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oneup
Harmless
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Hydrofluoric Acid experiments
A few days ago I learned that >95% sulfuric acid could displace acids from their salts.
So I thought I might be able to displace Hydrofluoric Acid (HF) from Sodium Fluoride (boil down from mouthwash solution.)
The reaction should go like this:
H2SO4 + NaF --> HF + NaHSO4
Hydrofluoric acid is an extremely dangerous chemical, capable of dissolving glass. Now that's something i've gotta try! 
MSDS: Click
Molarity of >95% Sulfuric Acid is 18, so to get 1 mole we need 1/18 = 0.0555
0.0555 * 1000 = 55.5mL
Molar mass of Sodium Fluoride is 42g/mol, so 55.5ml Sulfuric Acid and 42g Sodium Fluoride.
I think about doing to expirement in a plastic container or so, or anything that H2SO4/HF can not dissolve.
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Nerro
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You are aware that you will be making HF(g) right?? If you make HF please do it in water so the HF stays in solution and use every
precautionary measure possible even if it may seem rediculous because this stuff is about as nasty as they come.
[Edited on Mon/Jan/2006 by Nerro]
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oneup
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HF boils at 19C so if I use an ice bath I will be making HF(l)
and if i do it in water i will be diluting the sulfuric acid and it no longer works.
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gsd
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you will have to distill the HF gas out of reaction mixture and then dissolve it in water in separate container.
you can refer to the aparatus and procedure for making gaseous HCl from liquid HCl and conc. H2SO4 in any std. organic synthesis text book (e.g.
Vogel.)
plastic won't do for this job but you can use mild steel.
Ice bath doesn't make sense as when you add >95 % H2SO4 to an aquous solution, heat of dilution is so much that the mixture comes to boiling. Ice
bath will not keep the "intrinsic temperature" below 19 Deg. C. even if overall reaction mixture temperature may remain below 19.
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chromium
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I do not think that steel can be used for distilling HF. This distillation can be done only in lead or platinum retort (lead retort can be made from
lead tubing).
In my opinion its mad idea to make HF without lots of experience with less dangerous fluids. Nitric or hydrochloric acid are more usefull in lab and a
lot more safe. There are not many interesting things that can be done with HF. Glass can be dissolved with fused NaOH or even with hot sodium silicate
as well and this is almost all (expect in case you want to do some specific metalwork where only HF can be used as cleaner or solvent).
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gsd
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Industrially Mild Steel (MS) is used for handling HF Vapours. It forms a passive layer on the contact surface and prevents any further corrosion.
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Microtek
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Even dilute sulfuric acid will work. It will be somewhat safer to add NaF to dilute H2SO4 and then distill this mixture. That way you will end up with
dilute HF. The concentrated acid ( HF ) is not primarily dangerous because of its corrosiveness but because of its toxicity. Placing a drop of HF on
the skin of some kind of animal ( I don't know which mammal they used; probably rabbit or rat ) caused a moderate burn, but killed the animal due to
fluoride poisoning.
I also remember reading about an amateur experimentalist who accidentally knocked over a beaker of dilute HF, spilling it into his lap. Realising the
potentially lethal nature of his accident, he jumped into a nearby swimming pool and tore off his clothes in the water. He was immediately
hospitalized, but died a few days later anyway.
In short, I reccomend that you stay away from this one - or if you must, experiment with much smaller amounts of dilute material ( less than one gram
of NaF ).
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woelen
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Oneup, it is nice to be a mad scientist, but please be not mad. HF is not something to think of lightly. If handled carelessly, it will kill you,
slowly and painfully. Many great scientists from the past such as Davy, have suffered terrible pains. Have a read of this:
http://www.lateralscience.co.uk/Fluorine/Fluorine.html (the entire site is a nice read on its own, but don't try these things at home  ).
If you really want to do some experiments with HF, then simply dissolve some NaF in dulute H2SO4 or dilute HCl and then use that liquid to etch some
glass. There is no need to distill off the HF, the chloride (or sulfate) and sodium ions do not interfere. But please do not play around with gaseous
HF if you value your health. As a young boy I already had NaBr, KBr, NaI, KI and of course NaCl and KCl, and I also wanted NaF and/or KF, but thank
God I did not have access to NaF 20 years ago in my younger and unwise years .
Fluoride is not just another halogenide, like the others.
Even the aqueous solution must be handled with extreme care. I bet I prefer having concentrated HCl on my skin than having dilute HF at my skin. This
stuff is soooo nasty.
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Darkblade48
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I wouldn't even dream of working with HF unless I had a bottle of calcium gluconate nearby (think on your belt loop or something). HF burns are
very nasty indeed.
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chromium
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Does anyone know what is "safe" dose of HF when absorbed through skin? I know that small drops do not kill just make burns that turn very painful
after some hours or a day.
Some mouthwashing liquids contain sodium fluoride and our stomatch contains acids. How is that this combination is not dangerous? Can anyone explain?
[Edited on 2-1-2006 by chromium]
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woelen
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The fluoride in commercial mouth washing liquids and also in tooth-pastes is present in very small amounts. At most a few 100's of ppm. Even then it
is not advised to swallow these, but just use them to rinse your mouth (or brush your teeth). For this reason, children's tooth paste does not contain
fluoride or only very limited amounts, because little children usually swallow the paste, they use for brushing their teeth.
Indeed, having HF on your skin can cause exceedingly painful wounds. The nasty thing is that these do not appear immediately, but only hours later at
the time that you already 'forget' about the exposure. That is one of the nasty things of HF, it is not a 'honest' chem which 'bites' right now on
exposure (such as Cl2 gas), but it slowly hurts, hours after the exposure, but once it starts hurting it does so in a terrible way.
If you work with HF (or solutions of NaF in acidic liquids) for chemical experiments, then you may safely assume that the concentration of HF is
sufficiently high to cause serious and painful wounds. Otherwise the concentration is so low that you cannot do any interesting experiments with it
.
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evil_lurker
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From what I hear, if you get HF on 2% of the area your skin, you will be dead.
Keep some calcium gluconate gel handy!
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Fleaker
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Hydrofluoric acid is definitely a very hazardous reagent, so much so, I know of several colleges that do not keep it on hand. If you're going to use
it, have calcium gluconate gel on hand (what is it, just 2.5% gluconate, the remainder KY jelly?) If anything, the chief danger of concentrated HF is
the fuming! That is what is quickly absorbed and what quickly leads to edema. Off topic, but is it true that a spill of phenol over 10 square inches
will kill? I remember reading it in a chemical catalog.
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oneup
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I think i'll just put a gram or so sodium fluoride in a test tube, outside of course, pour is some concentrated sulfuric acid and run!
BTW, how do I get/make calcium gluconate? sounds like a good idea.
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12AX7
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Hm, looks like gloconate is a mildly oxidized form of glucose, so you could get some glucose (aka dextrose), dissolve it in water, oxidize with
whatever to kick the aldehyde group up to a carboxylate, then maybe crystallize the salt with sodium or potassium or something. Calcium gluconate
isn't very soluble (2%) so I suppose that could be precipitated right away too, but that depends on the solubility and quantity of side products.
It's listed as a chelating agent so will be good for sequestering transition ions, if you happen to have any need of that (???).
Dropping acid on NaF is a pretty stupid assed idea, not to mention useless...well it'll frost the glass, but it'll boil nicely too...
Hey Vulture, you should give him a few more posts -- he's clearly not harmless but a hazard to himself
Tim
[Edited on 1-3-2006 by 12AX7]
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oneup
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Can I oxidize the glucose with potassium permanganate? or nitric acid?.
I'm thinking of this:
first dissolve glucose in water, oxidize it with acidified permanganate/nitric acid
precipitate the calcium salt with a calcium base.
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neutrino
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This thread may be of some help:
Calcium Gluconate Preparation
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Pyrovus
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Not that I'd touch HF in a million years, but just out of interest would other soluble calcium salts have the same effect at treating HF burns? I
assume the idea is to get rid of the fluoride ions by precipitating as CaF2?
Never accept that which can be changed.
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woelen
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Are you mad, Oneup? Adding a whole gram of NaF to concentrated H2SO4? Take much less! That is more than enough for your wanted effect. If you want to
see what HF does to glass, have a look at an experiment I did with this.
http://woelen.homescience.net/science/chem/exps/KMnO4+NaF+H2SO4/index.html
If you do this experiment, I really want to urge you to use the small quantities I mention at my site and not scale up things to 1 gram!!  !!! Also do the experiment in a WELL ventilated area. If you have any doubt about
the ventilation, do the experiment outside!
EDIT(woelen): Changed link, so that it works again.
[Edited on 17-1-13 by woelen]
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oneup
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Wow. that's impressive. but where's the KMnO4 for?
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12AX7
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Uh...it's a demonstration of a permanganate complex. The KMnO4 supplies the Mn(7+)...
Tim
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neutrino
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woelen, I'm a little confused. On the page you lined to, you referred to hydrogen fluoride and hydrofluoric acid as two different compounds. Aren't
they both just HF?
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oneup
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hydrogen fluoride is the gas, hydrofluoric acid is just hydrogen fluoride dissolved in water. just like with HCl. Hydrogen Chloride is the gas,
Hydrochloric acid is HCl dissolved in water.
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woelen
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| Quote: | Originally posted by oneup
Wow. that's impressive. but where's the KMnO4 for? |
This experiment originally was meant to see if manganese forms manganyl (VII) compounds with fluoride, just as chromium forms chromyl (VI) compounds
(Cr2O2F2 and Cr2O2Cl2). I was just wondering, so I tried. The experiment confirms this. As a side reaction I also observed the intense corrosiveness
of the wet HF and when I observed that, I decided to put this quite impressive experiment on my website .
So, if you just want to see glass eaten away, take a spatula of NaF, add 0.2 to 0.3 ml of conc. H2SO4, heat a little (to 60 C) and then add a drop of
water, which you let run along the glass.
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oneup
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I will try the experiment next week as i don't have NaF yet.
I think doing it outside/near an open window would be a good idea.
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