Sciencemadness Discussion Board - Low(est) boiling point salts?

Low(est) boiling point salts?

Junk_Enginerd - 18-1-2021 at 10:35

I'm experimenting putting substances in electric discharge lamps, and I'm thinking about what to put in there. I thought there would be a zillion things, but I found surprisingly few things actually have a suitable vapor pressure. (Close to 0 at room temp, and maybe <20 Pa at say 100°C?)

Anyway, I was thinking about salts and how they should provide interesting emissions. Tried it first with good old sodium chloride, and got some sodium emissions. Of course only if the salt was very hot and had the arc basically going through it, no vapor pressure to speak of there.

But as I'm trying to think of salts that boil at less than, I dunno, 800°C, I can't think of any. Actually, can salts even boil at all?

A little guidance here would be awesome. Thanks

mackolol - 18-1-2021 at 10:50

I can give you a little guidance. UTFSE

unionised - 18-1-2021 at 12:21

Does ferric chloride count as a salt?
Copper Chloride comes in just below the 1000C mark.
Zinc chloride boils (just) below 800C

DraconicAcid - 18-1-2021 at 12:45

The higher the oxidation state of a metal, the more covalent character it will have in its compounds, and the more likely it is for the compound to have a high vapour pressure (unless it's an oxide). AlCl3 will sublime at a fairly low temperature if it's anhydrous. Several anhydrous metal tetrachlorides are liquids at room temperature.

Metallophile - 18-1-2021 at 13:13

Indium(III) bromide has a B.P. of 656C. From the trend, maybe the iodide is lower? Indium is supposed to have a nice indigo color in its spectrum, which it was named after.

[Edited on 1/18/2021 by Metallophile]

Junk_Enginerd - 18-1-2021 at 15:18

Quote: Originally posted by unionised

Does ferric chloride count as a salt?
Copper Chloride comes in just below the 1000C mark.
Zinc chloride boils (just) below 800C

You're asking the noob here, but it sure sounds like a salt to me.

Way too high, I'd expect. I'm hoping for at most 200°C.

Quote: Originally posted by DraconicAcid

The higher the oxidation state of a metal, the more covalent character it will have in its compounds, and the more likely it is for the compound to have a high vapour pressure (unless it's an oxide). AlCl3 will sublime at a fairly low temperature if it's anhydrous. Several anhydrous metal tetrachlorides are liquids at room temperature.

Hm. Okay, that's helpful. I did manage to find a website with a bunch of salt boiling points listed, then I lost it unfortunately, but yeah I remember seeing AlCl3 there, and also CCl4, which seems to line up with what you're saying about oxidation state. Also some Iodine and Bromine salts, but I don't have any source for those elements...

Twospoons - 18-1-2021 at 19:51

copper bromide lasers are typically operated around 400C, so you could try that.

B(a)P - 19-1-2021 at 00:43

Nickel nitrate boils just under 140 ^oC.

mackolol - 19-1-2021 at 01:28

Quote: Originally posted by mackolol

I can give you a little guidance. UTFSE

All right, I could have been a little mean. There was a topic about lowest melting point salts and I misremembered it as lowest boiling point salts.
After all, I can't find the topic neither. That;s a pity it was quite an interesting one. Could one link to it?

Also, the nickel nitrate is said to be boiling under 140C, but that's its hydrated form. So how is that, it forms something like an azeotrope with water? Or would be decomposed if attempted to distill when it's anhydrous?

TheMrbunGee - 19-1-2021 at 06:25

Quote: Originally posted by B(a)P

Nickel nitrate boils just under 140 ^oC.

I believe that is the hydrate, so it is water that boils at said temperature.

njl - 19-1-2021 at 06:30

I'm guessing its the water of crystallization boiling off... I would expect nickel nitrate to just decompose. Mack, I also remember a thread like that but I can't find it right now. I have found that the search engine is less useful when my internet connection is weaker, couldn't say why though.

mackolol - 19-1-2021 at 06:59

Quote: Originally posted by njl

I have found that the search engine is less useful when my internet connection is weaker, couldn't say why though.

Well is it? That's interesting... My internet is good and neither did I find the thread. There is small chance of it being in some short questions thread, but even then it would have been found by searching inside of the topic...
Maybe it was somehow deleted...

Maybe this topic will be of some help? : https://www.sciencemadness.org/whisper/viewthread.php?tid=15...

Ammonium chloride seems to be pretty low boiling 520C. Although it's way higher than you opt for, it still is achievable in amateur lab.

B(a)P - 19-1-2021 at 11:58

Quote: Originally posted by njl

I'm guessing its the water of crystallization boiling off... I would expect nickel nitrate to just decompose. Mack, I also remember a thread like that but I can't find it right now.

Many sources simply say that it boils at ~138 ^oC,I had always assumed that meant it lost water prior to the anhydrous product boiling. After a bit of digging I found this on pubchem.

Nickel nitrate hexahydrate loses water on heating and eventually decomposes forming nickel oxide. The loss of the individual waters of hydration upon heating the hexahydrate can be studied and the existence of the anhydrous covalent compound Ni(NO3)2 ... can be observed, before it decomposes, using differential thermal analysis and thermogravimetric analysis techniques.

Kirk-Othmer Encyclopedia of Chemical Technology. 3rd ed., Volumes 1-26. New York, NY: John Wiley and Sons, 1978-1984., p. 15(81) 802

Does anyone have access to Kirk-Othmer Encyclopedia of Chemical Technology. 3rd ed? I would be very curious to see the full entry.

TheMrbunGee - 19-1-2021 at 13:44

Quote: Originally posted by mackolol

Ammonium chloride seems to be pretty low boiling 520C. Although it's way higher than you opt for, it still is achievable in amateur lab.

Ammonium chloride decomposes, I guess forms some sort of equilibrium:

NH4Cl <- t° -> NH3 + HCl

Quote: Originally posted by B(a)P

Crystal hydrate salt vapor just sounds weird

So I checked and every BP came up for hydrate.

[Edited on 19-1-2021 by TheMrbunGee]

DraconicAcid - 19-1-2021 at 14:23

Anhydrous copper(II) nitrate is surprisingly volatile and soluble in ethyl acetate. You just can't make it from the hydrate.

clearly_not_atara - 20-1-2021 at 08:30

It depends on what you call a "salt". Is tungsten hexafluoride a salt? How about trimethylammonium acetate? Nitrosonium tetrafluoroborate? Trichlorosulfonium tetrachloroaluminate?

Junk_Enginerd - 21-1-2021 at 01:21

Quote: Originally posted by DraconicAcid

Anhydrous copper(II) nitrate is surprisingly volatile and soluble in ethyl acetate. You just can't make it from the hydrate.

That could be interesting. Doesn't seem too complex to make. Condense NO2 onto copper powder, dissolve in ethyl acetate, deposit into discharge tube and let the vacuum boil off rhe ethyl acetate?

unionised - 21-1-2021 at 05:10

Quote: Originally posted by mackolol

I can give you a little guidance. UTFSE

Well, at least you had the decency to accept that you were ... in the wrong.

http://www.sciencemadness.org/talk/viewthread.php?tid=154704...
is about ionic liquids
And there's this one about deep eutectics and ionic liquids.
http://www.sciencemadness.org/talk/viewthread.php?tid=62263#...

I found them by UTFSE with the right search criteria.

Maurice VD 37 - 2-2-2021 at 13:59

Silicon tetrachloride boils at 57°C. Silicon tetra bromide boils at 153°C.
Tin tetrachloride boils at 114°C
Phosphorous trichloride boils at 75°C. Phosphorous pentachloride sublimes at 162°C.

DraconicAcid - 2-2-2021 at 14:40

Quote: Originally posted by Maurice VD 37

Silicon tetrachloride boils at 57°C. Silicon tetra bromide boils at 153°C.
Tin tetrachloride boils at 114°C
Phosphorous trichloride boils at 75°C. Phosphorous pentachloride sublimes at 162°C.

You'd be hard-pressed to find anyone who considers those to be salts rather than molecular halides.

j_sum1 - 2-2-2021 at 14:42

Quote: Originally posted by Junk_Enginerd

Quote: Originally posted by DraconicAcid

Anhydrous copper(II) nitrate is surprisingly volatile and soluble in ethyl acetate. You just can't make it from the hydrate.

That could be interesting. Doesn't seem too complex to make. Condense NO2 onto copper powder, dissolve in ethyl acetate, deposit into discharge tube and let the vacuum boil off rhe ethyl acetate?

IIRC, it was only recently (like the last couple of years) that this salt was characterised. It proved remarkably elusive. So, not easy.

DraconicAcid - 2-2-2021 at 15:37

Quote: Originally posted by j_sum1

Quote: Originally posted by Junk_Enginerd

Quote: Originally posted by DraconicAcid

Anhydrous copper(II) nitrate is surprisingly volatile and soluble in ethyl acetate. You just can't make it from the hydrate.

That could be interesting. Doesn't seem too complex to make. Condense NO2 onto copper powder, dissolve in ethyl acetate, deposit into discharge tube and let the vacuum boil off rhe ethyl acetate?

IIRC, it was only recently (like the last couple of years) that this salt was characterised. It proved remarkably elusive. So, not easy.

I could have sworn I read about it in Cotton & Wilkinson's Advanced Inorganic Chemistry, 4th edition, which would have been decades ago. I could be wrong about where I remember reading it, though.

ETA: http://www.sciencemadness.org/smwiki/index.php/Copper(II)_nitrate says 1969.

[Edited on 2-2-2021 by DraconicAcid]