Iodine with thiosulfate

Titrate liberated iodine with thiosulfate Ee/1 = 55.847 Ee203/2 = 79.845 I2 + 2 820 = 2 D + 8401 [titrate solution (pH ° 7.0) with thiosulfate until color is pale yellow. Add K1 and starch and continue titration to disappearance of blue color. I2/2 =... 

The kinetics of this reaction, the conditions under which it goes to completion, and subsequent titration of the iodine with thiosulfate solutions have ah been investigated (53—55). 

Balance the equation for the reaction of iodine with thiosulfate ion ... 

Ammonia is determined by the Kjeldahl method. Cobalt is determined by decomposing the salt with aqueous sodium hydroxide, dissolving the cobalt(III) oxide in acidified potassium iodide, and titrating the liberated iodine with thiosulfate. Anal. Calcd. for Co(NH3)3H20(C1)2C1 Co, 25.0 NH3, 21.6. Found Co, 24.6 NH3, 21.8. 

Strong oxidants generally oxidize thiosulfate to a mixture of tetrathionate, sulfate, and sulfur. The reaction between the oxidant and excess iodide must, therefore, be allowed to go to completion before titration of the iodine with thiosulfate. 

Starch decomposes irreversibly in solutions containing large concentrations of iodine. Therefore, in titrating solutions of iodine with thiosulfate ion, as in the indirect determination of oxidants, addition of the indicator is delayed until the color of the solution changes from red-brown to yellow at this point, the titration is nearly complete. The indicator can be introduced at the outset when thiosulfate solutions are being titrated directly with iodine. 

F, in N, was bubbled slowly through a well-stirred suspension of NaOAc HOAc(14 g. from equimolar amounts of both components) in CFC1, (450 mL) at —78 C. The oxidizing power of the solution was determined by treating aliquots with acidic K1 soln. followed by titration of the liberated iodine with thiosulfate. 

The (SCN)2 content of the solutions is determined by treatment of a portion with an excess of 10% aqueous potassium iodide and titration of the liberated iodine with thiosulfate ... 

Ferrari (1949) studied the HSppler method for the chemical determination of alcohol. This is based on oxidation with dichromate in the presence of sulfuric acid, adding iodide, and titrating the iodine with thiosulfate. He studied temperature, time of reaction, order of adding the solutions, volume, and concentration of alcohol and the reagent. Results comparable to those of the pycnometer method were obtained. Cordebard (1939) and Jaulmes (1951) reported better results using a nitric acid-dichromate mixture. 

If this oxidation is carried out in the presence of sulfanilic acid, the latter is diazotized and there is no redox reaction between the nitrous acid and the hydriodic acid (compare page 366). After removal of the excess iodine with thiosulfate, the diazonium salt may be coupled with a-naphthylamine to give a red azo dye. (See page 364 regarding this sensitive Griess test for nitrites.)... 

Titration of iodine with thiosulfate or phenylarsin oxide titrant is an everyday task in iodometric analysis. The iodine content of water samples, however, is much lower than the detection limit of this titration, even with amperometric endpoint location. Some of the highly sensitive electrometric inverse methods have been successfully used. 

Iodide colors a solution of PtCU red to brown (sensitive to 0.3 mmol Pt) (Fe , Cu , and other oxidants interfere) and may precipitate black PU4. Excess of KI forms K2[Ptl6], brown, shghtly soluble, and unstable enough that platinum may be determined volumetrically by treating [PtCle] with excess r and titrating the liberated iodine with thiosulfate, which shifts the Pt -Pl equilibrium completely toward reduction (as the O2 and acidic CO2 three paragraphs above shift it toward oxidation) ... 

Add KI and back-titrate iodine liberated with thiosulfate. Cd/8 = 14.05... 

Chlorine and bromine add vigorously, giving, with proper control, high yields of 1,2-dihaloethyl ethers (224). In the presence of an alcohol, halogens add as hypohaUtes, which give 2-haloacetals (225,226). With methanol and iodine this is used as a method of quantitative analysis, titrating unconsumed iodine with standard thiosulfate solution (227). 

Ofner Method. This method is for the determination of invert sugar in products with up to 10% invert in the presence of sucrose and is a copper-reduction method that uses Ofner s solution instead of Fehling s. The reduced cuprous oxide is treated with excess standardized iodine, which is black-titrated with thiosulfate using starch indicator. 

The butanals form the conventional aldehyde hydra2one, semicarba2one, and dimedone-type derivatives. In the absence of other aldehydes and ketones, -butyraldehyde can be deterrnined by addition of sodium bisulfite and the excess bisulfite deterrnined with iodine or thiosulfate (34). 

Ana.lysls. The available chlorine (av CI2) in hypochlorite solutions or soHds is deterrnined by reaction with aqueous KI, followed by acidification with either acetic or sulfutic acid and titration of the Hberated iodine with standard thiosulfate. The av CI2 in a hypochlorite is a measure of the oxidi2ing capacity expressed in terms of elemental chlorine one hypochlorite ion is equivalent to one CI2 molecule. Thus pure Ca(OCl)2 has an av CI2 of 2 x mol wt... 

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

A number of methods have been proposed for the detection of rancidity. The determination of active oxygen consists of dissolving the fat in a suitable medium such as chloroform and acetic acid, adding potassium iodide, and titrating the liberated iodine with a standard thiosulfate solution (16, 20). This is perhaps the most widely used method at the present time. Another procedure which has been proposed for the detection of peroxides employs ferrous ammonium sulfate and ammonium thiocyanate in acetone. The resulting red color of ferric thiocyanate is measured spectrophotometrically, and is said by the authors to yield more reproducible results than do the usual titration methods (21). 

A fresh sample of this 40% peracetic acid contains about 1.54 equivalents, or 0.77 mole, of peroxide per 100 ml. of solution, corresponding to 1.34 equivalents per 100 g. The concentration can be determined by treating the peroxide solution with potassium iodide and titrating the liberated iodine with standard sodium thiosulfate. The concentration of peroxide in peracetic acid decreases somewhat on long standing and should be checked before the peracetic acid is used. The yield of diacetate is lowered if the concentration of the peroxide is less than 1.0 equivalent per 100 g. of peracetic acid. The total amount of peroxide used should be 2.4 moles, or 4.8 equivalents, for each mole of iodo-benzene. 

Iodine was determined by an iodometric titration adapted from White and Secor.(3) Instead of the normal Carius combustion, iodide was separated from the samples either by slurrying in 6M NaOH, or by stirring the sample with liquid sodium-potassium (NaK) alloy, followed by dissolving excess NaK in ethanol. Precipitated plutonium hydroxides were filtered. Iodine was determined in the filtrate by bromine oxidation to iodate in an acetate buffer solution, destruction of the excess bromine with formic acid, acidifying with SO, addition of excess KI solution, and titrating the liberated iodine with standard sodium thiosulfate. The precision of the iodine determination is estimated to be about 5% of the measured value, principally due to incomplete extraction of iodine from the sample. 

Cd Cd(anthranilate)2 + 4 Br2 = 2 NH2C6H2Br2COOH + 4 Br" Titrate with KBr03—KBr until color of indigo changes to yellow. Add KI and back-titrate iodine liberated with thiosulfate. Cd/8 = 14.05... 

Analysis of this substance, just prior to use, is carried out in the following manner. A sample is dissolved in water and treated with a solution of potassium iodide in 2N sulfuric acid. After 5 minutes the solution is titrated with thiosulfate solution near the end of the titration the solution is boiled to ensure completeness of iodine liberation. Instead of the 90% product, a correspondingly greater amount of the 80% product can be employed. 

Elemental composition Rh 49.17%, Cl 50.83%. Rhodium is analyzed in an aqueous solution (or after dissolving in water) by AA or other techniques. Insoluble chloride is extracted with aqua regia, diluted, and analyzed to determine the rhodium content using various instrumental techniques. The chloride may be decomposed at elevated temperatures and liberated chlorine identified by color and other physical properties. Chlorine may be measured quantitatively by dissolving in an acidified solution of potassium iodide and titrating liberated iodine with a standard solution of sodium thiosulfate, using starch indicator. 

It was proposed to replace the final titration of Is in the standard method with a redox potentiometric method, which is less laborious, fast and prone to automation. The LOD is 0.16 meqkg, allowing determination of POV in fresh oil. A method based on the potentiometric determination of the equilibrium in equation 54, in aqueous solution containing a large excess of I, with a Pt electrode vs. SCSE, was proposed to replace the standard iodometric titrations of Section IV.B.2 for determination of the POV of oils. The proposed method is fit for purpose, based on the measurement uncertainties, as compared to those of the standards based on iodine titration with thiosulfate solution. The analytical quality of the potentiometric method is similar to that of the standards based on titrations for oils with POV >0.5 meqkg however, for fresh oils, with much lower POV, the potentiometric method is bettef . 

The bromine atom of 153 can be exchanged to iodine with sodium iodide, after which elimination of HI occurs upon treatment with sodium hydrogen carbonate and sodium thiosulfate (Scheme 12) <1984H(22)2789>. 

A) Anon, IEC, NewEdn, 14, 305(1936)(Peroxide formation in ethers and a test for peroxides in ether) [Procedure a) Add 10ml ether (sample to test) to 150ml of 2N sulfuric acid soln, followed by 3 drops of 1% soln of Amm molybdate (a catalyst to favor the liberation of dine) and 15ml of 10% KI soln. Shake well aiiJ allow to stand for 15 mins b) Titrate the liberated iodine with 0.05N Na thiosulfate and shake well after each addn until near discoloration of soln c) Add a few cc of starch soln and continue titration until disappearance of blue color]... 

As an illustration of the use of electrode potentials, consider the classical method of analysis of copper in brass, which involves dissolving the weighed sample in nitric acid to obtain Cu2+(aq), adjusting the pH to a weakly acidic level, allowing the Cu2+ to react completely with excess potassium iodide to form iodine and the poorly soluble Cul, and then titrating the iodine with sodium thiosulfate solution that has been standardized against pure copper by the same procedure ... 

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