Faraday's Law of Electrolysis: Definition, Key Factors and Real-Life Applications

Faraday's Law of Electrolysis is one of the most important concepts in electrochemistry. It explains how the amount of substance deposited or liberated during electrolysis depends on the quantity of electric charge passed through an electrolyte. Do you know? The law is proposed by the English scientist Michael Faraday, these laws form the foundation of many industrial processes such as electroplating, metal extraction and metal purification. 

The article focuses on Faraday's Law of Electrolysis, the first and second laws, important formulas,examples and more in easy-to-understand manner. 

Table of Contents 

• What is Electrolysis
• What is an Electrolytic Cell
• What is Faraday's Law of Electrolysis
• Important Formulae of Faraday’s Law of Electrolysis
• Solved Example of Faraday's Law of Electrolysis
• Applications and Limitations of Faraday's Law of Electrolysis
• Difference Between Faraday's First and Second Law
• Frequently Asked Questions about Faraday's Law of Electrolysis

What is Electrolysis

Electrolysis is a chemical process in which electrical energy is used to bring about a chemical reaction that does not occur on its own. The process takes place in an electrolytic cell containing an electrolyte, two electrodes and an external source of electricity.

During electrolysis its observed that: 

• Positive ions (cations) move towards the cathode and gain electrons.
• Negative ions (anions) move towards the anode and lose electrons.

Electrolysis is widely used in electroplating, extraction of metals, purification of metals and industrial chemical manufacturing.

Also Read: Electrons 

What is an Electrolytic Cell

An electrolytic cell is the apparatus used to carry out electrolysis.

Its main components are:

• Electrolyte: A molten salt or aqueous solution that conducts electricity through ions.
• Cathode: Negative electrode where reduction takes place.
• Anode: Positive electrode where oxidation occurs.
• Power Source: Supplies electrical energy required for the reaction.

Unlike galvanic cells, electrolytic cells require an external source of electricity.

Mechanism of Electrolysis

When electric current passes through the electrolyte:

At the Cathode

Positive ions gain electrons and get deposited as neutral atoms.

Example:

$Na^+ + e^- \rightarrow Na$

At the Anode

Negative ions lose electrons.

$2Cl^- \rightarrow Cl_2 +2e^-$

Overall reaction:

$2NaCl \rightarrow 2Na + Cl_2$

What is Faraday's Law of Electrolysis

Faraday's Law of Electrolysis explains the quantitative relationship between the electric charge passed through an electrolyte and the amount of substance deposited or liberated at the electrodes.

These laws were proposed by Michael Faraday in 1834 and are widely used in electrochemistry and industrial manufacturing.

Faraday proposed two laws:

• Faraday's First Law of Electrolysis
• Faraday's Second Law of Electrolysis

Faraday's First Law of Electrolysis

The first law states that:

The mass of a substance deposited or liberated at an electrode is directly proportional to the quantity of electricity passed through the electrolyte.

Mathematically,

$m \propto Q$

Since

Q=It

Therefore,

m=ZIt

Where

• m = mass deposited (g)
• I = current (A)
• t = time (s)
• Q = charge (C)
• Z = electrochemical equivalent

The Electrochemical Equivalent (Z) is the mass of a substance deposited by one coulomb of electric charge.

Also Read: Cathode Ray Experiment 

Faraday's Second Law of Electrolysis

The second law states that:

When the same quantity of electricity passes through different electrolytes, the masses of substances deposited are directly proportional to their chemical equivalent masses.

Mathematically,

$\frac{m_1}{m_2}=\frac{E_1}{E_2}$

where

$E=\frac{M}{n}$

Here,

• E = equivalent weight
• M = molar mass
• n = number of electrons exchanged

This law helps compare the amount of different substances deposited during electrolysis.

Important Formulae of Faraday’s Law of Electrolysis 

Formula	Expression
Charge	Q=It
First Law	m=ZIt
Electrochemical Equivalent	$Z=\frac{E}{F}$
Equivalent Weight	$E=\frac{M}{n}$
Mass Deposited	$m=\frac{QM}{nF}$
Faraday Constant	$F=96485\;C\;mol^{-1}$

Solved Example of Faraday's Law of Electrolysis 

Question: Calculate the mass of copper deposited when a current of 2 A is passed through copper sulphate solution for 600 seconds.

Given:

• Current = 2 A
• Time = 600 s

Charge,

$Q=It=2\times600=1200C$

Using

$m=\frac{QM}{nF}$

where

• M = 63.5 g/mol
• n = 2
• F = 96485 C/mol

Substituting the values gives the mass of copper deposited.

Read More: Cathode and Anode 

Applications and Limitations of Faraday's Law of Electrolysis

Faraday's laws have numerous industrial and laboratory applications.

Some important applications include:

• Electroplating jewellery and automobile parts
• Purification of copper and other metals
• Extraction of aluminium and sodium
• Manufacture of chlorine and hydrogen
• Electroforming of machine components
• Quantitative electrochemical calculations
• Industrial metal recovery

Limitations

• Applicable only to electrolysis.
• Assumes 100% current efficiency.
• Side reactions may affect practical results.
• Does not explain reaction mechanisms.

Difference Between Faraday's First and Second Law

Faraday's First Law	Faraday's Second Law
Relates mass with electric charge.	Compares masses deposited in different electrolytes.
Depends on the quantity of electricity.	Depends on equivalent weight.
Formula: m=ZIt	Formula:  $m_1/m_2=E_1/E_2$
Used to calculate deposited mass.	Used to compare different substances.

The basis of electrochemistry is Faraday’s Law of Electrolysis that describes the chemical changes caused by electrical energy. These laws find extensive application in electroplating, in the extraction and purification of metals and in industrial manufacturing.