Sciencemadness Discussion Board

hydrofluoric acid, storage, hazards and usefulness?

Sulaiman - 16-5-2023 at 23:33

Here I can buy 55% hydrofluoric acid cheaply from shopping sites,
How 'easy' would it be to store?

eg I find typical 36% HCl quite difficult because it corrodes nearby steel/iron,
but 98% H2SO4 stores quite easily.

Charts indicate that the partial vapour pressure is up to 100mm Hg at 55% w/w and 120F so it looks easy to store,
Is it?
I've seen photos of hydrofluoric acid burns and read about it's toxicity
but I don't have a real appreciation of how hazardous it really is in practice.
I (almost) always use goggles in my 'lab',
and I have a hosepipe ready if I anticipate any emergencies.
If I buy the acid I'll get some calcium gluconate gel,
What other precautions should I take?
I'm considering buying the hydrofluoric acid just because I can.
Does hydrofluoric acid have much use in a hobbyists lab?
I've not noticed it mentioned much.

[Edited on 17-5-2023 by Sulaiman]

Keras - 17-5-2023 at 04:27

I've been storing a bottle of 60% HF for quite a long time. Granted, it is unopened (I bought it on a whim). It arrived in a lidded plastic bottle itself wrapped in a plastic bag sealed with a tightly clenched hose clamp (plastic type, not a Jubilee clip). There is no perceptible leakage so far.

[Edited on 17-5-2023 by Keras]

Bezaleel - 22-5-2023 at 14:35

Maybe check with Woelen. I know he had some (not so great, iirc) experience storing HF solution a few years back.

Texium - 22-5-2023 at 21:09

DON’T buy HF if you don’t know what to do with it. Working with it is hardly ever worth the risks. If you get some on your skin, you may not notice at first, and burns may not be felt for over a day after contact. By that time it could have already started absorbing into your bloodstream where it precipitates calcium ions, which can ultimately lead to cardiac arrest. If you buy it, you’ll have to store it, and eventually have to deal with it one way another. Better to hold off unless you come across something you absolutely need it for.

woelen - 23-5-2023 at 01:25

I indeed have some HF (40% by weight) and it stores fairly well. It is less of an issue than 36% HCl on storage. But 55% acid probably will be much more troublesome.

I have 30% HCl and that stores quite well, while 36% HCl is a nuisance and wet frost can be found nearby.

I have some HF, but I hardly used it in any experiments. I have a 1 liter HDPE bottle with the acid, and I transferred 100 ml to a small HDPE bottle, from which I do experiments. From that 100 ml I only used 25 ml or so over a period of 7 years.
Actually, HF is not that interesting, and it is extremely dangerous. That's the reason, why I only have done a few experiments with it, and never at larger scale than test tubes. I feel more comfortable working with NaCN, liquid Br2, or even stuff like SOCl2 or PCl5 than working with HF. The latter is insidiously toxic, with only weak warning properties. If you wet an area of your body of appr. 10 cm times 10 cm, then that may kill you. E.g. a spill of a few tens of ml on your clothes can produce such an area of wet skin.

I actually am considering converting all of my HF to HBF4 by carefully adding H3BO3 or B2O3 to the acid. This reaction is quite exothermic, but if it is done slowly, then it can be done safely. HBF4 is MUCH less risky than HF and is quite interesting on its own. I then keep the 100 ml of HF.

I now have NaF, NH4HF2, and KHF2 and these chemicals serve quite well for experiments with fluoride. They are solids and much less risky to work with. If acidified with dilute H2SO4, you can get HF in solution and many experiments can be done with that. If acidified with conc. H2SO4 you even can get fuming HF, dissolved in H2SO4. That stuff of course also is very dangerous. The fumes are really dangerous on inhalation.

If you don't know what to do with HF, or if you are not yet sufficiently experienced with home chemistry, then my advice is to steer away from it.

Thanks for the good advice

Sulaiman - 23-5-2023 at 09:36

Too risky for my present circumstances,
Maybe one day, if I'm prepared.
Thanks for clarifying my thoughts.
So no whimsical hydrofluoric acid purchase by me.

Texium - 23-5-2023 at 09:52

Good plan. If you want to stock up on a safer fluoride source without a definite use in mind, in case of future unavailability, I’d recommend buying some NaF or KF. These are soluble fluoride salts, so they are still quite toxic and should be handled with care, but they are nowhere near as dangerous as HF, since they are non-volatile and can not directly kill you from skin contact. NaF is even used (in small amounts) in some toothpastes and mouthwashes. As woelen explained, you can still generate solutions of HF in situ from these salts, so if you do come across an experiment that requires it, you’d be able to prepare the exact amount you need on demand rather than having to store HF long term.


MadHatter - 23-5-2023 at 18:08

I agree with most people here. That's one beast I won't tangle with. I've had
NaF for use in perchlorate cells. I've heard of people, professionals at that,
dying from skin contact with this material. I would never take a job which
involved that. So on that one I'll take a pass.