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In the practice of electrolysis it is of great interest to predict which substances are deposited during electrolysis. The electrochemical series of voltages (Fig. 1) shows which redox reactions take place voluntarily in a galvanic element and which redox processes can only be enforced with electrolysis. The reduced form of a redox system only reacts voluntarily with the oxidized form of another redox system, which is in the voltage series below (galvanic element).
- Electrolysis takes place between a reduced form of a redox system and the oxidized form of a redox couple in the voltage series above.
The type of deposited substances depends on the composition of the solution. If you electrolyze an aqueous solution that contains different types of ions, the individual types of ions - according to the series of voltages - separate out one after the other as the voltage increases. The more noble a metal, the easier it is to reduce its ions. At the cathode, the type of cation with the most positive potential is discharged first. At the anode, those ions are first oxidized that have the most negative redox potential. The conversion of the electrode reaction depends, among other things, on the electrode surface.