User:Pat.rick.flower/Iodine-starch test

Starch is often used in chemistry as an indicator for redox titrations where triiodide is present.[1] Starch forms a very dark blue-black complex with triiodide. However, the complex is not formed if only iodine or only iodide (I−) is present. The colour of the starch complex is so deep, that it can be detected visually when the concentration of the iodine is as low as 20 µM at 20 °C.[8] During iodine titrations, concentrated iodine solutions must be reacted with some titrant, often thiosulfate, in order to remove most of the iodine before the starch is added. This is due to the insolubility of the starch–triiodide complex which may prevent some of the iodine reacting with the titrant. Close to the endpoint, the starch is added, and the titration process is resumed taking into account the amount of thiosulfate added before adding the starch.

The color change can be used to detect moisture or perspiration, as in the Minor test or starch–iodine test.

'''Starch is also useful in detecting an enzyme called amylase. Many bacteria like Bacillus subtilis can produce such an enzyme to help scientists identify unknown bacterial samples -- the starch-iodine test is one of many tests needed to identify the exact bacterium.[9] The positive test for a bacteria that has starch hydrolysis capabilities (able to produce amylase) is the presence of a yellow zone around a colony when iodine is added to detect starch.[10]'''

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