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.