I am not sure what I was expecting to happen with this but I created a circuit to electrolyze various household liquids. My electrodes are copper — or at least claim to be, I think they might just be zinc wires with some copper-colored coating.

Now I'm trying it on urine, which seems to eat through the wire rather rapidly. It produces some sort of gas with tiny bubbles. When these bubbles come into contact with the other electrode, they turn gray and fall to the bottom of the container. This gray material is almost green and that makes me think it is a copper salt rather than zinc. What are the bubbles and what is this salt?

Also, as a side question, how can I isolate this salt without potentially exploding whatever is in the bubbles?

If it's important: I'm using ~6 V, but I don't know the current.

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    $\begingroup$ Just to be sure I understand: both electrodes are copper, and the bubbles that form at one electrode migrate to the other. When they come in contact with the other electrode, a gray/green solid is formed. On which electrode does the solid form? $\endgroup$
    – airhuff
    Jan 22 '17 at 21:29

The main components of urine are water and then urea. Water makes up 90% to 95% of urine with urea making up about 50% of the remainder. It's likely that your reaction is mainly the hydrolysis of water. In that case, you are forming hydrogen gas at cathode and oxygen gas at the anode. Also, some $\ce{NaCl}$ will be electrolyzed and form $\ce{Cl2}$.

As you stated, you are likely oxidizing copper, probably making $\ce{CuCl2}$. Most zinc salts that you could be forming in your reaction would be white. If urea is being electrolyzed, then you would also be forming nitrogen and carbon dioxide at the anode. It's possible that at least some of the migrating bubbles contain $\ce{Cl2}$ gas which then could form solid $\ce{CuCl2}$.

You could do a quick test of some aspects of my answer by observing the hydrolysis of water using your system. Just conduct your procedure exactly as you do for urine, but instead of urine use water. The main salt present in urine is $\ce{NaCl}$, whose concentration varies quite a bit but is on the order of 3 g/L. So just conduct your experiment on a 3 g/L $\ce{NaCl}$ in water solution and compare your results to the urine experiment.


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