elementcollector1
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KOH Impurity
I've been scratching my head over this recently. Upon electrolysis of KCl in two half-cells, with a steel cathode and carbon (lantern battery) anode,
I have obtained a yellow solution. This yellow color also seems to appear in VERY concentrated solutions of store-bought NaOH, but the KOH in this
beaker can't possibly be that strong. What, then, is this? I would think iron, but as far as I know iron metal and steel are not amphoteric. Also,
it's the cathode: no ions should be going *into* solution on that end. Your thoughts?
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bahamuth
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Not that I am a electrolysis guru but it is well known that carbon gives a brown yellowish solution if present in small enough amounts. So it sounds
reasonable that it would be in the store bought NaOH too..
Any sufficiently advanced technology is indistinguishable from magic.
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elementcollector1
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Carbon? I was completely unaware that carbon gives this color solution. Are you sure it's not resins and such embedded in the carbon to hold it
together?
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ewalcacer
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I have no clue about what they use to make those batteries electrodes but it might not be pure carbon. You should try this type of grafite electrode:
http://www.asia.ru/images/target/img/product/11/67/01/116701...
It's a welding grade grafite electrode and it's what I use for aqueous electrolysis. Never had a problem.
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blogfast25
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Quote: Originally posted by elementcollector1  | | Carbon? I was completely unaware that carbon gives this color solution. Are you sure it's not resins and such embedded in the carbon to hold it
together? |
Yes, resins are the likely cause. Try adding some hydrogen peroxide and gentle heating. If the colour disappears, organics are the most likely cause
of discolouration.
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Adas
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Usually, graphite contains some verry smelly resin (it smells and smokes when you heat it).
Rest In Pieces!
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elementcollector1
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Why did this resin only come out when I was making KOH and not NaOH? I used the same electrodes and power-supply for both, and the NaOH turned out
barely, if at all, colored. Granted, the KOH was in a smaller beaker, if that affects anything.
Also, there was an iron cathode in this cell. How did the resin migrate across the two cells?
Furthermore, how can I prevent this?
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ManBearSwine
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In my experience, carbon electrodes gradually disintigrate, leaving a yellow to brown colliodal suspension of carbon. You can usually just filter the
solution through hard paper to remove it.
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elementcollector1
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Define 'hard paper', is it regular printer paper?
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vmelkon
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| Quote: Originally posted by elementcollector1 | Why did this resin only come out when I was making KOH and not NaOH? I used the same electrodes and power-supply for both, and the NaOH turned out
barely, if at all, colored. Granted, the KOH was in a smaller beaker, if that affects anything.
Also, there was an iron cathode in this cell. How did the resin migrate across the two cells?
Furthermore, how can I prevent this? |
Please clarify. Are you saying you did electrolysis of NaOH and no yellow color appeared and then you did the KOH and it got colored?
That would be odd.
I have used D cell battery carbon rod to do electrolysis of NaCl.
My first run gave a yellow solution. The runs after that were only very very slightly yellow. My anode was copper. Why are you using iron? It will
rust.
[Edited on 6-6-2012 by vmelkon]
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elementcollector1
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Yes, that is what I'm saying. Some of the anodes have been used at least once before, so the resins may have leaked out in previous runs. That still
does not explain how the resin managed to travel up a paper towel and into the other half-cell, though. 
I'll switch out the iron cathode, but I don't have much in the way of nice, thick copper wire. Would tin solder or a copper nugget work?
Have yet to figure out what 'hard paper' is. Google reveals NOTHING! D:<
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bahamuth
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| Quote: Originally posted by elementcollector1 | Yes, that is what I'm saying. Some of the anodes have been used at least once before, so the resins may have leaked out in previous runs. That still
does not explain how the resin managed to travel up a paper towel and into the other half-cell, though.
I'll switch out the iron cathode, but I don't have much in the way of nice, thick copper wire. Would tin solder or a copper nugget work?
Have yet to figure out what 'hard paper' is. Google reveals NOTHING! D:< |
Some filter papers are hardened, that is, very well compressed. These papers have a slow "pass-through" compared to standard qualitative filters.
These hardened filter papers are used when a quantitative filtration is due. The porosity usually lies in the lowest ranges possible with filter
papers. Read more on the different types of filter papers at whatmans pages.
Edit: Regardless on the hardened papers, a KOH solution will soften and dissolve cellulose papers. Glass or polymer filters would be the only choice
IMO.
But why go to the hassle, NaOH or KOH are easily procured and usually is cheap, the latter approx 3X the cost of the former.
[Edited on 6-6-2012 by bahamuth]
Any sufficiently advanced technology is indistinguishable from magic.
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elementcollector1
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That would explain why my filters feel oily, and my salt bridge keeps dissolving. (It's probably in my NaOH solution too... ugh...)
What salt bridge doesn't dissolve in chlorine, hydrochloric, or hydroxide solutions? (Preferably something less expensive than, say, Nafion).
EDIT: What about a towel? They're made of cotton (cellulose), but would dissolve much slower, if at all.
[Edited on 7-6-2012 by elementcollector1]
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elementcollector1
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Just had a thought: What of carbonates for alkali-hydroxide production? As far as I know, neither the carbonate ion nor CO2 gas will react with NaOH
(if driven by electrictity to continually lose the CO2, thus raising pH, etc.). Therefore, the carbonate or even bicarbonate of sodium or potassium
could be electrolyzed in a single cell, eliminating the need for a membrane, to obtain their resulting hydroxides. I may also need something to absorb
gaseous and atmospheric CO2, just to be safe. Any ideas?
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