Iodate, potassium

Simple ABO compounds in addition to BaTiO are cadmium titanate [12014-14-17, CdTiO lead titanate [12060-00-3] PbTiO potassium niobate [12030-85-2] KNbO sodium niobate [12034-09-2], NaNbO silver niobate [12309-96-5], AgNbO potassium iodate [7758-05-6], KIO bismuth ferrate [12010-42-3], BiFeO sodium tantalate, NaTaO and lead zirconate [12060-01 -4], PbZrO. The perovskite stmcture is also tolerant of a very wide range of multiple cation substitution on both A and B sites. Thus many more complex compounds have been found (16,17), eg, (K 2 i/2) 3 ... 

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. 

Potassium iodate [7758-05-6] KIO, mol wt 214.02, 59.30% I, forms white, odorless crystals or a crystalline powder. It has a density 3.98 g/mL and mp of 560°C with partial decomposition. Potassium iodate is rapidly formed when potassium iodide is fused with potassium chlorate, bromate, or perchlorate. The solubihty in water is 9.16 g/100 g H2O at 25°C and 32.2 g/100 g H2O at 100°C. KIO is extensively used as an oxidizing agent in analytical chemistry and as amaturing agent and dough conditioner (see Bakery processes and leavening agents). 

Approximately 80 wt % of the potassium iodate [7758-05-6] KIO, crystallizes from the reaction mixture and is separated for sale. Of the remainder, 90 wt % is removed by evaporation, fusion, and heating to ca 600°C. 

Iodized Salt. Iodized table salt has been used to provide supplemental iodine to the U.S. population since 1924, when producers, in cooperation with the Michigan State Medical Society (24), began a voluntary program of salt iodization in Michigan that ultimately led to the elimination of iodine deficiency in the United States. More than 50% of the table salt sold in the United States is iodized. Potassium iodide in table salt at levels of 0.006% to 0.01% KI is one of two sources of iodine for food-grade salt approved by the U.S. Food and Dmg Administration. The other, cuprous iodide, is not used by U.S. salt producers. Iodine may be added to a food so that the daily intake does not exceed 225 p.g for adults and children over four years of age. Potassium iodide is unstable under conditions of extreme moisture and temperature, particularly in an acid environment. Sodium carbonate or sodium bicarbonate is added to increase alkalinity, and sodium thiosulfate or dextrose is added to stabilize potassium iodide. Without a stabilizer, potassium iodide is oxidized to iodine and lost by volatilization from the product. Potassium iodate, far more stable than potassium iodide, is widely used in other parts of the world, but is not approved for use in the United States. 

Analytical Methods. A classical and stiU widely employed analytical method is iodimetric titration. This is suitable for determination of sodium sulfite, for example, in boiler water. Standard potassium iodate—potassium iodide solution is commonly used as the titrant with a starch or starch-substitute indicator. Sodium bisulfite occurring as an impurity in sodium sulfite can be determined by addition of hydrogen peroxide to oxidize the bisulfite to bisulfate, followed by titration with standard sodium hydroxide (279). 

Tin ores and concentrates can be brought into solution by fusing at red heat in a nickel cmcible with sodium carbonate and sodium peroxide, leaching in water, acidifying with hydrochloric acid, and digesting with nickel sheet. The solution is cooled in carbon dioxide, and titrated with a standard potassium iodate—iodide solution using starch as an indicator. 

The determination of tin in metals containing over 75 wt % tin (eg, ingot tin) requites a special procedure (17). A 5-g sample is dissolved in hydrochloric acid, reduced with nickel, and cooled in CO2. A calculated weight of pure potassium iodate (dried at 100°C) and an excess of potassium iodide (1 3) are dissolved in water and added to the reduced solution to oxidize 96—98 wt % of the stannous chloride present. The reaction is completed by titration with 0.1 Af KIO —KI solution to a blue color using starch as the indicator. 

Cinnolin-4(lF/)-one and its 6-chloro, 6-bromo, 6-nitro and 8-nitro derivatives react with sulfuryl chloride or bromine in acetic acid to give the corresponding 3-halo derivatives in about 20% yields. lodination of 8-hydroxycinnolin-4(lF/)-one with a mixture of potassium iodide and potassium iodate gives the 5,7-diiodo derivative the 6,8-diiodo derivative is formed from 5-hydroxycinnolin-4(lF/)-one. 

Developed methods have been checked up by analysis of kitchen salt which contains potassium iodate. Preliminary oxidation of iodate in the salt to periodate was performed by hydrogen peroxide in the acidic solution. The results of analysis coincide with certificate data of iodinated kitchen salt. 

Potassium iodate [7758-05-6] M 214.0, pK 0.80 (for HIO3). Crystd twice from distilled water (3mL/g) between 100° and 0°, dried for 2h at 140° and cooled in a desiccator. Analytical reagent grade material dried in this way is suitable for use as an analytical standard. 

Kalium-hydrat, n. potassium hydroxide, -hy-drid, n. potassium hydride (KH). -hydroxyd, n. potassium hydroxide, -hydriir, n. potassium subhydride (IC2H or K4H2). -iridi-chlorid, n. potassium eh loroiridate. -jodat, n. potassium iodate. 

The saturated solution of potassium iodate in water at 25°C has a molality equal to 0.43. Taking the activity coefficient y in this saturated solution to be 0.52, find the conventional free energy of solution at 25°C, and calculate in electron-volts per ion pair the value of L for the removal of tho ions K+ and (IOs) into water at 25°C. 

In the second method a solution of the approximate strength required is prepared, and this is standardised against some standard alkaline substance, such as sodium tetraborate or anhydrous sodium carbonate standard potassium iodate or pure silver may also be used (see Section 10.84). If a solution of an exact strength is required, a solution of an approximate strength somewhat greater than that desired is first prepared this is suitably diluted with water after standardisation (for a typical calculation, see Appendix 17). 

Preparation ofpure potassium hydrogeniodate. Dissolve 27 g of potassium iodate in 125 mL of boiling water, and add a solution of 22 g of iodic acid in 45 mL of warm water acidified with six drops of concentrated hydrochloric acid. Potassium hydrogeniodate separates on cooling. Filter on a sintered-glass funnel, and wash with cold water. Recrystallise three times from hot water use 3 parts of water for 1 part of the salt and stir continuously during each cooling. Dry the crystals at 100 °C for several hours. The purity exceeds 99.95 per cent. 

Method A With arsenic(III) oxide. This procedure, which utilises arsenic(III) oxide as a primary standard and potassium iodide or potassium iodate as a catalyst for the reaction, is convenient in practice and is a trustworthy method for the standardisation of permanganate solutions. Analytical grade arsenic(III) oxide has a purity of at least 99.8 per cent, and the results by this method agree to within 1 part in 3000 with the sodium oxalate procedure (Method B, below). 

M Potassium iodide = 0.41 g KI L1. 0.0025M Potassium iodate = 0.54g KIOjL-1. 

It seems appropriate to refer at this point to the uses of a standard solution containing potassium iodide and potassium iodate. This solution is quite stable and yields iodine when treated with acid ... 

The standard solution is prepared by dissolving a weighed amount of pure potassium iodate in a solution containing a slight excess of pure potassium iodide, and diluting to a definite volume. This solution has two important uses. The first is as a source of a known quantity of iodine in titrations [compare Section 10.115(A)] it must be added to a solution containing strong acid it cannot be employed in a medium which is neutral or possesses a low acidity. 

For the preparation of standard iodine solutions, resublimed iodine and iodate-free potassium iodide should be employed. The solution may be standardised against pure arsenic(III) oxide or with a sodium thiosulphate solution which has been recently standardised against potassium iodate. 

B) With standard sodium thiosulphate solution. Sodium thiosulphate solution, which has been recently standardised, preferably against pure potassium iodate, is employed. Transfer 25 mL of the iodine solution to a 250 mL conical flask, dilute to 100 mL and add the standard thiosulphate solution from a burette until the solution has a pale yellow colour. Add 2 mL of starch solution, and continue the addition of the thiosulphate solution slowly until the solution is just colourless. 

The standardisation of thiosulphate solutions may be effected with potassium iodate, potassium dichromate, copper and iodine as primary standards, or with potassium permanganate or cerium)IV) sulphate as secondary standards. Owing to the volatility of iodine and the difficulty of preparation of perfectly pure iodine, this method is not a suitable one for beginners. If, however, a standard solution of iodine (see Sections 10.112 and 10.113) is available, this maybe used for the standardisation of thiosulphate solutions. 

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 ... 

Its relative molecular mass is 214.00 a 0.02M solution therefore contains 4.28 g of potassium iodate per litre. 

Weigh out accurately 0.14-0.15 g of pure dry potassium iodate, dissolve it in 25 mL of cold, boiled-out distilled water, add 2 g of iodate-free potassium iodide (Note 1) and 5 mL of 1M sulphuric acid (Note 2). Titrate the liberated iodine with the thiosulphate solution with constant shaking. When the colour of the liquid has become a pale yellow, dilute to ca 200 mL with distilled water, add 2 mL of starch solution, and continue the titration until the colour changes from blue to colourless. Repeat with two other similar portions of potassium iodate. 

Only a small amount of potassium iodate is needed so that the error in weighing 0.14-0.15 g may be appreciable. In this case it is better to weigh out accurately 4.28 g of the salt (if a slightly different weight is used, the exact molarity is calculated), dissolve it in water, and make up to 1 L in a graduated flask. Twenty-five millilitres of this solution are treated with excess of pure potassium iodide (I g of the solid or 10 mL of 10 per cent solution), followed by 3 mL of IM sulphuric acid, and the liberated iodine is titrated as detailed above. 

Potassium iodate is a powerful oxidising agent, but the course of the reaction is governed by the conditions under which it is employed. The reaction between potassium iodate and reducing agents such as iodide ion or arsenic(III) oxide in solutions of moderate acidity (0.1-2.0M hydrochloric acid) stops at the stage when the iodate is reduced to iodine ... 

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