24 February 2005
This is one of my favorite experiments of the semester. The students play around with all sorts of things, including elemental iodine, shown here and in the rollover image in its solid and gaseous forms. Iodine is one of the few compounds that sublimes directly from its solid phase to its gas phase, skipping the liquid phase altogether. (Carbon dioxide does this too, forming dry ice at low temperatures, without first becoming a liquid.)
In this experiment, we put some solid iodine into a beaker and heat it up on a hot plate. The iodine sublimes into purple I2 gas. On the top of the beaker, we place an evaporating dish full of ice. The iodine vapors deposit onto the cold underside of the dish, forming beautiful crystals. I like to call them iodine whiskers.
DWL
