Iodine requirements for

Coulometric titration is used to determine relatively low concentrations of water (10. ig to 10 mg) and requires two reagents a catholyte and an anolyte (the generating solution). The iodine required for the reaction is generated in situ by the anodic oxidation of iodide. 

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. 

For the determination of higher amounts of hydrogen monosulphide (0.5-20 mg 1 ) and sulphides a iodometric method can be used. In this case sulphides and hydrogen monosulphide are separated in the form of a mixture of insoluble CdS and Cd(OH)2. The precipitate is separated, and known amounts of iodine and HCl are added. Iodine required for oxidation is determined from the difference between the added and remaining quantity of iodine, by titration with thiosulphate [13, 14]. 

The daily iodine requirement for prevention of iodine deficient goiter in adults is approximately 1 ig/kg weight, that is 50 to 75 pg/day. An allowance of 150 pg/day is recommended in order to provide an extra margin of safety and to meet increased demands that may be imposed by natural goitrogens under certain conditions... 

The most widely used reactions are those of electrophilic substitution, and under controlled conditions a maximum of three substituting groups, e.g. -NO2 (in the 1,3,5 positions) can be introduced by a nitric acid/sul-phuric acid mixture. Hot cone, sulphuric acid gives sulphonalion whilst halogens and a Lewis acid catalyst allow, e.g., chlorination or brom-ination. Other methods are required for introducing fluorine and iodine atoms. Benzene undergoes the Friedel-Crafts reaction. ... 

These two equations can be combined by recognizing that a conservation of mass for iodine requires that... 

Cobalt, copper, molybdenum, iodine, iron, manganese, nickel, selenium, and zinc are sometimes provided to mminants. Mineral deficiency or toxicity in sheep, especially copper and selenium, is a common example of dietary mineral imbalance (21). Other elements may be required for optimal mminant performance (22). ExceUent reviews of trace elements are available (5,22). 

Plant investment and maintenance costs are relatively high for a new iodine plant in the United States or in Japan because of the deep weUs required for brine production and disposal as weU as the corrosive nature of the plant streams. The principal materials cost is for chlorine and for sulfur dioxide, although in the United States the additives used for the brines, such as scale inhibitors and bactericides, also have a considerable influence on costs. 

Account must be taken in design and operation of the requirements for the production and consumption of xenon-135 [14995-12-17, Xe, the daughter of iodine-135 [14834-68-5] Xenon-135 has an enormous thermal neutron cross section, around 2.7 x 10 cm (2.7 x 10 bams). Its reactivity effect is constant when a reactor is operating steadily, but if the reactor shuts down and the neutron flux is reduced, xenon-135 builds up and may prevent immediate restart of the reactor. 

The three fluorides CIF5, Brp5 and IF5 are the only known hexa-atomic interhalogens, and IF7 is the sole representative of the octa-atomic class. The first to be made (1871) was IF5 which is the most readily formed of the iodine fluorides, whereas the more vigorous conditions required for the others delayed the synthesis of BrFs and IF7 until 1930/1 and CIF5 until 1962. The preferred method of preparing all four compounds on a large scale is by direct fluorination of the element or a lower fluoride ... 

Direct bromination readily yields the 6-bromo derivative (111), just as with uracil. Analogous chlorination and iodination requires the presence of alkalies and even then proceeds in low yield. The 6-chloro derivative (113) was also obtained by partial hydrolysis of the postulated 3,5,6-trichloro-l,2,4-triazine (e.g.. Section II,B,6). The 6-bromo derivative (5-bromo-6-azauracil) served as the starting substance for several other derivatives. It was converted to the amino derivative (114) by ammonium acetate which, by means of sodium nitrite in hydrochloric acid, yielded a mixture of 6-chloro and 6-hydroxy derivatives. A modified Schiemann reaction was not suitable for preparing the 6-fluoro derivative. The 6-hydroxy derivative (115) (an isomer of cyanuric acid and the most acidic substance of this group, pKa — 2.95) was more conveniently prepared by alkaline hydrolysis of the 6-amino derivative. Further the bromo derivative was reacted with ethanolamine to prepare the 6-(2-hydroxyethyl) derivative however, this could not be converted to the corresponding 2-chloroethyl derivative. Similarly, the dimethylamino, morpholino, and hydrazino derivatives were prepared from the 6-bromo com-pound. ... 

The alkaline solution of thymol is made up to 100 or 200 c.c. as the case may require, using a 5 per cent, soda solution. To 10 c.c. of this solution in a graduated 500 c.c. flask is added a normal iodine solution in shgbt excess, whereupon the thymol is precipitated as a dark reddish-brown iodine compound. In order to ascertain whether a sufficient quantity of iodine has been added, a few drops are transferred into a test tube and a few drops of dilute hydrochloric acid are added. When enou iodine is present, the brown colour of the solution indicates the presence of io ne, otherwise the liquid appears milky by the separation of thymol. If an excess of iodine is present, the solution is slightly acidified with dilute hydrochloric acid and diluted to 500 c.c. From this 100 c.c. are filtered,off, and the excess of iodine determined by titration with normal solution of sodium thiosulphate. For calculation, the number of cubic centimetres required is deducted from the number of cubic centimetres of normal iodine solution added and the resultant figure multiplied by 5, which gives the number of cubia centimetres of iodine required by the thymol. 

Half-lives span a very wide range (Table 17.5). Consider strontium-90, for which the half-life is 28 a. This nuclide is present in nuclear fallout, the fine dust that settles from clouds of airborne particles after the explosion of a nuclear bomb, and may also be present in the accidental release of radioactive materials into the air. Because it is chemically very similar to calcium, strontium may accompany that element through the environment and become incorporated into bones once there, it continues to emit radiation for many years. About 10 half-lives (for strontium-90, 280 a) must pass before the activity of a sample has fallen to 1/1000 of its initial value. Iodine-131, which was released in the accidental fire at the Chernobyl nuclear power plant, has a half-life of only 8.05 d, but it accumulates in the thyroid gland. Several cases of thyroid cancer have been linked to iodine-131 exposure from the accident. Plutonium-239 has a half-life of 24 ka (24000 years). Consequently, very long term storage facilities are required for plutonium waste, and land contaminated with plutonium cannot be inhabited again for thousands of years without expensive remediation efforts. 

Perhaps the most important application of redox chemicals in the modern laboratory is in oxidation or reduction reactions that are required as part of a preparation scheme. Such preoxidation or prereduction is also frequently required for certain instrumental procedures for which a specific oxidation state is essential in order to measure whatever property is measured by the instrument. An example in this textbook can be found in Experiment 19 (the hydroxylamine hydrochloride keeps the iron in the +2 state). Also in wastewater treatment plants, it is important to measure dissolved oxygen (DO). In this procedure, Mn(OH)2 reacts with the oxygen in basic solution to form Mn(OH)3. When acidified and in the presence of KI, iodine is liberated and titrated. This method is called the Winkler method. 

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