Iodine test
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2008-05-04T10:44:30Z
Janm67
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[[WP:UNDO|Undid]] revision 209991842 by [[Special:Contributions/76.214.122.54|76.214.122.54]] ([[User talk:76.214.122.54|talk]])
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The '''Iodine test''' is used to test for the presence of [[starch]]. Iodine solution — [[iodine]] dissolved in an aqueous solution of [[potassium iodide]] — reacts with [[starch]] producing a deep blue-black color.
This reaction is the result of the formation of polyiodide chains from the reaction of starch and iodine. The [[amylose]], or straight chain portion of starch, forms helices where iodine molecules assemble, forming a dark blue/black color. The [[amylopectin]], or branched portion of starch, forms much shorter helices and iodine molecules are unable to assemble, leading the color to be of an orange/yellow hue. As starch is broken down or [[hydrolyzed]] into smaller carbohydrate units, the blue-black color is not produced. Therefore, this test can determine completion of hydrolysis when a color change does not occur.
Iodine solution will also react with [[glycogen]], although the color produced is browner and much less intense.
==References==
* http://antoine.frostburg.edu/chem/senese/101/redox/faq/starch-as-redox-indicator.shtml
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[[Category:Chemical tests]]
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