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I want to test a supplement for the presence of iodine. Iodine should turn starch blue-black. So, can I powderize the supplement tablet, add water to it, drop it on a piece of bread, and if it turns blue-black, that would be an accurate way to test?

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marked as duplicate by andselisk, Todd Minehardt, Nilay Ghosh, Karsten Theis, Jon Custer Mar 31 at 17:48

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  • $\begingroup$ I'm not too sure that'd work very well. Is the tablet colourised? Does it have an ingredients label? Assuming (giant IF here) that it contains iodine, and the amount is great enough that adding it to water results in an aqueous solution of iodine, AND that there's nothing else in the tablet that may react with either reactant, then yes, you may observe it. $\endgroup$ – ANZGC FlyingFalcon Mar 30 at 14:51
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Just keep in mind that only elemental iodine will cause a blue-black coloration. Nobody add elemental iodine to a supplement just like nobody can eat chlorine out of table salt (NaCl). The typical compound they add is KIO3, which will not color starch right away, until and unless you reduce it to KI and then oxidize KI to free I2. In any case, search natural foods which contain iodine.

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