We will prepare extremely useful solid iodine

using a very quick and simple reaction involving potassium iodide and a

persulfate salt. Start by weighing out 50 grams of potassium iodide and then

dissolve it in 100 ml of water. Then take 38 grams which is a slight excessive

what's needed of ammonium persulfate or another persulfate salt. Dissolve in 150

unlike other oxidizing agents which require acid, persulfate will oxidize

directly to iodine. Slowly add the potassium iodide solution to the

persulfate solution with stirring. Immediately you will see a red-brown

color due to iodine being formed. Since iodine dissolves in potassium iodide

solution you first obtain a solution and then as more iodide oxidizes the iodine

drops.

out as a precipitate. The temperature will increase to around 40 degrees. Keep

stirring the mixture for a few minutes and add a few ice cubes to help keep the

liquid cool. Soon you'll see sparkling crystals of iodine separating and

dancing in the liquid.

Stop stirring and allow the solid to settle. Pour off the liquid or filter the

mixture and add

cold water. Stir and repeat this process until the liquid turns a pale color.

Vacuum filter the product and dry very thoroughly on the pump. Here's the

slightly damp product weighing 40 grams. This can be dried by storing in a

desiccator over anhydrous calcium chloride to yield a final weight of

around 34 grams of solid iodine. This is a nearly 90 percent yield and could be

improved given more care with the washing and decanting stage. Incidentally

the process also works with bromides although it is much slower. This is an

equivalent reaction mixture of sodium bromide and ammonium persulfate dissolved

in the smallest amount of water possible.

Soon gets warm and must be cooled in ice. If left for a long period a bottom

layer of liquid bromine separates.

Iodine is fun but don't get it on your fingers. In case of any stains or spills have a ready-made solution of sodium thiosulfate ready to mop up.