Telluric acid is a

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

with the formula , often written as . It is a white crystalline solid made up of octahedral molecules which persist in aqueous solution. In the solid state, there are two forms, rhombohedral and monoclinic, and both contain octahedral molecules, containing one hexavalent

tellurium Tellurium is a chemical element with the symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionall ...

(Te) atom in the +6 oxidation state, attached to six

hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydro ...

(–OH) groups, thus, it can be called tellurium(VI) hydroxide. Telluric acid is a weak acid which is dibasic, forming tellurate

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...

s with strong bases and hydrogen tellurate salts with weaker bases or upon hydrolysis of tellurates in water.Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. . It is used as tellurium-source in the synthesis of oxidation catalysts.

Preparation

Telluric acid is formed by the

oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...

or tellurium dioxide with a powerful

oxidising agent An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ). In other words, an oxid ...

such as

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%� ...

, chromium trioxide or sodium peroxide. : Crystallization of telluric acid solutions below 10 °C gives telluric acid tetrahydrate . It is an oxidising agent, as shown by the

electrode potential In electrochemistry, electrode potential is the electromotive force of a galvanic cell built from a standard reference electrode and another electrode to be characterized. By convention, the reference electrode is the standard hydrogen electrode ( ...

for the reaction below, although it is kinetically slow in its oxidations. :, ''E''^o = +1.02 V

Chlorine Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...

, by comparison, is +1.36 V and

selenous acid Selenous acid (or selenious acid) is the chemical compound with the formula . Structurally, it is more accurately described by . It is the principal oxoacid of selenium; the other being selenic acid. Formation and properties Selenous acid is a ...

is +0.74 V in oxidizing conditions.

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 ), and allotelluric acid, an acid syrup of unknown structure (approximate composition ). Typical salts of the acid contains the anions and . The presence of the tellurate ion has been confirmed in the solid state structure of . Strong heating at over 300 °C produces the α crystalline modification of tellurium trioxide, α-. Reaction with

diazomethane Diazomethane is the chemical compound CH2N2, discovered by German chemist Hans von Pechmann in 1894. It is the simplest diazo compound. In the pure form at room temperature, it is an extremely sensitive explosive yellow gas; thus, it is almost ...

gives the hexamethyl ester, . Telluric acid and its salts mostly contain hexacoordinate

. This is true even for salts such as magnesium tellurate, , which is isostructural with magnesium molybdate and contains octahedra.

Other forms of telluric acid

Metatelluric acid, , the tellurium analogue of sulfuric acid, , is unknown. Allotelluric acid of approximate composition , is not well characterised and may be a mixture of and .

Other tellurium acids

Tellurous acid , containing tellurium in its +4 oxidation state, is known but not well characterised.

Hydrogen telluride Hydrogen telluride is the inorganic compound with the formula H2 Te. A hydrogen chalcogenide and the simplest hydride of tellurium, it is a colorless gas. Although unstable in ambient air, the gas can exist at very low concentrations long enough ...

is an unstable gas that forms hydrotelluric acid upon addition to water.

References

{{Authority control Hydroxides Tellurates Oxidizing acids Oxidizing agents