18thTimeLucky
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Mood: 0 Kelvin and still won't crystallise from solution
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Mystery chromium compound identification?
I made some potassium hydroxide a few months ago by the electrolysis of potassium chloride. The goal was to use the potassium hydroxide solution in a
hydrogen and oxygen electrolysis-based generator.
I at the same time tried using a sodium hydroxide solution which worked well and produced plenty of hydrogen and oxygen that made a loud bang. I
therefore stuck to the use of sodium hydroxide.
A few weeks later I remembered I had that potassium hydroxide solution (the concentration was about 4% if I can remember so quite dilute) and so I
decided to try it in the generator. Big mistake. When I turned on the current (12V, 1.5A) the stainless steel knife electrodes started to produce this
green and orange compound on the surface. I stopped and poured out the solution along with some of the orange green compounds (picture below). I added
the sodium hydroxide solution again, turned the current on, and hydrogen and oxygen started to be produced again, causing all of the orange and green
compounds to flake off completely.
I left these contaminated solutions sealed away in a corner, meaning to get back to them but forgetting until today.
What I am asking is what the hell are the green and orange compounds? A quick search right now didn't give me any answers. I take it that they are
some oxidation state of chromium from the stainless steel, although this scares me. If nobody can tell me what I have made I would at least like to
know where I have accidently made any carcinogenic chromates or dichromates. My best guess is that the green was chromium(III) oxide as it was
insoluble but in the picture it shows that the green has now gone after the few months it was sitting?
Thank you for your time!!
![IMG_7863[2].JPG - 1.7MB](https://www.sciencemadness.org/whisper/files.php?pid=501057&aid=63400)
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"Amateur chemistry does seem like being in a relationship with someone very beautiful and seductive but has expensive taste, farts a lot and doesn't
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Σldritch
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The red one is iron in (III) and the green is chromium in (III). Probably little to no chomium (VI) formed.
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MrHomeScientist
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Cr (VI) would likely be soluble if it did form, but it's strongly colored so you'd notice it in the solution even in tiny amounts. But I agree, it's
unlikely to have oxidized that far.
Odd that KOH caused it but NaOH didn't. They're usually interchangeable. What was the concentration of your NaOH solution?
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Mothman
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Are chloride contaminants a possible cause for this reaction? Did you purify the KOH product after you produced it? I can see chloride ions reacting
with the metal during electrolysis like what happens to copper in a sodium chloride solution during electrolysis, but I am not very knowledgeable
regarding electrochemistry.
You can be happy
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18thTimeLucky
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Mood: 0 Kelvin and still won't crystallise from solution
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Ok good, I doubted there would be chromates or dichromates, but my knowledge is limited and so I wanted reassurance as you can imagine. Still though I
am interested why the potassium hydroxide solution caused this.
'MrHomeScientist' I am not sure what the sodium hydroxide solution concentration was as I had prepared it quickly and had just dumped in an arbitrary
amount of sodium hydroxide drain cleaner but it would have been much more concentrated. I have made sodium hydroxide by the same method as I did the
potassium hydroxide but I have not actually used it in my hydrogen and oxygen generator as I only made 200ml which is would not even enough to half
satisfy the required volume and it is hard work to synthesise the alkali hydroxides in the way I did. Drain cleaner is much easier.
'Mothman' that is an extremely good point, I don't know why I hadn't thought of that. No, I had not purified the potassium hydroxide, mainly because I
don't know how I would go about purifying something like potassium hydroxide, so there is definitely some potassium chloride contamination. I am still
confused about why the attacking of the stainless steel happened so quickly (immediately as I turned on the current). I assume steel is always used by
amateurs to synthesise iron(III) oxide by electrolysis and not stainless steel for the reason of chromium(III) oxide forming, but where has the
chromium gone as the green has since disappeared? Unless I am going crazy (only memory proof, no photos I don't think) I swear there was green. If the
chromium had gone into solution it should be coloured but it is not, it is colourless...
Yep, I have a chemistry blog!
18thtimelucky.wordpress.com
"Amateur chemistry does seem like being in a relationship with someone very beautiful and seductive but has expensive taste, farts a lot and doesn't
clean up after themselves, but you love them anyway" - a dear friend |
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Diachrynic
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Maybe the Fe(III) oxides/hydroxides gradually generated from Fe(II) just has a more intense colouring than the chromium has.
Also, Cr(OH)3 seems to have a lot of different colours. Wiki lists it as green/blue/black. https://de.m.wikipedia.org/wiki/Chrom(III)-hydroxid.
The green stuff at the beginning could be some Fe(II) as well... I noticed something similar while electrolysis of sodium carbonate with a non
stainless steel nail. Blue/green, which turned over time into the rusty red we all know.
[Edited on 20-12-2017 by Diachrynic]
we apologize for the inconvenience
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