Iodine number
Encyclopedia
The iodine value in chemistry
is the mass of iodine
in grams that is consumed by 100 grams of a chemical substance
. An iodine solution is yellow/brown in color and any chemical group in the substance that reacts with iodine will make the color disappear at a precise concentration. The amount of iodine solution thus required to keep the solution yellow/brown is a measure of the amount of iodine sensitive reactive groups.
One application of the iodine number is the determination of the amount of unsaturation contained in fatty acids. This unsaturation is in the form of double bonds which react with iodine compounds. The higher the iodine number, the more unsaturated fatty acid bonds are present in a fat. In a typical procedure, the acid is treated with an excess of the Hanuš or Wijs solutions, which are, respectively, solutions of iodine monobromide (IBr) and iodine monochloride
(ICl) in glacial acetic acid. Unreacted iodine monobromide (or monochloride) is reacted with potassium iodide
, converting it to iodine, whose concentration can be determined by titration with sodium thiosulfate
.
Standard methods for analysis are for example ASTM D5768-02(2006) and DIN
53241.
For a simple analysis, 0.2 grams of the fat is mixed with 20 ml Wijs solution and 10 ml 1,1,1-trichloroethane
. It is then left in the dark for 30 minutes. Next, 15 ml of 10% potassium iodide
solution and 10 ml of deionized water is added. This is then titrated against 0.1 M sodium thiosulfate
(VI) solution. 1 ml of 0.1 M sodium thiosulfate solution = 0.01269 g of iodine
. The difference between a control titration and the titration with the fat present multiplied by this factor gives the mass of iodine absorbed by the oil.
A 2010 study reported on its importance in health.
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
is the mass of iodine
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
in grams that is consumed by 100 grams of a chemical substance
Chemical substance
In chemistry, a chemical substance is a form of matter that has constant chemical composition and characteristic properties. It cannot be separated into components by physical separation methods, i.e. without breaking chemical bonds. They can be solids, liquids or gases.Chemical substances are...
. An iodine solution is yellow/brown in color and any chemical group in the substance that reacts with iodine will make the color disappear at a precise concentration. The amount of iodine solution thus required to keep the solution yellow/brown is a measure of the amount of iodine sensitive reactive groups.
One application of the iodine number is the determination of the amount of unsaturation contained in fatty acids. This unsaturation is in the form of double bonds which react with iodine compounds. The higher the iodine number, the more unsaturated fatty acid bonds are present in a fat. In a typical procedure, the acid is treated with an excess of the Hanuš or Wijs solutions, which are, respectively, solutions of iodine monobromide (IBr) and iodine monochloride
Iodine monochloride
Iodine monochloride is an interhalogen compound with the formula ICl. It is a red-brown compound that melts near room temperature. Because of the difference in the electronegativity of iodine and chlorine, ICl is highly polar and behaves as a source of I+....
(ICl) in glacial acetic acid. Unreacted iodine monobromide (or monochloride) is reacted with potassium iodide
Potassium iodide
Potassium iodide is an inorganic compound with the chemical formula KI. This white salt is the most commercially significant iodide compound, with approximately 37,000 tons produced in 1985. It is less hygroscopic than sodium iodide, making it easier to work with...
, converting it to iodine, whose concentration can be determined by titration with sodium thiosulfate
Sodium thiosulfate
Sodium thiosulfate , also spelled sodium thiosulphate, is a colorless crystalline compound that is more familiar as the pentahydrate, Na2S2O3•5H2O, an efflorescent, monoclinic crystalline substance also called sodium hyposulfite or “hypo.”...
.
Standard methods for analysis are for example ASTM D5768-02(2006) and DIN
Din
DIN or Din or din can have several meanings:* A din is a loud noise.* Dīn, an Arabic term meaning "religion" or "way of life".* Din is one of the ten aspects of the Ein Sof in Kabbalah ....
53241.
For a simple analysis, 0.2 grams of the fat is mixed with 20 ml Wijs solution and 10 ml 1,1,1-trichloroethane
1,1,1-Trichloroethane
The organic compound 1,1,1-trichloroethane, also known as methyl chloroform, is a chloroalkane. This colourless, sweet-smelling liquid was once produced industrially in large quantities for use as a solvent...
. It is then left in the dark for 30 minutes. Next, 15 ml of 10% potassium iodide
Potassium iodide
Potassium iodide is an inorganic compound with the chemical formula KI. This white salt is the most commercially significant iodide compound, with approximately 37,000 tons produced in 1985. It is less hygroscopic than sodium iodide, making it easier to work with...
solution and 10 ml of deionized water is added. This is then titrated against 0.1 M sodium thiosulfate
Sodium thiosulfate
Sodium thiosulfate , also spelled sodium thiosulphate, is a colorless crystalline compound that is more familiar as the pentahydrate, Na2S2O3•5H2O, an efflorescent, monoclinic crystalline substance also called sodium hyposulfite or “hypo.”...
(VI) solution. 1 ml of 0.1 M sodium thiosulfate solution = 0.01269 g of iodine
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
. The difference between a control titration and the titration with the fat present multiplied by this factor gives the mass of iodine absorbed by the oil.
A 2010 study reported on its importance in health.