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  • [Dr. Poliakoff] Most chemists are fascinated by what they've always been told,

  • that HF, hydrofluoric acid, eats human flesh.

  • We thought that we should try it.

  • Now, obviously, we can't try human flesh,

  • and Brady decided that a chicken's leg,

  • that's an uncooked leg from a dead chicken,

  • is a reasonable approximation to a finger.

  • We decided that we should try and do a demonstration,

  • but with some controls so we could compare them.

  • And what we wanted to know was, what was special about HF?

  • Was it the acid, or was it the fluorine?

  • So we thought if we took two other acids,

  • HCl, hydrogen chloride, and sulfuric acid,

  • both of those have the H, the acid part, but they don't have the fluorine.

  • I have been told that HF attacked your nerves so quickly that if you stuck your finger in it,

  • and none of us, obviously, would try this,

  • that it destroyed the nerves really quickly so you could hardly feel anything.

  • There are stories of people whose gloves have leaked,

  • and they've taken out their hands and bits are missing.

  • And of course, HF features in the TV show, Breaking Bad,

  • which I'm glad to say I've never seen.

  • [Brady] Why are you glad to say that? It's really good!

  • Well, perhaps... perhaps one day I might watch it, when I'm old.

  • After 5 minutes, nothing!

  • [Brady] Fred; this is 5 minute, 5 minute mark.

  • After half an hour, nothing!

  • [Brady] This is half an hour.

  • At the end of the day,

  • something slightly might have happened.

  • We decided to call it a day, but just in case, to leave it overnight in the acid.

  • In the morning, it was really interesting.

  • The two chicken legs in the control acids, HCl, sulfuric acid,

  • had made quite strong color in the liquid.

  • And the bits of the chicken leg sticking out still looked quite healthy.

  • You could almost imagine cooking them!

  • But the leg in the HF was pale, looked decidedly dead.

  • So we lifted them out, where the ones in HCl and sulfuric acid had turned rather jelly-like...

  • [lab technician] Eww.

  • [Brady] Yeah... she's done.

  • ...and really looked almost like an advertisement for being a vegetarian.

  • Really yucky.

  • But, with the HF, it was quite different.

  • It was as if a surgeon had chopped the bottom off.

  • It was moderately interesting what had happened below the surface,

  • but really what was much more interesting to me is

  • why the chicken leg in HF looked as if it was dead.

  • And, clearly, what had happened is that some of the pigment,

  • some of the red color of the meat, had been bleached away.

  • The reason that meat is red is because it contains a molecule called myoglobin.

  • This is related to hemoglobin, which we have in our blood,

  • and myoglobin stores oxygen in the muscles,

  • and myoglobin is a very similar color to hemoglobin.

  • If you cook beef, roast beef, so it's rare, and red juice comes out, the red juice is myoglobin.

  • Well, in fact, it's myoglobin that's reacted with carbon monoxide, which makes it such bright red.

  • My theory is that the HF is bleaching away, that's, attacking the structure of the myoglobin,

  • in particular the so-called "heme group", the iron-porphyrin group in the middle,

  • and breaking some of the bonds,

  • so that it no longer absorbs light and is colorless.

  • And that's why the solution that was left of HF

  • was completely colorless!

  • It looked as if the stuff had just disappeared,

  • there wasn't any sludge in the HF beaker.

  • [Brady] From school, I thought acid was acid,

  • and we always learned that H+ is the big deal here and doing all the work,

  • whether the H+ is coming from hydrochloric acid or sulfuric acid, or hydrofluoric acid.

  • Why do they- why do the three all do their work so differently?

  • The reason is that the chicken leg is made up of a mixture of organic compounds.

  • Proteins, a bit of fat, and also bone, which is a mixture of mineral.

  • Now if you break these organic molecules,

  • you are breaking carbon-hydrogen, carbon-carbon bonds.

  • And you can't just break them, you have to, if you like,

  • cap them off with some other group.

  • And carbon-fluorine bonds are very strong.

  • In fact, HF is not a very strong acid.

  • If you dissolve HF in water, especially when it's dilute,

  • it is not as acid as HCl,

  • because the bond doesn't dissociate, the HF bond, quite so much.

  • But hydrogen fluoride, HF, is very reactive,

  • because although the bond's strong,

  • the bonds in the products that you make are even stronger.

  • [Brady] So in terms of HF having a reputation for being a bad boy,

  • that's really got nothing to do with its acidity or its hydrogen, it's just the fact it's got fluorine.

  • [Dr. Poliakoff] It is because it has got fluorine and it will react very easily.

  • [Brady] Is there anything with fluorine?

  • No, because if you take something with, say, carbon-fluorine bonds,

  • the bonds are so strong that it's very difficult to break them.

  • They are very inert.

  • They use this refrigerant, for example, because they're very stable.

  • [Brady] So it's a bit like fluorine has come to the dance with hydrogen,

  • but *really* wants to dance with someone else.

  • Precisely.

  • Well, it wants not so much to dance, but to bond for life.

  • [Dr. Poliakoff] The reason why I think my explanation is correct is because we then went the whole hog,

  • cut the strings, and dunked the chicken legs completely in the acid.

[Dr. Poliakoff] Most chemists are fascinated by what they've always been told,

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人肉を食べるフッ化水素酸 - 動画の周期表 (Flesh-Eating Hydrofluoric Acid - Periodic Table of Videos)

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    林宜悉 に公開 2021 年 01 月 14 日
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