I am not exactly sure what purpose the salt bridge has.
In the above image, I understand that electrons flow from $\ce{Zn}$ through the wire to $\ce{Cu}$ due to the redox reaction. However, I do not understand how the Salt bridge neutralizes the charges in each half cell. image from https://en.wikipedia.org/wiki/Galvanic_cell

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    $\begingroup$ Hello and Welcome to Chemistry SE. This question, I'm afraid is too broad and would require an entire book or chapter of a book to explain it. This question is a bad fit for SE. Consider referring a book, and come back if you have any conceptual doubts in it. Happy learning. $\endgroup$ Jun 5 '17 at 16:26
  • $\begingroup$ I just need a very simple answer for a high school Chemistry class. Nothing too specific. $\endgroup$
    – Naoki H
    Jun 5 '17 at 16:27
  • $\begingroup$ Then, the first paragraph of the English wikipedia about the topic (en.wikipedia.org/wiki/Galvanic_cell) -- where the original figure appears, too -- condenses the definition to the bare minimum. Equally, some keywords mentioned are introduced there with a hyperlink; and it lists additional references / textbooks, too. For future reference (and not only for the purpose of addressing questions and providing answers on ChemSE), it is good practice to quote sources accessed, which includes to cite the origin of data and figures used. $\endgroup$
    – Buttonwood
    Jun 5 '17 at 22:01

The galvanic cell use the theromdynamic preference of the mixture of $\ce{(Zn^{2+}|Cu)}$ over $\ce{(Zn|Cu^{2+})}$ (which results in the transfer of electrons from zinc to copper(II) ions) and forces this process to occur through a wire.

The salt bridge completes the circuit without allowing the zinc and copper(II) ions to mix directly. If they did, they would react by touching and no electrons would pass through the wire.

  • $\begingroup$ If you don't want the Zn and Cu to touch, why can't you completely leave out the salt bridge? $\endgroup$
    – Naoki H
    Jun 5 '17 at 21:34
  • $\begingroup$ Have you tried using a battery where you didn't complete the circuit? $\endgroup$
    – Zhe
    Jun 5 '17 at 21:47
  • $\begingroup$ I know that you have to complete a circuit, but I'm not completely sure as to of what purpose the salt serves. Why doesn't it work if you just have Zn and Cu(II) connected to each other? $\endgroup$
    – Naoki H
    Jun 5 '17 at 21:53
  • $\begingroup$ The solutions will immediately build up excess charge due to the flow of electrons. You need some ions to shift also to balance out the charge distribution. It can't be the reacting ions, so you use a salt bridge to mediate the ion flow. $\endgroup$
    – Zhe
    Jun 5 '17 at 21:57

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