March 17 2012 7 17 /03 /March /2012 14:58
Lead iodide is a yellow solid insoluble in cold water but slightly soluble in hot water. It is easily produced from a few basic substances.
Caution: Lead iodide is toxic, as are all lead compounds. Do not breathe dust. Dispose of lead iodide at hazardous waste facility or just use small amounts of lead.
Needed: Lead metal, white vinegar, hydrogen peroxide, tincture of iodine, ascorbic acid (or sodium metabisulfite)
First, prepare solution 1. Add hydrogen peroxide to white vinegar in a 1:1 ratio. Add lead. Fizzing is observed and some of the lead dissolves. If any antimony, tin, or arsenic is present, it is left behind. Copper may dissolve but it will not effect the reaction. After 24 hours, filter the solution to remove the lead and any precipitate. This is a dilute solution of lead acetate.
Second, prepare solution 2. Add ascorbic acid (or sodium metabisulfite) crystals to tincture of iodine until it is colorless. Add about 1/5 more of the crystals to provide an excess of reducing agent. This is a dilute solution of sodium iodide, along with other compounds.
Third, mix the solutions. Begin by adding a few drops of solution 2 to solution one. A startlingly yellow precipitate will form from the two colorless solutions. Add more of the iodide solution until no more precipitate is formed upon addition. The excess hydrogen peroxide in the lead solution should be neutralized by the excess ascorbic acid (or sodium metabisulfite). If it is not, the resulting solution will be brownish and the lead iodide will begin turning brown. If this is the case, add more reducing agent to turn the lead iodide yellow again. Filter the precipitate and discard of the solution down the drain. (Since all of the lead was precipitated out, the solution contains little remaining lead and can be safely disposed of in this manner.)
Allow the precipitate to dry and place it in a small amount of water. Heat the slurry in a boiling water bath until the lead iodide dissolves. If it does not completely dissolve, add a little more water. Once it is almost completely dissolved (the residue is probably impurities), turn off the heat and place the lead iodide solution (now turned colorless) in an ice bath (salt is unnecessary). The solution will cool down and lead iodide will precipitate again. This lead iodide can be filtered and dried again. This lead iodide is now pure.
Here is a video of the reaction between the lead acetate and the sodium iodide solution.
Here is a video of the purification in an ice bath.
Have fun with lead chemistry, but be safe with small amounts! All of my lead experiments (I also formed the sulfate, bromide, chloride, dioxide, monoxide, etc.) used about 200 mg of lead, which is quite a small amount of metal.