electrode

Meaning: An electrode is a conductor, usually a metal or graphite, where electrons pass between the external circuit and species in the electrolyte. Oxidation occurs at the anode and reduction at the cathode, in galvanic and electrolytic cells alike. Electrons flow through the wire from anode to cathode, while ions move through a salt bridge or the solution to balance charge. An inert electrode such as platinum only supplies a surface for the reaction.

Equation: E°cell = E°cathode − E°anode, where each E° is a standard reduction potential in volts (V).

On the MCAT: Passages give a cell diagram or line notation such as Zn(s) | Zn²⁺(aq) || Cu²⁺(aq) | Cu(s), with the anode written on the left. You name the anode and cathode, give the direction of electron flow, predict which electrode gains mass (metal plating out at the cathode) or loses mass (a metal anode dissolving), and calculate E°cell. Electrolysis and electroplating questions use the same labels.

Common confusion: Students tie the labels to charge and assume the cathode is always positive. The sign flips between cell types: in a galvanic cell the anode is negative and the cathode positive, while in an electrolytic cell the reverse holds because an external source drives the reaction. The definitions never change: anode = oxidation, cathode = reduction.