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(8)IODIMETRY AND IODOMETRY

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allelipraise's version from 2018-06-06 18:33

Section 1

Question Answer
Iodimetrydirect processess in which a standard of iodine is the titrating agent
Iodometry indirect processes in which the sample, an oxidizing agent, is reduced with excess potassium iodide and an equivalent amount of iodine is produced. The iodine thus formed is titrated with a standard solution of sodium thiosulfate.
iodine value (number) the number of grams of iodine (I) absorbed under specified conditions by 100 g of oil, fat, wax, or other substance.
iodine value (number)quantitative measure of the proportion of unsaturated fatty acids present, both free and combined as esters, that have the property of absorbing iodine.
Drying oils- have high iodine numbers, usually above 120 - contain a large proportion of unsaturated fatty acids
Semi-drying oilshave intermediate iodine numbers, between 100 and 120
Non-drying oilshave relatively low iodine values, below 100
Drying oilsexamples: linseed oil and fish oils, such as cod-liver oil
Semi-drying oilsexamples: cottonseed oil and sesame oil
Non-drying oilsexamples: olive oil and almond oil
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Section 2

Question Answer
USP Method I (Hanus Method)uses a solution of iodobromide (iodine monobromide) in glacial acetic acid as iodinating agent. Iodine alone is not used because it is absorbed very slowly by the oil.
USP Method I (Hanus Method)the method resembles iodometric titrations where the liberated iodine is titrated with standard sodium thiosulfate
USP Method II (Wijs Method)uses a solution of iodochloride (iodine monochloride), Wijs’ solution, instead of iodobromide, in glacial acetic acid
Hübl Methoda solution of a known weight of the oil or fat in CCl4 is allowed to react with a known excess of a standard solution of iodine in ethanol in the presence of HgCl2, forming iodochloride:
Hübl Methodthe excess iodine is determined by a standard sodium thiosulfate solution
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