ampakine
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Distilling fuming hydrochloric acid
If I was to produce a concentrated HCl solution (lets say 70% w/w) by reacting NaCl with H2SO4 then distilling this solution would I be right in
assuming I'll end up with a constant boiling HCl solution of 20% (or whatever its azeotropic ratio is) w/w?
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DJF90
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You're never going to reach a concentration of 70% w/w. It'll only dissolve so much - 37% is about the point where it is saturated. Distillation of
37% will first drive off hydrogen chloride gas, and then the azeotrope of 20ish% will come over. Personally I wouldn't bother; concentrated
hydrochloric acid fumes enough without trying to distil it!
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mr.crow
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You may be thinking of HCl the same way as nitric acid. Hydrochloric acid is HCl gas dissolved in water, where as nitric acid is a liquid mixed with
water.
You can make HCl gas (nasty!) with NaCl and H2SO4, then dissolve it in water with an inverted funnel. Keep the water in an ice bath too.
If you really want to distill it (like hardware store acid) dilute it to 20% first then distill the azeotrope.
Double, double toil and trouble; Fire burn, and caldron bubble
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ampakine
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mr.crow: I assumed the HCl would be dissolved in the water as soon as its formed. Can you elaborate on this inverted funnel setup a bit? Sounds like
there'd be no need for distillation if the only thing you're dissolving in the water is HCl gas.
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entropy51
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Quote: Originally posted by ampakine  | | mr.crow: Can you elaborate on this inverted funnel setup a bit? Sounds like there'd be no need for distillation if the only thing you're dissolving in
the water is HCl gas. |
| Quote: Originally posted by woelen | A suckback IS bad in your case. The melt is hot and contains a lot of H2SO4. If you get the water in this hot melt, then you'll severely regret what
you have done! BE CAREFUL!
A safe way of preventing suckback is the use of a small inverted funnel, which you immerse just a mm into the liquid, which must be in a fairly tall
beaker (total surface of liquid must not be much larger than surface liquid, covered by the inverted funnel opening). If HCl gas reaches the surface
of the liquid, and liquid is sucked into the inverted funnel, then the level of the liquid will go down, and the funnel is no longer immersed in the
liquid. Some tweaking may be needed to get the level of immersion adjusted well, but this method definitely works and is safe. At any cost should
suckback be prevented with your hot NaCl/H2SO4 melt. |
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