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Electrogravimetry is a method used to separate and quantify ions of a substance, usually a metal. In this process, the analyte solution is electrolyzed. Electrochemical reduction causes the analyte to be deposited on the cathode. The mass of the cathode is determined before and after the experiment, and the difference is used to calculate the mass of analyte in the original solution. Controlling the potential of the electrode is important to ensure that only the metal being analyzed will be deposited on the electrode.
The process is similar to electroplating.
The phenomenon of polarization exerts a back EMF in electrolysis, which reduces the actual EMF of the cell. Thus electrolysis of an electrolyte is possible only when this back EMF is overcome. If two separated platinum electrodes are placed in a dilute solution of copper sulfate and if a source of potential is applied, no appreciable current will flow through the system, until some minimum potential is applied after which the current will increase as the applied potential increases. The applied voltage which is just sufficient to overcome the back EMF due to polarization and also to bring about the electrolysis of an electrolyte without any hindrance is known as decomposition potential.
The decomposition potential Ed is composed of various potentials and is given by:
- Ea (min)= Ed= Eb+ Es+ Ev
where:
- Ea = applied potential
- Ed = decomposition potential
- Eb = theoretical counter or back potential
- Ev = overvoltage.