I was watching some videos on the lemon battery, and found an incongruity that I haven't been able to solve.
In the lemon battery, a zinc anode is connected by a wire to a copper cathode. Zince oxidizes and the two electrons travel over the wire to the copper cathode where they interact with the electrolyte (H+ ions in the acidic lemon solution) to produce hydrogen gas (H2). Given that the oxidation of zinc is spontaneous at standard conditions, and that the reduction potential of H+ is zero, why do we need a copper cathode at all? Why doesn't the redox reaction occur directly between the zinc anode and the H+ that surrounds it? I see no reason why electrons need travel to the copper cathode, especially when it plays no part in the overall redox reaction.
One final, slightly related question. In other, more formal, galvanic cells, the two half-cells are often connected by a salt bridge. Some sources I have looked at mention that the ions in solution can move up the salt bridge and into the other half-cell; I have always been under the assumption that ions in the salt bridge themselves moves to remove polarity and that they interact with the ionic solutions of each half cell, but the ions in the half cells don't themselves move up into the salt-bridge and across. For example, in the following galvanic cell, Zn(s) l ZnSO4 ll CuSO4 l Cu(s) (with KCl salt bridge), would Zn2+ move across the salt bridge and into the CuSO4 half cell? Likewise, would SO42- move across the salt bridge and into the ZnSO4 solution? I contend that only the K+ and Cl- ions will move in this galvanic cell, as these ions will interact and remove the growing charge before Zn2+ or SO42- can make it across.
I'm curious to know what everyone thinks; all input is highly appreciated