Sciencemadness Discussion Board

Odd zinc-copperII reaction

darkflame89 - 23-6-2005 at 23:48

I just encountered something strange while fiddling around today. I had some cheapo AA batteries that once you peeled off the plastic covering, you could see the zinc can. As i had copper(II) sulphate solution lying around, I decided to plonk the battery into solution, hoping to let the solution eat its way through to the interior.

The moment the battery contacted the solution, copper immediately formed on the battery. Nothing out of ordinary so far...It was after a while, i decided to pick up the cup with the solution and battery and hold it to sunlight to observe the battery. It was at this point that i noticed a thin current of liquid rising upwards from the battery continuously. Could this be due to the formation of the zinc ions that rises upwards from the battery thus bringing some of the surrounding liquid along with it?

Anyway, I also noticed that the liquid became quite warm after a while. I do not know whether this is due to the heat from reaction, or due to resistance from the conductive liquid that completes the circuit to the terminals of the battery.

Anybody that can shed an idea on why there are micro liquid currents rising up from the battery?

12AX7 - 23-6-2005 at 23:58

Hm, could be ZnSO4 forming, convection, or if the casing has been eaten through, don't forget the formation of Cu(OH)2 and/or Zn(OH2) if it's an alkaline (I presume it is).


Esplosivo - 24-6-2005 at 01:00

The reaction is quite exothermic. Hot water has a lower density than cool (4deg C) water, therefore the currents you are observing might be due to a hotter region of the solution 'flowing' upwards due to a lower density. At least I think that's the only valid answer. What else could it be?

darkflame89 - 24-6-2005 at 23:13

Yes, I didn't think of that... Now I think a reaction has reached an end, all the zinc has been eaten away, leaving behind what appears to a papery(greenish in colory) covering the battery. There's another battery within the battery, strange. I thought after the zinc covering is gone, what's left should be the electrolyte. But there appears to be membrane of some sort separating the zinc covering from the rest of the battery...

akcapr - 25-6-2005 at 00:09

probably the MnO2 shell, which then contains the electrolyte, then the carbon rod i belive.

12AX7 - 25-6-2005 at 00:09

Was it magnetic? Is the solution green or brown? It could be an iron casing.

Come to think of it, instead of that it might be an ionic membrane to prevent the zinc from being eaten away by the basic electrolyte (potassium zincate).