This blog is my attempt to reconnect with the world of chemistry. I have a PhD in Inorganic Chemistry and make a living doing research for a large company in Michigan. As times have changed, that company has changed its focus and I no longer have as much chance to do the basic, fundamental research which I most enjoy. Through this blog, I am hoping to recapture the magic which I felt during my graduate (and undergraduate) days in college. Expect topics on chemistry and alchemy along with some non-chemistry related items which I think might be interesting.

"The chymists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasure among smoke and vapour, soot and flame, poisons and poverty; yet among all these evils I seem to live so sweetly that may I die if I would change places with the Persian King."

Johann Joachim Becher (phlogistonist)
Acta Laboratorii Chymica Monacensis, seu Physica Subterranea, (1669).

Tuesday, August 11, 2009

Back on the Air Again

Here’s hoping that my long hiatus from blogging is about over. I returned from my Grand Canyon trip several weeks ago, but I just spent the last two weeks in Missouri with my family. After a long battle with Parkinson’s disease, my father passed away last week. He taught me a lot about life and I’ll miss him. Who knows how my life would have turned out had not my parents bought that chemistry set for my birthday back in grade school? Thanks for everything, Dad.


In a lighter bit of news, my wife came across Mythbusters the other night, a television show dedicated to proving or disproving various myths, commonly accepted beliefs, and stunts enacted on TV. I haven’t seen many episodes, but in this one the hosts were attempting to reenact a scene from an old MacGiver show, where MacGiver used the sodium+water reaction to blow up a masonry wall. Chemical experiments on TV? Okay, I’ll watch for a while. Unfortunately, anyone who has ever handled sodium would know the small piece of sodium which they were using (duplicating the MacGiver episode) was doomed to failure. I threw larger pieces than that into buckets of water back in high school. (Not that that means it’s a particularly smart thing to do, I might add). The safety precautions used by the show’s hosts were a little over the top, but then again, I don’t know how much experience these guys have with chemicals. When the sodium failed to make more than a loud noise, they eventually turned to using potassium (which is much more reactive) while also increasing the amount of metal to 500 grams. The explosion was more impressive visually, but as expected, the wall wasn’t even touched.

Of course the reason why sodium or potassium explodes is due to its reaction with water to form hydrogen and heat, which then proceeds to ignite with the oxygen in air. Despite the rather impressive sound produced by hydrogen explosions, the actual explosive force is rather low, unless large quantities are present (or if one tries to constrain it within a vessel that might shatter). Two summers ago, my kids attended a demonstration where hydrogen and air were bubbled through dishwashing soap to create a pile of foam which was scooped up by the demonstrator and ignited while still clinging to his hand. Impressive noise, but no damage to the fingers. Now I’m not knocking the potential dangers of hydrogen here. After all, I work on fuel cells, and we pipe pure hydrogen all over the lab, so our detection and alarm systems are quite elaborate, let me assure you. But hydrogen is usually only a problem if large amounts of it collect somewhere, like near the ceiling, which is why hydrogen detectors are always placed up there.

Hydrogen explosions are interesting in that most explosives, such as TNT, work because their ignition produces a huge volume of gas (much of it carbon dioxide) which rapidly expands. The combustion of hydrogen

H2 + 0.5O2 ----> H2O

actually results in the loss of ½ molecule of gas, which might be expected to create an implosion instead, except that the large amount of energy released during the reaction heats the gas, causing it to expand rapidly per the ideal gas law. The thing that makes hydrogen particularly dangerous is its extremely fast flame propagation speed, which allows all the hydrogen to react nearly simultaneously, greatly increasing its explosive power.



I didn’t watch the whole show. Can anyone tell me if they were successful in making a working hang glider using the motor from a portable cement mixer?

10 comments:

Chemgeek said...

Do you know how your hydrogen detectors work? What kind of chemistry is going on in one of those things.

Ψ*Ψ said...

Sorry to hear about your father...my deepest sympathies.

chemgeek: if i had to venture a guess, i'd think that the hydrogen probably adsorbs onto a surface of some sort and changes its electronic properties (or something)...

Chemist Ken said...

Chemgeek, I'm not sure how ours work. They may be similar to the hydrogen detectors I've used in the past, which were basically detectors for combustable materials, which meant they would also be activated by hydrocarbons at high enough levels. Unfortunately, I don't know what the mechanism is for detecting combustables either.

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James Moore said...

Unfortunately you've gotten some spam comments, but to summarize:

The glider soared like a wingless bird. It was bad. Humorous, but ineffective. Someone else on the comments was asking how hydrogen sensors work. It depends on the sensor type, but most portable are sporting an electrochemical sensor. In fact, in a pinch of you have just a normal CO detector for PPM range, you can go into a Hydrogen environment. Just multiply your visible number by .5 in most monitors and then when you have 400ppm on your alarm you're at 2% LEL Hydrogen. Cheap trick, and I don't usually recommend it, but it works in an emergency.

If you guys want more boring detailed talks about the internal construction of the electrochems, send me an email (james@idealgases.com) as all I do is monitor related work.

Love the blog by the way, you can check ours over at http://incidentcommander.blogspot.com/

James

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