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Saerynide
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Quote: Originally posted by bquirky  | Ive not tried it but i had been under the impression that electrolising salt water with a split cell and a porous membrane (like the old clay pot in
another container) whould create a solution of HCL on one side and solution of NaOH on the other.. has anyone done this and gotten a result ?
Assuming you can only generate a fairly dilute solution of HCL you may be able to upgrade it by heating one sealed vesle of the dilute solution and
bubling it through a smaller volume of cold water.
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I tried this many times years ago. Tried the clay pot, paper towel salt bridge, and aquarium tubing stuffed with polyester. The NaOH solution is
incredibly dilute, and Cl2 is generated, not HCl.
Dissolving the Cl2 in very cold water does not really yield HCl, but just water with a shitload of Cl2 in it. When the solution warms up, ALL the Cl2
will be released. This is how I got poisoned. Took months to get better. Please don't do it.
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Elawr
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....And another intriguing question: anybody knows how the human body synthesizes HCl? I can hardly imagine our body producing sulphuric acid as a
first step; not to speak of elemental chlorine and hydrogen. But how then is it done? ....
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In our bodies HCl is generated by gastric parietal cells using a subcellular organelle called a proton pump. This is a structure that spans the
mitochondrial membrane, creating a channel through which individual protons are selectively moved. The hydrolysis of ATP to ADP provides energy to
drive a conformational change within the proton pump which forces protons through. An excess of protons outside the mitochondria results, creating an
electrochemical gradient that moves chloride ions passively across the gap through another specific channel.
The mechanism is sufficiently robust that pH levels as low as around 2 are attained for gastric juice, before being transported out of the cell into
the gastric secretory ducts.
Pretty strong stuff stomach acid is!
[Edited on 11-4-2009 by Elawr]
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Daddy
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This is very interesting. So our body is still much more "advanced" technology than our laboratories!
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Heating NaHSO4 with NaCl (in a test tube or flask) is probably the easiest OTC method for HCl production.
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... but in order to produce NaHSO4 I would still need sulphuric acid, wouldn't I? Or how else could I obtain it?
- Somebody has tried with phosphoric acid? (I have not so much time for experiments, but once I find out how to make phosphoric acid, I might try it.)
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hissingnoise
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Sulphuric acid will react with NaCl at RT; heat is needed only when the initial vigorous reaction subsides.
If you can get H2SO4 draincleaner you don't need bisulphate. . .
[Edited on 11-4-2009 by hissingnoise]
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woelen
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In a place where HCl will be taken off the shelves, conc. H2SO4 certainly will not be available. So, I'm afraid this method is not of any use for
Daddy. The method, suggested by garage chemist with NaHSO4 indeed is the best one. I tried this as well and it works quite well. You only need to use
some excess NaHSO4 and need to provide sufficient heat. NaHSO4 (pH-minus for swimming pools) melts fairly easily. You can do this in a metal vessel.
The vessel certainly will corrode, but the HCl still is pure, all contamination will remain behind in the vessel.
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hissingnoise
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It's hard to see how the PTB could justify outlawing HCl for cleaning masonry or H2SO4 for unblocking drains---but if Daddy was really stuck he could
surely get battery acid and boil that down---failing that there's always the volcanos.
OK, that's not really serious---lugging filled carboys down a steep cone might be heavy exertion.
But then, there's always coca leaves. . .
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JohnWW
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HCl is commonly industrially produced as a byproduct of chlorination reactions; for example, the chlorination of slaked lime, Ca(OH)2, to obtain
"chloride of lime" used as a swimming-pool disinfectant; and chlorinations of hydrocarbons to produce chlorinated hydrocarbons for various purposes,
e.g. vinyl chloride used to make PVC, and chlorocarbon insecticides although these are now banned for agricultural use.
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Daddy
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| Quote: |
but if Daddy was really stuck he could surely get battery acid and boil that down
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yes, that was the only way I was able to obtain H2SO4... now, I have still a bottle of HCl in stock and I am not using a lot, so it is not that
urgent.
I was just curious about the alternative with phosphoric acid, and I have not a lot of experience, but I would be interested to know if someone has
tried that.
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hissingnoise
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Yes, you can do it with phosphoric acid, but heating may be necessary to start the reaction.
If getting phosphoric is easy for you, your problem is solved. . .
Making H3PO4 is a different story, though!
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woelen
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Yes, with H3PO4 it actually is very simple. First boil down the H3PO4, such that it becomes concentrated. Keep on boiling, until the temperature of
the liquid goes well above 100 C (e.g. 130 C). Then stop boiling. You should not go further, as that makes glassy and syruppy derivatives of
phosphoric acid like pyrophosphoric acid and metaphosphoric acid.
To the acid you add solid NaCl and then you carefully heat. Gaseous HCl escapes and this can be dissolved in water by putting an inverted funnel just
a few mm below the surface of the water and leading the HCl gas to this funnel through a flexible tube. In this way you can also make HBr.
Do the heating of the phosphoric acid in a metal can, not in good glassware. Hot concentrated phosphoric acid slowly attacks glassware. So, use old
glassware which may become matte/milky, or use some throw-away metal can.
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chief
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There's no way around electrolyzing Na2SO4, from some starting-batch of H2SO4 and NaCl ;
:: then by electrolysis : Na2SO4 ==> H2SO4 + NaOH
:: H2SO4 + cheap NaCl ==> more HCl and Na2SO4, etc.
Also worth implementing because of the constant souce of NaOH. Maybe the electrodes for this don't have to be as good as for the chlorate cell ; eg.
Pb as anode should do, and stainless steel as kathode _will_ do.
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hissingnoise
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I hope I haven't misread your post chief, but electrolysis of Na2SO4 does not produce H2SO4 + NaOH, if that's what you're suggesting. . .
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nitric
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the home method for those without H2SO4 is to use NaHSO4 + NaCl --> HCl + Na2SO4
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DJF90
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woelen: I apologise, I should have checked my electrodes before posting.
nitric: If you cared to read the thread then you'll see this was covered by garage chemist in the last post of the first page. With this hobby there
is often more than one way to skin a cat, as it were, so saying "the home method for" this or that is often only one of many, which may or may not be
appropriate depending upon the resources of the individual members.
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nitric
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oh sorry, i've just didn't have the patience to read it all, i've just seen this method a lot for easy, OTC, HCl
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DJF90
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Any HCl formed would instantly react with the carbonate. You said yourself that the Gibb's free energy is positive over most temperatures...
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sakshaug007
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| Quote: Originally posted by DJF90 | | Any HCl formed would instantly react with the carbonate. You said yourself that the Gibb's free energy is positive over most temperatures...
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Oh carbonate duh. lol!
Thanks
"Think before you type.."
"If everyone knew everything what would be the point?"
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DJF90
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We all do it sometimes. I've always wandered how easy it would be to control the reaction between hydrogen and chlorine gases... I'm sure I read
somewhere that the reaction can be explosively fast.
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Saerynide
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I was always under the impression that the reaction occurs exhorably slowly without UV light, but once UV hits it, it pretty much explodes.
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chief
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@hissingnoise" Wasn't there a thread by "der alte", where he did exacly that ? With a diaphragma, of course ... .
What else would one expect from electrolysis of Na2SO4 ??? The NaHSO4, although available even here in germany, must always be bought (6-7 EUR/kg),
while a set-up electrolytic cell can just be used ever again ...
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hissingnoise
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I haven't seen it, chief; if I had I'd be real excited.
H2SO4 and NaOH by electrolysis would be breakthrough-stuff, surely?
Am I still missing something here?
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chief
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Where's the problem ?
==> SO4(2-) goes to the anode, reacting with water to H2SO4
==> menawhile 2Na+ go to the Kathode, givin NaOH
Without a diaphragma both then can react again, to Na2SO4 + H2O ; but with a diaphragma ....
Same possible for many other acids from their salts ...
"Der Alte" really tried this, is described in some H2SO4-manufacturing thread ; so the H2SO4 can forever be recycled, and just reacted with fresh NaCl
each time for new HCl ; NaCl in ==> HCl + NaOH out.
In industry there are more efficient ways to produce each of the compounds, on the larger scale ...
[Edited on 16-4-2009 by chief]
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hissingnoise
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You're right chief, I found DerAlte's thread, I posted on it myself (absentmindedly), but it's impractical as the conc. afforded was only 20%---way
too dilute and the process, IIRC seriously energetically inefficient.
Using that process would be frustrating in the extreme. . .
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chief
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Only 20 %, but that doesn't matter in this case:
==> HCl-gas has some solubility, which decreases with temperature, so some of it may be gassed out even from a dilute solution like that, which
would stem from reacting such a 20 %-Solution with NaCl
==> since the wanted educt is a gas, HCl, it doesn't matter if the H2SO4 is impure and contains any salts etc.
==> alls the salts in solution are part of the process, and can be left there
So at most, depending on the HCl-solubility, the 20% H2SO4 would at most have to be concentrated to 40 % or something like that.
Also: Since the purity of the H2SO4 plays no role, the conc. of it may be driven up way higher ; "der alte" surely hat to consider the end-purity of
the H2SO4 in his process, but for making HCl it plays no role.
And finally: The energetic efficiency may be not too bad when compared to having to buy any chemicals ; also: Will it be worse than with the more
complicated chlorate-production ? H2SO4 from a salt is only a electrolytic separation, not such a complicated oxidation like with the chlorate ... ;
and even on the chlorate it's agreed upon that making it oneself is economically competitive ...
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chief
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Well, second thought about it: Maybe after a while of electyrolyzing/ reusing the H2SO4-brine there would be some buildup of HClO3 or HClO4 ...
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