Electrogravimetry is a method used to separate and quantify ion

Ion

An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

s of a substance, usually a metal

Metal

A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...

. In this process, the analyte solution is electrolyzed

Electrolysis

In chemistry and manufacturing, electrolysis is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction...

. Electrochemical reduction

Redox

Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....

 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

Electric potential

In classical electromagnetism, the electric potential at a point within a defined space is equal to the electric potential energy at that location divided by the charge there...

 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

Electroplating

Electroplating is a plating process in which metal ions in a solution are moved by an electric field to coat an electrode. The process uses electrical current to reduce cations of a desired material from a solution and coat a conductive object with a thin layer of the material, such as a metal...

.

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

where:

• Ea = applied potential
• Ed = decomposition potential
• Eb = theoretical counter or back potential
• Ev = overvoltage.