Tellurate ions, reactions

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... 

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

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 ... 

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... 

These results clearly indicate that in the tellurium tetrachloride addition to alkenes the main reaction pathway does not occur via a telluronium ion intermediate a radical addition pathway could explain the poor selectivity observed in many of these additions (see Tables 15 and 16). The strong effect of 4-benzoquinone on the syn/anti ratio supports the involvement of a radical pathway in chloro-telluration with tellurium tetrachloride. A possible radical chain reaction is shown87. 

When a drop of a caustic alkali solution containing AsOa , SbOg- or SnOg- is brought together with a drop of a freshly prepared solution of ammonium tellurate (which contains ions), there is an immediate precipitation of black elemental tellurium. The underl5dng reactions may be ... 

In acid solution, ferrous salts act as reductants. This effect can be enhanced by the addition of concentrated phosphoric acid which forms the complex Fe(P04)2 ion with the Fe+ ions that are produced when Fe+ ions enter into redox reactions. This enhancement of the redox potential of the Fe+ ion can be employed for the rapid detection of salts of noble metals, selenic and selenious acid and also telluric and tellurous acid. 

Selenites and selenates are quantitatively reduced to elementary selenium when their acid solutions are warmed with ferrous sulfate. In contrast, tellurite and tellurate solutions remain unaltered because the redox potential of iron is not sufhcient to accomplish the reaction Fe i + Teiv(vi) Fe -f Te°. However, the reducing power of Fe+ ions can be raised considerably if the Fe+ ions are removed as soon as they are produced. Phosphoric acid is excellent for this purpose it immediately converts the Fe+ ions into [Fe(P04)2] " ions. Fluorides act analogously through the formation of [FeF,]- ions. Consequently, when tellurites or tellurates are warmed with a ferrous sulfate-phosphoric acid mixture there is complete reduction to free tellurium. 

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