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      Redox Reactions and Electrochemical Potential

The main purpose of the barrier is to keep Cu2+ ions away from direct contact with the Zn electrode. The positive Cu2+ ions have no tendency to migrate by electrostatic forces from right to left, but they could be brought up to the zinc metal by stirring or agitation. This is what the barrier prevents.

The electrode at which oxidation takes place always is called the anode, and the reducing electrode, the cathode. In the Zn-Cu cell, the zinc electrode is the anode, and the copper is the cathode.

Negative ions are called anions because they flow toward the anode in an electrochemical cell, and positive ions are cations because they migrate toward the cathode.

Negatively charged sulfate anions, for example, migrate from the copper sulfate compartment, through the porous barrier, and into the zinc sulfate compartment where the anode is found.

The logic in naming the anode arises because it is the electrode from which electrons flow up and out of the cell (Greek: ana, meaning up), and the cathode is the pole at which electrons flow back into the cell (Greek: cata, meaning down). This is as hard to remember as the terms themselves.

The best memory device is to recall that Anode and Oxidation begin with vowels, Cathode and Reduction with consonants, or that Anode precedes Cathode in the alphabet, and Oxidation precedes Reduction. (It may not be elegant, but it works.)

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