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Author: Subject: HCl acid in situ
artemov
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[*] posted on 29-12-2019 at 21:54
HCl acid in situ


Is it possible to make HCl acid in situ from sulphuric acid and common salt?

From my calculation (hopefully it's correct), battery acid (37% sulfuric acid) would stoichiometrically give me 30.4% HCl acid. I can put it in the freezer to precipitate out the sodium sulfate and also ensure the HCl gas stays dissolved. Either decant or cold filter afterwards to get my HCl acid.

Would this work?

So far everything I have read involved generating HCl gas which is then dissolve in water.
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Fery
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[*] posted on 30-12-2019 at 10:38


HCl pKa = some sources -6.3, other sources -8
H2SO4 pKa1 = some sources -10, other sources -3, other sources -2...
H2SO4 pKa2 = +1.9
so no Na2SO4 formed when mixing 37% H2SO4 with common salt like NaCl
NaHSO4 formed instead
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PirateDocBrown
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[*] posted on 30-12-2019 at 12:06


Quote: Originally posted by Fery  
HCl pKa = some sources -6.3, other sources -8
H2SO4 pKa1 = some sources -10, other sources -3, other sources -2...
H2SO4 pKa2 = +1.9
so no Na2SO4 formed when mixing 37% H2SO4 with common salt like NaCl
NaHSO4 formed instead


Hmm, where do you think the chlorine goes?




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artemov
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[*] posted on 30-12-2019 at 20:25


Quote: Originally posted by PirateDocBrown  

Hmm, where do you think the chlorine goes?


So the reaction is

H2SO4 + NaCl -> NaHSO4 + HCl ?

But isn't NaHSO4 + NaCl -> Na2SO4 + HCl used to make HCl as well?
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Fery
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[*] posted on 30-12-2019 at 23:54


Quote: Originally posted by artemov  
So the reaction is
H2SO4 + NaCl -> NaHSO4 + HCl ?

yes

you can neglect the second reaction because pKa2 of H2SO4 = 1.9 and you have very strong acidic solution with pH certainly less than 0
Quote: Originally posted by artemov  

NaHSO4 + NaCl -> Na2SO4 + HCl
the direction of the reaction is not from left to right but from right to left

solubility of NaHSO4 in water is higher than Na2SO4 so putting your solution into freezer is not the right way to go
perhaps BaCl2 could be better (BaSO4 very low solubility) but why to waste BaCl2 when HCl is much more cheaper than BaCl2 and you should also recalculate whether ever Ksp of BaSO4 overpowers pKa2 of H2SO4 so BaSO4 (s) would be formed and not only Ba(HSO4)2
or if your goal is to obtain HCl for some organic reaction maybe you can extract it from the mixture using some organic solvent in which HCl is soluble and which is immiscible with water?
or maybe NaHSO4 present in the solution would not cause any problem for the reaction for which you want to obtain HCl (aq) ?
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artemov
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[*] posted on 31-12-2019 at 00:16


Thanks Fery. Either I will distil off the HCl or use it as it is ... I want to make CrCl3 from chromium metal and HCl, eventually leading to chromate/dichromate.
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