Jacob
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Does excess hydrochloric acid evaporate?
Lets say you neutralize a base (eg NaOH) with excess HCl then put it on a heater to evaporate the water to dry. Does excess HCl go away too, or do you
get acid contaminated salt?
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mackolol
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It evaporates too and I would even say that first, because HCl is a gas dissolved in water (in this case). It doesn't form complex with alkali salts,
but with some salts of heavier metals it forms complexes, although they're quite thermally unstable, so you can get rid of it by heating.
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Jacob
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Quote: Originally posted by mackolol  | | It evaporates too and I would even say that first, because HCl is a gas dissolved in water (in this case). It doesn't form complex with alkali salts,
but with some salts of heavier metals it forms complexes, although they're quite thermally unstable, so you can get rid of it by heating.
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Thanks for the reply!
I figured if heating removes water from hydrated salts, it will do for HCl, too. I will report back the result for a diamine dihydrochloride salt.
The solution is quite acidic right now.
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Tsjerk
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It will evaporate, but it will first concentrate to about 20 percent. HCl and water like each other quite a lot.
Not all compounds like 20% hydrochloric acid.
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woelen
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If you have an amine HCl salt or an ammonium salt, then only the really excess HCl will evaporate. If you e.g. mix excess hydrochloric acid with a
solution of methyl amine, then you get methyl ammonium chloride in solution, with excess HCl. On evaporation, water and HCl are released, and methyl
ammonium chloride remains behind. Do not expect the appearance of free emthyl amine again.
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mayko
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Be aware that HCl vapors will find and rust every piece of iron and many of steel in its wake - do this outside/with good ventilation!
al-khemie is not a terrorist organization
"Chemicals, chemicals... I need chemicals!" - George Hayduke
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Jacob
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| Quote: Originally posted by Tsjerk | It will evaporate, but it will first concentrate to about 20 percent. HCl and water like each other quite a lot.
Not all compounds like 20% hydrochloric acid. |
Gotcha. HCl and water form an unusual 20% azeotrope that boils at 110°C. I set the heater slightly higher.
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Jacob
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| Quote: Originally posted by woelen | | If you have an amine HCl salt or an ammonium salt, then only the really excess HCl will evaporate. If you e.g. mix excess hydrochloric acid with a
solution of methyl amine, then you get methyl ammonium chloride in solution, with excess HCl. On evaporation, water and HCl are released, and methyl
ammonium chloride remains behind. Do not expect the appearance of free emthyl amine again. |
Thanks, that's a relief. Ethylene diamine dihydrochloride here.
Water is such a pain in the ass to get rid of. I will avoid it in the future and use alcohols and ethers if possible. They evaporate quickly and
cleanly.
[Edited on 14-5-2020 by Jacob]
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unionised
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20% isn't some magical number, fixed for all time and all circumstances.
It's roughly the azeotrope concentration if there isn't anything else present and at 1 atmosphere pressure.
And much the same is true of 110C.
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Jacob
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| Quote: Originally posted by mayko | | Be aware that HCl vapors will find and rust every piece of iron and many of steel in its wake - do this outside/with good ventilation!
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I've had this accident before with a leaky HCl bottle. Never again! That's why I set up an ammonia solution spill nearby for a free smoke show.
Call me crazy.
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Jacob
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| Quote: Originally posted by unionised | 20% isn't some magical number, fixed for all time and all circumstances.
It's roughly the azeotrope concentration if there isn't anything else present and at 1 atmosphere pressure.
And much the same is true of 110C.
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This place is high. Air is about 0.85 bar.
Doesn't matter anyway. I wanted it gone.
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unionised
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| Quote: Originally posted by Jacob | | Quote: Originally posted by mayko | | Be aware that HCl vapors will find and rust every piece of iron and many of steel in its wake - do this outside/with good ventilation!
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I've had this accident before with a leaky HCl bottle. Never again! That's why I set up an ammonia solution spill nearby for a free smoke show.
Call me crazy. |
Ammonium chloride smoke is also corrosive to metals.
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