4.10: Electrodeposition
Electrodeposition is a technique used to separate an analyte from interferents by electrochemical processes. Here, the analyte is a metal ion that can be deposited on an electrode immersed in the sample solution. The electrochemical setup consists of an anode and a cathode. When an electric current is applied to the setup, oxidation occurs at the anode. At the cathode, which consists of a large metal surface, metal ions undergo reduction and deposit onto the surface.
Electrodeposition can separate metals with significant differences in reduction potentials. For example, copper and nickel in the same solution can be separated by electrodeposition. In this process, the solution is first made acidic. When an electric current is applied, water molecules in the solution undergo oxidation, producing oxygen, and copper is deposited onto a platinum cathode. After weighing the cathode to determine the weight of the copper, the copper is removed from the cathode. The solution is then made basic, nickel is deposited onto the same platinum cathode, and its weight is determined by weighing the electrode.
Electrodeposition can also be used to separate ions that simultaneously deposit on different electrodes, such as copper(II) and lead(II). Lead(II) ions undergo oxidation in a nitric acid solution and deposit as lead dioxide on a platinum anode. Meanwhile, copper(II) ions undergo reduction and deposit as copper metal on a platinum gauze cathode. The quantitative results of electrodeposition depend on the potential and sizes of electrodes, the deposition time, and the stirring rate.
