Chemistry:Tellurous acid

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Tellurous acid
Tellurous acid
IUPAC name
Tellurous acid
Other names
Tellurium dioxide hydrate, tellurium(IV) oxide hydrate
3D model (JSmol)
Molar mass 177.616 grams
Appearance colorless crystals
Density ~ 3 g/cm3
Boiling point decomposes
Acidity (pKa) pKa1 = 2.48, pKa2 = 7.70 [1]
Conjugate base Tellurite
pyramidal at Te
Related compounds
Other anions
Selenous acid
Sulfurous acid
Other cations
Sodium tellurite
Related compounds
Telluric acid
Selenic acid
Sulfuric acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Tellurous acid is an inorganic compound with the formula H2TeO3. It is the oxoacid of tellurium(IV).[2] This compound is not well characterized. An alternative way of writing its formula is (HO)2TeO. In principle, tellurous acid would form by treatment of tellurium dioxide with water, that is by hydrolysis. The related conjugate base is well known in the form of several salts such as potassium hydrogen tellurite, KHTeO3.


In contrast to the analogous compound selenous acid, tellurous acid is only metastable. Most tellurite salts contain the TeO2−3 ion. Oxidation of its aqueous solution with hydrogen peroxide gives the tellurate ion. It is usually prepared as an aqueous solution where it acts as a weak acid.[1][3]

H2TeO3 + H2O ⇌ H3O+ + HTeO3 Ka1 = 2×10−3
HTeO3 + H2O ⇌ H3O+ + TeO2−3 Ka2 = 1×10−8


  1. 1.0 1.1 Catherine E. Housecroft; Alan G. Sharpe (2008). "Chapter 16: The group 16 elements". Inorganic Chemistry (3rd ed.). Pearson. p. 524. ISBN 978-0-13-175553-6. 
  2. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8. 
  3. "Ionization Constants for Weak Acids".