Group 7: Halogens
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Can you explain the theory behind extracting iodine from seaweed from the experiment 6.1, in the Nuffield Advance Chemistry book, e.g. what would be the equation between the distilled product with hydrogen peroxide and sulphuric acids?
Corrie writes ...
The procedure in the Nuffield book does not involve distillation, only heating the mixture of seaweed ash and water to boiling for a few minutes. This is to dissolve out any iodine in the form of iodide salts, such as NaI.
To form iodine from the iodide ion (I-) in these salts, hydrogen peroxide is used as an oxidising agent, in the presence of acid.
The ionic equation for the reaction is:
2I- + H2O2 + 2H+(from the acid) -> I2 + 2H2O
Iodine, being a non-polar covalent molecule, is not very soluble in water, but is soluble in non-polar hydrocarbon solvents, such as hexane. To separate the iodine from the other in the brown mixture, it is shaken with some hydrocarbon solvent. The iodine moves to the hydrocarbon layer, forming a purple solution.
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updated: 05 February 2007
