Potassium Iodide Solution, Acidic

Iodine-Potassium Iodide Solution, Acidic Reagent... 

The ability of the solid chlorates(V) to provide oxygen led to their use in matches and fireworks. Bromates(V) and iodates(V) are used in quantitative volumetric analysis. Potassium hydrogen diiodate(V), KHflOjlj, is used to standardise solutions of sodium thiosulphate(Vf) since in the presence of excess potassium iodide and acid, the reaction... 

Alternatively, a known weight of the pyrolusite may be heated with concentrated hydrochloric acid and the chlorine evolved passed into potassium iodide solution. The iodine liberated is titrated with sodium thiosulphate ... 

Absolute diethyl ether. The chief impurities in commercial ether (sp. gr. 0- 720) are water, ethyl alcohol, and, in samples which have been exposed to the air and light for some time, ethyl peroxide. The presence of peroxides may be detected either by the liberation of iodine (brown colouration or blue colouration with starch solution) when a small sample is shaken with an equal volume of 2 per cent, potassium iodide solution and a few drops of dilute hydrochloric acid, or by carrying out the perchromio acid test of inorganic analysis with potassium dichromate solution acidified with dilute sulphuric acid. The peroxides may be removed by shaking with a concentrated solution of a ferrous salt, say, 6-10 g. of ferrous salt (s 10-20 ml. of the prepared concentrated solution) to 1 litre of ether. The concentrated solution of ferrous salt is prepared either from 60 g. of crystallised ferrous sulphate, 6 ml. of concentrated sulphuric acid and 110 ml. of water or from 100 g. of crystallised ferrous chloride, 42 ml. of concentrated hydiochloric acid and 85 ml. of water. Peroxides may also be removed by shaking with an aqueous solution of sodium sulphite (for the removal with stannous chloride, see Section VI,12). 

CAUTION. Ethers that have been stored for long periods, particularly in partly-filled bottles, frequently contain small quantities of highly explosive peroxides. The presence of peroxides may be detected either by the per-chromic acid test of qualitative inorganic analysis (addition of an acidified solution of potassium dichromate) or by the liberation of iodine from acidified potassium iodide solution (compare Section 11,47,7). The peroxides are nonvolatile and may accumulate in the flask during the distillation of the ether the residue is explosive and may detonate, when distilled, with sufficient violence to shatter the apparatus and cause serious personal injury. If peroxides are found, they must first be removed by treatment with acidified ferrous sulphate solution (Section 11,47,7) or with sodium sulphite solution or with stannous chloride solution (Section VI, 12). The common extraction solvents diethyl ether and di-tso-propyl ether are particularly prone to the formation of peroxides. 

Dissolve 0 1 g. of the quinone in a little rectified spirit. Add 10 ml. of 10 per cent, aqueous potassium iodide solution to a mixture of 5 ml. of aicohol and 5 ml. of concentrated hydrochloric acid, and then introduce the quinone solution. Iodine is liberated immed iately. This test is also given by other oxidising agents. 

Prepare a solution containing about 100 g, of potassium hypochlorite from commercial calcium hypochlorite ( H.T.H. ) as detailed under -Dimethylacrylic Acid, Section 111,142, Note 1, and place it in a 1500 ml. three-necked flask provided with a thermometer, a mechanical stirrer and a reflux condenser. Warm the solution to 55° and add through the condenser 85 g, of p-acetonaphthalene (methyl p-naphthyl ketone) (1). Stir the mixture vigorously and, after the exothermic reaction commences, maintain the temperature at 60-70° by frequent cooling in an ice bath until the temperature no longer tends to rise (ca. 30 minutes). Stir the mixture for a further 30 minutes, and destroy the excess of hypochlorite completely by adding a solution of 25 g. of sodium bisulphite in 100 ml. of water make sure that no hypochlorite remains by testing the solution with acidified potassium iodide solution. Cool the solution, transfer the reaction mixture to a 2-litre beaker and cautiously acidify with 100 ml. of concentrated hydrochloric acid. Filter the crude acid at the pump. 

Recovery of the wopropyl alcohol. It is not usually economical to recover the isopropyl alcohol because of its lo v cost. However, if the alcohol is to be recovered, great care must be exercised particularly if it has been allowed to stand for several days peroxides are readily formed in the impure acetone - isopropyl alcohol mixtures. Test first for peroxides by adding 0-6 ml. of the isopropyl alcohol to 1 ml. of 10 per cent, potassium iodide solution acidified with 0-6 ml. of dilute (1 5) hydrochloric acid and mixed with a few drops of starch solution if a blue (or blue-black) coloration appears in one minute, the test is positive. One convenient method of removing the peroxides is to reflux each one litre of recovered isopropyl alcohol with 10-15 g. of solid stannous chloride for half an hour. Test for peroxides with a portion of the cooled solution if iodine is liberated, add further 5 g. portions of stannous chloride followed by refluxing for half-hour periods until the test is negative. Then add about 200 g. of quicklime, reflux for 4 hours, and distil (Fig. II, 47, 2) discard the first portion of the distillate until the test for acetone is negative (Crotyl Alcohol, Note 1). Peroxides generally redevelop in tliis purified isopropyl alcohol in several days. 

Bismuth ttiiodide may be prepared by beating stoichiometric quantities of the elements in a sealed tube. It undergoes considerable decomposition at 500°C and is almost completely decomposed at 700°C. However, it may be sublimed without decomposition at 3.3 kPa (25 mm Hg). Bismuth ttiiodide is essentially insoluble in cold water and is decomposed by hot water. It is soluble in Hquid ammonia forming a red triammine complex, absolute alcohol (3.5 g/100 g), benzene, toluene, and xylene. It dissolves in hydroiodic acid solutions from which hydrogen tetraiodobismuthate(Ill) [66214-37-7] HBil 4H2O, may be crystallized, and it dissolves in potassium iodide solutions to yield the red compound, potassium tetraiodobismuthate(Ill) [39775-75-2] KBil. Compounds of the type tripotassium bismuth hexaiodide [66214-36-6] K Bil, are also known. 

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. 

On hydrolysis by boiling aqueous solution of barium hydroxide, isatidine (p. 603) yields two acid products. Isatinedc acid, CioHigOg, m.p. 148-5°, [a]ff° + 86° (HjO), which appears to contain one ethylenic linkage, one carboxyl group and one per-carboxyl group (R. CO. O. O), the evidence for the latter being the liberation of iodine from neutral or alkaline potassium iodide solution. The second product is isatinedc monolactonic add, CiqH 405, m.p. 197-8°, + 108-8°, which contains... 

In order that the reaction may proceed rapidly it is important to shake the mixture thoroughly after adding the iodine solution. When this is done the iodine compound is formed completely within one minute. With thymol it affords thymol di-iodide. In order to make sure that any iodine wnich may have entered into the hydroxyl-group is again liberated, care should be taken that a little hydriodic acid is always present hence the addition of the potassium iodide solution before the exc ess of iodine is titrated back with thiosulphate. Titration can only be regarded as complete when the blue coloration does not return in 10 minutes. 

The filtrate was adjusted to a pH of 9 by adding concentrated ammonia, and than a 1 N aqueous iodine-potassium iodide solution was added dropwise, whereby the tetrahydro-pyrimido-[5,4-d] pyrimidine obtained by hydrogenation with zinc in formic acid was converted by oxidation into 2,6-bis-(diethanolamino)-8-piperidino-pyrimido-[5/4-d]-pyrimidine. The completion of the oxidation was checked by means of a starch solution. The major amount of the oxidation product already separated out as a deep yellow crystalline precipitate during the addition of the iodine solution. After the oxidation reaction was complete, the reaction mixture was allowed to stand for a short period of time, and than the precipitate was separated by vacuum filtration, washed with water and dried. It had a malting point of 157°C to 158°C. The yield was 8.0 g, which corresponds to 95% theory. 

Notes. (1) For elementary students, it is sufficient to weigh out accurately about 1.25 g of arsenic(III) oxide, dissolve this in 50 mL of a cool 20 per cent solution of sodium hydroxide, and make up to 250 mL in a graduated flask. Shake well. Measure 25.0 mL of this solution by means of a burette and not with a pipette (caution — the solution is highly poisonous) into a 500 mL conical flask, add 100 mL water, 10 mL pure concentrated hydrochloric acid, one drop potassium iodide solution, and titrate with the permanganate solution to the first permanent pink colour as detailed above. Repeat with two other 25 mL portions of the solution. Successive titrations should agree within 0.1 mL. 

A) With potassium iodate. Potassium iodate has a purity of at least 99.9 per cent it can be dried at 120 °C. This reacts with potassium iodide in acid solution to liberate iodine ... 

Alternative procedure. The following method utilises a trace of copper sulphate as a catalyst to increase the speed of the reaction in consequence, a weaker acid (acetic acid) may be employed and the extent of atmospheric oxidation of hydriodic acid reduced. Place 25.0 mL of 0.017M potassium dichromate in a 250 mL conical flask, add 5.0 mL of glacial acetic acid, 5 mL of 0.001M copper sulphate, and wash the sides of the flask with distilled water. Add 30 mL of 10 per cent potassium iodide solution, and titrate the iodine as liberated with the approximately 0.1M thiosulphate solution, introducing a little starch indicator towards the end. The titration may be completed in 3-4 minutes after the addition of the potassium iodide solution. Subtract 0.05 mL to allow for the iodine liberated by the copper sulphate catalyst. 

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. 

Procedure. Weigh out accurately about 10 g of the salt and dissolve it in 250 mL of water in a graduated flask. Pipette 25 mL of this solution into a 250 mL conical flask, add about 20 mL of 10 per cent potassium iodide solution, 2 mL of 1M sulphuric acid, and 15 mL of a solution containing 2.0 g crystallised zinc sulphate. Titrate the liberated iodine immediately with standard 0.1M sodium thiosulphate and starch add the starch solution (2 mL) after the colour has faded to a pale yellow. The titration is complete when the blue colour has just... 

Soluble sulphides. Hydrogen sulphide and soluble sulphides can also be determined by oxidation with potassium iodate in an alkaline medium. Mix 10.0 mL of the sulphide solution containing about 2.5 mg sulphide with 15.0 mL 0.025M potassium iodate (Section 10.126) and 10 mL of 10M sodium hydroxide. Boil gently for 10 minutes, cool, add 5 mL of 5 per cent potassium iodide solution and 20 mL of 4M sulphuric acid. Titrate the liberated iodine, which is equivalent... 

The hydroxylamine solution is treated with a measured volume of 0.02M potassium bromate so as to give 10-30 mL excess, followed by 40 mL of 5M hydrochloric acid. After 15 minutes the excess of bromate is determined by the addition of potassium iodide solution and titration with standard Q.1M sodium thiosulphate (compare Section 10.134). 

Discussion. The procedure is based on the formation of yellow tetraiodo-antimonate(III) acid (HSbI4) when antimony(III) in sulphuric acid solution is treated with excess of potassium iodide solution. Spectrophotometric measurements may be made at 425 nm in the visible region or, more precisely, at 330 nm in the ultraviolet region. Appreciable amounts of bismuth, copper, lead, nickel, tin, tungstate, and molybdate interfere. 

Reagents. Potassium iodide solution. Dissolve 14.0 g potassium iodide and 1.0 g crystallised ascorbic acid in redistilled water and dilute to 100 mL. 

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