Tellurate ion

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). 

The Fe203 catalysts treated with tellurate ion are effective for the selective conversion of ethanol to acetone (183). The synthesis of acetone from ethanol (2EtOH + H20 - Me2CO + C02 + 4H2) is of interest from the point of view of using biomass as a chemical resource. 

In reactions where there is no change in the number of charges on the ions the ionic strength does not change and the reaction rates are somewhat simpler. A reaction of interest in this connection is the oxidation of the arsenite ion by the tellurate ion.18 The reaction was chosen because it goes with conveniently measurable velocity at the temperature of boiling water and the reaction can be followed easily by direct titration with iodine. More reactions of this type would undoubtedly be available for study at the higher temperatures if suitable analytical methods could be found. The reaction is... 

The anodic oxidation of silver metal in strong KOH solution gives the yellow tetrahydroxoargentate(III) ion [Ag(OH)4]-, which has a half-life of 100 min in 1.2 M NaOH, (<30 min in 0.1 M NaOH), decomposing to AgO and 02. The anion reacts rapidly with tellurate or periodate to give very stable complexes, which are usually obtained by direct oxidation of Ag+ alkaline solutions by K2S208 in the presence of periodate or tellurate ions. Representative are the ions Ag [Te04(OH)2]2 5 and Ag[I05(0H)]2 5 copper(III) complexes (Section... 

TeOj" reactions Reactions of tellurate ions To study these reactions use a 0.1m solution of sodium tellurate, Na2Te04. 

Roy, G. L., A. L. Laferriere, and J. O. Edwards A comparative study of polyol complexes of arsenite, borate, and tellurate ions. J. Inorg. Nucl. Chem. 4, 106... 

The kinetics of complexation of silver(in) by periodate and tellurate ions have been measured by the stopped-flow method. Both reactions result in a rate law attributable to stepwise formation of the bis-complex ... 

Gopal, N. G. S. and Frapart, P. Chromatographic Separations of Iodide, lodate. Tellurite and Tellurate Ions on Ion-Exchange Cellulose Papers and Control of Na Gelatin Capsules. Int. J. Appl. Radiat. Isotop. 17, 129 (1966). 20 16372... 

Selenium and tellurium react similarly, forming selenides and selenates(IV), and tellurides and tellurates(IV) respectively. Like the sulphide ion, S , the ions Se and Te form polyanions but to a much lesser extent. 

The electrodeposition of tellurium and silver has been investigated in dilute aqueous solutions of tellurous acid and Ag " ions (concentrations in the order of 10 to 10 " M) in 0.1 M HCIO4 [164], In particular, cyclic voltammetry experiments were conducted with rotating glassy carbon disk electrodes in baths with various concentration ratios of Ag(I) and Te(IV) precursors, and their outcome was discussed in terms of the voltammetric features. For a Ag(I)/Te(IV) ratio close to 0.8, formation of quasi pure silver telluride, Ag2Te, was reported. The authors, based on their measurements and on account of thermodynamic predictions, assumed that silver is deposited first on the electrode (Ag" + e Ag), and then Te(IV) is reduced on the previous silver deposit with formation of Ag2Te according to the reaction... 

Generally, oxo-selenates can be classified according to the oxidation state of the selenium atom as oxu-selenates(IV), and o.Yo-selenates(VI). The same applies for the respective tellurates. Besides this systematically correct naming, chemists usually use the terms selenites and tellurites instead of o. o-selenates(IV) and oxo-tellurates(IV), and selenates and tellurates instead of OAO-selenates(VI) and oxo-tellurates(VI). Therefore, both nomenclatures will be used in parallel throughout this chapter. Compared to the respective sulfur species, the oxo-selenate(IV) and oxo-tellurates(IV) ions are very stable so that numerous compounds with these anions have been prepared. 

A new structure type is found for Ag2Hg(Se03)2. Both Ag+ and Hg2+ ions are in octahedral coordination in this compound.137 The polyhedra are linked by the pyramidal shaped selenite anions.138 In the crystal structure of the red tellurate Ag2Hg2(Te04)3, the tellurium atoms are in octahedral coordination of oxygen atoms, and the octahedra are linked to infinite chains running along the u-axis. 

How can we be sure that the U +(Q2-) complex in a mixed metal oxide is present as the UO octahedron This can be done by studying solid solution series between tungstates (tellurates, etc.) and uranates which are isomorphous and whose crystal structure is known. Illustrative examples are solid solution series with ordered perovskite structure A2BWi aUa 06 and A2BTei-a Ua 06 91). Here A and B are alkahne-earth ions. The hexavalent ions occupy octahedral positions as can be shown by infrared and Raman analysis 92, 93). Usually no accurate determinations of the crystallographic anion parameters are available, because this can only be done by neutron diffraction [see however Ref. (P4)]. Vibrational spectroscopy is then a simple tool to determine the site symmetry of the uranate complex in the lattice, if these groups do not have oxygen ions in common. In the perovskite structure this requirement is fulfilled. 

An acidic solution of tellurium (IV) or tellurium (VI) is treated with sulfur dioxide and hydrazine hydrochloride. Tellurium precipitated from solution can be estimated by gravimetry. Selenium interferes with this test. A volumetric test involves converting tellurium to tellurous acid and oxidizing the acid with excess ceric sulfate in hot sulfuric acid in the presence of Cr3+ ion as catalyst. The excess ceric sulfate is measured by titration with a standard solution of ferrous ammonium sulfate. 

Metal Coatings. Tellurium chlorides, as well as tellurium dioxide in hydrochloric acid solution, impart permanent and attractive black antique finish to silverware, aluminum, and brass. Anodized aluminum is colored dark gold by tellurium electro deposition. A solution containing sodium tellurate and copper ions forms a black or blue-black coating on ferrous and nonferrous metals and alloys. Addition of sodium tellurite improves the corrosion resistance of electroplated nickel. Tellurium diethyldithiocarbamate is an additive in bright copper electroplating (see Electroplating). 

Evaporation of solutions of alumina in sulfuric acid yields crystals of A12(S04)3T6H20. If a group I sulfate is also present, the products are alums MA1(S04)2T2H20, in which aluminum exists as [Al(OH2)fi]3+. Analogous selenates but not tellurates have been prepared. Basic salts, e.g. Al2(OH)2(SO4)210H2O, and solids obtained from aluminum sulfate solutions above 100 °C also contain complex ions in which the coordination sphere of Al3+ is occupied by OH groups and/or water molecules rather than sulfate ions. Thermal decomposition of the hydrate A12(S04)3-16H20 yields practically anhydrous A12(S04)3 at 450 °C further decomposition to... 

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... 

In aqueous solution the acid has a metallic taste and only feebly affects litmus the latter characteristic is in accord with the evidence of its electrical conductivity, which is small and indicates relatively slight dissociation, comparable with that of hydrogen sulphide rather than with that of sulphuric acid. Measurements of the hydrogen-ion concentration of normal telluric acid solution gave [IT ] =4 x 10 5 gram-ion per litre. On the assumption that the acid is ionised in accordance with the equation (see p. 387)... 

The oxyaeids of tellurium, like those of selenium, have an inhibitory action on the growth of many bacilli in cultures. The ions of selenious and tellurous acids seem to be much more inhibitory than those of selenie and telluric acids. In the case of the growth of diphtheria bacilli 3 it has been shown that the active concentrations of selenium and tellurium are, for selenites, 1 1160, for selenates, 1 666, for tellurites, 1 420, and for tellurates, 1 125.4... 

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