The anode is the electrode where oxidation occurs; in electrolysis it is the positive electrode, where anions are oxidised by losing electrons.
The anode is the electrode where oxidation occurs. In electrolysis it is the positive electrode, and anions move to it and are oxidised by losing electrons. Malay: anod · Chinese: 阳极.
The anode attracts the negative ions, the anions, because opposite charges attract. At its surface those anions give up electrons, which flow away through the external circuit; this loss of electrons is oxidation. A memory link that helps is that anode and anion both begin with the same sound, and both are tied to the same electrode. In an inert-electrode cell a gas such as oxygen, chlorine or bromine is usually released at the anode; with an active electrode the anode metal itself dissolves.
Example. In the electrolysis of molten lead(II) bromide, bromide ions move to the anode and are oxidised: 2Br− to Br2 plus 2e-. Brown bromine vapour is seen at the positive electrode, confirming oxidation there.
Confusion to avoid. Do not fix the anode as always positive. In electrolysis the anode is positive, but in a voltaic cell the anode is the negative terminal, because it is now the source of electrons for the circuit. The safe definition is by process, not sign: the anode is always where oxidation happens, no matter which cell it is.
Active anodes. In the purification of copper and in electroplating, the anode is deliberately made of the metal being transferred, so instead of releasing a gas it dissolves into the electrolyte, feeding ions that are later discharged at the cathode.
Following the ions. During electrolysis the anions drift through the electrolyte towards the anode while electrons flow away from it through the wire, so the anode is where negative ions arrive and give up their extra electrons. Watching the anode also tells you a great deal about the electrolyte: a gas bubbling off means an inert electrode discharging an anion, while a shrinking metal electrode means an active anode dissolving. Reading these signs correctly turns an observation into the right half-equation.
Naming the anode reaction, and writing its oxidation half-equation, is a routine electrolysis task, so this term threads through the whole electrolysis and cells section of SPM Chemistry.
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