Faraday’s laws of electrolysis are two fundamental laws in electrochemistry. They describe the quantitative relationships between the amount of chemical change at an electrode. This chemical change relates to the quantity of electricity passed through an electrolyte. These laws were formulated by Michael Faraday in 1833.
Faraday’s First Law of Electrolysis
This law states that the mass of a substance deposited at an electrode is directly proportional to the electricity quantity. The same is true for a substance liberated at an electrode. Mathematically, it can be expressed as:
m ∝ Q
where:
- m = mass of the substance deposited or liberated (in grams)
- Q = quantity of electricity passed (in coulombs)
The constant of proportionality, Z, is known as the electrochemical equivalent (ECE) of the substance. It represents the mass of the substance deposited or liberated per unit charge (coulomb).
Faraday’s Second Law of Electrolysis
This law states that when the same quantity of electricity is passed through different electrolytes. The masses of the substances deposited at the electrodes are directly proportional. The masses of the substances liberated at the electrodes are also directly proportional. They are proportional to their equivalent weights. Mathematically, it can be expressed as:
m1/m2 = E1/E2
where:
- m1 and m2 are the masses of substances deposited or liberated at the electrodes of two different electrolytes
- E1 and E2 are their respective equivalent weights
Equivalent Weight
The equivalent weight of a substance is defined as its molar mass divided by its valence (or n-factor). The valence of an ion is the number of electrons it gains or loses during a chemical reaction.
Applications of Faraday’s Laws
Faraday’s laws have numerous applications in various fields, including:
- Electroplating: It is used to coat a metal object with a thin layer of another metal.
- Electrorefining: It is used to purify metals by removing impurities.
- Electrolysis of water: It is used to produce hydrogen and oxygen gas.
- Electrochemical cells: It is used to understand the operation of batteries and fuel cells.
- Quantitative analysis: It is used to determine the amount of a substance in a solution.