dettoo456
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Issue with electrolysis of NaI & Na2Cr2O7
I am far out of my depth when it comes so electrochem, so please pardon the ignorant question. I looked around to see if anyone else encountered the
same problem but I couldn’t find much.
Basically, I’m electrolyzing a jam jar filled with saturated NaI with a pinch of dichromate at 1.4A and around 4.5V. The cathode is Ti, the anode is
Chinese Pt foil. Temp is approx 50C with stirring but no active cooling. pH is 9
Immediately on running the power to the cell, the liquid turned maroon with some crystalline precipitate, and stayed the same dark color for the
duration. After I turned it off at 3hrs in, the Pt foil was fine but the Ti was coated in what looked like I2 and crystals of something. It looks
pretty ugly and I believe this isn’t very optimal.
Does anyone know any solutions to this issue with the Ti cathode or general conditions? I think I should at least drop the pH but I don’t know what
else could help. Thanks
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woelen
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What do you want to make?
Using electrolysis on iodides is not the best thing to do. Electrolysis is nice for bromides (making bromate) and chlorides (making chlorate), but
with iodides you get too many side reactions. Iodate is easily reduced to iodine at the cathode, you also can get some periodate at the anode. If you
use dichromate, then I think that you get immediate oxidation to iodine and formation of chromium(III) compounds. You get a nasty mix of different
chemicals.
From NaI you can make iodate or even orthoperiodate. I have done that by bubbling Cl2 through a solution of NaI.
Making iodine can simply be done by adding H2O2 to an acidified solution of NaI. Iodine precipitates and can be filtered from the solution. With conc.
H2SO4 you can dry the wet, vacuum filtered I2, and then drive off the I2 from the acid slurry by gentle heating and crystallizing it on a cool
surface.
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dettoo456
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I’m trying to make NaIO3, and you’re right about the mix of oxidized crap in the solution. I’m seeing some green material which I can only
assume is Cr2O3 along with some other precipitate. I will just heat up everything, filter, and attempt to recover any NaIO3 or just NaI left.
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woelen
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This may be interesting for you: https://woelen.homescience.net/science/chem/exps/Na2H3IO6/in...
This is a procedure for making periodate.
Making iodate in this way can also be done, but it is harder to determine when to stop adding chlorine. With periodate you just add enough chlorine
and if you add too much, there is no problem. With making iodate, you have to stop adding chlorine before periodate is formed. The reaction goes
through iodate towards periodate.
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