| Dec. 3rd, 2008 @ 12:16 am Belousov-Zhabotinsky Reaction |
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Don't let the white lab coats fool you. Chemists have some really cool party tricks up their sleeves. One of these goes by the admittedly clunky moniker of the Belousov-Zhabotinsky reaction, or BZ for short, but don't let that put you off, as it's really quite a nifty thing. It was initially discovered by Boris Belousov in the late 1950s, and after his results received the equivalent of an incredulously raised eyebrow from his fellow chemists, it sank into obscurity for a few years, before being rediscovered independently by Anatol Zhabotinsky in the early 1960s.
To someone unschooled in the complexities of non-equilibrium thermodynamics, the BZ reaction must appear almost magical. As Arthur C. Clarke's Third Law says, 'Any sufficiently advanced technology is indistinguishable from magic.' Surprisingly though, the BZ reaction is really quite easy to set up. Well, at least for someone with access to a good chemistry lab, its chemicals, and most importantly, its chemists. So here you go, your step-by-step guide to a cool party trick:
Step 1: Mix dilute sulphuric acid, malonic acid, potassium bromate, cerium ammonium nitrate and ferroin in a beaker. Warm gently. (Don’t worry about getting all the proportions right by yourself! Any chemist friend worth his white lab coat should be able to help. Unless you actually are a chemist trying this as a party trick, in which case you should know all of this already.)
Step 2: Stare. Fascinatedly.
If you've done everything right, what you should be getting is a beaker of liquid that's changing colour from red to blue, back and forth. This is what the chemists mean by oscillation. What is really happening is that the iron in ferroin is alternately jumping up to and falling down from a higher oxidation state, as it gains and loses an electron in its molecular home. The former occurs when ferroin meets bromous acid, formed when the bromate salt dissolves in dilute sulphuric acid. The latter takes place when ferriin, which is what chemists call the oxidised form of ferroin, encounters malonic acid in the solution. Of course, this is a very simplified explanation of the complex chemical dance that goes into producing the BZ reaction. Think of it as being like square dancing, where the chemicals swap partners from time to time.
This isn't the end of the party trick though! If you've got a petri dish handy, pour a bit of the solution into it, so that the solution forms a very thin layer in it. What should begin to happen is that waves form and begin to spread out, from one or several points in the petri dish. This happens because of completely random things, like the petri dish’s base not being perfectly even, or even just some dust particles alighting on the surface of the solution layer. Now give the petri dish a gentle shake. The waves will vanish, only to magically reappear and begin spreading once more.
Chemists have found more than just waves in exploring the BZ reaction. They've also found spirals, which form when waves are broken, as if the wave is curling up in reaction to being disturbed, much like earthworms curl up when they're prodded. Spirals can occur singly, or as conditions change, interlocked in patterns that can even come to resemble the petals of flowers. Going still further, the BZ reaction can be made to produce a liquid scroll of paper, unreeling from a central spool. With a bit of mood lighting, beakers of BZ reactions could be just the thing to add some zing to a chemist's party. Of course, you would need someone to be replenishing the ingredients, since the oscillations don't go on forever. Small price to pay though, for what is a really neat trick. To think that it was nearly buried by the unappreciative eyes of Belousov’s fellow chemists! |
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