When starch reacts with iodine, why does it create the
characteristic blue-black colour?

Answer Posted / tejaswini.b

Amylose in starch is responsible for the formation of a deep blue color in the presence of iodine & iodine molecule slips inside of the amylose coil. Iodine is not very soluble in water, iodine reagent is made by dissolving iodine in water in the presence of potassium iodide. This makes a linear triiodide ion complex which is soluble that slips into the coil of starch causing an intense blue/black color.

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