Starch thiosulfates

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 pH must be kept at 7.0—7.2 for this method to be quantitative and to give a stable end poiut. This condition is easily met by addition of soHd sodium bicarbonate to neutralize the HI formed. With starch as iudicator and an appropriate standardized iodine solution, this method is appHcable to both concentrated and dilute (to ca 50 ppm) hydraziue solutious. The iodiue solutiou is best standardized usiug mouohydraziuium sulfate or sodium thiosulfate. Using an iodide-selective electrode, low levels down to the ppb range are detectable (see Electro analytical techniques) (141,142). Potassium iodate (143,144), bromate (145), and permanganate (146) have also been employed as oxidants. 

An alternative method for the analysis of permanganate is the use of conventional iodometric methods (177) where excess potassium iodide is added to a solution of permanganate under acidic conditions. The Hberated iodide is then titrated with standard thiosulfate solution using starch as an indicator. 

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. 

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. 

Determination. The most accurate (68) method for the deterrnination of copper in its compounds is by electrogravimetry from a sulfuric and nitric acid solution (45). Pure copper compounds can be readily titrated using ethylene diamine tetracetic acid (EDTA) to a SNAZOXS or Murexide endpoint. lodometric titration using sodium thiosulfate to a starch—iodide endpoint is one of the most common methods used industrially. This latter titration is quicker than electrolysis, almost as accurate, and much more tolerant of impurities than is the titration with EDTA. Gravimetry as the thiocyanate has also been used (68). 

In this reaction, iodine is liberated from a solution of potassium iodide. This reaction can be used to assess the amount of ozone in either air or water. For determination in air or oxygen, a measured volume of gas is drawn through a wash bottle containing potassium iodide solution. Upon lowering the pH with acid, titration is effected with sodium thiosulfate, using a starch solution as an indicator. There is a similar procedure for determining ozone in water. 

Suppose 25.00 mL of an aqueous solution of iodine was titrated with 0.0250 M Na2S20,(aq), with starch as the indicator. The blue color of the starch-iodine complex disappeared when 27.65 mL of the thiosulfate solution had... 

Carboxymethylcellulose, polyethylene glycol Combination of a cellulose ether with clay Amide-modified carboxyl-containing polysaccharide Sodium aluminate and magnesium oxide Thermally stable hydroxyethylcellulose 30% ammonium or sodium thiosulfate and 20% hydroxyethylcellulose (HEC) Acrylic acid copolymer and oxyalkylene with hydrophobic group Copolymers acrylamide-acrylate and vinyl sulfonate-vinylamide Cationic polygalactomannans and anionic xanthan gum Copolymer from vinyl urethanes and acrylic acid or alkyl acrylates 2-Nitroalkyl ether-modified starch Polymer of glucuronic acid... 

The disappearance of the faint yellow color of triiodide ion was used to determine the end point of the titration with sodium thiosulfate. This gave better results than were obtained when the solution was diluted with sufficient water to use the starch triiodide end point in the presence of ethyl alcohol. 

Iodine liberation is one of the oldest and most commonly used methods for assessing lipid substrate oxidation. In this method, hydroperoxides and peroxides oxidize aqueous iodide to iodine, which is then titrated with standard thiosulfate solution and starch as endpoint indicator. The peroxide value is calculated as milliequivalents of peroxide oxygen per kilogram of sample. 

In this step the reddish brown color of the triiodide begins to fade to yellow and finally to clear, indicating only iodide ions present. However, this is not the best procedure for determining when all of the I3 has disappeared since it is not a sensitive reaction and the change from pale yellow to colorless is not distinct. A better procedure is to add a soluble starch solution shortly prior to reaching the end point, since if it is added to soon, too much iodine or triiodide ion may be present forming a complex that may not be reversible in the titration. The amount of thiosulfate is proportional to the amount of hypochlorite ion present. 

On standing, the filtered solids take on a color characteristic of iodine the solids can be decomposed by treatment in water with sodium thiosulfate or bisulfite to a negative starch-iodide endpoint. 

The compound is digested with nitric acid and the solution is analyzed for antimony by AA or ICP spectrophotometry (see Antimony). To determine the chlorine content a measured amount of substance is heated at 300°C and the liberated CI2 is passed into an acidic solution of KI and analyzed by iodomet-ric titration using a standard solution of sodium thiosulfate or phenyl arsine oxide and starch indicator. 

Chlorine gas may be identified readdy by its distinctive color and odor. Its odor is perceptible at 3 ppm concentration in air. Chlorine may be measured in water at low ppm by various titrimetry or colorimetric techniques (APHA, AWWA and WEF. 1999. Standard Methods for the Examination of Water and Wastewater, 20th ed. Washington DC American Pubhc Health Association). In iodometric titrations aqueous samples are acidified with acetic acid followed by addition of potassium iodide. Dissolved chlorine liberates iodine which is titrated with a standard solution of sodium thiosulfate using starch indicator. At the endpoint of titration, the blue color of the starch solution disappears. Alternatively, a standardized solution of a reducing agent, such as thiosulfate or phenylarsine oxide, is added in excess to chlorinated water and the unreacted reductant is then back titrated against a standard solution of iodine or potassium iodate. In amperometric titration, which has a lower detection limit, the free chlorine is titrated against phenyl arsine oxide at a pH between 6.5 and 7.5. 

Hydrazine reduces iodine to hydrogen iodide. Thus, an excess of standard solution of iodine is added to a measured volume of aqueous hydrazine solution and the excess iodine is back titrated at pH 7.0 to 7.2 (buffered by sodium bicarbonate) against a standard solution of sodium thiosulfate using starch indicator. 

Iodic acid can be analyzed by iodometric titration. Its acidic aqueous solution reacts with potassium iodide to liberate iodine (as shown above). Liberated iodine may be titrated against a standard solution of sodium thiosulfate using starch indicator. At the end point, the blue color of the solution... 

Iodine in aqueous solution may be measured quantitatively by acidifying the solution, diluting it, and titrating against a standard solution of sodium thiosulfate, sodium arsenite or phenyl arsine oxide using starch indicator. The blue color of the starch decolorizes at the end point. The indicator must be added towards the end of titration when the color of the solution turns pale yellow. Prior to titration, iodine in the dilute acidic solution is oxidized to iodate by adding bromine water or potassium permanganate solution. Excess potassium iodide is then added. The liberated iodine is then titrated as above. 

Elemental composition K 23.41%, Br 47.85%, O 28.74%. Aqueous solution of the salt after sufficient dilution may be analyzed for its potassium content by AA, ICP, or flame photometry (see Potassium) and for bromate anion by ion chromatography. Also, bromate content can be measured by iodometric titration using a standard solution of sodium thiosulfate and starch as indicator. The redox reactions are as follows ... 

Liberated iodine is titrated against a standard solution of thiosulfate until the starch solution s blue decolorizes. 

Elemental composition K 35.62%, Fe 16.96%, C 21.89%, N 25.53%. An aqueous solution of the salt may be analyzed for potassium and iron by various instrumental methods (see Iron, and Potassium Analysis). Its concentration in aqueous solution may be measured by adding excess potassium iodide to an acidified solution and titrating the iodine hberated with a standard solution of sodium thiosulfate using starch indicator. 

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. 

The hypochlorite ion may be identified most distinctly by ion chromatography. Its concentration in the aqueous solution combined as CIO and molecular CI2 (which is partly formed when hypochlorite is dissolved in water) can be measured by iodometric titration. A measured volume of sodium hypochlorite solution is added to a small volume of an acidified solution of potassium iodide (in excess). Iodine liberated is titrated with a standard solution of sodium thiosulfate or phenyl arsine oxide using starch as indicator. Blue color of starch solution decolorizes at the end point. 

Elemental composition Na 15.34%, I 84.66%. Aqueous solution is analyzed for sodium by AA or ICP and for iodide ion by ion chromatography or leuko-crystal violent colorimetry (See Iodine). Alternatively, in an acidified solution of sodium hypochlorite, a measured amount of sodium iodide is titrated against a standard solution of sodium thiosulfate or phenyl arsine oxide using starch indicator to detect the end point. 

Elemental composition Concentration of sodium thiosulfate in aqueous solution can he measured hy titration with a standard solution of potassium iodate, potassium hiiodate, or potassium dichromate using starch indicator. The oxidant is added to an acidified solution of excess potassium iodide before titrating with the thiosulfate solution. 

Although simple in conception and straightforward, the standard methods for POV determination require strict observance of analytical quality to avoid interference of artifacts. For example, according to the AOCS methods , the sample dissolved in AcOH-CHCI3 (method Cd 8-53) or AcOH-isooctane (method Cd 8b-90) solvent is treated with aqueous KI and the liberated iodine is titrated with standard thiosulfate solution, using starch indicator. Similar standard methods and modifications have been reported in various countries . 

Determination of ether. Transfer one-half (25ml) of dichromate soln from bubbler F into an Erlenmeyer flask, add about 20ml coned sulfuric acid, heat on a steam bath for 20 mins, cool to RT, add KI soln and titrate the liberated iodine by means of N/lO Na thiosulfate soln using starch indicator]... 

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]... 

A sample (approximately 0.2 g.) is weighed accurately and dissolved in 25 ml. of water then 25 ml. of 0.1 N hydrochloric acid and 0.2 g. of potassium bromide are added. The solution is titrated with 0.017 M potassium bromate until a permanent yellow color is produced. Potassium iodide (0.1 g.) is added, and the solution is backtitrated to a starch end point with 0.1 N sodium thiosulfate. The blue color returns in about a minute since the high acidity promotes air oxidation of excess iodide. The accuracy is only slightly less if the appearance of a faint yellow bromine color is taken as the end point. One mole of potassium bromate is equivalent to 3 of sodium /8-styrenesul-fonate. 

Active oxygen content is determined iodometrically 3 In an iodine flask, an accurately weighed sample (0.1-0.3 g.) is dissolved in 20 ml. of an acetic acid-chloroform solution (3 2 by volume), and 2 ml. of saturated aqueous potassium iodide solution is added. The flask is immediately flushed with nitrogen, stoppered, and allowed to stand at room temperature for 15 minutes. Fifty milliliters of water is then added with good mixing, and the liberated iodine is titrated with 0.1 A sodium thiosulfate, employing starch as indicator. A blank titration, which usually does not exceed 0.2 ml., is also run. One milliliter of 0.1 N sodium thiosulfate is equivalent to 0.00821 g. of tetralin hydroperoxide. 

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