate is a common ingredient in multivitamins and livestock feed as a source of selenium. The anhydrous salt is used in the production of some glass. Although the selenates are much more toxic, many physical properties of sodium selenate and sodium sulfate are similar.

<span class="mw-page-title-main">Sodium bismuthate</span> Chemical compound

Sodium bismuthate is an inorganic compound, and a strong oxidiser with chemical formula NaBiO3. It is somewhat hygroscopic, but not soluble in cold water, which can be convenient since the reagent can be easily removed after the reaction. It is one of the few water insoluble sodium salts. Commercial samples may be a mixture of bismuth(V) oxide, sodium carbonate and sodium peroxide.

<span class="mw-page-title-main">Potassium selenate</span> Chemical compound

Potassium selenate, K
2SeO
4, is an odorless, white solid that forms as the potassium salt of selenic acid.

Iron(II) selenate (ferrous selenate) is an inorganic compound with the formula FeSeO4. It has anhydrous and several hydrate forms. The pentahydrate has the structure, [Fe(H2O)4]SeO4•H2O, isomorphous to the corresponding iron(II) sulfate. Heptahydrate is also known, in form of unstable green crystalline solid.

A selenate selenite is a chemical compound or salt that contains selenite and selenate anions (SeO32- and SeO42-). These are mixed anion compounds. Some have third anions.

Praseodymium(III) selenate is an inorganic compound, the salt of praseodymium and selenic acid with the chemical formula Pr2(SeO4)3. It forms green crystals when hydrated.

<span class="mw-page-title-main">Erbium(III) selenate</span> Chemical compound

Erbium(III) selenate is an inorganic compound, with the chemical formula Er2(SeO4)3. It exists as an anhydrate or an octahydrate.

References

  1. ↑ Magdi Selim, H. (2011-03-15). Dynamics and Bioavailability of Heavy Metals in the Rootzone. CRC Press. ISBN   9781439826232.
  2. ↑ "Selenic acid". pubchem.ncbi.nlm.nih.gov. Retrieved 16 December 2021.
  3. ↑ Bernd E. Langner "Selenium and Selenium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. doi : 10.1002/14356007.a23_525.
  4. 1 2 3 4 Don M. Yost (2007). Systematic Inorganic Chemistry. Read Books. pp. 343–346. ISBN   978-1-4067-7302-6.
  5. ↑ Mathias S. Wickleder (2007). Francesco A. Devillanova (ed.). Handbook of Chalcogen Chemistry: New Perspectives in Sulfur, Selenium and Tellurium. Royal Society of Chemistry. p. 353. ISBN   978-0-85404-366-8.
  6. 1 2 3 Anil Kumar De (2003). A Text Book of Inorganic Chemistry. New Age International. pp. 543–545. ISBN   81-224-1384-6.
  7. ↑ Lenher, V.; Kao, C. H. (June 1925). "The preparation of selenic acid and of certain selenates". Journal of the American Chemical Society. 47 (6): 1521–1522. doi:10.1021/ja01683a005.
  8. 1 2 Seppelt, K. “Selenoyl Difluoride” Inorganic Syntheses, 1980, volume XX, pp. 36-38. ISBN   0-471-07715-1. The report describes the synthesis of selenic acid.
  9. ↑ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 782. ISBN   978-0-08-037941-8.
  10. ↑ Lenher, V. (April 1902). "Action of selenic acid on gold". Journal of the American Chemical Society. 24 (4): 354–355. doi:10.1021/ja02018a005.
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