Tellurous acid

Description

H2TeO3 has been synthesized as a solid but it is not well characterized. If tellurium dioxide, TeO2, is added to water, tellurous acid does not easily form, but it can be made other ways. Its CAS number is 10049-23-7.
Tellurous acid can be formed from the chlorides. Two chlorides are known, the dichloride, TeCl2, and the tetrachloride, TeCl4. They are both obtained by passing chlorine over tellurium, the product being separated by distillation (the tetrachloride is the less volatile). The dichloride is an amorphous, readily fusible, almost black solid. It is decomposed by water with formation of tellurium and tellurous acid:
2TeCl2+ 3H2O ? Te+H2TeO3+ 4HCl
However, pure tellurous acid, H2TeO3, can be obtained when the tetrachloride is decomposed by water, or on dissolving tellurium in nitric acid and pouring the solution into water. It is a colorless solid and behaves as a dibasic acid. The alkali tellurites are soluble in water. They also gives rise to super acid salts, such as KHTeO3·H2TeO3.

Chemical properties

White, crystalline powder. Soluble in dilute acids, alkalies; slightly soluble in water, alcohol.

Hazard

As for tellurium.