Telluric acid

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Telluric acid
Telluric acid
IUPAC name Telluric(VI) acid
Other names orthotelluric acid
Identifiers
CAS number [7803-68-1]
Properties
Molecular formula H6TeO6
Molar mass 229.64 g/mol
Appearance White crystalline solid.
Density 3.07 g/cm3, solid.
Melting point

136°C (409.15 K)
Solubility in water Soluble
Structure
Molecular shape octahedral
Dipole moment 0 D
Hazards
Main hazards corrosive
Related compounds
Related compounds Teflic acid,
Sulfuric acid
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and 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 and this structure persists in aqueous solution.[1] There are two forms, rhombohedral and monoclinic, and both contain octahedral Te(OH)6 molecules.[2] Telluric acid is a weak acid,dibasic, forming tellurate salts with strong bases.[2][3]

Contents

[edit] 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.[2]

TeO2 + 2H2O2 + 2H+ → Te(OH)6

Crystallisation of telluric acid solutions below 10°C gives Te(OH)6.4H2O.[1] It is oxidizing, as shown by the electrode potential for the reaction below, although it is kinetically slow in its oxidations.[2]

H6TeO6 + 2H+ + 2e− ⇌ TeO2 + 4H2O2 Eo = +1.02 V


[edit] 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).[1]
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.[1]

Telluric acid and its salts mostly contain hexacoordinate tellurium.[2] This is true even for salts such as magnesium tellurate, MgTeO4, which is isostructural with magnesium molybdate and contains TeO6 octahedra.[2]

[edit] Metatelluric acid - H2TeO4,Tellurous acid - H2TeO3

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.[1]
Tellurous acid, H2TeO3 is known but not well characterised.

[edit] References

  1. ^ a b c d e Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements, 2nd Edition, Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4. 
  2. ^ a b c d e f Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; Bochmann, Manfred (1999). Advanced Inorganic Chemistry (6th Edn.) New York:Wiley-Interscience. ISBN 0-471-19957-5.
  3. ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
  4. ^ Inorganic Chemistry,Egon Wiberg, Arnold Frederick Holleman Elsevier 2001 ISBN 0123526515

[edit] Sources

  • Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; Bochmann, Manfred (1999). Advanced Inorganic Chemistry (6th Edn.) New York:Wiley-Interscience. ISBN 0-471-19957-5.
  • Lide, D. R. (ed.) (2002). CRC Handbook of Chemistry and Physics, 83rd ed., Boca Raton, FL: CRC Press. 
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