Salt Bridge

[Nathan_Barney_2A]

What was the purpose of the salt bridge in the anode/cathode battery? Why did it need to be there?

[Chem_Mod]

The salt bridge allows for ions to flow between the solution with the cathode and the solution with the anode. Electrons flow from the anode to the cathode, and as this happens, the cathode solution gets more negatively charged as the cathode species are reduced, and the anode solution gets more positively charged as the anode species are oxidized.

If the cathode solution gets too negative, this will slow and ultimately stop the electron flow, because flowing of a negatively charged species (electron) into a negative solution would be too unfavorable. To remedy this, the salt bridge is added so that the positively charged ions can go to the negatively charged cathode solution, and thus neutralize the charge imbalance as a result of the reaction.

The salt bridge allows for a lot more electron flow to occur for a longer time than without it.

[Joyce Zhang 2D]

Is it always a positively charged ion? also, is it the salt ions being transferred or the metal ions?

[Zulfiqar Lokhandwala 1H]

The metal acts as the conductor so that the electrons can move, so I wouldn't believe the metal ions would be the one that is being transferred as the electrons are moving from areas of high concentration to areas of low concentration causing the charge of the two substances to increase or decrease. The salt bridge just allows it to transfer

[Nathan Wise 2C]

What forces cause the salt bridge to allow for a flow of ions, and how do the salts not affect the cell reactions?

[Joyce Zhang 2D]

Someone explained this to me:

It's easier to think of this in terms of charge. As the electron transfers from one cell to another, one of the cells will be more positive and the other more negative. Salt ions, like NaCl-->Na+ + Cl-, have a positive charge or negative charge. Since the cells are seperated so that the metal ions can't move to balance the charge, the salt ions will feel the need to cross the salt bridge/semipermeable membrane to neutralize the built up charges created by the redox reactions. By neutralizing charges through the salt bridge, it allows the redox reaction to occur for a longer time before reaching equilibrium.

[Kiara Quinn 3B]

In the book it asks which salts you definitely cannot use for a salt bridge, but I'm not exactly sure which those would be. I know that ions should not affect the cell reaction, and that KCl is a common one used, but I am not sure which salts you would avoid and why.