Tetrathionate ion

The oxidation of the thiosulphate ion SjOj to tetrathionate ion, is used to estimate iodine. 

Iodine reacts with thiosulfate ion, S 2-, to give iodide ion and the tetrathionate ion, S4062-. 

In acid solution, iodine is a weak oxidizing agent. The redox potential is —0.534 V at 25°C. It readily oxidizes thiosulfate to tetrathionate ion ... 

Much important aqueous sulfur chemistry involves oxosulfur species of the type C S—Sx—SO3- (x = 0 to 20 or more), such as the tetrathionate ion (x = 2) which results when thiosulfate ion (S2O32-) is oxidized by, for example, iodine (the basis of the classical analytical technique known as iodometry) ... 

It follows from reactions 15.11 and 15.20 that copper(II) ion can oxidize iodide to iodine, and from reactions 15.11 and 15.21 that thiosulfate can reduce I2 back to I- while forming the tetrathionate ion (Section 3.4). Because the relevant AE° values are several hundred millivolts, the equilibrium constants are large, and these reactions go to essential completion. 

Sodium thiodulfate, Na2S203 is the most commonly used reductant in iodo-metric titration. It is a moderately strong reducing agent. It reduces iodine to iodide ion. The thiosulfate ion is quantitatively oxidized to tetrathionate ion. The half-reaction is ... 

Decolorized a colorless solution of tetrathionate ions is formed White precipitate of barium thiosulfate White precipitate of silver thiosulfate... 

Adding an excess of sodium thiosulphate to the solution, tri-iodide ions are reduced to colourless iodide ions and die white colour of the precipitate becomes visible. The reduction with thiosulphate yields tetrathionate ions ... 

Triiodide ion is determined by titration with a sodium thiosulfate (Na2S203) solution. The products are iodide ion and tetrathionate ion (S4062-). 

Sodium thiosulfate the thiosulfate ion the tetrathionate ion thio acids (sulfo... 

Using Numbers Examine the net ionic equation below for the reaction that occurs when the thiosulfate ion (8303 ) is oxidized to the tetrathionate ion... 

In the tetrathionate ion, studied in BaS406- 2 H20 and Na2S406. 2 H20, the S4 chain has the configuration of Fig, 16.7(b), with dihedral angles close to 90°. There appears to be a definite difference between the lengths of the central and terminal S-S bonds, (a), and this also seems to be the case in dimethane sulphonyl disulphide, (b), with the same S4 skeleton, though it is doubtful if... 

The reaction between the tetrathionate ion and the cyanide ion in acetonitrile has been studied.192 Product analysis showed that when 1 mole of ionic tetrathionate and 2 mole of cyanide reacted together, 1 mole of ionic thiocyanate and 1 mole of ionic thiosulphate were obtained. A kinetic analysis gave a rate-determining step similar to that observed in aqueous solution ... 

The quantitative reaction with iodine is unique. Other oxidants can oxidize the tetrathionate ion to sulfate ion. 

The quantitative conversion of thiosulfate ion to tetrathionate ion shown in Equation 20-1 requires a pH smaller than 7. If strongly acidic solutions must be titrated, air oxidation of the excess iodide must be prevented by blanketing the solution with an inert gas, such as carbon dioxide or nitrogen. 

A useful analytical procedure involves the oxidation of iodide ions to free iodine. The free iodine is then titrated with a standard solution of sodium thiosulfate, Na2S203. Iodine oxidizes 8203 ions to tetrathionate ions, and is reduced to 1 ions. Write the balanced net... 

Fig. 1. The tetrathionate ion as seen along its twofold axis in the sodium salt 101).

The isomorphous potassium (218) and rubidium (91) salts have large cells with two tetrathionate ions in the asymmetric unit. 

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