Hydrofluoric Acid - Breaking Bad
Tuesday February 12, 2008
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Hydrofluoric acid attacks the silicon oxide in most types of glass. It also dissolves many metals (not nickel or its alloys, gold, platinum, or silver), and most plastics. Fluorocarbons such as Teflon (TFE and FEP), chlorosulfonated polyethylenene, natural rubber and neoprene all are resistant to hydrofluoric acid. Hydrofluoric acid is so corrosive because the fluorine ion is highly reactive. Even so, it is not a 'strong' acid because it does not completely dissociate in water.
I'm surprised Walt settled on hydrofluoric acid for his body-disposal plan, when the well-known method for dissolving... um... flesh... is to use a base rather than an acid. A mixture of sodium hydroxide (lye) with water can be used to liquefy dead animals such as farm animals or roadkill (with obvious extensions to victims of crime). The carcass is reduced to a brownish sludge, leaving only brittle bones. Lye is used to remove clogs in drains so it could have been poured into a bathtub and rinsed away, plus it is much more readily available than hydrofluoric acid. The fumes from reacting large quantities of either hydrofluoric acid or sodium hydroxide would have been overwhelming to our buddies from Breaking Bad.
What Is the Strongest Acid? | Common Acids Quiz
Photo: Chemist with a gun but no pants, in the pilot episode of the AMC drama Breaking Bad. (Doug Hyun/AMC)
Comments
“I suspect most chemistry teachers don’t keep big jugs of hydrofluoric acid in their labs”
At least one did. When I was in high school (70’s), the chemistry teacher disappeared several weeks into a new school year. Didn’t resign or get fired — just stopped showing up, apparently having left town with no notice.
Eventually a new teacher was hired, and I became a lab assistant under him. One responsibility was keeping the chemicals storage closet in order. On the floor were kept several big jugs of hydrofluoric acid — far more of it than any other acid we had. The new guy couldn’t figure out why his predecessor had stocked it. There was no conceivable use for it in high school chem, even in small quantities. Hoping to find some use for it, and perhaps a way to dispose of it, he tried pouring a little in a stained porcelain sink in the prep room. It removed the stains. Plus all the glaze on the porcelain. All of us — teacher and lab assistants — were scared to death of the stuff.
As far as I know, the mystery of the missing chemistry teacher and the superfluous hydrofluoric acid was never solved.
I have used HF acid to prepare a porcelain bathtub and ceramic tile for refinishing [this is what the pros use]. It had very little effect on the tub or tile and I was not impressed with it as an etcher.
After I graduated college my first job was in an oil refinery. HF acid was used in a process to remove calcium from crude oil in the refining process. We had to use rubber suits and gloves, special glass lined tanks and on the wall in the lab was a picture of an employee who had used a pair of gloves with a pin hole in the thumb of the right glove. It seems that HF is very active in the concentration used in the refining process. The acid that got through the glove ate his thumb away seemingly from the inside out…
HF eats concrete like it was bread. I suspect that the reader that uses the HF for etching old bathtuhs is using a lesser concentration. And I wonder if the acid has a shelf life in the diluted state?
One lungful of the gas from 70% hydrofluoric acid is enough to kill a person, and getting the same concentration of the acid on just 2% of skin results in death. It is very scary stuff!
I agree that a base such as NaOH would have been a better choice, I suppose dissolving the tub made for better drama…
Geologists use HF to break down silicate rocks. Geochemists will use 20-30 mL at a time to dissolve a few mg of mineral separates to prepare samples for U-Pb dating, for example.
In grad school I had a project that involved breaking down 10s of grams of quartz at a time, so I used HF by the liter, so I was the only one in my department who placed orders for 4 gallon cases of the stuff.
Since it is a weak acid exposure, even to the concentrated acid, does not immediately cause the type of burns a strong oxidizer might.
The problem comes later, as the fluoride ions are a great calcium scavenger. Over time they work their way through soft tissues and attack bone. The solution is to flood the exposure with a source of calcium.
We used to keep tubes of calcium gluconate gel in the lab. A friend was exposed to a tiny amount through a pinhole in a glove; he went to the emergency room later that evening when he became aware of the exposure (near the tip of his finger), and he was treated with a local injection of calcium gluconate…
It is too bad some people here think HF is such a joke. It isn’t! It is extremely dangerous in concentrated form and should be handled as if it were a bomb. HF is a calcium seeker. If it comes in contact with skin it will cause irreversible tissue/bone damage, not to mention the highly toxic effect of the “raw” fluorine ion. I would not even want to work with the dilute form without the proper gear. It WILL eat through glass, porcelain, rock, and metal by the way. Don’t toy with it, or use it unless you respect it!