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dann2
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[*] posted on 28-11-2007 at 19:53


Hello,

Reading an 'H2SO4' thread Chloric1 said:

The cheap black stuff I bought is 90%. If diluted with water the black separates. It is charcoal. I get crystal clear dilute acid but why trouble with the boiling scenario. Would like to try rooto or that stuff labeled "liquid fire". Any case any of these would be satisfactory for drying chlorine or other gasses that don't dissolve/react,dissolving ammonium chloride to make anhydrous hydrochloric acid,catalyst in ester or ether prep etc. If you decide to concentrate the dilute acid by heat make sure it boils at 338 degrees C!

Can 37% HCl acid be make using H2SO4 (Conc.) + Ammonium Chloride.?? (Sorry for doubting you Chloric1 :()
Sounds like the way to go if you need conc. HCl, much handier than messing around making HCl gas and bubbling into water or more dilute HCl acid.
Then again adding dilute HCl to conc. Sulphuric is fairly easy but you still need a distilling outfit.

Dann2
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cnidocyte
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[*] posted on 25-1-2011 at 01:08


Sorry if this has been asked a million times but what temperature does hydrochloric acid distill at? Does it distill over at the same temperature as the water?
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cnidocyte
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[*] posted on 31-1-2011 at 13:07


I almost had a serious accident just there. I was distilling HCl and I checked on it and noticed it was bumping heavily because I forgot to turn the stirrer on. I turned the stirrer on. Big mistake. The still head went flying and acid shot out of the flask. To make matters far worse, I was using an oil bath so the acid solution got into the hot oil. Its a good thing I wasn't standing too near to the setup or I would probably be in the back of an ambulance right now. Luckily I didn't get any acid or oil on me. I learned a lesson I'll never forget. Never turn on the stirrer when the solution is already boiling. I knew that its dangerous to add boiling chips to an already boiling solution but I didn't know the same thing went for turning on the stirrer. Lesson learned.
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Cynic
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[*] posted on 1-2-2011 at 12:37


>I almost had a serious accident just there. I was distilling HCl and I checked on it and noticed it was bumping heavily because I forgot to turn the stirrer on.

Been lurking here for some time and am learning a great deal - thanks. Still not too up-to-speed on the practical side of things. Could some one please explain to a chemistry newbie how this operation should be performed. So I don't kill myself when I try it.

I looked up "bumping" so I now know what that means. I have never seen anything other than water boil - do other mixtures have a different boiling pattern (more violent etc)? After thinking a bit I can see how this might be the case due to poor heat transmission in the liquid, different viscosities etc. How should the distillation have been done? Should the hot plate temperature have been kept lower to just barely boil the HCL? Should anti-bumping chips have been added as a matter of course. Do you always add them? Are there safe ways of doing it without them? What solutions do the bumping chips react with and so you cannot add them to it. I know none of this and I would welcome all advice.

I was thinking of buying a bit of distillation glassware on ebay and having a go myself. If I wanted to practice this sort of separation by distillation does anybody have a suggestion regarding two common household liquids could I mix together and then separate due to the different boiling temperatures? Ideally it would be two liquids where the only danger is the heat rather than hot and caustic and explosive.

Edit: a bit more thought on the above suggested cheap vodka might not be a bad thing to try distillation on. Any opinions and advice on that?




[Edited on 1-2-2011 by Cynic]
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bbartlog
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[*] posted on 1-2-2011 at 13:24


Quote:
Should anti-bumping chips have been added as a matter of course.


Yes. IMO anytime you are boiling something you need boiling chips (water, too, will bump violently if it's distilled and the vessel is clean). I used to use some little rugose bits of quartz but have switched to carbon boiling chips. Graphite doesn't react with much... I guess if I were trying to distill piranha solution or something they might be attacked.
Keeping temperatures low doesn't help all that much. If you're pushing enough heat to boil something, it will be possible for it to superheat if there are not enough nucleation sites. Statistically I suppose there might be a little less bumping but then you'd also be boiling for longer, so it's not much of a solution.
One easy distillation if you just want practice is methanol and water; in the USA windshield washer fluid is 25-30% methanol and can easily be distilled to separate the methanol and water (along with colorants). Has the advantage over ethanol distillation that you have no azeotrope to deal with.
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[*] posted on 1-2-2011 at 13:49


Boiling in lab glass does tend to result in bumping as the surfaces are so smooth.
Normal cooking pans have rough areas that let bubbles form and allow boiling.
So we either use stirrers, bumping granules or an air leak to provide nucleation sites where bubbles can form.
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cnidocyte
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[*] posted on 2-2-2011 at 12:11


Quote: Originally posted by Cynic  

Been lurking here for some time and am learning a great deal - thanks. Still not too up-to-speed on the practical side of things. Could some one please explain to a chemistry newbie how this operation should be performed. So I don't kill myself when I try it.

I know exactly what I did wrong now. What I wasn't aware of was that when a solution is bumping (huge bubbles forming that cause the whole flask to shake as opposed to many little bubbles) it means that the solution is superheated and very unstable. Even a small shock (in my case turning on the stirrer) can cause the solution to "flash boil" meaning all the superheated liquid turns to vapour at once. If you understand this concept then you won't make the mistake I did. How I should have performed the operation is I should have had the stirrer on or put some boiling chips in the flask before I heated the solution which would have prevented superheating and allowed it to boil smoothly. Instead I forgot to turn the stirrer on so there was nothing to help the solution start boiling and as a result it became superheated. If a solution becomes superheated then remember that any small aggitation could cause the thing to explode (doesn't actually explode but I like to think of it like that) so just turn off the heat and let it cool down so you can put in some boiling chips or turn on the stirrer and start over. You'll know what bumping is when you see it, if the beaker or flask isn't clamped down then it'll shake every time one of those massive bubbles forms.

I've never seen water bump myself either but I don't see why it wouldn't. You need the hotplate temperature to be over the boiling point of what your distilling because there will always be heat losses. Yep if you don't have a magnetic stirrer or other means of facilitating boiling then you should always add boiling chips. Safe ways of boiling without them are stirring, bubbling inert gas into the solution and probably many more methods I'm not aware of. The boiling chips don't "react" with anything, they provide nucleation sites which are basically just air pockets where gas bubbles can form.

I highly recommend getting a distillation kit on ebay. You can find some insanely good deals there as sometimes people who just need to get rid of lab equipment put it up there. I recommend you start with a substance with a low boiling point such as dichloromethane from paint stripper or acetone from nail varnish remover or even methanol from paint stripper. A water bath will provide enough heat to distill each of those compounds and if those solvents superheat, I don't think the flash boiling would be as violent as higher BP solvents.
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edgecase
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[*] posted on 14-6-2012 at 05:09


Old topic but I thought I'd reply for completeness:

Boiling chips apparently don't work for vacuum distillation, since the air pockets are essentially missing. Also, the alumina variety I have "tamer tabs" says on the label it isn't compatible with conc. H2SO4.

This is the first I've heard of the air leak though.

I was searching for this topic since I have produced weak (pH 0) HCl solution by pyrolysis of polyvinylchloride. It works as an analytical technique, but let me tell you, you'd have to be *way* more desperate than the guy who started this thread to try to produce HCl this way.
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metalresearcher
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[*] posted on 21-10-2012 at 03:43


I have 10% hardware store grade hydrochloric acid which I want to concentrate to 36%.

I can distill it thereby concentrating the residu approaching the 20% azeotrope and then letting it cool down and adding CaCl2 to it and filtering the CaCl2, but many of the CaCl2 will dissolve in the water.

In found this site:

http://www.erowid.org/archive/rhodium/chemistry/equipment/ca...

Has somebody ideas on this ?

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triplepoint
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[*] posted on 21-10-2012 at 09:04


I know this sounds obvious and self-evident, but if you do get something bumping and boiling after having forgotten boiling chips or stirring, TURN OFF the heat. Let it cool, then begin again.
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weschem
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[*] posted on 12-11-2012 at 22:28


There is a method. youll need 3 containers that are safe to hold HCl. 1 container must be able to fit the other 2. Fill one container with HCl and fill the other container with distilled water. Put both containers in a larger container and seal it air tight with parafilm or wax around the edges. what happens is the hcl fumes from the impure hcl will infuse the distilled water to virtually 100% pure acs reagent grade HCl. Downside it cuts the concentration to about half and takes about a week or 2. This is not too big of a deal because you end up diluting HCl to this concentration or lower.
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Oromis
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[*] posted on 13-11-2012 at 17:13


I don't know how it is else where but in Australia you can buy 37% HCl solution from pool shops for about $10-$15. So it may be worth checking out to your local pool shop for a more pure starting solution. (The solution is very clear and when the bottles open fumes pour out)
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tetrahedron
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[*] posted on 14-11-2012 at 03:34


Quote: Originally posted by weschem  
There is a method. youll need 3 containers that are safe to hold HCl. 1 container must be able to fit the other 2. Fill one container with HCl and fill the other container with distilled water. Put both containers in a larger container and seal it air tight with parafilm or wax around the edges. what happens is the hcl fumes from the impure hcl will infuse the distilled water to virtually 100% pure acs reagent grade HCl. Downside it cuts the concentration to about half and takes about a week or 2. This is not too big of a deal because you end up diluting HCl to this concentration or lower.

nobody says you have to take the same volume of crude 37% hydrochloric acid and distilled water. if the former is about twice the latter then you'll end up with 2/3 the initial concentration (25%), if three times then 3/4 (28%) etc, so any concentration up to 37% can be reached.
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weschem
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[*] posted on 18-11-2012 at 20:43


[/rquote] nobody says you have to take the same volume of crude 37% hydrochloric acid and distilled water. if the former is about twice the latter then you'll end up with 2/3 the initial concentration (25%), if three times then 3/4 (28%) etc, so any concentration up to 37% can be reached.[/rquote]

That's not exactly how it works. You're assuming that all of the HCl in its entirety is infusing into the water. Doesn't matter if you put more or less water. The process of diffusion applies. Diffusion is where particles in an area of high concentration move to an area of low concentration till the two areas have the same concentration and are isotonic. So already you know it'll be half. Plus you must account for some of the concentration still in gaseous form so it'll be a little less than half. You can cut down on the gaseous concentration by cooling the system.
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tetrahedron
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thumbdown.gif posted on 19-11-2012 at 05:32


Quote: Originally posted by weschem  
till the two areas have the same concentration and are isotonic.

this is about the only smart thing you said. think about it: you put 1L conc HCl (12M) and 1mL H2O in your device and you claim you obtain 1001mL 6M acid? how do you account for the loss of 5.994 moles of HCl?

ok this is an extreme case, but as i said the whole range of concentrations (0-12M) is attainable.
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weschem
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[*] posted on 19-11-2012 at 09:21


Wow really? There is no loss smart guy. The 1L of the impure muriatic acid still contains about half the concentration and the container containing the water contains the rest of the concentration and there is still some left over as fumes in the container. Doesnt matter if you put less distilled water it will still have the same concentration. Look why don't you try this experiment out yourself before you start running your mouth and see what kind of results you get. I have done this experiment and have done titrations to verify results.
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[*] posted on 19-11-2012 at 11:24


Where I live, crude muriatic is cheap, and pure HCl unobtainium, so I tried the "1 week slow HCl gas diffusion" method.

I didn't get fancy... a PE shoe box storage container, and a 1 liter beaker. Into the beaker I added about 500 ml of distilled H2O. Into the floor of the box, I dumped a load of muriatic. The idea is to have large surface areas available.

After a week, I removed the beaker. Dumped the muriatic into my pool, which needed it anyhow, and the rig can be re-set with fresh muriatic. This can be repeated until the clean HCl in the beaker is close to the concentration of the original muriatic, which around here is 32%.

I have not tested yet the clean HCl thus produced, but it is quite strong, colorless, and free of those nasty impurities. The process is slow but super low-tech.

[Edited on 19-11-2012 by Swede]
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Swede
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[*] posted on 19-11-2012 at 12:10


I just checked the single gas diffusion run. From about 2/3 gallon of crude muriatic into 500 ml of distilled H2O, the 20 baume muriatic produced 16 baume clean HCl.

That's 1.160 vs. 1.125 specific gravity, or 32% to about 25%. Not bad at all. Obviously, to get results like that, you have to overwhelm the distilled water volume with a LOT of crude muriatic.

Just for fun, I set it back up; put the 500 ml of clean 25% HCl back into the rig, and added another 2000ml or so 32% muriatic. My guess would be, after another week, the sweet HCl will probably be close to 28% or 29%.
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watson.fawkes
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[*] posted on 19-11-2012 at 15:04


Quote: Originally posted by tetrahedron  
nobody says you have to take the same volume of crude 37% hydrochloric acid and distilled water. if the former is about twice the latter then you'll end up with 2/3 the initial concentration (25%), if three times then 3/4 (28%) etc, so any concentration up to 37% can be reached.
These assertions are in contradiction to Henry's law, which is that the concentration of gas that will dissolve in liquid is proportional to the partial pressure of the gas. Henry's law is valid at constant temperature, and there's no mention of anything like a temperature difference.

EDIT: I have misunderstood the language tetrahedron used. Retracted.

[Edited on 20-11-2012 by watson.fawkes]
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tetrahedron
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shocked.gif posted on 19-11-2012 at 16:29


whoa i didn't expect so much criticism for an observation that seemed completely straightforward to me.

my only assumption was that various strengths of HCl solutions, when enclosed in the same container, would tend to become
Quote: Originally posted by weschem  
isotonic.


accordingly, from a volume V1 of HCl at molarity c1 and a volume V2 of H2O you'll get a total volume V1 + V2 containing c1 * V1 moles of HCl, i.e. the concentration (in both solutions) is eventually reduced to V1 / (V1 + V2) of the original. of course it will take time to reach arbitrarily close to the equilibrium.

swede's result is corroborating:
Quote: Originally posted by Swede  
From about 2/3 gallon of crude muriatic into 500 ml of distilled H2O, the 20 baume muriatic produced 16 baume clean HCl.

That's 1.160 vs. 1.125 specific gravity, or 32% to about 25%.


the half-assed invocation of
Quote: Originally posted by watson.fawkes  
Henry's law, which is that the concentration of gas that will dissolve in liquid is proportional to the partial pressure of the gas

(which holds only for asymptotically dilute solutions of gases that don't dissociate in the solvent) does not lead to a contradiction: both solutions keep exchanging HCl with the atmosphere. the partial pressure of HCl in the container is sustained by the stronger 'crude' solution, until the 'absorbing' solution has reached the same strength. at equilibrium, the partial pressure is constant, which means that the rate of exchange is the same (no matter the exact mathematical relationship that exists between partial pressure and concentration). the diffusion can be accelerated by placing the container in a warmer environment, then cooling it back down in order to reabsorb the extra HCl pressure, and this has no influence on the final equilibrium (a state function).

as a final remark, given the quantities mentioned, the actual amount of gaseous HCl present at any time in the container is negligible. the only reasonable complaint that i would have expected (about the small change in volumes due to the solute being a gas) didn't come up.
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[*] posted on 15-12-2017 at 22:37


I'm giving this a go in real time, inspired by Nux Vomica's YouTube.

https://www.youtube.com/watch?v=WQ5Vn0is9_Y

1513406188072-2023411064.jpg - 981kB

Differences between his and mine:
He used a Graham condenser, with the coils loaded with water, I only had a Leibig, and bubbled the output into the receiver, which started out with a small bit of water.
He used boiling stones, I had a mag stirbar.
Looks like his boiling flask is 500, mine is 1000. I monitored temp, and saw it hold at the azeotropic BP.
I treated the fume exhaust through a grad cylinder bubbler.


[Edited on 12/16/17 by PirateDocBrown]
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PirateDocBrown
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[*] posted on 15-12-2017 at 23:56


So, yeah, lots of HCl outgassing, the boiling flask bubbles away merrily, yet little condenses. The receiver started out with some distilled water, with a tube attached to the adapter, so as to allow it to bubble under the water level. The gas takeoff was set to bubble into NaHCO3 in the grad cylinder.

I ran out of ice, so more later.

Takeaway:
LOTS of HCl comes off, more than a small amount of water can absorb, even at 0 degrees.
There was nowhere near enough NaHCO3, it was rapidly neutralized, with HCl then coming off after.
Therefore, good ventilation is a must. PPE too.
Don't use NaOH as your neutralizer, the heat of neutralization is enough to boil the water, then melt the Tygon, and even char it.
Suckback is a major consideration here, plan ahead.

Output is limited by the azeotrope of HCl/H2O, about 20%, but if HCl gas is absorbed into that cold, it could be more.
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