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Author: Subject: Are HCl fumes not that strong or are these fumes not HCl?
alking
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[*] posted on 11-6-2017 at 11:53
Are HCl fumes not that strong or are these fumes not HCl?


I gassed some HCl into some isopropanol awhile back and I keep it stored around 0C, at this point it's upwards of a year old, I don't know. It's significantly above saturation so the HCl slowly leaks and it is incredibly fumey when opened, even being so old now. It is an amber glass bottle with one of those blue teflon caps many of the chinese suppliers use, it does slowly eat something in the cap it seems, but it's minimal if so.

Anyway I was just salting out some amines (or possibly just ammonia, I've yet to find out), the solution got to the point where when I'd add HCl it would fume and escape, I also had fumes pouring out of the small IPA/HCl solution. It was at this point I noticed the room was considerably foggy, yet the fumes did not irritate me in the least as I would expect.

So does dilute enough HCl vapor still create considerable haze below the threshold to cause irritation or is this likely something else? It seems like the former just due to the sheer amount of fumes present and a lack of ability to form any known volatile side products, but I want to verify this before I risk exposing myself to something potentially unknown.

The amine solution did have some acetone and likely some xylene present, otherwise it should have just been IPA and water. HCl reactes with acetone, but it shouldn't make any fumes, and I would not expect any kind of reaction with xylene. The amines, if formed, would be mono and diisopropylamine.
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unionised
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[*] posted on 11-6-2017 at 12:16


Was there ammonia in this witches brew?
Ammonia and HCl vapours mix and form a fog of NH4Cl which is much less irritant than HCl.
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[*] posted on 11-6-2017 at 13:43


Bingo! There very likely was ammonia present.
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RogueRose
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[*] posted on 11-6-2017 at 15:02


Quote: Originally posted by unionised  
Was there ammonia in this witches brew?
Ammonia and HCl vapours mix and form a fog of NH4Cl which is much less irritant than HCl.


I have a similar situation where I think some NH4Cl is present. Would the NH4Cl create a cloud/fog if heated in a microwave? Would the fog have little smell (not very pungent but with slight HCl or Cl2)?
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[*] posted on 11-6-2017 at 15:18


Most likely. In my experiment the fog occurred after the solution reached 50-60C or so, before that it was soluble, so either the heat rapidly drives it off or it had simply reached capacity for me. It also had virtually no smell or taste despite being quite thick. I smelled no HCl fumes at all, but that would be expected as they should have all been neutralized in my case.
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Archenemy_6
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[*] posted on 11-6-2017 at 16:43


I don't know about the other stuff but I accidentally left some muriatic acid open and a noticeable fog formed in the room. I didn't feel any irritation at all, I notched the fog before anything.
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[*] posted on 13-6-2017 at 05:11


I'm not trying to be negative, but if you are allowing your lab to fill with what you assume is HCl gas, you should probably be more careful and ventilate your lab better. Back to the original question: I have used it in a fume hood and took a flask out to set it into the sink. Some fumes escaped. I found it quite irritating. I left the room with water running into a flask until everything cleared.
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[*] posted on 13-6-2017 at 07:40


Don't rule out other amines, either. I've seen rooms fogged spectacularly by HCl interacting with triethylamine and ethylenediamine fumes.
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[*] posted on 13-6-2017 at 09:20


Any idea what causes the fog? I assume it's the same mechanism regardless if it's ammonia or an amine? I don't know about ammonia, but the amines themselves, TEA ad EDA anyway, are not especially volatile compared to the fog and the salts would obviously be much less so. Is the amine/ammonia simply acting as a carrier?
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[*] posted on 13-6-2017 at 10:24


The fog (more accurately, "smoke") consists of tiny crystals of ammonium chloride, formed from the gas phase reaction between hydrogen chloride and ammonia.
NH<sub>3</sub> (g) + HCl (g) == NH<sub>4</sub>Cl (s)
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[*] posted on 13-6-2017 at 12:00


When you say a gas phase reaction do you simply mean gases on the surface of the solution, or the dissolved gases as well and it's driven off via vapor pressure? I ask because if it's the later then I would not expect much smoke from amines that are liquid at STP and when I introduced the HCl I did so by squirting it into the solution as opposed to dropping it on top yet the smoke formation seemed to be the same either way. So I'm wondering if that could be an indication of ammonia as opposed to amines in this case.
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[*] posted on 13-6-2017 at 13:34


By 'gas phase reaction' I mean two gases reacting together; not dissolved in anything, just floating around in air. Place open bottles of ammonia solution and hydrochloric acid near each other, and you'll see the same smoke is formed as gases escaping the solutions interact in the space above the bottle openings.
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[*] posted on 13-6-2017 at 14:14


Gotcha, thanks. So it was likely either due to the temperature increase or from the salt formation causing the solution to become saturated, or a combination there of, thus rapidly ejecting the gases allowing such a reaction to take place in my case.
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