Phenolphthalein, iodination

The detection and determination ot the perchlorates.—The perchlorates give no precipitates with silver nitrate or barium chloride soln. cone. soln. give a white crystalline precipitate with potassium chloride. Unlike all the other oxy-acids of chlorine, a soln. of indigo is not decolorized by perchloric acid, even after the addition of hydrochloric acid and they do not give the explosive chlorine dioxide when warmed with sulphuric acid unlike the chlorates, the perchlorates are not reduced by the copper-zinc couple, or sulphur dioxide. Perchloric acid can be titrated with —iV-alkali, using phenolphthalein as indicator. The perchlorates can be converted into chlorides by heat and the chlorides determined volumetrically or gravimetrically they can be reduced to chloride by titanous sulphate 28 and titration of the excess of titanous sulphate with standard permanganate they can be fused with zinc chloride and the amount of chlorine liberated can be measured in terms of the iodine set free from a soln. of potassium iodide and they can be... 

The I2O7 content of the periodates described is determined as follows The weighed sample is covered with 20 ml. of water, and 5 to 10 drops of 6N HC1 is added to hasten solution. No chlorine is liberated from the acid of this concentration. The solution is diluted to 100 ml., made just alkaline to phenolphthalein paper with borax, buffered with borax and boric acid (Muller and Wegelin Z. anal. Chem., 52, 755-759 (1913), and an excess of potassium iodide is added. Under these conditions, the periodate is reduced to iodate. The liberated iodine is titrated with 0.1N arsenite. 

Assay Mix about 1.5 g of sample, accurately weighed, with 100 mL of recently boiled and cooled water contained in a 250-mL Erlenmeyer flask, add phenolphthalein TS, and titrate with 0.5 N sodium hydroxide to the first appearance of a faint-pink endpoint that persists for at least 30 s. Each milliliter of 0.5 N sodium hydroxide is equivalent to 37.04 mg of C3H602. Aldehydes (as propionaldehyde) Transfer 10.0 mL of sample into a 250-mL glass-stoppered Erlenmeyer flask containing 50 mL of water and 10.0 mL of a 1 80 aqueous solution of sodium bisulfite, stopper the flask, and shake vigorously. Allow the mixture to stand for 30 min, then titrate with 0.1 N iodine to the same brown-yellow endpoint obtained with a blank treated with the same quantities of the same reagents (see General Provisions). The difference between the volume of 0.1 N iodine required for the blank and that required for the sample is not more than 1.75 mL. 

Procedure of Kline and Acree. For the determination of the aldose present it is preferable to take an aliquot of the sugar solution, or a weighed amount of the solid substance, which will react with approximately 20 ml. of 0.1 A iodine. Titrate this solution with 0.1 A sodium hydroxide or hydrochloric acid until it is exactly neutral to phenolphthalein. Add the phenolphthalein at this point only when it is necessary to bring the solution to neutrality and use only one drop, as the alcohol introduces a potential source of error involving a loss of iodine. A water solution of this indicator or of phenol red or thymol blue might be used for this titration. Add 5 ml. of 0.1 A iodine from a buret then add drop by drop from a buret 7.5 ml. of 0.1 A sodium hydroxide. Repeat this process until 22 ml. of iodine and 35 ml. of alkali have been added. This operation takes about five to six minutes. Allow a two-minute interval for the completion of the oxidation. Acidify with 0.1 A (or 0.2 A) hydrochloric acid to free the iodine from any sodium iodate present and titrate the liberated iodine with... 

Tlie (deep blue-)black solution in the first beaker is due to the starch-iodine complex formed in the reaction the red color formed in the second beaker is caused by the indicator phenolphthalein and the p-nitrophcnol component in an alkaline medium, while elemental sulfur and A.S2S3 are mainly responsible for the golden yellow color generated in the third beaker. 

Gravimetric methods have been developed for most inorganic anions and cations, as well as for such neutral species as water, sulfur dioxide, carbon dioxide, and iodine. A variety of organic substances can also be easily determined gravimetri-cally. Examples Include lactose in milk products, salicylates in drug preparations, phenolphthalein in laxatives, nicotine in pesticides, cholesterol in cereals, and benz-aldehyde in almond extracts. Indeed, gravimetric methods are among the most widely applicable of all analytical procedures. 

The mixing time can be determined by chemical means, if the tank contents is mixed with a reaction component and the component to be added is mixed with a (1 4- x)-fold equivalent of the second reaction component, so that after intimate mixing the two reaction partners react with one another. The disappearance of the reaction partner is shown by a color indicator, which experiences a sudden color change. ( Method of the last color change is used, in contrast with decolorizing reaction which is proportional to the degree of conversion, see e.g. Kappel [262]). The redox reactions of thiosulfate with iodine (indicator starch) and the neutralization of sodium hydroxide with sulfuric acid (indicator phenolphthalein) have been found to be simple fast ionic reactions, suitable for this purpose. 

It should be noted that some iodinated phthalein dyes, e.g., tetraiodo-phenolphthalein and phenol tetraiodophthalein have been used in cholecystography. These compounds are very similar to BSP structurally and probably competitively inhibit uptake and excretion of the dye. 

Chloral hydrate is easily decomposed by alkali into chloroform and alkali formate. This reaction is used stoichiometrically to determine chloral hydrate purity by measuring the amount of an excess of IN sodium hydroxide consumed in the reaction (titration with IN sulfuric acid to phenolphthalein)15,99,127,T28,152 to l66. Alternatively, the formate generated in the reaction may be determined by reaction with an excess of iodine (O.IN), followed by back titration w ith... 

To a slightly acid solution (excess of acid or alkali being neutralised to phenolphthalein) add 2 g of sodium bicarbonate, to neutralise the hydriodic acid liberated during the titration, and titrate with 0-1N iodine. 1 ml O IN = 0 004945 g AsgOg. 

Weigh accurately into a 250-ml conical flask an amount of sample expected to contain from 0 08 to 0 09 g As. If (a) soluble in water, dissolve in 30 ml of water (b) insoluble in water, dissolve in 5 ml of N sodium hydroxide and 20 ml of water and add 5 ml of N sulphuric acid (c) containing chloride, dissolve in 50 ml of water. Place several glass beads in the flask and a small funnel in the neck, add 8 g of ammonium persulphate and boil briskly until colourless and for two minutes longer. (In the case of sodium cacodylate heat for about five minutes after ebullition commences.) Add cautiously 50 ml of approximately N oxalic acid and boil vigorously for five minutes. Add cautiously 40 ml of dilute sulphuric acid and 10 ml of potassium iodide solution. Boil vigorously until the volume is reduced to about 40 ml. Cool, just remove the pale yellow colour by the addition of approximately 01N sodium sulphite drop by drop (1 to 3 drops usually) and immediately add about 60 ml of water. Add 1 drop of phenolphthalein solution and sufficient sodium hydroxide test solution to render just alkaline. Add 10 ml of dilute sulphuric acid, mix, cool, neutralise with sodium bicarbonate, add up to 5 g in excess and titrate with 0 1 N iodine. If starch solution is used add it just before the end-point is reached. 

To 40 ml of sodium hydroxide test solution add 80 ml of dilute sulphuric acid, 1 drop of phenolphthalein solution and dilute sulphuric acid until colourless then add 10 ml of acid in excess, 10 ml of potassium iodide solution and cool. Neutralise with sodium bicarbonate and add up to 5 g in excess. Titrate with O IN iodine and deduct the reading from that obtained above. 1 ml of O IN iodine = 0 003746 g As. 

Add about 25 ml of boiled-out distilled water to about 0.5 g accurately weighed (by difference method) lime sample taken in an iodine titration flask and boil for 5-10 minutes. Cool, add a few clean dry glass beads and about 100 ml of a 10% sucrose solution. Stopper the flask and shake for 1 minute after every 5 minutes for a period of half an hour. Filter, by suction, through a Buchner funnel. Wash the residue 3-4 times with 10-ml portions of a 5% sucrose solution. Collect the filtrate and washings in a 250-ml measuring flask and make up to the mark with boiled-out distilled water. Take 50 ml of this solution in a titration flask. Add 2 drops of phenolphthalein indicator and titrate with N/10 HCI solution until the pink coiour disappears. Take concordant readings. 

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