#23: Isolating Elemental Iodine

Experimentation is an important part of science. Unfortunately, it comes at a cost. That being, it costs money. This is especially true of chemistry experiments in which chemicals can be quite expensive. So while I would love to sit around throwing random chemicals together all day, it is simply not possible if I want to maintain a college fund. When it comes to my projects, I must be wise so as not to waste what I have. I also have to be resourceful with where and how I obtain my chemicals. A good way to do this is to buy them from places like pharmacies or hardware stores. Although they can be hard to find, many chemicals can be obtained much cheaper from commercial products such as cleaners. However, they are typically sold in a diluted form where they are often mixed with other substances. Fortunately, with a little bit of work, they can usually be purified.

Iodine (the 53rd element) is a very interesting chemical. On the periodic table, it lies in the same column as chlorine which makes it quite reactive. Despite being somewhat dangerous, it has many uses in the medical industry. While I would love to explore its chemistry, it costs nearly $30 per ounce. Plus, you often need to get a license just to buy it. Luckily for me, I can get it through the black market, aka CVS pharmacy. Yes, iodine is commonly found in antiseptics where it is usually called "tincture of iodine." These products contain a small percentage of pure iodine along with potassium iodide (KI) dissolved in water and/or alcohol. For me, this form of iodine is only useful if I want to keep myself from getting an infection. To make it suitable for chemistry experiments, I would have to purify it.

As I said before, the amount of pure iodine in antiseptics is very small. To obtain a useful quantity of the chemical, I knew I would need to isolate it from the larger portion of potassium iodide. To do that, I added an equal amount hydrochloric acid (HCl). The acid removed the potassium ion from the potassium iodide and replaced it with a hydrogen ion (HI). To separate the iodine from the hydrogen, I then mixed in a solution of dilute hydrogen peroxide (H2O2) which I also got from the drug store. The hydrogen peroxide molecules oxidized the hydrogen atoms whereupon water (H2O) was created. As for the iodine, it was now free. 

Here are the two reactions that occurred:
1. KI + HCl → KCl + HI
2. 2HI + H2O2 → 2H2O + I2

Because the iodine by itself was no longer soluble in water, it precipitated out in solid form. After all of it had gathered at the bottom of my beaker, I poured it over a filter and washed it with water. This left me with a black sludge of impure iodine.

To further refine my iodine, I relied on one of its fascinating properties. While most substances melt when they are heated, iodine sublimates. That means it goes from a solid state directly to a gaseous state. To take advantage of this, I dropped my globs of iodine in a beaker and placed it over my burner. As it began to heat, I covered the beaker with a watch glass to contain any gases that might escape. It wasn't long before a dark purple cloud of sublimated iodine appeared inside the beaker. As the gas thickened, I poured some cold water on top of the watch glass. This would cause the gas near the top of the beaker to cool and condense. Unlike hot water vapor, which becomes liquid when cooled, iodine gas becomes a solid. In doing so, it rapidly forms into crystals. In my case, the sharp crystals that appeared were astounding. When the iodine at the bottom of the beaker had disappeared, I turned off the heat. Once everything had cooled, I removed the watch glass which had been covered in a silvery layer of iodine. After scraping all of the crystals into a glass vial, I had my purified product. 

Here is the heated beaker containing sublimated iodine gas which cooled near the top to form tiny crystals.

My impure iodine slurry.

Here's the crust of pure iodine that formed beneath the watch glass.

Wet iodine before sublimation.