Sciencemadness Discussion Board

Ammonium bifluoride

Melgar - 19-2-2018 at 19:04

I'm surprised I haven't read much about this stuff here. It's fairly easy to obtain, appears legal to ship, and yet has the potential to be extremely dangerous when misused. It's essentially an adduct of NH4F and HF and can substitute for hydrofluoric acid in many applications. It can dissolve mineral samples and glass by itself, and can be converted to sodium bifluoride. Sodium bifluoride will give off HF gas when heated.

Since ammonium bifluoride works in a similar manner as hydrofluoric acid, but without being quite so dangerous, I'd think it'd be more popular. The only downside is how quickly it eats through glass.

Texium - 19-2-2018 at 19:18

I have some in the impure form of a glass etching paste- which I have used for that purpose alone. It works quite well, and is much easier and less scary to handle than HF. I have pottery grade sodium fluoride as a source of F- for chemistry purposes

RawWork - 19-2-2018 at 19:39

I like adducts. One which proved easily obtainable source of hydrogen peroxide is sodium carbonate peroxyhydrate. Which is actually Sodium carbonate & Hydrogen Peroxide. Much cheaper than pharmacy 3% hp. Adducts are simply liquids of crystallization, instead of water of crystallization. Or simply mix of 2 chemicals. I don't know should I consider ammonium bifluoride or any acid salt an adduct. :o

woelen - 19-2-2018 at 23:52

Ammonium bifluoride is a real adduct, but of peculiar composition. F(-) ions can coordinate to HF molecules, forming the ion HF2(-). This ion is quite stable and it is unique to fluoride. Other halogens do not form such an ion. So, ammonium bifluoride is NH4(+)/HF2(-) in the solid state and in solution it also still contains quite some HF2(-), but also a little free HF and F(-).

I myself have NH4HF2 and also KHF2. They are hardly interesting for me. They are just very corrosive towards glass and extremely dangerous to human tissue. This combination makes them not particularly pleasant to work with, the more so because their aqueous chemistry is not very exciting. Just colorless ions. Very few interesting transition metal coordination complexes (the only interesting one I found is a complex with titanium(III)). Chloride and bromide are more rewarding for the home chemist and also MUCH safer, even if you oxidize them to elemental chlorine and bromine.

Melgar - 20-2-2018 at 00:12

Yeah, figures. I've seen plenty of questions about mineral sample analysis, where people reply with inane answers like "phosphoric acid" for dissolving granite. I wouldn't use it much if at all myself, but I did some research for a friend who was trying to analyze some ore samples. Advising him to use hydrofluoric acid seemed like a bad idea, but then I discovered that ammonium bifluoride should work just fine, and could be legally shipped in the mail.

The other similar adduct that I'm aware of is potassium silver cyanide. Except with Ag+ instead of H+.

woelen - 20-2-2018 at 05:08

Quote: Originally posted by Melgar  
The other similar adduct that I'm aware of is potassium silver cyanide. Except with Ag+ instead of H+.

This is of quite a different nature. It has two cyanide ions coordinated to the silver ion and it can be written as:

K(+)/[Ag(CN)2](-).

The name potassium silver cyanide is a bad name for this compound. Its correct name is potassium dicyanoargentate(I).

Much better known compounds of this structure are the yellow and red prussiates of potash. Their correct names are

yellow one: potassium hexacyanoferrate(II), K4[Fe(CN)6]
red one: potassium hexacyanoferrate(III), K3[Fe(CN)6]

The cyanide ligands are so tightly coordinated to the iron ion (especially in the yellow one) that virtually all toxicity is lost and no properties of the cyanide ion can be detected in solutions of these compounds. These two salts hence can be purchased easily, without being frowned upon. They are only weakly toxic.

AJKOER - 20-2-2018 at 08:08

Quote: Originally posted by RawWork  
I like adducts. One which proved easily obtainable source of hydrogen peroxide is sodium carbonate peroxyhydrate. Which is actually Sodium carbonate & Hydrogen Peroxide. Much cheaper than pharmacy 3% hp. Adducts are simply liquids of crystallization, instead of water of crystallization. Or simply mix of 2 chemicals. I don't know should I consider ammonium bifluoride or any acid salt an adduct. :o


Like many, laundry products based on sodium carbonate peroxyhydrate, also called sodium percarbonate, per one of my prior threads, is not a source solely of H2O2 as one would think.

In fact, upon addition of water together with other unmentioned additives normally included in the laundry directed percarbonate products, one may then understand what is up with those stern warning labels for safe H2O2?!

See http://www.sciencemadness.org/talk/viewthread.php?tid=73626#...

Also, even with a pure percarbonate product, note apparently there is an equilibrium reaction between aqueous carbonate and H2O2:

CO3(2-) + H2O2 = CO4(2-) + H2O

and H2O2 itself is apparently less stable in non-acidic conditions. Interestingly, my observation was that adding bleach (NaOCl) to an aqueous mix of H2O2/carbonate liberates less oxygen gas than expected based on hydrogen peroxide concentration!

[Edited on 20-2-2018 by AJKOER]

RawWork - 20-2-2018 at 08:27

Well, practically the same. It is oxidant, with O as active element. I oxidized copper in sulfuric acid with that. Also MnO2 reacted just like it would with H2O2. In fact, if you wanna philosophy, any "per" anion is just a mix of anion of that acid + hydrogen peroxide. Percarbonate, Persulfate, Peracetate...whatever. I heard that it's not stable in alkaline anyways, so something (acid) must be added to slow the decomposition. Don't know exact details.

Also it's very practical to make per-something instead of pure hydrogen peroxide.

Nobody on youtube tried Weissenstein process for hydrogen peroxide production, which i plan to do together with 5 other videos before spring (exactly 1 month from now). Await!

[Edited on 20-2-2018 by RawWork]

MrHomeScientist - 20-2-2018 at 08:37

I've got quite a lot of ammonium bifluoride, something like 500g, which I used somewhere deep in the "The Trouble with Neodymium..." thread to precipitate NdF3 from a solution. I did not want to buy that much, but it was the only listing I'd seen on eBay and it doesn't show up often. Scary stuff to work with. I put a drop on a glass bottle to see if it would etch it; it didn't do much (probably too dilute) but I did get a brief whiff of what I think was HF. Hard to describe smells, but it was like HCl in that it was sharp and biting, but also "cleaner" smelling.

Chemetix - 20-2-2018 at 22:16

I know it's meant to etch glass but not borosilicate it seems.
I tried with the Potassium salt and it did nothing. Even along with 40% sulphuric it was ignored. I use a 30%HNO3 5% HF mix fairly regularly to clean borosilicate and that wont touch boro even when hot. Only 40%HF and above seems to attack borosilicate.

ave369 - 21-2-2018 at 04:49

Never in my life as an amateur chemist I ever needed HF or a substitute (well, except that one case when someone advised me to weld star cracks in flasks after "relaxing" the cracks with HF). I have a jar of NaF as a source of fluorine ions if I ever need them, but it sits idly there.

Melgar - 21-2-2018 at 10:07

Quote: Originally posted by woelen  
This is of quite a different nature. It has two cyanide ions coordinated to the silver ion and it can be written as:

K(+)/[Ag(CN)2](-).

The name potassium silver cyanide is a bad name for this compound. Its correct name is potassium dicyanoargentate(I).

Yeah, I just meant that it was the only other adduct I knew of where the anion was a +1 alkali/alkaloid and the cation consisted of two halides/pseudohalides on either side of an atom with a charge of +1, for a net charge on the cation of -1. It's just sort of an unusual to have a linear cation that's symmetric like that too. The only other one I know of is azide.

Though apparently gold can do that too:

https://en.wikipedia.org/wiki/Gold_cyanidation

Reading about this, I've noticed alkyl fluorides mentioned here and there, but they seem more or less useless. They can be prepared, but mention of them seems to stop there. My guess is that they're like acyl chlorides, except no good for use with glass, and require more dangerous chemicals to synthesize?