Iodide, potassium

Potassium iodide (poe-TAS-ee-yum EYE-oh-dide) is a white crystalline, granular, or powdered solid with a strong, bitter, salty taste. It is used as a feed additive, a dietary supplement, in photographic films, and in chemical research. 

A number of methods are available for the preparation of potassium iodide. In one procedure, elemental iodine (I2) is added to a solution of potassium hydroxide ( ) I2 + 6K0H — 5KI + KI03 + 3H20. The potassium iodide formed is separated from the potassium iodate (KI03) by fractional crystallization. That is, the solution is warmed and then cooled. As the temperature falls, the two compounds, potassium iodide and potassium iodate, crystalize out at different temperatures and can be separated from each other. The potassium iodate can then be heated, causing it to decompose and make additional potassium iodide 2KI03 — aKI + 02. 

Potassium iodide. Green atom is iodine and turquoise atom is potassium, publishers 

Potassium iodide can also be produced by reacting hydriodic acid (HI) with potassium bicarbonate HI + KHC03 - KI + C02 + H20. 

Finally, the compound can be made by reacting iron (1 iodide with potassium carbonate (K2C03) Fe3I8 + 4K2C03 — 8KI + 4C02 + Fe304. 

Data reported for the protolysis constant of water in potassium iodide media are listed in Table 5.26. The data are solely for a temperature of 25 C, as reported by Lucas (1967). 

Robinson and Stokes (1959) listed osmotic coefficient data for potassium iodide solutions. Water activity data were derived from these data using Eq. (5.18). The dependence of the water activity data on the ionic strength in potassium iodide solutions can be described using Eq. (5.19), and the values derived for and are 0.03256 0.00011 x 10 and 3.98 0.25 X10 kg mol , respectively. 

INTRODUCTION This data sheet presents properties of single crystal potassium iodide. 

Linear Expansion Coeff. (°K l) 42. 6 X 10 (313°K) Dispersion Equation Not available 

Optical Engineering Handbook , General Electric Co., Scranton, Pa., (1963). 

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Liberate iodine from a potassium iodide solution acidified with... 

Liquid sulphur dioxide is a solvent for a number of substances, for example iodine, sulphur, some sulphites, potassium iodide and sulphur dichloride oxide, SOClj (see below). The liquid can be assumed to ionise slightly, thus ... 

In what way does a solution of hydrogen peroxide react with (a) chlorine water, (b) potassium permanganate solution, (c) potassium dichromate solution, (d) hydrogen sulphide 50 cm of an aqueous solution of hydrogen peroxide were treated with an excess of potassium iodide and dilute sulphuric acid the liberated iodine was titrated with 0.1 M sodium thiosulphate solution and 20.0 cm were required. Calculate the concentration of the hydrogen peroxide solution in g 1" ... 

Iodine is a dark-coloured solid which has a glittering crystalline appearance. It is easily sublimed to form a bluish vapour in vacuo. but in air, the vapour is brownish-violet. Since it has a small vapour pressure at ordinary temperatures, iodine slowly sublimes if left in an open vessel for the same reason, iodine is best weighed in a stoppered bottle containing some potassium iodide solution, in which the iodine dissolves to form potassium tri-iodide. The vapour of iodine is composed of I2 molecules up to about 1000 K above this temperature, dissociation into iodine atoms becomes appreciable. 

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... 

Iodine as such finds few uses but a solution in alcohol and water, also containing potassium iodide ( tincture of iodine was commonly used as an antiseptic for cuts and wounds, but had rather an irritant action. Iodoform (triiodomethane), CHI3, is also an antiseptic, but newer compounds of iodine are now in use. Silver iodide, like silver bromide, is extensively used in the photographic industry. 

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 ... 

In water pollution studies, the oxygen content can be measured by making the water alkaline and shaking a measured volume with an oxygen-free solution containing Mn- (aq). The solution is acidified with sulphuric acid, potassium iodide added and the liberated iodine titrated with sodium thiosulphate. 

Copperil) iodide, Cul, is obtained as a white precipitate on addition of potassium iodide to a solution containing copper(II) ... 

Anhydrous cupric sulphate is white but forms a blue hydrate and a blue aqueous solution. The solution turns yellow when treated with concentrated hydrochloric acid, dark blue with ammonia, and gives a white precipitate and brown solution when treated with potassium iodide. A yellow-brown aqueous solution of ferric chloride becomes paler on acidification with sulphuric or nitric... 

The reactions involved are similar in both cases, and closely parallel to those which give rise to chloroform. The sodium hypochlorite probably first oxidises the potassium iodide to potassium hypoiodite, which then oxidises the ethanol to acetaldehyde and then iodinates the latter to tri-iodo ... 

IODOFORM FROM ACETONE. (Semi-micro Scale.) Required Acetone, 0 5 ml. 10% potassium iodide solution, 20 ml. 10% sodium hydroxide solution, 8 ml. zM sodium hypochlorite solution, 20 ml. 

Place 0 5 ml. of acetone, 20 ml. of 10% aqueous potassium iodide solution and 8 ml. of 10% aqueous sodium hydroxide solution in a 50 ml. conical flask, and then add 20 ml. of a freshly prepared molar solution of sodium hypochlorite. Well mix the contents of the flask, when the yellow iodoform will begin to separate almost immediately allow the mixture to stand at room temperature for 10 minutes, and then filter at the pump, wash with cold w ater, and drain thoroughly. Yield of Crude material, 1 4 g. Recrystallise the crude iodoform from methylated spirit. For this purpose, place the crude material in a 50 ml. round-bottomed flask fitted with a reflux water-condenser, add a small quantity of methylated spirit, and heat to boiling on a water-bath then add more methylated spirit cautiously down the condenser until all the iodoform has dissolved. Filter the hot solution through a fluted filter-paper directly into a small beaker or conical flask, and then cool in ice-water. The iodoform rapidly crystallises. Filter at the pump, drain thoroughly and dry. 

To ensure the presence of a slight excels of nitrous acid, potassium iodide-starch paper is sometimes used as an external indicator, a drop of the solution being removed from time to time during the addition of the sodium nitrite, and then dropped on to the paper. When an excess of nitrous acid is present, iodine is liberated, and gives the familiar... 

When potassium iodide or hydrogen iodide is added to an aqueous solution of a diazonium salt, nitrogen is readily evolved (no catalyst being necessary) and the corresponding iodo-compound is formed. lodo-compounds can thus... 

Required Aniline, 15 ml. hydrochloric acid, 40 ml. sodium nitrite, 12-5 g. potassium iodide, 35 g. 

When all the sodium nitrite has been added and diazotisation is complete, transfer the cold solution to a 600 ml. round-bottomed bolt-head flask. Dissolve 35 g. of potassium iodide in 50 ml. of water, and add this solution slowly with shaking to the cold... 

To the cold solution, add about 2 ml. of 10% potassium iodide solution. A brisk effervescence of nitrogen occurs, and iodobenzene separates, usually as drops so small that in spite of their density they float on the surface. 

Both chloramine-T and dichloramine-T can be readily estimated, because they liberate iodine from potassium iodide quantitatively in the presence of... 

J) By acidified potassium iodide. To an aqueous KI solution containing a few drops of dil. H2SO4, add i ml. of aqueous benzoquinone... 

Iodine Solution. Cold saturated aqueous solution. (If a more concentrated solution is required, add i g. of powdered iodine to a solution of 2 g. of potassium iodide in a minimum of water, and dilute the solution to 100 ml.)... 

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). 

By the interaction of aleohols or glyeols with potassium iodide and 95 per eent. orthophosphoric aeid (the last named is prepared from the eommercial 85 per eent. aeid and phosphoric oxide), for example ... 

In a 500 ml. three-necked flask, equipped with a thermometer, a sealed Hershberg stirrer and a reflux condenser, place 32-5 g. of phosphoric oxide and add 115-5 g. (67-5 ml.) of 85 per cent, orthophosphoric acid (1). When the stirred mixture has cooled to room temperature, introduce 166 g. of potassium iodide and 22-5 g. of redistilled 1 4-butanediol (b.p. 228-230° or 133-135°/18 mm.). Heat the mixture with stirring at 100-120° for 4 hours. Cool the stirred mixture to room temperature and add 75 ml. of water and 125 ml. of ether. Separate the ethereal layer, decolourise it by shaking with 25 ml. of 10 per cent, sodium thiosulphate solution, wash with 100 ml. of cold, saturated sodium chloride solution, and dry with anhydrous magnesium sulphate. Remove the ether by flash distillation (Section 11,13 compare Fig. II, 13, 4) on a steam bath and distil the residue from a Claisen flask with fractionating side arm under diminished pressure. Collect the 1 4-diiodobutane at 110°/6 mm. the yield is 65 g. 

Mix together 1 0 g. of pure p-naphthol and the theoretical quantity of 50 per cent, potassium hydroxide solution, add 0-5 g. of the halide, followed by sufficient rectified spirit to produce a clear solution. For alkyl chlorides, the addition of a little potassium iodide is recommended. Heat the mixture under reflux for 15 minutes, and dissolve any potassium halide by the addition of a few drops of water. The p-naphthyl ether usually crystallises out on cooling if it does not, dilute the solution with 10 per cent, sodium hydroxide solution untU precipitation occurs. Dissolve the p-naphthyl ether in the minimum volume of hot alcohol and add the calculated quantity of picric acid dissolved in hot alcohol. The picrate separates out on cooling. Recrystallise it from rectified spirit. 

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. 

Place 32 g. of potassium ethyl xanthate (Section 111,166) and 50 ml. of absolute ethyl alcohol in a 500 ml. round-bottomed flask provided with a double surface condenser. Add 32 g. (16-5 ml.) of ethyl iodide. No reaction appears to take place in the cold. Heat on a water bath for 3 hours a reaction sets in within 15 minutes and the yellow reaction mixture becomes white owing to the separation of potassium iodide. Add about 150 ml. of water, separate the lower layer, and wash it with water. Dry it with anhydrous calcium chloride or anhydrous calcium sulphate and distil from a 50 ml. Claisen flask. Collect the ethyl S-ethyl xanthate at 196-198°. The yield is 23 g. 

The interaction of iodoaobenzene and iodoxybenzene in the presence of aqueous sodium hydroxide yields the soluble diphenyllodonium iodate (IV) upon adding potassium iodide solution, the sparingly soluble diphenyliodonium iodide (V), analogous to ammonium iodide is precipitated ... 

I) The filtrate contains some diphenyliodonium salts these may be recovered as the sparingly soluble diphenyliodonium iodide (about 8 g.) (Section IV,27) by the addition of potassium iodide. 

The experimental conditions necessary for the preparation of a solution of a diazonium salt, diazotisation of a primary amine, are as follows. The amine is dissolved in a suitable volume of water containing 2 5-3 equivalents of hydrochloric acid (or of sulphuric acid) by the application of heat if necessary, and the solution is cooled in ice when the amine hydrochloride (or sulphate) usually crystallises. The temperature is maintained at 0-5°, an aqueous solution of sodium nitrite is added portion-wise until, after allowing 3-4 minutes for reaction, the solution gives an immediate positive test for excess of nitrous acid with an external indicator—moist potassium iodide - starch paper f ... 

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