Never Mix Alkalai Metals with Water

October 3, 2006 | By | 6 Replies More

Okay, this is (sort of) just silliness. The Alkali metals appear on that left edge of the Periodic Table of the Elements under Hydrogen. What these metals below hydrogen all have in common is that they love oxygen even more than does hydrogen. So, if you drop any of these metals (Lithium, Sodium, Potassium, Rubidium, Cesium, or Francium) into water, they steal the oxygen from the water leaving the hydrogen to go free. But, the reaction gets hot, so as soon as this hydrogen hits more oxygen, it grabs it. Boom
This British video demonstrates the drama of dropping tiny pieces of these metals into water: “Like a grenade in a bathtub”.
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The throw-away line at the end about Francium implies that it would be the biggest bang ever, if they were allowed to do it. The real problem is that its most stable isotope only lasts a few minutes. Very radioactive, as well as explosive.


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Category: Humor, Science

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Comments (6)

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  1. Erich Vieth says:

    Thanks for sharing this. It certainly reminds me of high school chemistry lab, where we dropped sodium into water. One of those burning spinning bits flared off out of the water and across a piece of paper, producing a elegant parametric curve.

  2. Bruce Stephens says:

    Apparently the explosive effect (for caesium) may not be entirely genuine:

  3. Dan Klarmann says:

    Mr. Stephens is right! I shoulda seen it, myself. In order for this reaction to explode, it has to release the hydrogen and provide the ignition heat at the surface. But it makes science look cool, and the relative enthalpy of the reactions is well illustrated, even if it is faked.

  4. Bruce Stephens says:

    Right, but as Ben Goldacre comments, the real science is interesting and surely worth showing.

    Nothing wrong with getting a bang out of sodium, but there's surely something wrong in faking an explosion with caesium when there really wouldn't be one. Much more interesting to show (with suitable drama of hiding behine barriers and things) that there's no explosion, and explaining why. If you don't want to do that (because it's entertainment, and not serious), then just stop at the sodium, I'd have thought.

    (Of course the humour comes with the producers carefully trying to avoid both lying and admitting that any of it's faked (the program's promoted as being genuine).)

  5. grumpypilgrim says:

    When I was in high school, the (young, first-year) chemistry teacher found a quart-sized bag of sodium powder discarded in a corner of the chem lab storage room. Finding the sodium to be discolored from oxidation, and the powder mostly in clumps, she determined that the stuff was unusable, so she decided to discard it by flushing it down the lab's sink. Much to her surprise, the sodium inside the clumps was not fully oxidized, so when she dumped it down the sink and the clumps broke open…and she opened the water faucet…the sodium self-ignited, causing a column of flames to shoot out of the sink like a blowtorch.

    This all happened several hours after school had let out, so no students witnessed the incident, but the class rumormill, possibly relying on statements from the janitors who had seen the incident, reported that the column of flames was more than a yard high. All we knew for certain was that there was a large (1 yard in diameter & 6" high) cindercone of black soot and burned debris on the floor of the chem lab the next day, a very charred area in and around the sink, and the chem teacher seemed unusually quiet. Fortunately, no one was hurt, but there was a different chemistry teacher in that lab the following year.

  6. Dan Klarmann says:

    I had an incompetent substitute chem teacher in high school, as well. After the classic silver-nitrate experiment (where you extract the silver and then recombine it into silver nitrate with nitric acid) one student asked what we should do with the final solution. "Pour it down the drain," she said.

    Well, aside from OSHA, EPA, and MSD considerations, I saw an opportunity. I got most of the class to "dump" their residue into a beaker, ran the extraction, and then took the grey silver powder back to the art classes where I melted it down and cast it into a few silver rings.

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