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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 cathode is weighed before and after the experiment, and weighing by difference is used to calculate the amount 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.
It is known that in the phenomenon of polarization the products of electrolysis exerts a back emf, which reduces the actual emf of the cell. Thus electrolysis of an electrolyte is possible only when this back emf is overcome. Let us consider a case in which two more platinum electrodes are placed in a dilute solution of copper sulfate. 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
- Ea = applied potential
- Ed = decomposition potential
- Eb = theoretical counter or back potential
- Ev = overvoltage.
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