- Faraday’s Laws of Electrolysis Defined: Faraday’s law is a set of two scientific laws that quantify how chemical deposition during electrolysis is proportional to the electricity used.
- First Law Explained: The first law states that the mass of a substance deposited at an electrode during electrolysis is directly proportional to the amount of electricity that flows through the electrolyte.
- Second Law Elucidation: According to the second law, when electricity passes through different electrolytes, the substance mass deposited is proportional to their chemical equivalents.
- Electrolysis Process: Electrolysis involves ions moving to electrodes, where they gain or lose electrons, resulting in chemical deposition.
- Historical Insight: Michael Faraday, who formulated these laws in 1834, significantly advanced our understanding of electrolysis and its practical applications.
Faraday’s Laws of Electrolysis
Before understanding Faraday’s laws of electrolysis, we must first understand the process of electrolysis of a metal sulfate.
Whenever an electrolyte like metal sulfate is diluted in water, its molecules split into positive and negative ions. The positive ions (or metal ions) move to the electrodes connected with the negative terminal of the battery where these positive ions take electrons from it, becoming a pure metal atom and getting deposited on the electrode.
The negative ions (or sulphions) move to the electrode connected with the positive terminal of the battery, where these negative ions give up their extra electrons and become SO4 radical. Since SO4 cannot exist in an electrically neutral state, it will attack the metallic positive electrode – forming a metallic sulfate which will again dissolve in the water.
Faraday’s laws of electrolysis are quantitative (mathematical) relationships that describe the above two phenomena.
Faraday’s First Law of Electrolysis
The amount of current flowing through the battery circuit is determined by how many electrons are transferred from the cathode to the positive metal ions (cations). For cations with a valency of two, such as Cu++, two electrons are transferred to each cation. We know that every electron has negative electrical charge – 1.602 × 10-19 Coulombs and say it is – e. So for disposition of every Cu atom on the cathode, there would be – 2.e charge transfers from cathode to cation.
Now say for t time there would be total n number of copper atoms deposited on the cathode, so total charge transferred, would be – 2.n.e Coulombs. Mass m of the deposited copper is obviously a function of the number of atoms deposited. So, it can be concluded that the mass of the deposited copper is directly proportional to the quantity of electrical charge that passes through the electrolyte. Hence mass of deposited copper m ∝ Q quantity of electrical charge passes through the electrolyte.
Faraday’s First Law of Electrolysis states that the chemical deposition due to the flow of current through an electrolyte is directly proportional to the quantity of electricity (coulombs) passed through it.
i.e. mass of chemical deposition:
Where, Z is a constant of proportionality and is known as electro-chemical equivalent of the substance.
If we put Q = 1 coulombs in the above equation, we will get Z = m which implies that electrochemical equivalent of any substance is the amount of the substance deposited on the passing of 1 coulomb through its solution. This constant of the passing of electrochemical equivalent is generally expressed in terms of milligrams per coulomb or kilogram per coulomb.
Faraday’s Second Law of Electrolysis
So far we have learned that the mass of the chemical, deposited due to electrolysis is proportional to the quantity of electricity that passes through the electrolyte.
The mass of a chemical deposited by electrolysis depends not only on the electricity used but also on the substance’s atomic weight, meaning different substances will have different masses for the same number of atoms.
Again, how many atoms deposited on the electrodes also depends upon their number of valency. If valency is more, then for the same amount of electricity, the number of deposited atoms will be less whereas if valency is less, then for the same quantity of electricity, more number of atoms to be deposited.
So, for the same quantity of electricity or charge passes through different electrolytes, the mass of deposited chemical is directly proportional to its atomic weight and inversely proportional to its valency.
Faraday’s second law of electrolysis states that, when the same quantity of electricity is passed through several electrolytes, the mass of the substances deposited are proportional to their respective chemical equivalent or equivalent weight.
Chemical Equivalent or Equivalent Weight
The chemical equivalent, as defined by Faraday’s laws, is the weight of a substance that can combine with or replace a unit weight of hydrogen.
The chemical equivalent of hydrogen is, thus, unity. Since valency of a substance is equal to the number of hydrogen atoms, which it can replace or with which it can combine, the chemical equivalent of a substance, therefore may be defined as the ratio of its atomic weight to its valency.
Who Invented Faraday’s Laws of Electrolysis?
Faraday’s Laws of Electrolysis were published by Michael Faraday in 1834. Michael Faraday was also responsible
Michael Faraday not only discovered these laws but also popularizing terminologies like electrodes, ions, anodes, and cathodes, crucial for modern chemistry.
