Iodate

1 paper and methanol-water (85 15) as the developing solvent, Rp values of 0.70 for iodide and 0.40 for iodate were found (391). The mobility of the ions was unaffected by the pH of the solvent in the range from 2 to 12. 

In the electrophoretic method (391), the electrolyte was 0.025 M sodium barbiturate, 0.05 M sodium acetate, or 0.025 M sodium octoate, with the pH adjusted to 8.6 by means of 0.1 fi hydrochloric acid. The sample solution was applied on Whatman No. 1 paper which had been previously equilibrated with electrolyte. After 30 min at 5° 

Distances of Migration of Carrier-Free I-g, I , and lO from the Starting Point in the Direction of the Anode 

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Andrews deration An important titration for the estimation of reducing agents. The reducing agent is dissolved In concentrated hydrochloric acid and titrated with potassium iodale(V) solution. A drop of carbon tetrachloride is added to the solution and the end point is indicated by the disappearance of the iodine colour from this layer. The reducing agent is oxidized and the iodate reduced to ICl, i.e. a 4-eiectron change. 

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 Landolt reaction (iodate + reductant) is prototypical of an autocatalytic clock reaction. During the induction period, the absence of the feedback species (Irere iodide ion, assumed to have virtually zero initial concentration and fomred from the reactant iodate only via very slow initiation steps) causes the reaction mixture to become kinetically frozen . There is reaction, but the intemiediate species evolve on concentration scales many orders of magnitude less than those of the reactant. The induction period depends on the initial concentrations of the major reactants in a maimer predicted by integrating the overall rate cubic autocatalytic rate law, given in section A3.14.1.1. 

Another important reaction supporting nonlinear behaviour is the so-called FIS system, which involves a modification of the iodate-sulfite (Landolt) system by addition of ferrocyanide ion. The Landolt system alone supports bistability in a CSTR the addition of an extra feedback chaimel leads to an oscillatory system in a flow reactor. (This is a general and powerfiil technique, exploiting a feature known as the cross-shaped diagram , that has led to the design of the majority of known solution-phase oscillatory systems in flow... 

Florvath D and Showalter K 1995 Instabilities in propagating reaction-diffusion fronts of the iodate-arsenous acid reaction J. Chem. Rhys. 102 2471-8... 

In addition to flame fronts, which have been extensively studied experimentally, front instabilities have been investigated for the isothennal cubic autocatalytic iodate arsenous acid system [70] as well as for polymerization... 

Iodine occurs to a minute extent (less than 0.001 %) in sea water, but is found in greater concentration, combined in organic form, in certain seaweeds, in oysters and in cod livers. Crude Chile saltpetre, or caliche contains small amounts of sodium iodate, NalOj. from which iodine can be obtained (see below). Some insoluble iodides, for example liiose of silver and mercury(II), occur in Mexico. Iodine is found in the human body in the compound thyroxin in the thyroid gland deficiency of iodine in diet causes enlargement of this gland (goitre). 

Most iodine produced commercially comes from the sodium iodate(V) remaining after sodium nitrate has been crystallised from Chile saltpetre. The iodatefV) is first reduced to iodide by blowing sulphur dioxide into the solution (or by addition of sodium sulphite) ... 

More iodate is then added, and with the sulphuric acid formed (or added if sodium sulphite is used), iodine is liberated ... 

Reaction (11.4) is really a disproportionation reaction of the halate(I) anion 3XO 2X -E XO. ) Reaction (11.3) is favoured by the use of dilute alkali and low temperature, since the halate(I) anions, XO are thermally unstable and readily disproportionate (i.e. reaction (11.4)). The stability of the halate(I) anion, XO , decreases from chlorine to iodine and the iodate(I) ion disproportionates very rapidly even at room temperature. 

Generally the solubility of a given metal halate decreases from chlorate(V) to iodatef and many heavy metal iodates(V) are quantitatively insoluble. Like their parent acids, the halates(V) are strong oxidising agents, especially in acid solution their standard electrode potentials are given below (in volts) ... 

The ability of the solid chlorates(V) to provide oxygen led to their use in matches and fireworks. Bromates(V) and iodates(V) are used in quantitative volumetric analysis. Potassium hydrogen diiodate(V), KHflOjlj, is used to standardise solutions of sodium thiosulphate(Vf) since in the presence of excess potassium iodide and acid, the reaction... 

Iodine monochloride, formed when iodine reacts with the iodate(V) ion in the presence of an excess of concentrated hydrochloric acid. 

Principle. An organic compound which contains chlorine is mixed with sodium peroxide and ignited in a closed metal bomb. The chlorine is thus converted to sodium chloride, and after acidification the chloride is estimated by the Volhard volumetric method. Bromine and iodine, when constituents of organic compounds similarly treated, are converted largely into sodium bromate and iodate respectively these ions are therefore subsequently reduced by hydrazine to bromide and iodide ions, and estimated as before. 

Procedure for Bromine and Iodine Estimations. Again cover the beaker as before, but before adding the nitric acid add i g. of hydrazine sulphate and heat the solution on the water-bath until evolution of gas ceases. To ensure complete decomposition of an iodate, however, the heating should be continued for i hour. 

Add 1 drop (0 05 ml.) of concentrated nitric acid to 2 0 ml. of a 0 5 per cent, aqueous solution of paraperiodic acid (HjIO,) contained in a small test-tube and shake well. Then introduce 1 op or a small crystal of the compound. Shake the mixture for 15 seconds and add 1-2 drops of 5 per cent, aqueous silver nitrate. The immediate production of a white precipitate (silver iodate) constitutes a positive test and indicates that the organic compound has been oxidised by the periodic acid. The test is based upon the fact that silver iodate is sparingly soluble in dilute nitric acid whereas silver periodate is very soluble if too much nitric acid is present, the silver iodate will not precipitate. 

The interaction of iodoaobenzene and iodoxybenzene in the presence of aqueous sodium hydroxide yields the soluble diphenyllodonium iodate (IV) upon adding potassium iodide solution, the sparingly soluble diphenyliodonium iodide (V), analogous to ammonium iodide is precipitated ... 

In qualitative organic analysis, use is made of the fact that silver iodate is sparingly soluble in dilute nitric acid whereas silver periodate is very soluble. For water-insoluble compounds solutions in ethanol or in pure dioxan may be employed. 

Place 2 ml. of the periodic acid reagent in a small test tube, add one drop (no more—otherwise the silver iodate, if formed, will fail to precipitate) of concentrated nitric acid, and shake well. Add one drop or a small crystal of the compound to be tested, shake the mixture for 15-20 seconds, and then add 1-2 drops of 3 per cent, silver nitrate solution. The instantaneous formation of a white precipitate of silver iodate is a positive test. Failure to form a precipitate, or the appearance of a brown precipitate which redissolves on shaking, constitutes a negative test. 

Thirty isotopes are recognized. Only one stable isotope, 1271 is found in nature. The artificial radioisotope 1311, with a half-life of 8 days, has been used in treating the thyroid gland. The most common compounds are the iodides of sodium and potassium (KI) and the iodates (KIOs). Lack of iodine is the cause of goiter. 

Laughing gas, see Nitrogen(I) oxide Lautarite, see Calcium iodate Lawrencite, see Iron(II) chloride Lechatelierite, see Silicon dioxide Lime, see Calcium oxide Litharge, see Lead(II) oxide... 

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