Hydrogen tellurate

Synonyms orthotelluric acid telluric (VI) acid hydrogen tellurate... 

It is evident that telluric acid is notably different from what might be expected by analogy with sulphuric and selenic acids. One is hardly surprised, therefore, that isomorphism is exceedingly rare between the tellurates and the sulphates or selenates.3 The tellurates do not form alums, they do not as a rule form mixed crystals with the sulphates or selenates, the only fairly satisfactory case of mixed-crystal formation being with rubidium hydrogen sulphate and rubidium hydrogen tellurate. 

H2Te HYDROGEN TELLUR IDE 34.878 -1.1216E-02 5.2578E-05 -3.8397E-08 9.0281E-12 100 1500 gas... 

Tellurium trioxide, TeOa, is an orange yellow powder made by thermal decomposition of telluric(VI) acid Te(OH)g. It is a strong oxidising agent which will, like H2Se04, oxidise hydrogen chloride to chlorine. It dissolves in hot water to give telluric(VI) acid. This is a weak acid and quite different from sulphuric and selenic acids. Two series of salts are known. 

Tellur-verbindung, /. tellurium compound, -vorlegierung,/. tellurium prealloy, -wasser-stoff, m. hydrogen telluride. -wasserstoff-sSure, /. hydrotelluric acid (hydrogen telluride). -wismut, n. bismuth telluride. 

H2Te (hydrogen telluride, colorless), HTe (hydrogen telluride ion, colorless), Te (telluride ion, colorless), Te (ditelluride ion, red), Te" + (tellurous ion), HTeOj (telluryl ion), HTeO (acid tellurite ion, colorless), TeO " (tellurite ion, colorless), H2Te04 (telluric acid, colorless), HTeOJ (acid tellurate ion, colorless), TeO (tellurate ion, colorless). 

Also, telluric acid can be prepared by oxidation of tellurium or tellurium dioxide with a strong oxidizing agent such as hydrogen peroxide, sodium peroxide, chromic acid, or potassium permanganate in nitric acid. Molecular equations for overall reactions are shown helow ... 

Sodium tellurate [10101 -25-8], N TeO (53.7% Te theoretically), is made by oxidizing sodium tellurite solution with hydrogen peroxide. The reaction is exothermic. 

As regards the nature of their action on a human organism, tellurium and its compounds are similar to the inorganic compounds of selenium and arsenic. Hydrogen telluride is the most toxic. Tel-lurium(IV) oxide and aqueous solutions of the salts of tellurous and telluric acids are also toxic. Only tellurium ( metallic ) is not toxic if it gets into an organism. 

Different types of methods for purification have been applied. Brauner in 1889, by means of aqua regia, converted crude tellurium into telluric chloride, the aqueous solution of which on precipitation by sulphur dioxide deposited the element together with selenium and traces of copper and lead as the only impurities. The precipitate was dissolved in fused potassium cyanide in an atmosphere of hydrogen and the tellurium separated from the aqueous extract by treatment with a current of air. The element was then distilled in a current of hydrogen, 1 an alternative is distillation in a vacuum.5 Another method of treatment for the telluric chloride solution is to precipitate in three fractions using sulphur dioxide, when it is found that the middle fraction is of a high degree of purity.6... 

Another group of methods involves the conversion of the tellurium into some compound, inorganic or organic, which can be purified and then made to regenerate the element. Hydrogen telluride,7 crystalline telluric acid,8 basic tellurium nitrate 9 and diphenyl telluride 10 have all been made use of. 

Water is without effect on the element even at a red heat,3 but the combined action of water and ozone produces telluric acid at the ordinary temperature.4 The action of hydrogen peroxide upon tellurium is influenced considerably by the physical state of the element colloidal tellurium is readily oxidised, but crystalline tellurium is not readily attacked and has first to be dissolved in an aqueous solution of alkali hydroxide, when oxidation becomes possible with formation of tellurate.5 Hydrogen peroxide of 60 per cent, strength reacts very slowly with tellurium at a temperature of 100° C., but with increasing amount of telluric acid formed, the rate of dissolution increases. Amorphous tellurium as ordinarily prepared behaves in a similar manner to the crystalline variety, but if it is dried by treatment with alcohol and ether instead of by heating at 105° C. it will dissolve readily in a concentrated solution of hydrogen peroxide.6... 

The use of sulphur dioxide as precipitant was first proposed by Berzelius, but accurate results by this method are only obtainable under special conditions. Complete precipitation does not take place from a strongly acid solution, and in the presence of other metals small amounts of these are liable to be carried down. In the presence of heavy metals such as copper, bismuth and antimony, the following procedure has been recommended 2 The tellurium is oxidised to telluric acid by the addition of ammonium perdisulphate in the presence of potassium hydroxide, excess of perdisulphate being subsequently removed by boiling. The heavy metals present are next removed by means of hydrogen sulphide. The tellurium may then readily be estimated by reduction with hydrogen chloride and precipitation with sulphurous acid. 

Telluric acid may be determined iodometrically by reduction with either hydrogen bromide or hydrogen chloride.6 The substance is heated in a distillation llask with four times the theoretical quantity of potassium iodide in the presence of the acid, air being excluded from the apparatus by passing a stream of carbon dioxide. The liberated iodine is titrated in the receiver and in the residue.7... 

The presence of tellurite makes a special method necessary for the estimation of the fluoride, and it is found 1 that after hydrolysis the hydrogen fluoride may be titrated with alkali, using p-nitrophenol as indicator, the end-point not being affected by the presence of tellurous acid. 

Aqueous solutions of the alkali hydroxides readily dissolve tellurium dioxide with formation of the corresponding tellurite. In the presence of hydrogen peroxide the corresponding tellurate is formed.11 Ammonia and the alkali carbonates in cold aqueous solution have little effect, but the latter in hot solution or in the fused condition give rise to tellurites. Nitrates of the alkali metals on fusion with tellurium dioxide produce tellurates.12... 

The concentration of tellurous cation in solutions containing increasing amounts of hydrochloric acid has been determined by potential measurements, using a tellurium electrode, the total tellurium content of the solutions being determined chemically.3 The concentration of the tellurium ion was found to increase as the fourth power of the concentration of the hydrogen ions, the relation being in accordance with the expression... 

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