To define what of electrodes is the anode and what – the cathode, at first sight seems simply. It is considered to be that the anode has a negative charge, the cathode – positive. But in practice there can be confusions in definition.
Instruction
1. The anode – an electrode on which reaction oxidations proceeds. And the electrode on which there is a restoration is called the cathode.
2. Take a galvanic cell of Jacobi-Daniel for an example. It consists of the zinc electrode lowered in solution sulfate zinc and the copper electrode which is in copper sulfate solution. Solutions adjoin among themselves, but do not mix up – for this purpose between them the porous partition is provided.
3. A zinc electrode, being oxidized, gives the electrons which on an external chain move to a copper electrode. Copper ions from CuSO4 solution accept electrons and are restored on a copper electrode. Thus, in a galvanic cell the anode is charged negatively, and the cathode – is positive.
4. Now consider electrolysis process. Installation for electrolysis represents a vessel with solution or fusion of electrolyte in which two electrodes connected to a DC power source are lowered. The negatively charged electrode is the cathode – on it there is a restoration. The anode in this case the electrode connected to a positive pole. On it there is an oxidation.
5. For example, at electrolysis of CuCl2 solution on the anode there is a copper restoration. On the cathode there is a chlorine oxidation.
6. Therefore consider that the anode – not always a negative electrode as well as the cathode not in all cases has a positive charge. The factor defining an electrode is the oxidizing or recovery process proceeding on it.