Telluric acid

Orthotelluric

Colorless powder

Fixed

3.16 g · cm -3

136 ° C

7.70 ( PKS1 ); 10.95 ( pKa2 )

Moderately in water (100 g · l-1 at 20 ° C)

Attention

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Telluric acid is a very weak acid tellurium. The low acidity is due to the structure. The negative charge in the anion can not be delocalized. Tellurium has in the compound, the oxidation state VI.

Production

Telluric acid contains one of finely divided tellurium and aqueous chloric acid solution by oxidation of tellurium dioxide with potassium permanganate in nitric acid by the oxidation of tellurium or tellurium dioxide with hydrogen peroxide or by oxidation of tellurium with nitric acid and chromium trioxide.

Properties

Telluric acid is constructed octahedral, and is therefore also called orthotelluric. It forms colorless and water-soluble crystals. Since the first dissociation of telluric acid is already very small and the last ( 6 ) therefore vanishingly small, exist most tellurates (salts ) only as Hydrogentellurate, but there Silbertellurat, Ag6TeO6. The anhydride of telluric acid, tellurium ( TeO3 ), is a yellow crystalline powder. Telluric acid and ( water-soluble ) tellurates are toxic and have a very strong oxidizing. Telluric acid occurs in a monoclinic modification and a cubic modification. Large crystals are usually monoclinic, while the microcrystalline powder often consists of a mixture of both forms. On heating, the connection goes through between 100 and 220 ° C in solid, water Polymetatellursäure which decomposes above 220 ° C in tellurium and from 400 ° C in tellurium dioxide and oxygen. In a sealed tube telluric acid melts at about 136 ° C to form a concentrated aqueous solution of orthophosphoric acid and some Polymetatellursäure.