Galvanic Cells

[Medgen]

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I am a little confused as to what the purpose of a liquid junction is in a galvanic cell. A salt bridge can function as one- but I don't really understand why you need it. EK says that it is required to separate the solutions when a cell contains two different solutions... but that does not really make sense because the liquid junction does not separate the half-cells; it joins them.

If you happen to also understand why one galvanic cell would be separated, while another would not, I would greatly appreciate it if you could explain that also. EK doesn't address it very well (at least for me).

 

[flodhi1]

I am a little confused as to what the purpose of a liquid junction is in a galvanic cell. A salt bridge can function as one- but I don't really understand why you need it. EK says that it is required to separate the solutions when a cell contains two different solutions... but that does not really make sense because the liquid junction does not separate the half-cells; it joins them.

If you happen to also understand why one galvanic cell would be separated, while another would not, I would greatly appreciate it if you could explain that also. EK doesn't address it very well (at least for me).

Hopefully I'm addressing your question correctly, it seems like you're confused about the purpose of the salt bridge?
simply put the salt bridge is to exchange anions and cations to balance or dissipate the generated charges during the redox reaction. If these charges are not balanced as you can obviously tell the reactions will cease to exist simply based on the Le chatliers principle. If you have too much product the reaction will cease to move in the forward direction.

EDIT:- Stick to Berkley for Physical sciences, EK is the worst when it comes to PS review.

 

[justhanging]

I am a little confused as to what the purpose of a liquid junction is in a galvanic cell. A salt bridge can function as one- but I don't really understand why you need it. EK says that it is required to separate the solutions when a cell contains two different solutions... but that does not really make sense because the liquid junction does not separate the half-cells; it joins them.

If you happen to also understand why one galvanic cell would be separated, while another would not, I would greatly appreciate it if you could explain that also. EK doesn't address it very well (at least for me).

Can you give an example of a galvanic cell that didn't use a salt bridge? I seem to remember something about that from higher level chem courses. If you post an example it could be easier to explain.

 

[cheesier]

Can you give an example of a galvanic cell that didn't use a salt bridge? I seem to remember something about that from higher level chem courses. If you post an example it could be easier to explain.

There has to be ionic exchange to keep the charges balanced in voltaic cells, and some of them accomplish this with liquid barriers or membranes where the two chambers are actually connected but separated by something that's only permeable to ions.

Now as to why a membrane or liquid barrier would be preferable to a salt bridge, I'm not sure, but it's not going to matter in the context of the MCAT.