An electrode is a conductor through which electric current enters or leaves an electrolyte.
An electrode is a conductor through which electric current enters or leaves an electrolyte. Malay: elektrod · Chinese: 电极.
Every electrolytic and voltaic cell has two electrodes dipped into the electrolyte and joined to an external circuit. One electrode is the anode and the other is the cathode, and the ions in the electrolyte are discharged at their surfaces. Electrodes are usually made of a conductor that does not interfere with the reaction, such as carbon (graphite) or platinum, but in some cells the electrode is chosen precisely because it does take part, such as a copper electrode used in purification or electroplating.
Example. In the electrolysis of copper(II) sulfate solution with carbon electrodes, copper is deposited on the cathode while oxygen is released at the anode. If the same solution is electrolysed with copper electrodes instead, the anode dissolves and copper builds up on the cathode, showing that the material of the electrode changes the result.
Confusion to avoid. Do not assume the electrode is always inert. Whether an electrode is inert or active decides the anode product in particular, so read the question carefully. Also do not confuse the electrode, which is the solid conductor, with the electrolyte, which is the substance being decomposed around it.
Anode and cathode. By definition the anode is the electrode where oxidation happens and the cathode is where reduction happens; in electrolysis the anode is positive and the cathode negative, while in a voltaic cell the signs are reversed. Keeping the oxidation and reduction roles fixed, rather than the signs, avoids most errors.
Where the electrons go. Tracing the electrons ties the two electrodes together: electrons leave the anode, travel through the wires and the power supply, and arrive at the cathode, so the current in the external circuit is a flow of electrons while the current inside the electrolyte is a movement of ions. Seeing the whole loop, electrons outside and ions inside, makes the reactions at each electrode much easier to predict and to explain in words.
Electrodes are central to electrolysis, voltaic cells, electroplating and the purification of copper, so knowing what happens at each one is essential across this chapter and in SPM Chemistry.
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