Topic: Electrolysis – Electrolytes, Electrodes, Faraday’s Laws
Class: SS1
Specific Objectives:
By the end of the lesson, students should be able to:
- Define electrolysis and related terms like electrolyte and electrodes.
- Identify different types of electrolytes and electrodes.
- Explain the principles of electrolysis.
- State and apply Faraday’s First and Second Laws of Electrolysis.
- Solve basic calculations using Faraday’s laws.
Instructional Materials:
- Electrolysis setup (e.g., electrolytic cell with battery, wires, electrodes)
- Beaker with dilute acid (HCl or H₂SO₄), sodium chloride solution, or copper(II) sulfate
- Diagrams of electrolysis setup
- Chart showing Faraday’s laws
- Voltmeter, ammeter, stopwatch
Lesson Content:
Step 1: Meaning of Electrolysis
Electrolysis is the chemical decomposition of a compound (electrolyte) in molten or aqueous solution by the passage of electric current.
- It involves breaking chemical bonds using electricity.
Step 2: Important Terms
- Electrolyte: A substance that conducts electricity and undergoes chemical changes during electrolysis (e.g., NaCl solution, CuSO₄ solution).
- Electrodes: Conductors through which electric current enters or leaves the electrolyte.
- Anode: Positive electrode
- Cathode: Negative electrode
- Ions: Charged particles that move towards electrodes (Cations to cathode, Anions to anode).
- Electrolytic Cell: Apparatus used to carry out electrolysis.
Step 3: Electrolysis Process (Example: Electrolysis of Copper(II) Sulfate Solution)
Setup:
- Electrolyte: Copper(II) sulfate (CuSO₄) solution
- Electrodes: Copper electrodes
- When current passes:
- Cu²⁺ ions migrate to the cathode and gain electrons → deposited as Cu metal
- SO₄²⁻ or OH⁻ ions migrate to the anode and lose electrons → form oxygen gas
Half-equations:
- At cathode: Cu²⁺ + 2e⁻ → Cu(s)
- At anode: 2H₂O → O₂(g) + 4H⁺ + 4e⁻
Step 4: Faraday’s Laws of Electrolysis
First Law:
The mass of a substance deposited or liberated at an electrode is directly proportional to the quantity of electricity passed.
Mathematical expression:
Where:
- m = mass deposited (g)
- E = equivalent weight
- I = current (A)
- t = time (s)
- F = Faraday's constant (96500 C/mol)
Second Law:
When the same quantity of electricity is passed through different electrolytes, the mass of substances liberated is proportional to their chemical equivalent weights.
Step 5: Application of Faraday’s Laws (Sample Calculation)
Example:
Calculate the mass of copper deposited when a current of 2A is passed through copper(II) sulfate solution for 30 minutes.
Atomic mass of Cu = 63.5; n = 2
Solution:
So, 1.18 g of copper is deposited.
Evaluation:
- Define electrolysis.
- Differentiate between anode and cathode.
- State Faraday’s First Law of Electrolysis.
- What is the mass of silver deposited when 9650 C of electricity is passed through silver nitrate solution? (Ag = 108; n = 1)
- Write the electrode reactions for electrolysis of NaCl solution.
Homework:
- Draw and label the electrolysis setup for copper(II) sulfate using graphite electrodes.
- Explain what happens at each electrode.
- A current of 3 A is passed for 20 minutes through a solution of silver nitrate. Calculate the mass of silver deposited.
Conclusion:
Electrolysis is a vital chemical process used in industries like electroplating, metal extraction, and purification. Understanding the basic principles and calculations is essential for mastering electrochemistry.
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