How reactive can metal in water be?

May 18, 2006 5:15 PM

My friend swears that he once saw a video of a guy dropping highly reactive marble sized pieces of metal in a bathtub. The guy would drop in more reactive pieces of metal until eventually "a geyser shot up from the water and the tub split in twain." Is this remotely possible?

My buddy is a biomedical engineer who claims that by going up (maybe down?) on the periodic table of elements will yield such amazing results. Just metal in a tub of regular H2O. I remember in high school chemistry class dropping something in water and watching in catch fire, but that was hardly the tale that my friend spun of what these metals can really do. I can't find this tub footage or anything of the sort. And I'm not about to teach myself chemistry to understand whether or not it is possible. There have been a lot of "sciencey" questions lately so I thought I would throw this in the mix.

posted by comatose to science & nature (36 comments total)

Was it this video?
posted by martinrebas at 5:21 PM on May 18, 2006 [5 favorites]

Presumably he was going down the alkali metals. Sodium (the second lightest alkali metal, after lithium) reacts quite violently with water. See Theodore Gray's excellent periodic table website for some impressive videos. As you move to progressively heavier alkali metals (potassium, rubidium, cesium) they get progressively more reactive. I have no problem beliving that you could get enough energy to split a bathtub in twain.

If you want to try this yourself someone was recently selling 6 pound sodium ingots on Ebay, though I don't see them now. I should have bought one but I'm not quite sure what I would have done with it.
posted by pombe at 5:25 PM on May 18, 2006

Sodium added to water is explosive. That's probably what you used in high school, it's fairly standard. Other metals in the same group are more or less reactive (possibly only less reactive actually, it's been a while since I did chemistry). So the answer to 'how reactive can metal in water be' is: very.

For a cool story (with picutres and video footage) about exploding sodium see here: http://www.theodoregray.com/PeriodicTable/Stories/011.2/index.html
posted by shelleycat at 5:25 PM on May 18, 2006

Pure sodium or potassium metal will explode on contact with water. Lithium will burn too.
posted by Mr. Six at 5:25 PM on May 18, 2006

Eek, not only beaten to it but I forgot to make a link :P
posted by shelleycat at 5:26 PM on May 18, 2006

The alkali metals are very reactive, as the brainiac clip above shows.
posted by borkencode at 5:27 PM on May 18, 2006

martinrebas, that video was awesome. Much better than the braniac episodes I saw on TV while skiing recently.
posted by pombe at 5:28 PM on May 18, 2006

If you're inclined to try something this stupid, be informed that the resulting water that gets splashed all over the place is dreadfully corrosive. It's a strong solution of lye and it can burn your skin as badly and as rapidly as hydrochloric acid. If it gets into your eyes, you have a good chance of being blinded.
posted by Steven C. Den Beste at 5:50 PM on May 18, 2006

Thanks, Dr. Buzzkill!
posted by Justinian at 6:23 PM on May 18, 2006

Never heard it pronounced "frank-ium" before.
posted by Mapes at 6:37 PM on May 18, 2006

If you're inclined to try something this stupid, be informed that the resulting water that gets splashed all over the place is dreadfully corrosive. It's a strong solution of lye and it can burn your skin as badly and as rapidly as hydrochloric acid. If it gets into your eyes, you have a good chance of being blinded.

On the plus side, if you put that much lye down your drain, you are pretty guaranteed to not have any more clogged drains! Alternativley, if things get *really* exciting and you *do* split your 'tub in twain', then maybe being distracted by a painful blinding will be just the kind of thing you need to distract you from the 60 gallons of water you just dumped all over the floor...
posted by schwap23 at 6:41 PM on May 18, 2006

This was on Mythbusters just a week or so ago. They blew up about 3 bathtubs with various degrees of destruction. Don't try that at home.
posted by arimathea at 6:43 PM on May 18, 2006

A great video and informative too. I'll make sure not to mix alkaline metals and water in the future.
posted by ob at 6:56 PM on May 18, 2006

If I go blind, I want the last thing I see to be a bathtub being split in twain.
posted by danb at 7:06 PM on May 18, 2006

Not to thread-hijack (too badly...), I was JUST talking with a friend about a chemistry demonstration we saw in high school, where our teacher combined something he wouldn't name with regular table sugar. I think he then applied flame, and the sugar (and oxidizer?) burned like CRAZY. Anyone know what he would have added to accomplish this?
posted by autojack at 7:15 PM on May 18, 2006

Sugar and acid and I'm guessing he was probably starting a thermite reaction autojack. My cut-and-paste is broken but just do a search on Thermite in Google or Wikipedia.
posted by onalark at 7:20 PM on May 18, 2006

Potassium perchlorate
posted by MonkeySaltedNuts at 7:57 PM on May 18, 2006

The potassium chlorate, sugar, and sulfuric acid exothermic reaction here.
posted by junesix at 8:28 PM on May 18, 2006

It doesn't take much. Back when I was young and stupid I used to make rocket fuel by mixing sugar and potassium nitrate. Any of the standard oxidizing salts (nitrate, chlorate) will do that with sugar, which is a good source of burnable carbon and hydrogen (which is why it's good food).

If it's a potassium salt, the flame is a nice pale lavender color. Real pretty.
posted by Steven C. Den Beste at 8:39 PM on May 18, 2006

A student once blew up a toilet at my high school with sodium. Swiped it from the lab, and threw it in during study hall.
posted by middleclasstool at 8:58 PM on May 18, 2006

Of course, in the video they mixed in only two grams of cesium. You could just mix in more Sodium or potassium and get a bigger explosion.

It's actually related mostly to surface area, I would imagine.
posted by delmoi at 9:28 PM on May 18, 2006

That wasn't done on Mythbusters. Believe me.
posted by asavage at 12:25 AM on May 19, 2006 [9 favorites]

asavage--

Slacker.
posted by effugas at 3:10 AM on May 19, 2006

That wasn't done on Mythbusters. Believe me.
WTF??? What the hell do I pay my cable bill for, then?
posted by Thorzdad at 5:04 AM on May 19, 2006

martinrebas, that video was awesome.

Seconded. It justified every second of my life I've spent on MetaFilter. Why didn't they have SCIENCE videos like that when I was in school??
posted by languagehat at 5:51 AM on May 19, 2006

How long is it to be expected that the corrosive biproduct would be reactive?
posted by mhuckaba at 6:19 AM on May 19, 2006

It wasn't Mythbusters. It was that Brit TV show whose name I can't recall now. It's on G4 later at night.
posted by DieHipsterDie at 6:36 AM on May 19, 2006

Thermite involves aluminum and a metal oxide, not sugar.

Potassium or sodium react with water to give hydrogen and their respective hydroxides, and the reaction is exothermic enough to ignite the hydrogen. Potassium reacts more vigorously with water; I don't know about the rest of the group. I just know that I had a friend with scars across his back from when someone used potassium when they should have used sodium.

The metal hydroxide is the corrosive byproduct, and there's no reason to think it would ever stop being reactive until such time as it finds something to react with. As for how corrosive the solution is, that would depend on the amount of metal versus the amount of water, of course.
posted by solotoro at 6:40 AM on May 19, 2006

One of my organic chemistry professors in college told us the story of back when he was a grad student, after some heavy drinking, he and some of his chem student friends got into the supply room in the middle of the night and stole a kilogram brick of potassium.

The campus was on a lake, and they carried the brick out to the end of a pier and heaved it into the water. He said it made "a huge, beautiful, purple explosion, and a geyser of water shot twenty feet up into the air!"

After that, the chemistry dept started putting all the alkali metals under lock and key.
posted by Gamblor at 7:14 AM on May 19, 2006

How long is it to be expected that the corrosive biproduct would be reactive?

Until it finds something to react with. I'm sort of surprised in the British clip that they didn't hose down the splash area with some vinegar or something else mildly acidic to neutralize it.
posted by kindall at 9:23 AM on May 19, 2006

Actually, delmoi, increasing the surface area [by chopping up the alkali metal into smaller chunks] tends to result in a less dramatic explosion - what you get are a bunch of smaller, quieter explosions. It's visually a little more interesting, but less impressive. Perhaps cutting ridges and runnels into a chunk of sodium before dropping it into water would result in a more dramatic explosion, since you'd have all of the sodium hitting the water at the same time but still have an increased surface area. I have never seen sodium prepared that way, though.

Regardless, I'd suggest that any hypothetical experiments with alkali metals be carried out in a very large outdoor body of water.

And pombe - as far as I can tell, eBay has been taking down auctions for large chunks of alkali metal relatively quickly. Certainly, it used to be a lot more common to see auctions for large amounts of sodium [or, more rarely, potassium or even cesium] hanging around for days. I've been assuming that it has to do with the fact that states are beginning to outlaw private possession of alkali metals, due to their potential use in meth synthesis. I'm not sure if this is actually the case, though.
posted by ubersturm at 10:13 AM on May 19, 2006

It wasn't Mythbusters. It was that Brit TV show whose name I can't recall now. It's on G4 later at night.

Brainiac. (Which I always type as Braniac, for some reason.)
posted by smackfu at 11:51 AM on May 19, 2006

Sorry for the confusion earlier. My chemistry teacher in high school used the sugar-acid thing to jump-start a thermite reaction. I was assuming that the thermite was the 'mystery' substance being set off.
posted by onalark at 9:18 PM on May 19, 2006

For it to be on Mythbusters, we'd have to make up a myth about it. So think, people!
posted by graventy at 8:13 AM on May 20, 2006

ubersturm - glad to see I'm not the only person who's been looking for alkali metals on Ebay. I had no idea it was used in meth synthesis - I just assumed they were taken down due to the general hazard of owning a big chunk of sodium.
posted by pombe at 1:09 PM on May 20, 2006

I've heard that if you make an alkali metal turducken, it doesn't react with water, even if the total weight is over 50kg, and it's launched into the water from a compressed air cannon with immense force!

If only there was someone who could prove this to my satisfaction. Possibly involving a crash test dummy somehow.
posted by The Monkey at 5:06 PM on May 30, 2006 [1 favorite]