| Telluric acid | |
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Telluric(VI) acid |
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Other names
orthotelluric acid |
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| Identifiers | |
| CAS number | 7803-68-1 |
| PubChem | 61609 |
| ChemSpider | 55517 |
| ChEBI | CHEBI:30463 |
| Jmol-3D images | Image 1 |
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| Properties | |
| Molecular formula | H6O6Te |
| Molar mass | 229.64 g/mol |
| Appearance | White monoclinic crystals |
| Density | 3.07 g/cm3 |
| Melting point |
136°C (409.15 K) |
| Solubility in water | 50.1 g/100 ml at 30°C[1] |
| Acidity (pKa) | 7.68, 11.0 at 18°C[2] |
| Structure | |
| Molecular shape | octahedral |
| Dipole moment | 0 D |
| Hazards | |
| Main hazards | corrosive |
| Related compounds | |
| Other anions | hydrotelluric acid tellurous acid hydrogen telluride |
| Related compounds | Teflic acid, Sulfuric acid Selenic acid |
| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| 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.[3] There are two forms, rhombohedral and monoclinic, and both contain octahedral Te(OH)6 molecules.[4] 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]
Contents |
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]
Crystallisation of telluric acid solutions below 10°C gives Te(OH)6.4H2O.[3] It is oxidizing, as shown by the electrode potential for the reaction below, although it is kinetically slow in its oxidations.[4]
Chlorine, by comparison, is +1.36V and selenious acid is +0.74V in oxidizing conditions.
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).[3]
Strong heating at over 300°C produces the α- crystalline modification of tellurium trioxide, α-TeO3. [6]
Reaction with diazomethane gives the hexamethyl ester, Te(OMe)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]
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.[3]
Tellurous acid, containing tellurium in its +4 oxidation state, (H2TeO3) is known but not well characterised. Hydrogen telluride is an unstable gas that forms hydrotelluric acid upon addition to water.
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