Iodine, hydrogen peroxide titration

Iodine, hydrogen peroxide titration, 627 Iodine-iodide buffer, potentiometry, 699 Iodine number, unsaturated polyolefins, 740 lodobenzene, dioxirane oxidation, 1158 lodohydrins, dioxirane oxidation, 1158 lodometry... 

In what way does a solution of hydrogen peroxide react with (a) chlorine water, (b) potassium permanganate solution, (c) potassium dichromate solution, (d) hydrogen sulphide 50 cm of an aqueous solution of hydrogen peroxide were treated with an excess of potassium iodide and dilute sulphuric acid the liberated iodine was titrated with 0.1 M sodium thiosulphate solution and 20.0 cm were required. Calculate the concentration of the hydrogen peroxide solution in g 1" ... 

The Reich test is used to estimate sulfur dioxide content of a gas by measuring the volume of gas required to decolorize a standard iodine solution (274). Equipment has been developed commercially for continuous monitoring of stack gas by measuring the near-ultraviolet absorption bands of sulfur dioxide (275—277). The deterrnination of sulfur dioxide in food is conducted by distilling the sulfur dioxide from the acidulated sample into a solution of hydrogen peroxide, foUowed by acidimetric titration of the sulfuric acid thus produced (278). Analytical methods for sulfur dioxide have been reviewed (279). 

Wet-Chemical Determinations. Both water-soluble and prepared insoluble samples must be treated to ensure that all the chromium is present as Cr(VI). For water-soluble Cr(III) compounds, the oxidation is easily accompHshed using dilute sodium hydroxide, dilute hydrogen peroxide, and heat. Any excess peroxide can be destroyed by adding a catalyst and boiling the alkaline solution for a short time (101). Appropriate ahquot portions of the samples are acidified and chromium is found by titration either using a standard ferrous solution or a standard thiosulfate solution after addition of potassium iodide to generate an iodine equivalent. The ferrous endpoint is found either potentiometricaHy or by visual indicators, such as ferroin, a complex of iron(II) and o-phenanthroline, and the thiosulfate endpoint is ascertained using starch as an indicator. 

The most characteristic property of the oxaziranes is tlieir strong oxidizing character which is approximately equal to that of hydrogen peroxide. Oxaziranes react with hydrochloric acid the chlorine thus liberated is, however, used up in secondary reactions. " Two equivalents of iodine are formed from acid iodide solutions according to Eq. Titration of the free iodine allows a simple estimation of... 

Other examples are the use of osmium(VIII) oxide (osmium tetroxide) as catalyst in the titration of solutions of arsenic(III) oxide with cerium(IV) sulphate solution, and the use of molybdate(VI) ions to catalyse the formation of iodine by the reaction of iodide ions with hydrogen peroxide. Certain reactions of various organic compounds are catalysed by several naturally occurring proteins known as enzymes. 

Better results are obtained by transferring 25.0 mL of the diluted hydrogen peroxide solution to a conical flask, and adding 100 mL 1M(1 20) sulphuric acid. Pass a slow stream of carbon dioxide or nitrogen through the flask, add 10 mL of 10 per cent potassium iodide solution, followed by three drops of 3 per cent ammonium molybdate solution. Titrate the liberated iodine immediately with standard 0.1M sodium thiosulphate in the usual way. 

These and similar results can be explained if the simultaneous reduction of hydrogen peroxide is due to an induced reaction. To show the characteristic features of this reaction some results are presented in Table 19 and Table 20. The procedure for these measurements was as follows. The solution of peroxy compounds given in columns 1 and 2 was made up to 20 ml and the pH was adjusted to the given value. Then potassium thiocyanate solution was added and, after the reaction time noted, the process was quenched by adding potassium iodide solution (0.3 g KI). After 5 sec the solution was acidified with 1 ml 2 iV sulphuric acid then using, molybdate catalyst solution, the iodine liberated was titrated with standard thiosulphate. 

An attractive modification of this method is to treat the neutralised polythionate solution with neutral hydrogen peroxide and a known excess of standard sodium hydroxide solution on the water-bath and to determine the quantity of acid formed by the amount of standard alkali neutralised during the oxidation.3 All polythionates except the dithionates are completely oxidised to sulphate by heating in a closed tube for one hour with iodine and sodium bicarbonate by titrating the excess of iodine the total polythionate present may be estimated.4... 

The recovery of iodine from waste liquids.—E. Beilsteini2 recovered iodine from laboratory residues by evaporation to dryness with an excess of sodium carbonate and calcination until the organic matter is all oxidized. The mass is dissolved in sulphuric acid and treated with the nitrous fumes, obtained by treating starch with nitric acid, until all the iodine is precipitated. The iodine is washed in cold water, dried over sulphuric acid, and sublimed. Other oxidizing agents less unpleasant than the nitrous fumes employed by F. Beil stein—e.g. hydrogen peroxide—-were recommended by G. Torossian for the residues obtained in copper titrations. F. Beilstein s process is applicable to soluble but not to insoluble, oxidized forms of ioffine. F. D. Chattaway... 

The contents of the flask are then boiled, being taken almost to dryness and taken up with water several times (generally twice) so as to remove the hydrogen peroxide completely. The residue is diluted once more with 50 ml. water and a solution of sodium carbonate added until a slight precipitate is formed, this being then redissolved with a few drops of dilute acetic acid. Excess potassium iodide is added and the liberated iodine is titrated with a decinormal solution of sodium thiosulphate. 

Peracetic acid (b), commercial 40% peracetic acid. Material available from the Buffalo Electro Chemical Co. (Becco) has the composition 40% peracetic acid, 5% hydrogen peroxide, 39% acetic acid, 1% sulfuric acid, and 15% water. The density is 1.15 g. per ml. A fresh sample contains 0.77 mole of peracetic acid per 100 ml. Since the peracid content decreases somewhat on standing, an old sample should be analyzed by treating an aliquot with potassium iodide and titrating the liberated iodine with standard sodium thiosulfate. For certain uses it is advisable to neutralize the sulfuric acid present by addition of sodium acetate. 

Several methods exist for the identification and quantification of the HO and H02 radicals generated by the sonolysis of water. These species can oxidize ionic moieties e.g. Fe2+ into Fe3+ (the Fricke dosimeter) and I- into iodine. In addition, either can dimerize to form hydrogen peroxide (Schemes 2 and 3), which can then be titrated using conventional techniques. The HO will also react with terephtha-late anion in aqueous solution to produce hydroxyterephthalate anion, a fluorescent material which can then be estimated using fluorimetry. 

Determination of ozone in aqueous solution is perhaps the most problematic for a variety of reasons (1) ozone is unstable (2) ozone is volatile and easily lost from solution and (3) ozone reacts with many organic compounds to form products such as ozonides and hydrogen peroxide that are also good oxidants. Careful study of the use of iodometric methods for the determination of ozone in aqueous solution has revealed that the stoichiometric ratio of ozone reacted with iodine produced in the reaction varies from 0.65 to 1.5, depending on pFI, buffer composition and concentration, iodide ion concentration, and other reaction conditions. As a result, iodometric methods are not recommended. Ozone can be determined iodimetrically by addition of an excess of a standard solution of As(III), followed by titration of the excess As(III) with a standard solution of iodine to a starch endpoint. Methods using DPD, syringaldazine, and amperometric titrations have also been developed. 

An alternative to the hydrogen peroxide/sulfuric acid titration with alkali is distillation of sulfur dioxide from the acidified sample into excess iodine solution. A proportion of the iodine, equivalent to the amount of sulfur dioxide, is reduced to iodide, and the residual iodine is titrated with sodium thiosulfate using starch as indicator. This more rapid method is suitable for meat products where other volatile sulfur compounds do not interfere, and it has been developed for use with automated distillation systems. 

Other possibilities include absorption of SO2 in a 3% solution of hydrogen peroxide followed by titration of the solution with a lead(II) standard solution (indication - lead(II) ISE), or the reduction of iodine by SO2 with determination of the iodide formed with an iodide ISE. 

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