Cathode
Definition and meaning of Cathode in chemistry.
Cathode is the electrode of an electrochemical cell at which reduction occurs, meaning it is the site where a chemical species gains electrons supplied by the external circuit.
In more detail
Every electrochemical cell has two electrodes: reduction always happens at the cathode, and oxidation always happens at the anode (the mnemonic "RED CAT" and "AN OX" helps). The cathode's electrical polarity depends on the type of cell: in a galvanic (voltaic) cell, which generates current spontaneously, the cathode is the positive terminal; in an electrolytic cell, which consumes electrical energy to drive a non-spontaneous reaction, the cathode is the negative terminal because it is connected to the negative pole of the external power source. Conventional current flows into the cathode from the external circuit, while electrons flow into the cell at the cathode and are consumed by the reduction half-reaction.
Key facts
| Field | Physical Chemistry |
|---|---|
| Half-reaction type | Reduction (electron gain) |
| Polarity in a galvanic cell | Positive electrode |
| Polarity in an electrolytic cell | Negative electrode |
In the electrolysis of molten sodium chloride, the cathode is the electrode where Na+ ions are reduced: Na+(l) + e- -> Na(l), producing liquid sodium metal.
Frequently asked questions
Is the cathode always the negative electrode?
No. The cathode is defined by function (where reduction occurs), not fixed charge. It is negative in an electrolytic cell but positive in a galvanic cell like a discharging battery.
How can I remember which electrode is the cathode?
Use the mnemonic 'RED CAT': REDuction occurs at the CAThode. Correspondingly, 'AN OX' reminds you that oxidation occurs at the anode.