ChemistryForever
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37% HCl from 20%HCl
Would you need to bubble a large excess of HCl gas to a 20% HCl solution to get to 37% ? I mean, are the last percentages, like after 33 or 34% hard
to obtain or the hcl solution will continue to "eat" the gas pretty much the same as at lower concentrations ?
I want 36-37% because i like when i open the bottle and it fumes, so basically this is the concentration i want, if it is let's say, 34%, it is not as
cool as at 37%. I'm thinking of cooling the water close to 0 degrees C , because at that point is more soluble so i can get to 37-38% and then let it
warm so that if the concentration is over 37% the excess of HCl will evaporate until it reaches 37%
By the way, i have one more question : looking on wikipedia, i see at 20 C that the solubility of HCl is 420g/L of water, which would mean a
concentration of 41.8%. So then, why is there no 41-42% HCl ? Or am I making a calculation mistake ?
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DavidJR
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The dissolution of HCl is quite exothermic, and also the solubility decreases with increasing temperature. So you will definitely want to use good
cooling.
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woelen
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You make a calculation mistake.
If you have 420 grams of HCl and add that to 1 liter of water, then you have 1420 grams of liquid. The concentration then is (420/1420)x100%.
What Wikipedia states, however, is not 420 grams HCl, added to a liter of water, but that in a concentrated solution you have 420 grams of HCl per
liter of that solution. The density of concentrated HCl is larger than 1 kg/liter (IIRC somewhere around 1.15 kg per liter). So, one liter of conc.
HCl is appr. 1150 grams. If you have 420 grams of HCl and the total weight is around 1150 grams, then you have a percentage (by weight) of 36% to 37%,
and that is exactly what you can buy at most. Such 36...37% solutions are strongly fuming. For this reason, commercial HCl frequently has a somewhat
lower concentration (around 30% by weight). This still is fuming, but not as badly as the 37% stuff.
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Sulaiman
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I've not tried but this document should help.
Distillation from 25% w/w CaCl2 looks straightforward.
Attachment: Hydrochloric Acid Concentration.pdf (73kB)
This file has been downloaded 937 times
P.S. I am considering diluting my 36% HCl to 20% to reduce the fuming 
[Edited on 23-1-2019 by Sulaiman]
CAUTION : Hobby Chemist, not Professional or even Amateur
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AJKOER
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Now that you have more concentrated HCl, read my comment below before perhaps unnecessarily using it all up!
Apparently, you can composed a mix of your weaker HCl with a strong dose of CaCl2, to increase the so called activity coefficient. My prior research
(see a cited source at http://www.sciencemadness.org/talk/viewthread.php?tid=38378#... claiming that 2M HCl in 3M MgCl2 or CaCl2,..behaves like 7M HCl ) suggests, for
example, in a leaching application, the HCl/CaCl2 mix may be more effective (and cheaper) that your distillation derived more concentrated HCl.
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MrHomeScientist
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If your only reason for making such concentrated solution is that you "like" it or it's "cool", you may want to reconsider. Such strong fuming would
make working with it very unpleasant, and would quickly and severely corrode any metal in the same room as the bottle. Even if capped tightly, the
fumes have a higher likelihood of escaping. I wouldn't go through the trouble of concentrating your acid unless you actually need it for something.
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Sulaiman
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I disagree,
if you want to make a little then go ahead,
the reason that others can advise against it is because they have probably already 'been there, done that'
The warnings are good though and should be considered.
If you are afraid of a nosefull of HCl gas then you should choose a safer* forum
* dull, boring, uninspiring
CAUTION : Hobby Chemist, not Professional or even Amateur
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j_sum1
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Well, I might be tempted to make 50 mL or so of concentrated HCl just for the experience and to see how concentrated I could get it. But I cannot
actually think of any applications where I would need it. I would probably just dump it in my 30% bulk container when finished - after density
measurements and titration.
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woelen
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There is a remarkable difference between 30% HCl and 37% HCl. The latter is intensely fuming. It also, when mixed with water, leads to a noticeable
heating of the liquid. The mix does not become hot (such as when mixing conc. H2SO4 with water), but you definitely can feel the higher temperature.
This is because 37% HCl contains quite some molecular HCl, which on dilution is split into aquated H(+) and Cl(-).
For practical purposes, the 30% stuff works fine when conc. HCl is needed, and this is much easier on storage and handling.
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chornedsnorkack
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A table at Wikipedia:
https://en.wikipedia.org/wiki/Hydrochloric_acid
goes quite detailed about 38 % hydrochloric acid, specifying density 1,189, 452 g/l HCl, vapour pressure 28,3 kPa at 20 C and boiling at 48 Celsius.
For comparison, 36 % acid has vapour pressure at 20 C of just 14,5 kPa, and boils at 61 Celsius. 30 % acid has vapour pressure of 2,13 kPa and boils
at 90 Celsius.
It is understandable that commercial suppliers are reluctant to transport and sell 38 % and more acid. Does not mean you cannot make it at low
temperature, and boil off excess HCl on warming.
Nor are you limited to cooling to 0 Celsius - freezing point is lower! You might, for example, synthesize 50 % acid, freeze it at -18 Celsius as
HCl*H2O, and store as solid. What is the boiling point of 50 % acid?
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