mycotheologist
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Generating Cl2 to make hypochlorite
My attempts using electrolysis of brine as a method of producing reasonable quantities of NaClO were a complete failure but after learning a new
method of producing aqueous ammonia, I've become quite fond of gas bubbling. So I just read about this reaction:
MnO2 + 4 HCl ==> Cl2 + MnCl2 + 2 H2O
in which the MnO2 is heated with concentrated HCl. You bubble the gas through water first to filter out any HCl that escapes the reaction flask. I
don't have the apparatus for this unfortunately, can anyone recommend other simple methods for generating Cl2 gas.
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MrHomeScientist
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I've had good success using calcium hypochlorite and hydrochloric acid, both found at the pool supply store:
Ca(ClO)<sub>2</sub> + 4 HCl → CaCl<sub>2</sub> + 2 H<sub>2</sub>O + 2 Cl<sub>2</sub>
In my experience, the manganese dioxide method is very slow and requires heating. Potassium permanganate works much better instead, but again I prefer
calcium hypochlorite - cheap and easily available. Plus the calcium chloride byproduct can be handy.
I'm sure there are lots of methods around the forum, if you use the search tool.
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Pulverulescent
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| Quote: | | My attempts using electrolysis of brine as a method of producing reasonable quantities of NaClO were a complete failure . . .
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Electrolysis is by far the most convenient route to hypochlorites . . .
Reading up on the subject to avoid failure in future would be my suggestion!
"I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones"
A Einstein
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mycotheologist
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Quote: Originally posted by MrHomeScientist  | | Potassium permanganate works much better instead, but again I prefer calcium hypochlorite - cheap and easily available. Plus the calcium chloride
byproduct can be handy. |
Does the permanganate method require heating?
Really? I was mainly disuaded by the opinions of others on the forum rather than my failure but I've seen a few of your posts (and thus trust your
opinion) so I'll go back to the electrolysis approach. Thanks a lot!
[Edited on 10-4-2012 by mycotheologist]
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Pulverulescent
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You're welcome ─ a simple chlorate-cell run at low temp. and high pH will get the job done.
"I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones"
A Einstein
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MrHomeScientist
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Nope, it works just fine at room temperature. Permanganate can sometimes be expensive and hard to find for some people, though. See my video on
isolating the halogens for this reaction in action: http://www.youtube.com/watch?v=OoS3q1C8zts
The chlorine part starts at about 5:00 in.
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barley81
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TCCA (trichloroisocyanuric acid) is cheap and works quite well. Here is a link to the thread here:
(the method with calcium hypochlorite is also described)
http://www.sciencemadness.org/talk/viewthread.php?tid=9713#p...
Method for making sodium hypochlorite from chlorine (frogfot's site):
http://web.archive.org/web/20070416101853/http://frogfot.com...
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dann2
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Good ref is here:
http://www.oxidizing.110mb.com/chlorate/further/ullman.pdf
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annaandherdad
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| Quote: Originally posted by MrHomeScientist | I've had good success using calcium hypochlorite and hydrochloric acid, both found at the pool supply store:
Ca(ClO)<sub>2</sub> + 4 HCl → CaCl<sub>2</sub> + 2 H<sub>2</sub>O + 2 Cl<sub>2</sub>
In my experience, the manganese dioxide method is very slow and requires heating. Potassium permanganate works much better instead, but again I prefer
calcium hypochlorite - cheap and easily available. Plus the calcium chloride byproduct can be handy.
I'm sure there are lots of methods around the forum, if you use the search tool. |
I haven't tried to make chlorine but I anticipate a problem that suggests that the MnO2 method might be best. It is that in the other methods
(potassium permanganate, bleach, etc) you get the chlorine as soon as you add the HCl. Now I don't have a pressure equalized funnel, so I have to use
a thistle tube or some such thing for adding liquid (HCl in this case) to a reaction vessel (a flask). And some amount of gas will come back up the
thistle tube, which, considering that it's chlorine, is not so good.
But in the MnO2 method, I measure the amount of MnO2 and HCl I need, add them together cold, then stopper the flask and warm it for the Cl2 to come
over. It doesn't come out all at once, and none escapes.
I enjoy your videos, by the way. They're good science.
Any other SF Bay chemists?
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MrHomeScientist
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| Quote: Originally posted by annaandherdad | I haven't tried to make chlorine but I anticipate a problem that suggests that the MnO2 method might be best. It is that in the other methods
(potassium permanganate, bleach, etc) you get the chlorine as soon as you add the HCl. Now I don't have a pressure equalized funnel, so I have to use
a thistle tube or some such thing for adding liquid (HCl in this case) to a reaction vessel (a flask). And some amount of gas will come back up the
thistle tube, which, considering that it's chlorine, is not so good.
But in the MnO2 method, I measure the amount of MnO2 and HCl I need, add them together cold, then stopper the flask and warm it for the Cl2 to come
over. It doesn't come out all at once, and none escapes.
I enjoy your videos, by the way. They're good science. |
Thanks! That's a good point you make; I've ran into the same issue pretty often. I only recently got a pressure equalized addition funnel, so before
that I would have to add the reactants and quickly stopper the flask again. This inevitably would result in a burst of gas escaping, which is never
fun. I haven't had much luck with MnO2 myself, but that was back when I was first starting out in chemistry so maybe you'll do better. Good luck, and
always be careful working with chlorine! All the halogens always give me day-long headaches whenever I work with them  Really need to build that fume hood one of these days.
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woelen
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| Quote: Originally posted by Pulverulescent | | Quote: | Electrolysis is by far the most convenient route to hypochlorites . . .
Reading up on the subject to avoid failure in future would be my suggestion!
|
I strongly disagree. Making hypochlorites without chlorate contaminsation is nearly impossible with a
simple home-made electrolysis cell and besides that, this process is slow and if the wrong type of anode is used, it also produces a lot of crap (e.g.
finely powdered graphite) in your solution. In my opinion, electrolysis is next to useless for making hypochlorite.
I would indeed make chlorine by chemical means. Use MnO2 if you want a steady stream of chlorine, which can be controlled by means of heat. Use TCCA
or Ca(ClO)2 if you have a dripping funnel, with which you easily can regulate the amount of HCl, dripping on the solid material. If you use Ca(ClO)2
then you always will have some CO2 as well. Swimming pool Ca(ClO)2 always contains some CaCO3 as well. TCCA and MnO2 do not suffer from this problem.
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Pulverulescent
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| Quote: | | In my opinion, electrolysis is next to useless for making hypochlorite. |
Your negative opinion of the method surprises me woelen!
I still find electrolysis to be the most convenient method, requiring as it does only common salt, electrodes and a PSU . . .
No acid, alkali or oxidiser needed!
Low temperature electrolysis at high pH will prevent disproportionation to chlorate.
"I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones"
A Einstein
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