ion migration in galvanic cells

[rayden001]

Hey guys, quick question

Since in galvanic cells the anode is the negative electrode while the cathode is the positive electrode, so why do anions (negatively charged) migrate towards the anode? What about like-charges repelling? Thanks

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[cornpops21]

The ions flow that way in order to balance the charge difference due to the electron flow.

Since electrons flow from anode to cathode, the anions flow from cathode to anode to balance it out.

Cations flow towards the cathode for the same reason.

 

[HawkeyePostOp]

If the voltage difference came from the circuit and not the solution, that would make sense. Think about how a galvanic cell's anode gets a negative charge in the first place. It's from the anions themselves and because of reactivity and solubility, not the charge.

If you consider an electrolytic cell, where the circuit produces its own sufficient voltage, everything is flipped. Basically instead of connecting the two electrodes with just a wire, you connect them with a wire and a battery or some voltage source. The orientation of the voltage source has to be such that it forces current in the direction opposite the normal galvanic cell. Ion migration switches, and you are recharging the chemical solution. Then negative ions will go the cathode.

 

[AsuKa]

correct me if im wrong, but don't anions always go to the anode, regardless if it's negatively or positively charged?

 

[BerkReviewTeach]

correct me if im wrong, but don't anions always go to the anode, regardless if it's negatively or positively charged?

You are 100% correct for the typical cells we consider where each half reaction involves a cation/metal combination. In such cells, anions (spectator ions) migrate to the anode. The anions migrate to the anode to offset the flow of electrons which go from the anode to the cathode.

Cornpops is right on the mark.

Ion migration switches, and you are recharging the chemical solution. Then negative ions will go the cathode.

You are right about the switches and the recharging nature. But you might want to double check your source of this information, because they have ignored the fact that in an electrolytic cell, the electrodes reverse from their galvanic description. In essense, what would normally be the cathode in a galvanic cell is forced to be an anode by the applied voltage. The anions do in fact flow in the opposite direction when considering an electrolytic cell versus a galvanic cell, but because the electrodes have reversed, it's still a situation where the anions are migrating to the anode.