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Electrochemical cell question......

Discussion in 'Science' started by mangohead, Feb 15, 2011.

  1. Hello,

    Was hoping someone might clear something up for me. The salt or ion bridge in an electrochemical cell is a piece of filter paper soaked in potassium nitrate solution which means the ions can carry the current to complete the circuit. It doesn't allow mixing of the solutions, but what is to stop the mixing? Assuming we have a Cu/Zn cell. Is it basically that the current is passed from the Cu2+ soln to the potassium nitrate solution then the Zn2+ solution?

  2. Imagine the cell from your example without the salt bridge. If it worked, there would be a build up of zinc ions in its solution and a shortage of copper ions on that side. We need to get some more negative ions (nitrate) into the zinc side and more positive ions (potassium) into the copper side. The salt bridge allows that to happen.
    The current is actually the flow of electrons through the "wire". In this example, the zinc side ends up with too many electrons because the Zn has become Zn2+. The copper side has too few electrons because the Cu2+ have become Cu. The electrons flow from zinc to copper through the wire.
    You may see explanations in terms of "conventional current" or things that link the flow of electrons to the side undergoing reduction but I always find that it is simplest to think about the chemical reaction that is happening and decide which side needs electrons.


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