January 22, 2014
The Lab
So my chemistry students performed a lab on synthesis reactions today. They heated magnesium metal in air, which ignites in a dazzling white, silent flame. They sprinkled iron powder into Bunsen burners, which flickers and sparks, just like the sparklers you find for Independence Day (try it with iron wool a gas stove; iron will actually burn with enough heat). They produced a shower of ghostly, deep blue dancing fireflies by rapidly heating sulfur. And they backed away from a deep orange tongue of glistening flame they made by heating a mixture of iron powder and sulfur, producing a complicated mix of Fe2S3 and FeS.
Iron is a little surprising to most of the chemically uninitiated. It will burn. It will react with most acids. It will react with other metals. Some of its ions are pretty toxic. (Consult this lovely little gem on the mechanisms by which excess iron can cause your cell membranes to disintegrate.) Of course we all have the common and irritating experience of rust forming on the bottom edges of our car doors; this is a complex mix of iron oxides, iron hydroxides, and hydrates of iron. Other ions, such as Na+, Ca2+, and Cl-, which are found in road salts, sometimes accelerate the process. (The "axiom" that rust is iron (III) oxide is a gross oversimplification of a really complicated mixture and fails to express the nuanced processes by which it is created.)
Rust will show up anywhere that iron or one of its alloys is exposed to oxygen in the presence of water. This is why you should make sure the gas tank of a vehicle is full if you don't plan to drive it for a long while.
September, 2010 (?)
The BMW
So here is the point in the story (riveting so far, I know) where we arrive at the BMW motorcycle my friend Sam Girwarnauth picked up from an acquaintance of his up north. This was the summer of 2009 or 2010- I forget which- and Sam was on a veritable bike binge. I estimate that he has procured between 9 and 16 defunct and derelict motorcycles from 2008 to the present. This particular little pretty was "in great shape," that was believed to need simply "a tune-up." We arrived with Sam's trailer at said contacts house and loaded up the bike, which was really pretty nice-looking, until Sam found that the gas tank had been left empty for several years. The subsequent exposure to oxygen and moisture led the inside of the tank to fill with a flaky and friable layer of those iron oxides, hydroxides, and hydrates mentioned above. This, and the rubber lining of the tank had also badly rotted and was dropping little clods of hard, brittle rubber into the gas lines. Refusing to pass up a perfectly good BMW with a perfectly horrible tank, the bike was loaded, goodbyes were said, and Sam and I were on our way.
Fast forward to a lovely late summer weekend, about three weeks after the start of the school year at Grand Valley State University. Sam and I were living with our roommate Eli, who at the time must have been working at school or with his girlfriend Lane. On this day Sam was enjoying some tinker time with the bike and was considering how to deal with the gas tank. He had removed it from the bike and was out on our limestone gravel driveway.
After trying, with little result, to scour the inside of the tank with rocks and sand, Sam had gotten it into his head that the gas tank could really use a good American chemical stripping.
"So, Alex, I was looking online- on some chat rooms about bike repair- and found a lot of guys saying that you can clean out the inside of a gas tank with muriatic acid."
"Muriatic acid?" I have a minor in chemistry, so the name was familiar, but I couldn't quite remember what it was. I found it online and discovered that it was reliable old hydrochloric acid (HCl), running at a commercial grade of around 35%. For all you chemistry groupies, that comes out to a molarity of about 9.6 moles/liter, which is obscenely concentrated acid. Even a molarity of 0.25 M can burn you, and 4 M will put holes in your clothes. I explored the reactions that this acid would have on the metals in rust, and discovered the major product iron (III) chloride. Let me quote Wikipedia on some of the more attractive properties of this substance:
Iron(III) chloride is toxic, highly corrosive and acidic. The anhydrous material is a powerful dehydrating agent.
Although reports of poisoning in humans are rare, ingestion of ferric chloride can result in serious morbidity and mortality.
So I naturally relayed this prescient intelligence to Sam and asked him what he was considering doing with this substance, which would result in such serious morbidity and mortality.
Sam puffed out his cheeks, put his hands on his hips, and said, "Well, ah, you're the chemist, chap. What do you propose?"
"Maybe we can react it with something else to neutralize it after it dissolves the rust." Oh, the blinding soft chemical ignorance of youth! "Really I wouldn't use it until we know exactly what is going to happen. Let me at least figure out if there is a chemical recycling place around here we can dump it off at, or something."
I seem to remember doing no such thing, and a few hours later Sam came traipsing back from the hardware store with 1 gallon of 9.7 M hydrochloric acid. He probably said, "Well, bottoms up, I suppose," and forthwith glugged most of the gallon into the empty tank, and let it sit in the front driveway while he sat and read a book on Aristotle's metaphysics in the garage.
The 64th Avenue Chemical Spill
Sam and I sat in lawn chairs in the garage reading our books and chit chatting about God knows what abstruse idiocy. I kept looking toward the gas tank, still wondering what to do about the acid inside once Sam was done with it.
Urbane banter can only captivate one for so long, and suddenly Sam let out a sharp, "Woah, woah, woah!"
Looking at the tank, we saw a spreading greenish-yellow lake of smoking goo puddle out from under it. Little tendrils of white, treacherous steam idled away in deadly rafts, and Sam picked up the tank. A stream of the green acid poured out from one of the gas outlets, where the acid had eaten through the aluminum pipe.
"Aagh," Sam hissed and set the tank back down. A considerable cloud of white-grey vapor was hanging about the garage and driveway by this time, and the puddle on the limestone driveway fizzed angrily.
We looked at each other, and I went to get the hose from around the back of the house.
The tank was flushed out and copious water was sprayed upon the smoking puddle. The tank was still caked with rust. Setting it aside, we considered what to do about the chemicals. I kept spraying them down like an idiot, hoping the dilution would make everything okay, while Sam stroked his chin. After a while I shut off the hose and said, "Sam, the iron-three-chloride is really toxic."
He looked at me.
"We should probably dig up the rocks and dirt before the chemicals trickle into the water."
Sam immediately consented, and we went into the tool shed in the back yard, produced two shovels and a wheelbarrow, and began to furiously remove the first six inches of that portion of the driveway. About an hour's work resulted in a sagging wheelbarrow full of around 500 pounds of contaminated, hot, toxic, acidic lime slag. And I, chirping like a perfect dunce, said, "Well, there's got to be some facility that will take these and maybe put them in, like, a safe landfill that won't leak it into the water."
"Could be, could be," Sam said.
Meantime, we needed to get the pile of rocks out of the driveway, so we wheeled it back into the shed, where it remained.
For two years.
It must have been just before I started student teaching that I remembered the toxic monstrosity in our shed and wheeled it out again to the driveway. I stood pondering over it. Should I go out and seek that fabled facility I had so hopefully imagined? Upon careful reflection, I dumped the quarter ton of rocks back onto the driveway, a little surprised to find that they had taken on a weird brownish-red color and soft, crumbly consistency over the intervening years. I gave one a sniff and detected a sharp, earthy bitterness, which may have been the iron (III) chloride locked away in its limey pores.
The Rub
People are stupider when they are playing with chemicals. Even Sam, who has my most unqualified commendation as Place genius, lost I think about twenty IQ points as soon as that hydrochloric acid came into his possession.
And this is why chemical education is important, for everyone. I remember this every single day that I walk into my classroom and teach my students chemistry.
Chemicals make people stupid. Chemistry makes people smart.
No comments:
Post a Comment