Faraday’s Laws – [First ,Second] Law of Electrolysis -Water Equation, Application

At the end of the article, you will able to describe – Faraday’s Laws, First, Second Law of Electrolysis, Importance, and Examples of the first law of electrolysis, Water Equation, Application. Let’s start discussing one by one.

Faraday’s Laws of Electrolysis

In the early nineteenth century, Michael Faraday carried out a number of experiments on electrolysis and discovered two important laws of electrolysis as:

Must Read- What is Electrolysis process and its Uses

Faraday’s First Law of Electrolysis

It states that the amount of any substance deposited at an electrode is directly proportional to the quantity of electricity passed through the electrolyte solution.

Mathematically: W ∝ Q

where W is the weight (in grams) of the substance deposited and Q is the quantity of electricity (in coulombs) which is passed through the electrolyte.

Since the quantity of electricity Q = I x t, where I is the current strength in amperes and t is the time in seconds, therefore, the above expression can be written as:

W ∝ I x t  Or   W=Z×I×t

where z is a constant of proportionality and is called the electrochemical equivalent of the substance. If I = 1 ampere and t = 1 second, then: W = Z

Thus, an electrochemical equivalent is defined as the weight of a substance deposited by the passage of one ampere current for one second (or one coulomb of electricity).

Importance of First Law of Electrolysis

This law is used to calculate:

  • The values of electrochemical equivalents of different ions.
  • The weights of different ions deposited by passing different quantities of electricity through their electrolytes.

It has been found out experimentally that by passing one Faraday, i.e., 96500 coulombs of electricity through an electrolyte, it results in the decomposition of one gram equivalent (i.e., equivalent weight expressed in grams) of the substance being deposited on the electrode. Therefore:

On the other hand, one coulomb of electricity deposits electrochemical equivalent (z) of the substance Hence, we may conclude that:

One Faraday or 96500 coulombs deposit one gram equivalent of the substance.

Electrochemical equivalent (Z) x 96500 = Gram equivalent

Example of First Law of Electrolysis

A current of 3 amperes strength on passing through silver nitrate solution for 20 minutes deposits 4 grams of silver. What is the electrochemical equivalent of silver?


  • Strength of the current (I) = 3 amperes
  • Time (t) = 20 minutes = 20 x 60 seconds
  • Weight of silver deposited (W) = 4 grams

According to Faraday’s Law of Electrolysis:

  • W = Z x I x t
  • 4= Z×3×20×60
  • Z = 4/3600 = 0.00111 g

Faraday’s Second Law of Electrolysis

It states that when the same quantity of electricity is passed through different electrolytes,  the amounts of different substances produced at the electrodes are directly proportional to their equivalent weights.

Let us explain the above law. Consider three cells, one contains water and a little HCl, the second cell contains copper sulfate solution and the third cell contains silver nitrate solution. Let these cells be connected in series with an electric battery.Faraday’s Laws - [First ,Second] Law of Electrolysis -Water Equation, Application

Since all the three cells have been connected in series, they will receive the same quantity of electricity during the same period of time. On passing the electric current through these cells, hydrogen, copper, and silver will be deposited at their respective cathodes in the ratio of their chemical equivalent, i.e., 31.75: 108. In other words,

Faraday’s Laws - [First ,Second] Law of Electrolysis -Water Equation, Application

Electrolysis of Water Equation

Electrolysis of Water is used to generate oxygen for the International Space Station. The overall Equation for the electrolysis of water is given below.

  • Ions are attracted to the oppositely charged electrode.
  • Reduction at cathode: 2 H+(aq) + 2e → H2(g)
  • Oxidation at  Anode:  2 H2O(l) → O2(g) + 4 H+(aq) + 4e.

Application of Electrolysis

The phenomenon of electrolysis finds numerous applications in industry and theoretical chemistry. Let us explain some of the important applications of electrolysis.

  1. Electroplating. We may define electroplating as the process of depositing a superior metal like gold, silver or nickel over a baser metal like copper or iron with the help of electricity. 
  2. Electrorefining of Metals. We may define electro-refining as the process of removal of impurities from an impure metal by electrolysis. Metals like copper, silver, gold, tin, aluminum, etc. are nowadays refined electrolytically.
  3. Electrotyping. We may define electrotyping as the process of obtaining the impressions of letters with the help of electrolysis. This process is employed in large-scale printing.
  4. Electrometallurgy.We may define Electrometallurgy as the process of extraction of metals from their ores by electrolysis.
  5. Determination of Equivalent Weights. Equivalent weights of elements can be determined from Faraday’s second law of electrolysis.

This is all about the basics of – Faraday’s Laws, Faraday’s First, Second Law of Electrolysis, Water Equation, Application.