Take this picture to the left, for instance.
Sadly, this is wrong. That is - it shows the general idea without getting into details, but to someone trying to learn it is confusing as it ignores the fact when the cells are not isolated things can react directly (I believe you have correctly mentioned that earlier in the thread).
I did an experiment today. I took one strip of Zn and one strip of Cu, and put it in a beaker of 3,5 % acetic acid.
Here is what happend, along with my assertions and questions.
1. I got about 0,8V between the electrodes (old manual voltemeter). Zn connected to "ground". So Zn is negative pole, Cu is positive from the experiment.
2. Bubbles formed at both the Zn and Cu electrode, but much more on the Zn. I assume that H2 is formed at the Zn electrode. Zn is getting oxidized and H+ is getting reduced to make up H2.
3. What happends at the Cu electrode? First i thought that it is not part of the reaction, but when i removed the Cu and just
took the wire in the beaker (the wire clip was probably iron or something) the voltage went down. Is H2 gas formed at both the electrodes? How does this relate to the reduction potentials? Cu should not be oxidized by acetic acid? Is it oxygen from copperoxide?
4. Does electrons travel to both H+ at the Zn electrode AND to H+ at the Cu electrode, forming H2 at both places? If that is not happening, I dont understand how Zn can be the negative pole, since all the electrons then join the H+.
Hope to get some clarifications!