French
DeutschTelluric acid
 | |
 | |
| Names | |
|---|---|
| IUPAC name Hexahydroxidotellurium | |
Other names
| |
| Identifiers | |
3D model (JSmol) | |
| ChEBI | |
| ChemSpider | |
| ECHA InfoCard | 100.029.334 |
PubChem CID | |
| UNII | |
CompTox Dashboard (EPA) | |
| |
| |
| Properties | |
| Te(OH)6 | |
| Molar mass | 229.64 g·mol−1 |
| 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) | 7.5, 11, 14[2] |
| Conjugate base | Tellurate |
| Structure | |
| octahedral | |
| 0 D | |
| Hazards | |
| Occupational safety and health (OHS/OSH): | |
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). | |
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.[3] In the solid state, there are two forms, rhombohedral and monoclinic, and both contain octahedral Te(OH)6 molecules,[4] 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.[4][5] It is used as tellurium-source in the synthesis of oxidation catalysts.
Preparation
[edit]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.[4]
- TeO2 + H2O2 + 2 H2O → Te(OH)6
Crystallization of telluric acid solutions below 10 °C gives telluric acid tetrahydrate Te(OH)6·4H2O.[3] It is an oxidising agent, as shown by the electrode potential for the reaction below, although it is kinetically slow in its oxidations.[4]
- Te(OH)6 + 2 H+ + 2 e− ⇌ TeO2 + 4 H2O, E
o= +1.02 V
Chlorine, by comparison, is +1.36 V and selenous acid is +0.74 V in oxidizing conditions.
Properties and reactions
[edit]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 3·H2TeO4·4H2O).[6][3]
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 TeO2−4 has been confirmed in the solid state structure of Rb6[TeO5][TeO4].[7] Strong heating at over 300 °C produces the α crystalline modification of tellurium trioxide, α-TeO3. [5] Reaction with diazomethane gives the hexamethyl ester, Te(OCH3)6.[3]
Telluric acid and its salts mostly contain hexacoordinate tellurium.[4] This is true even for salts such as magnesium tellurate, MgTeO4, which is isostructural with magnesium molybdate and contains TeO6 octahedra.[4]
Other forms of telluric acid
[edit]Metatelluric acid, H2TeO4, the tellurium analogue of sulfuric acid, H2SO4, is unknown. Allotelluric acid of approximate composition 3·H2TeO4·4H2O, is not well characterised and may be a mixture of Te(OH)6 and (H2TeO4)n.[3]
Other tellurium acids
[edit]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
[edit]- ^ Lide, David R. (1998), Handbook of Chemistry and Physics (87 ed.), Boca Raton, Florida: CRC Press, ISBN 0-8493-0594-2
- ^ Perrin, D. D., ed. (1982) [1969]. Ionisation Constants of Inorganic Acids and Bases in Aqueous Solution. IUPAC Chemical Data (2nd ed.). Oxford: Pergamon (published 1984). Entry 219. ISBN 0-08-029214-3. LCCN 82-16524.
- ^ a b c d e Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
- ^ a b c d e f 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
- ^ a b Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
- ^ Loub, J.; Haase, W.; Mergehenn, R. (1979). "Structure of an adduct of orthotelluric acid and urea". Acta Crystallographica Section B: Structural Crystallography and Crystal Chemistry. 35 (12): 3039–3041. Bibcode:1979AcCrB..35.3039L. doi:10.1107/S0567740879011286.
- ^ 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.
| Authority control databases: National |
|---|