Telluric acid
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| Names | |
|---|---|
| IUPAC name
Hexahydroxidotellurium | |
| Other names
Orthotelluric acid | |
| Identifiers | |
7803-68-1  | |
| 3D model (Jmol) | Interactive image |
| ChEBI | CHEBI:30463  |
| ChemSpider | 55517 |
| ECHA InfoCard | 100.029.334 |
| PubChem | 62686 |
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| |
| Properties | |
| H6O6Te | |
| Molar mass | 229.64 g/mol |
| Appearance | White monoclinic crystals |
| Density | 3.07 g/cm3 |
| Melting point | 136 °C (277 °F; 409 K) |
| 50.1 g/100 ml at 30 °C[1] | |
| Acidity (pKa) | 7.68, 11.0 at 18 °C[1] |
| Structure | |
| octahedral | |
| 0 D | |
| Hazards | |
| Main hazards | corrosive |
| Related compounds | |
| Other anions |
hydrotelluric acid tellurous acid hydrogen telluride |
| Related compounds |
Teflic acid, Sulfuric acid Selenic acid |
| Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
| verify (what is ?) | |
| Infobox references | |
Telluric acid is a chemical compound with the formula Te(OH)6. It is a white solid made up of octahedral Te(OH)6 molecules which persist in aqueous solution.[2] There are two forms, rhombohedral and monoclinic, and both contain octahedral Te(OH)6 molecules.[3] 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.[3][4]
Preparation
Telluric acid is formed by the oxidation of tellurium or tellurium dioxide with a powerful oxidising agent such as hydrogen peroxide, chromium trioxide or sodium peroxide.[3]
- TeO2 + H2O2 + 2H2O → Te(OH)6
Crystallization of telluric acid solutions below 10 °C gives Te(OH)6.4H2O.[2] It is oxidizing, as shown by the electrode potential for the reaction below, although it is kinetically slow in its oxidations.[3]
- H6TeO6 + 2H+ + 2e− ⇌ TeO2 + 4H2O E
o= +1.02 V
Chlorine, by comparison, is +1.36V and selenous acid is +0.74V in oxidizing conditions.
Properties and reactions
The anhydrous acid is stable in air at 100 °C but above this it dehydrates to form polymetatelluric acid, a white hygroscopic powder (approximate composition (H2TeO4)10), and allotelluric acid, an acid syrup of unknown structure (approximate composition (H2TeO4)3(H2O)4).[2]
Typical salts of the acid contains the anions [Te(O)(OH)5]− and [Te(O)2(OH)4]2−. The presence of the tellurate ion TeO42− has been confirmed in the solid state structure of Rb6[TeO5][TeO4].[5]
Strong heating at over 300 °C produces the α- crystalline modification of tellurium trioxide, α-TeO3.
[4] Reaction with diazomethane gives the hexamethyl ester, Te(OMe)6.[2]
Telluric acid and its salts mostly contain hexacoordinate tellurium.[3] This is true even for salts such as magnesium tellurate, MgTeO4, which is isostructural with magnesium molybdate and contains TeO6 octahedra.[3]
Other forms of telluric acid
Metatelluric acid, H2TeO4, the tellurium analogue of sulfuric acid, H2SO4, is unknown. Allotelluric acid of approximate composition (H2TeO4)3(H2O)4, is not well characterised and may be a mixture of Te(OH)6 and (H2TeO4)n.[2]
Other tellurium acids
Tellurous acid (H2TeO3), containing tellurium in its +4 oxidation state, is known but not well characterised. Hydrogen telluride is an unstable gas that forms hydrotelluric acid upon addition to water.
References
- 1 2 Lide, David R. (1998), Handbook of Chemistry and Physics (87 ed.), Boca Raton, FL: CRC Press, ISBN 0-8493-0594-2
- 1 2 3 4 5 Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9.
- 1 2 3 4 5 6 Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; Bochmann, Manfred (1999), Advanced Inorganic Chemistry (6th ed.), New York: Wiley-Interscience, ISBN 0-471-19957-5
- 1 2 Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
- ↑ Catherine E. Housecroft; Alan G. Sharpe (2008). "Chapter 16: The group 16 elements". Inorganic Chemistry, 3rd Edition. Pearson. p. 526. ISBN 978-0-13-175553-6.