Full Length 4 CP Q40

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NS_Tutor_Sophia
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Joined: Tue Aug 01, 2017 11:49 am

Full Length 4 CP Q40

Post by NS_Tutor_Sophia » Mon Dec 31, 2018 9:17 am

A student recently asked us about the flow of electrons relative to the positioning of the cathode and anode in the following question: "A galvanic cell is constructed in which the anode is positioned on the right, while the cathode is on the left. The two half-cells are separated by a salt bridge. Of the following, what is the most likely purpose of this bridge?"

This brings up a point about electrochemical cells that can be really confusing! The first thing to remember is that, in any kind of electrochemical cell, oxidation (loss of electrons) always occurs at the anode, and reduction (gain of electrons) always occurs at the cathode. You can remember this using the mnemonic RED CAT & AN OX. The other thing to remember is that electrons always flow from the negative (-) electrode to the positive (+) electrode, as opposite charges attract.
  • In a galvanic cell, the cathode is positive and the anode is negative. Electrons flow from the negative anode on the right toward the positive cathode on the left. This uses redox reactions to create electrical energy in the form of current.
  • If this were instead converted into an electrolytic cell, energy would be supplied from a power source to power the flow of electrons in the opposite, otherwise nonspontaneous direction: from the cathode on the left back toward the anode on the right. However, the charges of the anode and cathode must be reversed, as electrons will always flow toward the more positive electrode. Thus, electrons flow from the (now NEGATIVE) cathode toward the (now POSITIVE) anode.
Because this question asks about a galvanic cell, electrons must flow from the negative anode on the right toward the positive cathode on the left. Meanwhile, spectator anions will travel in the opposite direction, from left to right, to balance out the charge.
Sophia Stone
PCAT Content Manager
Next Step Test Prep
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