Titration using diphenylamine

NaC103 volumetric by reaction of the clilorate with FeS04 in acid solution and titrating the excess FeS04 with potassium dichromate using diphenylamine sulfonic acid indicator... 

Chromium oxide (Cr203). Up to 0.1% colorimetrically with diphenylcarbizide at 540 nm. Above 0.1% but as a minor constituent, colorimetrically with EDTA at 550 nm. As a major constituent by oxidation to dichromate by peroxodisulfuric acid using a silver nitrate catalyst, destruction of permanganate with HCl and titration against ferrous ammonium sulfate using diphenylamine-4-sulfonate indicator. 

The amount of Fe in a 0.4891-g sample of an ore was determined by a redox titration with K2Cr20y. The sample was dissolved in HCl and the iron brought into the +2 oxidation state using a Jones reductor. Titration to the diphenylamine sulfonic acid end point required 36.92 mL of 0.02153 M K2Cr20y. Report the iron content of the ore as %w/w FeyOy. 

For the titration of colourless or slightly coloured solutions, the use of an indicator is unnecessary, since as little as 0.01 mL of 0.02 M potassium permanganate imparts a pale-pink colour to 100 mL of water. The intensity of the colour in dilute solutions may be enhanced, if desired, by the addition of a redox indicator (such as sodium diphenylamine sulphonate, AT-phenylanthranilic acid, or ferroin) just before the end point of the reaction this is usually not required, but is advantageous if more dilute solutions of permanganate are used. 

The green colour due to the Cr3+ ions formed by the reduction of potassium dichromate makes it impossible to ascertain the end-point of a dichromate titration by simple visual inspection of the solution and so a redox indicator must be employed which gives a strong and unmistakable colour change this procedure has rendered obsolete the external indicator method which was formerly widely used. Suitable indicators for use with dichromate titrations include AT-phenylanthranilic acid (0.1 per cent solution in 0.005M NaOH) and sodium diphenylamine sulphonate (0.2 per cent aqueous solution) the latter must be used in presence of phosphoric) V) acid. 

Elemental composition K 28.22%, Cl 25.59%, and 0 46.19%. An aqueous solution is analyzed for potassium by AA, ICP, and other methods (see Potassium). Perchlorate ion may be analyzed by ion chromatography or a liquid-membrane electrode. Iodide, bromide, chlorate, and cyanide ions interfere in the electrode measurement. Alternatively, perchlorate ion may be measured by redox titration. Its solution in 0.5M H2SO4 is treated with a measured excess standard ferrous ammonium sulfate. The excess iron(II) solution is immediately titrated with a standard solution of potassium dichromate. Diphenylamine sulfuric acid may be used as an indicator to detect the end point ... 

Ceric Sulfate, 0.01 N [3.322 g Ce(S04)2 per 1000 mL] Dissolve 4.2 g of ceric sulfate [Ce(S04)2-4H20] or 5.5 g of the acid sulfate [Ce(HS04)4] in about 500 mL of water containing 28 mL of sulfuric acid, and dilute to 1000 mL. Allow the solution to stand overnight, and filter. Standardize this solution daily as follows Weigh accurately about 275 mg of hydroquinone (CgHg02), dissolve it in sufficient 0.5 N Alcoholic Sulfuric Acid to make 500.0 mL, and mix. To 25.0 mL of this solution add 75 mL of 0.5 N sulfuric acid, 20 mL of water, and 2 drops of Diphenylamine TS. Titrate with the ceric sulfate solution at a rate of about 25 drops per 10 s until an endpoint is reached that persists for 10 s. Perform a blank determination using 100 mL of 0.5 N Alcoholic Sulfuric Acid, 20 mL of water, and 2 drops of Diphenylamine TS, and make any necessary correction. Calculate the normality of the ceric sulfate solution by the formula... 

The interest in the application of indicators in oxidation-reduction titrations has followed on the discovery that the familiar color change undergone by diphenylamine on oxidation could be used to determine the end-point of the titration of ferrous ion by dichromate in acid solution. Diphenylamine, preferably in the form of its soluble sulfonic acid, at first undergoes irreversible oxidation to diphenylbenzidine, and it is this substance, with its oxidation product diphenylamine violet, that constitutes the real indicator. ... 

A useful property of a potassium permanganate solution is its intense purple color, which is sufficient to serve as an indicator for most titrations. If you add as little as 0.01 to 0.02 mL of a 0.02 M solution of permanganate to 100 itlL of water, you can perceive the purple color of the resulting solution. If the solution is very dilute, diphenylamine sulfonic acid or the 1,10-phenanthroline complex of iron(II) (see Table 19-2) provides a sharper end point. 

The orange color of a dichromate solution is not intense enough for use in end point detection. Diphenylamine sulfonic acid (see Table 19-2) is an excellent indicator for titrations with this reagent, however. The oxidized form of the indicator is violet, and its reduced form is essentially colorless thus, the color change observed in a direct titration is from the green of chromium(III) to violet. 

The earliest known redox indicator is diphenylamine used for titration of Fe(II) with K2Cr20y. An intense blue violet colouration is produced at the end point. The action of... 

Methods of Chemical Analysis. During oxidation and hydrolysis studies of ferrous sulfate solutions, ferrous iron concentrations which ranged from 570 to 157 ppm were analyzed by titration with potassium dichromate solution using sodium diphenylamine sulfonate as an indicator (22). The same method was used to analyze for ferrous iron in mixed ferric-ferrous sulfate solutions. Total dissolved iron concentrations, which ranged from 560 to 100 ppm during hydrolysis of mixed ferric-ferrous... 

Percentages of vanadium(IV) relative to the total vanadium can be determined volumetrically. An acid solution of a sample is titrated with a standard solution of potassium permanganate and then successively titrated with a standard solution of ammonium iron(II) sulfate by the use of diphenylamine as an indicator. The first titration corresponds to the amount of vanadium(IV) and the second to the total amount of vanadium. 

A number of transition metals can be determined conveniently if their cations undergo a definite change of oxidation state see Oxidation Number) on titration with a standard solution of potassium permanganate, potassium dichromate, cerium(IV) sulfate, or ammonium hexanitratocerate(IV). Several visual indicators have been proposed, including diphenylamine and its derivatives, xylene cyanole FF, and especially A-phenylanthranilic acid and tris(l,10-phenanthroline)iron(II) sulfate ( ferroin ). Solutions of have been used in the determination of iron, copper, titanium, vanadium, molybdenum, tungsten, mercury, gold, silver, and bismuth, and standard solutions of and Sn F U, and and Mo have also... 

Iron in iron ores can, of course, also be analyzed by the classical redox titration with standard dichromate solution using a diphenylamine sulfonate indicator. Trace manganese in ores can also be determined using colorimetric methods or atomic absorption spectroscopy. An atomic absorption spectrophotometer, however, will cost a minimum of about 4500 and requires the periodic replacement of expensive hollow-cathode lamps. The point is that one usually has some choice of analytical methods, each with its particular advantages and disadvantages for the problem at hand. 

In the field of redox titrations, most of the problems were coimected with indicators. Hence, iodometry and permangometry, which are self-indicating methods, became the most widely used. The first redox indicatoi diphenylamine, for the dichromate titration of iron(n), was introduced by Knop in 1924. 

Finally, the formed diquinonediimine can be oxidized once more, but this time irreversibly (from a chemical standpoint—see the concept of reversibility in electrochemistry) when it stays too long in the presence of the oxidizing solution. Diphenylamine can be used in the case of the titration of ferrous ions by potassium dichromate. It is poorly soluble in water. This is the reason why the barium and sodium salts of diphenylaminesulfonic acid are used. Another interesting indicator deriving from diphenylamine is variamine blue. The structures of its reduced (colorless) and oxidized (blue-violet) forms are... 

A known volume of the iron ore solution is titrated directly with standard solution in a medium acidified with H2SO4 (or HCI) and H3PO4 using sodium diphenylamine sulphonate as internal indicator ... 

Preparation of TMPMgCI LiCI (64) A dried and argon-flushed 2 L 5c/i/e -flask, equipped with a magnetic stirring bar and rubber septum, was charged with /-PrMgCl LiCl (1.31 M in THF, 850 mL, 1.11 mol). Then, 2,2,6,6-tetramethylpiperidine (161 g, 194 mL, 1.14 mol, 1.02 equiv.) was added at once and the mixture was stirred until gas evolution ceases (48 h). Titration with benzoic acid using 4-(phenylazo)diphenylamine as indicator prior to use showed a concentration of 1.15 M. 

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