Geocachmaster - 12-9-2016 at 13:43
Hello all, I'm not sure where this goes, so feel free to move it if the location is wrong.
The other day I was doing some electrolysis using a new power supply. The anode and cathode were both some steel mesh because that's what I had lying
around. After running it at 7 amps for a little bit (1 minute or so) with sodium hydrogen carbonate as the electrolyte (near saturation) a definite
pink-red color emerged. Then for some reason I thought adding some magnesium sulfate would make it better, I added <50 grams. Upon the addition of
MgSO4 the pink color sater to fade, some bubbling took place (I detected no odor), and then the solution turned yellow. It was then I thought about
the steel and it's chromium content, and also about the very colorful chemistry of chromium compounds. I decided I was unprepared to deal with
possible hexavalent chromium, so I shut everything down, left it, washed my hands, took off my clothes, and took a shower just in case. I've done
nothing to it since. My question is what could have happened, and I'm looking for any advice on cleanup. If it was chromium VI I think I'll be fine,
because it had a cover (which means little of the aerosolized solution could have reached me), and my only other contact was a small patch
(<.5cm2) on my fingers. Also, even if 1 gram of the anode was dissolved (big overestimation), then there could have been no more than .3 grams of
chromium in the whole solution (~400mL). However, given it's many very harmful properties I am still concerned. Should I be?
Though it still could be some unreactive compound and I'm freaking out over nothing! I hope it's that.
Thanks
Texium - 12-9-2016 at 14:32
Were the electrodes stainless steel, or regular carbon steel? The only way you'd have a significant amount of chromium present would be if it was
stainless steel. Otherwise it is much much more likely to be iron(III).
If you have a reducing agent such as sodium metabisulfite or thiosulfate, try adding that and see what happens. If it goes colorless or pale green,
it's likely iron. If it goes dark green it could be chromium, and you would have successfully made it much less toxic by reducing it. There are many
tests to determine the presence of iron that could be done as well, but even if there is chromium present iron likely is too, so that won't help much.
j_sum1 - 12-9-2016 at 15:23
By electrolysis, I presume you mean to produce H2 and O2. (Otherwise I am not sure what you are up to.)
zts is right. The only way you would have any significant Cr(VI) is if the steel mesh was chromium plated or stainless steel. But let's assume a
worst case scenario. Let's suppose you had 100% conversion of Cr metal to Cr(VI) and no other reaction products:
You ran it at 7 amps for 60 seconds.
Faraday's constant is 96485 Amp seconds per mole. Therefore the number of moles of electrons that you ran through is
7×60/96485=0.0043 which translates to 4.3 millimoles.
Divide this by six because each chromium atom needs six electrons to attain Cr(VI) and you have 0.7mmol of Cr(VI)
This works out to be 38mg of hexavalent chromium.
I wouldn't be wanting to drink the whole solution but a little splash that you wash off is not going to harm you at all. Cr(VI) is known for its
chronic effects over prolonged exposure. It is carcinogenic. But it is not going to kill you if you look at it funny. It is not methyl mercury.
It reduces easily with vitamin C, thiosulfate, metabisulfite or even a lump of zinc left in the beaker for a few days. Then you can dispose of it
down the drain.
It is good to have a scare early in your experimentation career to highlight the importance of knowing what you are doing. But this particular one
ranks as trivial-to-harmless on the scale of mishaps.
If you need a placebo to ease your mind, pop a vitamin C tablet to reduce the chromium back to Cr(III).
Actually though, with the colours you have described I am really wondering what you have concocted. I doubt there is any significant Cr at all. But
you do have contaminants of some kind to get the red-pink. Was there any residual phenolphthalein on your beaker?