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HF - hydrofluoric acid is probably the most feared chemical compound that there is.
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The reason it's so feared is that is that it is very corrosive. It will burn through human skin.
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Even quite a small exposure on your skin can cause a heart attack.
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And I really wanted--and I still want--to do an experiment with HF.
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... or rather, I want Neil to do an experiment for me with HF.
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I want to see what happens if we put a lightbulb--an electric lightbulb--the old, not energy saving sort
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into a beaker of HF. The reason why it's interesting is because HF can dissolve glass.
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Glass, the chemist's friend: we use it for test tubes, bottles, Kipp's Apparatus
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but HF attacks glass. Chemically, it breaks the silicon-oxygen bonds and forms silicon-fluorine bonds
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and the compound that dissolves away in the liquid HF.
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It was really a bit disappointing. The lightbulb sat there glowing, peacefully in the HF
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The HF has to be in a special plastic beaker that is cloudy, so you can't see through the side.
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And it just sat there. And poor Brady had to stand with the camera: watching, watching, watching...
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in case something happened. Because the reaction produces some heat, that's the reaction of glass with HF.
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And also because the lightbulb--an electric lightbulb is energy inefficient--is also producing heat.
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The water warmed up. And just like when you have a hot bath in a cold bathroom the walls starting misting up.
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Of course the top didn't mist up because there was a large spotlight which was producing heat on the top
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so, the top was warmer. So fortunately we could still see what was going on.
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And then, rather like fishing where there's a a long, boring period and then everything happens quickly.
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Suddenly, the lightbulb shattered.
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[MUFFLED THUMP]
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[ELECTRICAL CRACKLING]
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But it didn't shatter in the way you would expect. It was not like firing a bullet or smashing it with a hammer
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It neatly cracked all the way around the surface exactly where the glass was at the surface
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between the liquid and the air. Which was something that we hadn't expected.
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And it produced a really quite neat cut.
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Then, as soon as that happened, the bottom part--which was very thin because a lot of it had dissolved--slowly
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sank away. The acid rushed in, dissolved the filament, and so, the light went out in a puff.
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And then, the electrodes--which are much thicker so they didn't dissolve so fast and which were still live--
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started sparking a bit because of some electrolytic reaction. Exactly what's happening, I'm not sure
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and because we were using alternating current it would be quite complicated because it was switching
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between positive and negative. And then Neil had to start clearing up. Now the clear up procedure is pretty
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simple chemistry. You add sodium carbonate and you make sodium fluoride. In principle, you could
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have used it in toothpaste but it's not the of right grade for using with humans.
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So, he added sodium carbonate. CO2 was released--lots of bubbling--and then it's safe.
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What I think it illustrates, yet again, that every time you do an experiment, it will often go in the way you plan
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but you learn things because there's always an unexpected aspect.
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And, it was a nice experiment because it went well. It didn't explode, but, it gave a really nice result
