Molecule of the Day

Hydrogen peroxide seems boring at first blush- after all, you can get it in those little brown bottles at the drugstore, and they don’t do much but fizz - and then, only when

you pour it on a cut (more on that later). H₂O₂ has a structure a lot like water - H-O-O-H instead of H-O-H. That O-O bond is the peroxide bond, and it’s what’s responsible for H₂O₂’s oxidizing power.

The drugstore H₂O₂, you’ve probably noticed, is only a 3% solution (and it can still burn your skin a little bit). Even in a lab, the highest concentration I can easily get is 30%. These bottles are vented, since peroxide tends to decompose to water plus oxygen. This is the bubbling reaction you obersrve when you pour it on a cut. This is due to the action of the enzyme catalase, which exists to do just this. Like many enzymes, catalase is present at an unusually high concentration in liver. Chop some liver up finely and pour some peroxide on it (3% from the store will do) and you’ll see what I mean. Certain other metal compounds will work, notably silver and manganese dioxide.

The 30% peroxide we get in the lab comes with dire warnings not to spill it on paper or anything combustible (because it would ostensibly start a fire). I believe it, but it’s never happened to me. Peroxide actually gets dangerous in the 70%+ range. It will happily propel a rocket. It’s really amazing how a 25-fold or so increase in concentration can make something act like a completely different substance.