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How to Extract Iodine From Brown Algae

Brown algae (kelp) is one of the most efficient iodide accumulators on earth. To obtain iodine from brown algae, first extract the iodide, then oxidize the iodide to iodine. Extracting the iodide involves burning the brown algae to ash. Thus, the iodide compounds convert to iodide anions, which are single, negatively charged, iodine atoms. Adding hydrogen peroxide in acidic solution oxidizes the iodide anions to iodine. Iodine is not very soluble in water, but is soluble in cyclohexane. In cyclohexane, iodide turns purple, allowing verification that iodine is, in fact, present. Cyclohexane is a volatile organic solvent that will evaporate, leaving behind iodine in the form of shiny black crystals.

Bunsen burner
Beakers
Cyclohexane
Hydrogen peroxide
Sulfuric acid
Distilled water
Separating funnel

Instructions

- 1
  Set up a tin lid above a Bunsen burner. Place the brown algae atop the tin lid. Burn it to ash using the Bunsen burner.
- 2
  Purify the ash by boiling it in distilled water. Filter the water and collect the filtrate, which contains the residue.
- 3
  Add about 2 ml sulfuric acid solution. Add hydrogen peroxide. The hydrogen peroxide is oxidizing the iodide to iodine when the solution turns deep brown.
- 4
  Add the solution, in a separation funnel, to cyclohexane. Shake. Vent, periodically, by turning the knob at the bottom. Shake again and vent. Allow the two layers to separate,into an organic layer of iodine in cyclohexane (on top) and the aqueous water later on the bottom. Open the bottom of the funnel to slowly drain the water layer into a beaker; be careful to retain the organic layer. Dispose of the water layer in a sink.
- 5
  Pour the organic layer into a beaker and leave in a fume hood overnight. The cyclohexane will evaporate, leaving behind shiny black crystals of iodine. Or, to expedite evaporation, use a rotovapor.

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