Faraday's law of electrolysis, formulated by the English scientist Michael Faraday in the 1830s, describes the quantitative relationship between the amount of chemical reaction occurring at an electrode during electrolysis and the amount of electric charge passed through the electrode. It is an essential concept in electrochemistry and is used to calculate the amount of substances produced or consumed during electrolysis.
The law is stated as follows:
"The amount of substance produced or consumed at an electrode during electrolysis is directly proportional to the quantity of electric charge passed through the electrode."
Mathematically, the law can be expressed as:
m = z * F * I * t
where:
m is the mass of substance produced or consumed in grams,
z is the number of moles of electrons exchanged per mole of substance (known as the stoichiometric coefficient),
F is Faraday's constant, approximately 96,485 C/mol (the electric charge in coulombs required to transfer one mole of electrons),
I is the electric current in amperes (A), and
t is the time in seconds (s) for which the current flows.
This law is applicable to electrolytic cells, where electrical energy is used to drive a non-spontaneous chemical reaction. During electrolysis, cations (positively charged ions) migrate to the cathode (negative electrode), where they gain electrons and are reduced to form a substance. Anions (negatively charged ions) migrate to the anode (positive electrode), where they lose electrons and are oxidized to form another substance.
Faraday's law allows scientists and engineers to determine the quantity of substances produced or consumed during the electrolysis process, which is crucial in various industrial applications. Some practical applications of Faraday's law of electrolysis include:
Electroplating: The process of depositing a thin layer of metal onto a conductive surface, such as jewelry, electrical components, or automotive parts. Faraday's law helps determine the amount of metal deposited, ensuring a consistent and controlled plating thickness.
Chlor-alkali production: In the electrolysis of brine (sodium chloride solution), chlorine gas is produced at the anode, while hydrogen gas and sodium hydroxide are generated at the cathode. Faraday's law helps optimize the process and calculate the amount of chlorine and other products produced.
Aluminum production: Electrolysis is used to extract aluminum from its ore (bauxite). Faraday's law is applied to determine the amount of aluminum metal obtained and optimize the production process.
Industrial synthesis: Electrolysis is utilized in the production of various chemicals, such as potassium hydroxide, sodium chlorate, and hydrogen peroxide. Faraday's law assists in determining the amount of product formed.
By understanding and applying Faraday's law, researchers and engineers can ensure efficient and controlled electrolytic processes in various industries, leading to improved product quality and cost-effectiveness.