Iodate ions

In Landolt -type reactions, iodate ion is reduced to iodide tlirough a sequence of steps involving a reductant species such as bisulfde ion or arsenous acid (H AsO ). The reaction proceeds through two overall... 

The equihbrium constant of this reaction is 5.4 x 10 at 25°C, ie, iodine hydrolyzes to a much smaller extent than do the other halogens (49). The species concentrations are highly pH dependent at pH = 5, about 99% is present as elemental at pH = 7, the and HIO species are present in almost equal concentrations and at pH = 8, only 12% is present as and 88% as HIO. The dissociation constant for HIO is ca 2.3 x 10 and the pH has tittle effect on the lO ion formation. At higher pH values, the HIO converts to iodate ion. This latter species has been shown to possess no disinfection activity. An aqueous solution containing iodate, iodide, and a free iodine or triodide ion has a pH of about 7. A thorough discussion of the kinetics of iodine hydrolysis is available (49). 

Chlorite ion is oxidized rapidly to chlorine dioxide by ozone at pH 4, yielding one mol CIO2 per mol O3 when chlorite is in excess (k > lO" (39). The oxidation of bromite to bromate by ozone is too rapid to measure. Chlorine dioxide is oxidized rapidly to chlorate. Chlorate, bromate, and iodate ions do not react with ozone. 

Iodide and iodate ions react under the influence of protons to yield iodine molecules which react with amylose to yield a blue clathrate complex ... 

The HP may then be removed by adding MgO to precipitate MgF2 and the colourless deliquescent solid Xe03 obtained by evaporation. The aqueous solution known as xenic acid is quite stable if all oxidizable material is excluded, but the solid is a most dangerous explosive (reported to be comparable to TNT) which is easily detonated. The X-ray analysis, made even more difficult by the tendency of the crystals to disintegrate in an X-ray beam, shows the solid to consist of trigonal pyramidal Xe03 units, with the xenon atom at the apex (cf. the isoelectronic iodate ion 103 p. 863). 

For example, the common use of sodium hypochlorite solution, NaOCl, as a bleaching solution depends upon the oxidizing action of hypochlorite, OC1-. Iodate ion, IO, also furnishes a strong oxidizing power, as shown by E° for the half-reaction I2-IO ... 

The chlorine and bromine counterparts, chlorate, ClO-f, and bromate, BrO, have E° s that are even more negative. Hence these ions are even stronger oxidizing agents than iodate ion. 

The E° for reaction (16) is more negative than that of reaction (15), hence iodate ion can react with I-. In 1 M acid solution, the E° for the net reactioh... 

Oxidation by iodate ion in a strong hydrochloric acid medium proceeds through several stages ... 

Sei f-Test 12.2B When iodide ions react with iodate ions in basic aqueous solution, triiodide ions, I,, are formed. Write the net ionic equation for the reaction. (Note that the same product is obtained in each half-reaction.)... 

Periodate and iodate ions may both be removed by reaction with iodide ion in acid solution this yields free iodine which can be removed by extraction209 or by centrifugation210-—or the iodine can be converted to iodide ion by titration with sodium thiosulfate.211 Periodate and iodate ions are also readily removed from solution by use of an anion-exchange resin.211a... 

The column is filled with ion-exchange resin containing zirconium hydroxide. Acidic brine containing iodate ion is supplied to the column from the top. Iodate ion is adsorbed in the following reaction by way of the fixed bed ... 

Figure 12.9 illustrates the influence of temperature on iodate removal. In the case of desorption at 25°C, iodate will remain on the resin particles. Flowever, desorption is fully completed at 50°C. Figure 12.10 provides an example of an adsorption isotherm of the iodate ion. 

It is, however, pertinent to mention here that iodometric assays are never performed in a strongly basic medium, because of the fact that the reaction between I2 and OH produces hypoiodide and iodate ions respectively as shown below ... 

Iodine also has an oxidation state of+5, when forming the iodate— ion ... 

Elemental composition Cl 21.84%, I 78.16%. The compound is hydrolyzed in water and the product chloride and iodate ions are analyzed by ion chro-... 

The chemistry underlying the clock can be thought of in the following terms. Iodate ion is reduced by iodide through the overall stoichiometric... 

We do not know how much La3+ or IOjf is dissolved, but we do know that there must be three iodate ions for each lanthanum ion dissolved. That is, the iodate concentration must be three times the lanthanum concentration. If La3+ and IOf are the only species derived from La(I03)3, then the mass balance is... 

The element was obtained by the reduction of an acidic solution of the iodate ion with sodium hydrogen sulfite, (a) Write the chemical equation for the reaction, assuming the oxidized product to be HS04. (b) Calculate the mass of sodium hydrogen sulfite needed to produce 50.0 g of iodine. 

A spectrophotometric method has been developed which utilises the stronger absorption of periodate ions at 222.5 nm compared to the iodate ion.153... 

The oxidation state of iodine in periodic acid is +7. In the presence of strong acid it is reduced to iodate ion. The half-reaction is as follows ... 

In view of the propensity of alkynyliodonium ions for Michael reactions with a wide range of nucleophiles, such displacements at iodine represent an unusual mode of reactivity. However, carbon ligand exchanges of this type at polyvalent iodine do find precedent in the literature106 and probably proceed via the tetrasubstituted iodate ions shown in equation 130. A similar mechanism was first proposed by Beringer and Chang to account for interconversions of diaryliodonium salts with aryllithium reagents (equation 131)106. 

Why the thienyl- and furyllithium compounds attack the iodine atom instead of the p-carbon atom of alkynyliodonium ions is not entirely clear. However, they are much harder nucleophiles than the enolate salts of /Ldicarbonyl compounds and might prefer the harder iodonium center3. The much higher basicity of the heteroaryllithium reagents might also facilitate the formation of iodate ions and the displacement of alkynyllithiums from such intermediates. 

It was found impossible to measure the rate of decomposition by the evolution of gases because the release of these gas bubbles is very slow and erratic. The course of the reaction was followed by analyzing samples for the ammonium ion. Small amounts of the decomposing amalgam were forced through a capillary tube into a chilled solution of an iodate. The ammonium reacted with iodate ion to give iodide ion. The solution was then acidified with acetic acid and the iodine distilled out, collected and titrated with sodium thiosulfate. The method was checked with samples... 

For these, it would be expected that the oxidizing ability of oxygen should increase as the acidity of the reacting solution increases. For acid solutions, oxygen ranks roughly between iodate ion (f 0 — 1.1 to —1.2 volt)... 

The chlorate, bromate, and iodate ions are stable in solution, and many salts derived from these anions are familiar compounds. Although, as we have seen, the halate ions result from basic hydrolysis of the elemental halogens in warm solution, such a hydrolysis is generally not the method of choice for preparation of pure halates, since five sixths of the halogen... 

---