Pulling Back the Curtain on some Chemical Magic

If you haven’t heard of the magical Oscillating Clock Reaction, you clearly fell asleep in gen chem

Organic Live
7 min readApr 27, 2022


In order to drum up interest in chemistry, instructors at all levels perform demonstrations (or demos) of chemical reactions. The power of demonstrations has been used to lure the uninitiated since the 18th century. Think about it, what better way is there to get the attention of a sleepy 18 year old gen chem student than this:

This is a quintessential demo in chemistry — the hydrogen balloon explosion… with a twist! The instructor above first demonstrates the explosion of plain old hydrogen, then shows the difference when you add oxygen to the mix. The video speaks for itself, but if I had to put it into words, I’d describe the hydrogen balloon explosion sound as more a “whuuuumpp” whereas the hydrogen plus oxygen balloon is more of a “POWWW!”

So yeah, that’s how you wake up the class on Monday morning. Also, I willingly admit that I unashamedly bribed my class with this demo on multiple occasions.

Chemistry instructors use all manner of demos in this fashion. One of the more tame (that is, much less noisy), yet still visually striking demonstrations is the “clock reaction” aka the “oscillating clock reaction” aka the Briggs-Raucher reaction.

(Is it obvious why it’s called the “oscillating clock” now?)

I’m not going to get into the specifics of the overall reaction because it’s ridiculously complicated. Ultimately, what we’re seeing boils down to the presence of large amounts of either iodine or iodide, which oscillate over time. Let’s break it down by color first, then we’ll get into some heavier chemistry…

“What are the colors I’m seeing?”

Let’s start with some facts: Iodine (“I2”) is reddish-brown in solution while iodide



Organic Live

I’m a former chemistry assistant prof that is out to prove that chemistry is both interesting and entertaining