jt - 8-1-2005 at 21:30
I have some drain cleaner that contains sodium hydroxide and potassium hydroxide. I want KOH only. How can I extract only the KOH?
I know that I could just buy the KOH but I would like to learn something from this.
Blind Angel - 9-1-2005 at 01:41
The same question is here
budullewraagh - 9-1-2005 at 05:08
actually thats the chlorides
jt - 9-1-2005 at 05:48
I am still not clear on this issue.
Sodium hydroxide and potassium hydroxide, both, are in a solution.
I need to isolate the potassium hydroxide, is there a way to do this?
BromicAcid - 9-1-2005 at 09:16
This seems in my mind to be a difficult separation, generally potassium hydroxide is more soluble in organic solvents then sodium hydroxide so some
may be recoverable with a liquid-liquid extraction.
Another possibility is that potassium peroxide may be less soluble then sodium peroxide, in that case adding concentrated H2O2 to the hydroxides
solution may result in precipitation of potassium peroxide hydrate which would be followed by filtration, washing, and subsequent dissolution and
boiling to destroy peroxide in solution. Those are two reasonable things to consider, if you want to get more radical and invest considerably more
resources, time, and money into the project then what it's worth, there are other ways.....
jt - 9-1-2005 at 09:28
Ok, so if I understand correctly,
1. I could observe the solution and determine if they separated over time.
2. I could add H2O2 and get the KOH to precipitate out, then wash, filter, and boil?
I have let the solution sit all night and I don't notice a separation so I'll try method 2 next.
Thank you for responding
I
BromicAcid - 9-1-2005 at 09:35
There is a little problem with your understanding. What I was saying in the first part was, if you take a solvent that is insoluble in water, an
organic solvent, benzene, or ether being good examples, and shook this solvent with your hydroxide solution then the organic solvent might have
dissolved some of your KOH and it would be dissolved in your organic solvent, which could be removed since it is insoluble in your aqueous solution
and then evaporated to recover your KOH (Although KOH is more soluble in organic solvents then NaOH, I can't think of a solvent that is insoluble
in water that would dissolve a significant amount of KOH, so this method may only give very very small yields).
As for the second part you would precipitate K2O2*2H2O, when you remove this from solution then boil in water it will decompose the peroxide present
and leave behind the KOH, but I don't know the differences in solubilities between the potassium peroxide and sodium peroxide, so your
precipitate will really be of an unknown composition (this precipitation must be done at low temps roughly 0C to work decently).
[Edited on 1/9/2005 by BromicAcid]
jt - 9-1-2005 at 10:47
I think I got it now.
I'm going to try the first method first.
Organic solvent shook with my solution, causes KOH to be dissolved into organic solvent an then I can separate the organic solvent from my solution
because the solvent is insoluble in water. I then evaporate the product and I have KOH, although poor yields.
What I really need to understand is why the solvent dissolves that KOH and not the other, also why the organic solvent isn't soluble in water. As
you can tell, I'm certainly a beginner
chemoleo - 9-1-2005 at 11:34
Jt, I wouldn't bother, not even the first method. It is hardly practical, and will require a large amount of solvents and experimentation, to get
this to work in the first place..
For a quantitative separation of K and Na ions, one normally starts off with a SALT, not a hydroxide, which then can be separated by different
solubilities in water.
Seriously, if you need NaOH, it will be easier to get it by electrolysis of table salt NaCl than by some solvent extraction methods.
Or... just buy NaOH.
jt - 9-1-2005 at 12:17
What I'm trying to achieve is KOH.
I do have some KOH starting to appear as my organic solvent is evaporating but it sure isn't much.
Is there a way to get KOH through electrolysis too? I have a rudimentary set-up with a liter pop bottle, cut in half, and some pencils as electrodes.
JohnWW - 9-1-2005 at 12:49
Alkali metal hydroxides are, in fact, salts; and the molten hydroxides in the absence of air and water can be electrolysed to the metal with the
application of appropriate voltages.
chemoleo - 9-1-2005 at 13:47
Lol, I just knew someone would comment on the 'salt'. Yes, hydroxide is a salt too. But I was referring to salts of stronger acids than
water, such as hydrochloric etc.
Anyway - yes, if, you have KCl or some other potassium salt, make solution in water, and electrolyse it at 15 V and however many Amps required. You
will need a good diaphragm, because the Chlorine being produced at the anode will eat up pretty much anything, including your pencil electrode. On the
cathode you will get the KOH. Make sure the KOH does not ever get into contact with the Cl2 from the anode, else you will get hypochlorite/chlorates,
which you dont want here.
It's quite simple really, as long as the chlorine does not backreact with the KOH.
There are plenty of threads on electrolysis, so you may want to read this to get some idea(s).
jt - 9-1-2005 at 13:58
This sounds interesting.
I will certainly research this but I need to ask a couple of questions.
1. JohnWW said something about doing this in absence of water and air. Does this mean I need to do it in a vacuum?
2. will my plastic soda bottle work as a container for this?
3. Will the KOH build-up on the electrode and/or how will I retrieve this KOH.
neutrino - 9-1-2005 at 16:37
1. No. Isolate it as much as possible from the atmosphere and keep it dry. You can have a small opening to the air without too much trouble or under
an inert blanket gas.
2. No. Strong bases tend to react with just about anything (organic materials, glass, most metals, etc).
3. The KOH should dissolve.
darkflame89 - 10-1-2005 at 02:48
Lol strong bases does react almost about everything, BUT we are producing KOH by electrolysis, which means we need many many days to produce any
sizable conc. of KOH for use, assuming that we are using a 9V battery. So, a plastic soda pop bottle should work just fine. The KOH produced is in
solution, you basically can't do anything about it. I don't you can retrieve it unless you have a good heat source(not sure about this).
unionised - 10-1-2005 at 11:53
KOH solutions will dissolve polyester bottles too.
JohnWW - 10-1-2005 at 12:06
I meant molten hydroxides. No plastic would stand up to the temperatures required. You would probably need a graphite crucible; platinum or nickel
just might stand up to the molten hydroxides.
chemoleo - 10-1-2005 at 12:12
I wonder why you're going on about producing potassium metal from molten KOH, which evidently confused jt .
Anyway, just to clarify - you can do an AQUEOUS electrolysis of KCl/K2SO4/K2CO3 in just about any container, glass, plastic etc is fine. Then
electrolyse this, keeping anode/cathode gasses separate. Also use a diaphragm to facilitate separation of the KOH from the Cl-/Cl2, and to keep
eaten-up electrode material away from the KOH. Beware that toxic chlorine is produced in the case of KCl.
The resulting KOH solution (which has to be tested for remaining chloride, sulphate, whatever) then is boiled down to dryness, and in THIS case you
shouldnt use glass/porcelaine (or polyester 
). Steel will be fine instead.
For storage, any plastic bottle will do.
[Edited on 10-1-2005 by chemoleo]
jt - 10-1-2005 at 16:06
I certainly appreciate all the help.
During the experience I have concluded that there is much to learn.
I'm going to do some reading and simple experiments before I attempt anything this
complicated. It's obvious that I don't understand, completely, what is happening
with electrolysis or any chemical reaction enough to get tricky.