iodine snake is an experiment to demonstrate homogenous catalysis. Basically, you add hydrogen peroxide and washing up liquid to a solution of iodine in a bottle. The hydrogen peroxide is catalysed by the iodide ions, releasing quite a lot of oxygen. This oxygen reacts with the washing up liquid producing nice orange coloured foam, which quickly escapes from the bottle in a snake like fashion.
All well and good, I hear you say. But what went so horribly wrong ? Needless to say, in our chemistry textbooks this experiment looked very, very cool - otherwise we wouldn't have hassled our teacher into letting us perform it. Eventually, the old bat relented, and covered her desk in black bin-liner in preparation for copious amounts of foam. The six of us that were in the class, all donned our safety goggles and then set it up as per her instructions.
Result? A pififul amount of foam and absolutely no velocity whatsoever! Being the brilliant chemists that we were , we tried again. Unknown to our teacher, a friend increased the concentration of all the reactants by, oh say a factor of ten . I, also had the genius idea of putting all this in a reaction vessel about 3 times smaller in size. To ensure maximum foam production, I also corked the vessel and started shaking it.
I'm sure you can guess what happened - it blew up :) One teacher, her handbag, six students, the floor, the ceiling and the black-board were all covered in orange foamy goodness. As break was next period, it was quite a sight to see all of us with orange faces, save for a silhouette of the safety goggles.
Thus, I became a chem-god and was never allowed to do an experiment ever again!