Anode vs. Cathode

[Jasmine Botello 2F]

In Monday's lecture, Lavelle explained how the anode is the negative side and the cathode would be the positive side. However, in my biology class, when we were discussing gel electrophoresis, the anode was the positive side and the cathode was the negative side. Is there a difference between the two situations that I'm missing?

[Jingyi Li 2C]

In general, the anode is the positive side and the cathode is the negative side. This refers to the movement of current. In electrochemistry, electrons flow the opposite way. The anode is the negative side and the cathode is the positive side.

[Natalie LeRaybaud 1G]

Yes there is a difference between a Galvanic cell and an Electrolytic cell.

In a Galvanic cell the reaction proceeds without an external potential helping it along. Since you have the oxidation reaction at the anode, this produces electrons and thus a build-up of negative charge in the course of the reaction until electrochemical equilibrium is reached. Thus the anode is negative. Whereas at the cathode you have the reduction reaction occuring which consumes electrons (leaving behind positive metal ions at the electrode). This leads to a build-up of positive charge during the reaction until equilibrium is reached, thus making the cathode positive.

However in an Electrolytic Cell there is an external potential (like an electrical current) applied to enforce the reaction to go in the opposite direction. Therefore the reaction reasoning is switched and the Anode houses the positive reaction while the Cathode is the source of the negative reaction.