Group 7: Halogens
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One of the experiments in topic 6 of the Nuffield Chemistry course removes iodine from seaweed. It says that at the end you are left with an 'iodine extract in a hydrocarbon solvent'. How would you remove this hydrocarbon solvent to leave only iodine?
Igloo replies
Having separated the upper (purple) hydrocarbon layer from the lower aqueous layer (using a separating funnel), the organic layer could be transferred to an evaporating dish and left to crystallise out in a fume cupboard. After a few hours, solid black iodine crystals are formed as the hydrocarbon solvent evaporates away, and these crystals could be removed from the remaining liquid using tweezers.
Note that it is important not to heat the mixture in an open dish. Hydrocarbons are highly flammable. Also iodine vaporises on gentle heating - it sublimes.
Ideally you would use rotatory evaporator and evaporate the solvent under reduced pressure and collect the hydrocabon solvent as well as the iodine.
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updated: 26 August 2004
