Faraday’s Second Law of Electrolysis: Faraday’s law is an important principle studied in chemistry. Faraday’s Second Law demonstrates the direct relationship between the electrical current passing through an electrolyte and the quantity of substance transformed during the electrolytic process. Michael Faraday, a British scientist formulated this law which you are going to know about in this article.
Electrolysis
Electrolysis is a chemical process that uses an electric current to trigger a non-spontaneous chemical reaction. It involves an electrolytic cell with two electrodes named as the anode (positive) and the cathode (negative). The electrolyte is the substance that changes chemically during the electrolytic process.
Faraday’s Second Law Definition
According to NCERT textbook Class 12 Part I Faraday’s second law of electrolysis states that “the amounts of different substances liberated by the same quantity of electricity passing through the electrolytic solution are proportional to their chemical equivalent weights (Atomic Mass of Metal ÷ Number of electrons required to reduce the cation).”
W2/W1=E2/E1
Where W1 and W2 are weights deposited of two elements 1 and 2 respectively, E1 and E2 are the equivalent weights of two elements 1 and 2 respectively.
Faraday’s Second Law Formula
Mathematically, faraday’s second law can be expressed as:
m = (Q × E) / (z × F)
Where:
m = Mass of the substance deposited (in grams).
z = valency or the number of electrons exchanged
F = Faraday’s constant (≅ 96,485 C/mol), the charge of one mole of electrons.
Q = Total electric charge passed through the electrolyte in coulombs.
E = equivalent weight of the substance (in grams)
Practical Applications of Faraday’s Second Law
Electroplating
Electroplating is one of the applications of Faraday’s Second Law. It is a process performed majorly in industries for manufacturing jewelry, decoratives and industrial components with a layer of different metal over them to make them look shiny. This is also helpful in corrosion prevention.
Water Treatment
In water treatment plants, Faraday’s second law of electrolysis is used to determine the chlorine and other disinfectants’ amount in the water.
Batteries
The amount of reactants consumed and products generated during the charging and discharging processes are calculated using Faraday’s second law. Apart from these, there are various other applications of Faraday’s second law that make it one of the most important laws of chemistry.
Solved Faraday’s Second Law Question Examples
Question: Suppose you are electroplating a metal object with copper. You pass a current of 2.0 amperes through a copper sulfate (CuSO4) solution for 45 minutes (or 2700 seconds). Calculate the mass of copper deposited on the object during this process.
Solution:
- Calculate the number of moles of electrons (Q) passed through the cell using the formula:
- Number of moles = (Current (A) × Time (s)) / (2 × Faraday’s constant)
- Number of moles = (2.0 A × 2700 s) / (2 × 96,485 C/mol) = 0.058 moles
- Determine the valency (z) of copper. For copper, it’s 2 because during the electroplating process, each copper ion (Cu²⁺) gains two electrons to become solid copper (Cu).
- Find the equivalent weight (E) of copper using its molar mass (Cu = 63.5 g/mol):
- Equivalent Weight of Copper (Cu) = Molar Mass (Cu) / Valency (Cu) = 63.5 g/mol / 2 = 31.75 g/equiv
- Now, apply Faraday’s Second Law formula to calculate the mass (m) of copper deposited:
- Mass (Cu) = (Q × E) / (z × F)
- Mass (Cu) = (0.058 moles × 31.75 g/equiv) / (2 × 96,485 C/mol) = 0.097 g
Question: Imagine you are conducting an experiment to produce chlorine gas (Cl2) through the electrolysis of a sodium chloride (NaCl) solution. You pass a current of 5.0 amperes for 90 minutes (or 5400 seconds). Calculate the volume of chlorine gas produced at standard temperature and pressure (STP).
Solution
- Calculate the number of moles of electrons (Q) passed through the cell using the formula:
- Number of moles = (Current (A) × Time (s)) / (2 × Faraday’s constant)
- Number of moles = (5.0 A × 5400 s) / (2 × 96,485 C/mol) = 0.139 moles
- Since the electrolysis of sodium chloride produces 1 mole of chlorine gas (Cl2) for every 2 moles of electrons passed, we need to find the number of moles of chlorine gas produced, which is half the number of moles of electrons: 0.139 moles / 2 = 0.0695 moles.
- To calculate the volume (V) of chlorine gas at STP (Standard Temperature and Pressure), we can use the ideal gas law:
- Volume (V) = (Number of moles) × (Molar volume at STP)
- Molar volume at STP is approximately 22.4 L/mol.
- Volume (V) = 0.0695 moles × 22.4 L/mol = 1.572 L
