Lesson Note on Electrolysis: Faraday’s Laws and Uses of Electrolysis for SSS 2

Class: Senior Secondary School 2 (SS2 / SSS2)
Term: 3rd Term
Week: 7
Age: 16 years
Duration: 45 minutes
Subject: Chemistry
Curriculum Theme: Energy and Chemical Reactions
Previous Lesson: Electrolysis: Meaning, Terms and Electrolysis of Water and Brine.
Topic: ELECTROLYSIS
Subject Matter: Faraday’s laws of electrolysis and calculations, uses of electrolysis (purification, extraction, electroplating of metals)

Specific Objectives

By the end of the lesson, pupils should be able to:

Cognitive Domain:

• Define electrolysis.
• State Faraday’s first and second laws of electrolysis.
• List and explain the uses of electrolysis.

Affective Domain:

• Appreciate the importance of electrolysis in industrial processes.
• Show interest in understanding the quantitative aspects of electrolysis.

Psychomotor Domain:

• Solve simple calculation questions based on Faraday’s laws.
• Identify practical applications of electrolysis in daily life.

Social Domain:

• Collaborate with peers to solve calculation problems.
• Participate actively in class discussions on the applications of electrolysis.

Reference Materials

The following resources were used in planning this lesson:

• Senior Secondary Schools Education Curriculum
• State Unified Scheme of Work
• New School Chemistry for Senior Secondary Schools by Osei Yaw Ababio
• https://www.britannica.com/science/Faradays-laws-of-electrolysis
• https://www.chemguide.co.uk/physical/electrolysis/farlaws.html

Instructional Materials

The teacher will teach this lesson with the aid of:

• Students’ textbooks
• Students’ workbook
• Copper sulphate solution
• Ammeter
• Voltmeter
• Connecting wires
• Electrodes (e.g., copper, graphite)
• Power source (battery)

Rationale for the Lesson

Understanding electrolysis is important for pupils because it explains how electricity can drive chemical reactions. This knowledge helps them grasp fundamental principles of electrochemistry and its wide applications in industries such as metal refining and coating.

Prerequisite/Previous Knowledge

Pupils should have prior knowledge of basic electricity, redox reactions, and concepts of oxidation and reduction.

Lesson Content/Board Summary

ELECTROLYSIS

Definition of Electrolysis

Electrolysis is the process by which an electric current is passed through an electrolyte to cause a non-spontaneous chemical reaction. An electrolyte is a substance that conducts electricity in its molten state or in solution due to the presence of mobile ions.

Faraday’s First Law of Electrolysis

Faraday’s first law of electrolysis 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 ∝ Q

m = ZQ

Since Q = It, then m = ZIt

Where:

• m = mass of substance deposited or liberated (in grams)
• Q = quantity of electricity passed (in Coulombs, C)
• I = current (in Amperes, A)
• t = time (in seconds, s)
• Z = electrochemical equivalent (in g/C)

Example 1:

A current of 0.5 A is passed through a solution of silver nitrate for 30 minutes. Calculate the mass of silver deposited. (Given: Electrochemical equivalent of silver = 1.118 x 10^-3 g/C)

Solution:

• Step 1: Identify given values and formula.

I = 0.5 A

t = 30 minutes = 30 x 60 = 1800 seconds

Z = 1.118 x 10^-3 g/C

Formula: m = ZIt

• Step 2: Substitute values into the formula.

m = (1.118 x 10^-3 g/C) x (0.5 A) x (1800 s)

• Step 3: Calculate the mass.

m = 1.0062 g

Faraday’s Second Law of Electrolysis

Faraday’s second law of electrolysis states that when the same quantity of electricity is passed through different electrolytes connected in series, the masses of the substances deposited or liberated at the electrodes are directly proportional to their chemical equivalent masses.

Mathematically:

m₁ / m₂ = E₁ / E₂

Where:

• m₁, m₂ = masses of substances deposited or liberated
• E₁, E₂ = chemical equivalent masses of the substances

The chemical equivalent mass (E) of an element is given by: E = Molar mass / Valency (or charge of ion)

Example 2:

Two electrolytic cells containing silver nitrate (AgNO₃) and copper(II) sulphate (CuSO₄) solutions are connected in series. If 2.7 g of silver is deposited in the first cell, what mass of copper will be deposited in the second cell? (Atomic mass of Ag = 108, Cu = 63.5)

Solution:

• Step 1: Determine the equivalent masses.

For Ag: Equivalent mass (E_Ag) = Molar mass / Valency = 108 / 1 = 108

For Cu: Equivalent mass (E_Cu) = Molar mass / Valency = 63.5 / 2 = 31.75

• Step 2: Apply Faraday’s second law.

m_Ag / m_Cu = E_Ag / E_Cu

2.7 / m_Cu = 108 / 31.75

• Step 3: Solve for m_Cu.

m_Cu = (2.7 x 31.75) / 108

m_Cu = 0.79375 g

Uses of Electrolysis

Electrolysis has various important applications in industries and everyday life. The following are some key uses:

• Extraction of Metals: Highly reactive metals like sodium, potassium, aluminium, and magnesium are extracted from their molten ores by electrolysis. For example, aluminium is extracted from molten alumina (Al₂O₃).
• Purification of Metals: Impure metals can be refined electrolytically to obtain high-purity metals. Copper purification is a common example, where impure copper acts as the anode and pure copper as the cathode.
• Electroplating: This is the process of coating one metal with a thin layer of another metal using electrolysis. It is done to improve appearance, prevent corrosion, or increase hardness. Examples include silver plating, gold plating, and chromium plating.
• Manufacture of Chemicals: Electrolysis is used to produce important chemicals such as chlorine, sodium hydroxide, and hydrogen gas from brine (aqueous NaCl solution).
• Anodizing: This process increases the thickness of the natural oxide layer on the surface of metal parts, especially aluminium, to enhance corrosion resistance and wear resistance.

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher introduces the topic by asking pupils what they understand by electricity and its ability to cause chemical changes. The teacher then defines electrolysis.
Pupils’ Activity: Pupils respond to the questions and listen to the definition of electrolysis.
Learning Point: Pupils are introduced to the concept of electrolysis.

Step 2: Faraday’s First Law of Electrolysis

Time: 10 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains Faraday’s first law of electrolysis, its mathematical representation (m = ZIt), and explains each variable. The teacher then guides pupils through Example 1 from the board summary.
Pupils’ Activity: Pupils listen, take notes, and ask questions for clarification. They follow along with the worked example.
Learning Point: Pupils understand the relationship between mass deposited and quantity of electricity.

Step 3: Faraday’s Second Law of Electrolysis

Time: 10 minutes
Teaching Skill: Explanation/Problem Solving
Teacher’s Activity: The teacher explains Faraday’s second law, its mathematical representation (m₁/m₂ = E₁/E₂), and how to calculate equivalent mass. The teacher then guides pupils through Example 2 from the board summary.
Pupils’ Activity: Pupils pay attention, take notes, and participate in solving the second example.
Learning Point: Pupils grasp the relationship between masses deposited and equivalent masses when electricity is passed through different electrolytes.

Step 4: Uses of Electrolysis (Part 1)

Time: 7 minutes
Teaching Skill: Discussion/Listing
Teacher’s Activity: The teacher initiates a discussion on the practical applications of electrolysis, focusing on the extraction and purification of metals. The teacher provides examples.
Pupils’ Activity: Pupils contribute ideas and note down the uses and examples discussed.
Learning Point: Pupils learn about the industrial importance of electrolysis in metal production.

Step 5: Uses of Electrolysis (Part 2)

Time: 5 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher continues the discussion on the uses of electrolysis, covering electroplating and the manufacture of chemicals.
Pupils’ Activity: Pupils listen and add to their notes on the applications of electrolysis.
Learning Point: Pupils understand further applications of electrolysis in various industries.

Step 6: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

1. Define electrolysis.
2. State Faraday’s first law of electrolysis.
3. State two uses of electrolysis.
4. A current of 0.2 A is passed through a copper (II) sulphate solution for 10 minutes. Calculate the quantity of electricity passed.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 7: Conclusion

Time: 3 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson, reinforcing the definitions of Faraday’s laws and their practical applications.
Pupils’ Activity: Pupils listen to the summary and ask any remaining questions.
Learning Point: The main concepts of the lesson are reinforced.

Lesson Keywords

• Electrolysis – Chemical decomposition produced by passing an electric current through a liquid or solution containing ions.
• Electrolyte – A liquid or solution that conducts electricity due to the presence of mobile ions.
• Faraday’s First Law – Mass deposited is proportional to the quantity of electricity passed.
• Faraday’s Second Law – Masses deposited by the same quantity of electricity are proportional to their equivalent masses.
• Electrochemical Equivalent (Z) – The mass of a substance deposited or liberated per unit quantity of electricity passed.
• Electroplating – Coating a metal with a thin layer of another metal using electrolysis.

Differentiation

For pupils who grasp concepts quickly, the teacher can provide more complex calculation problems or ask them to research other industrial applications of electrolysis. For pupils needing more support, the teacher can provide simplified examples, offer one-on-one guidance during calculations, and use diagrams to illustrate the processes.

Note for teachers using this lesson plan

Ensure that pupils clearly understand the difference between Faraday’s first and second laws and when to apply each. Emphasize the importance of correct units in calculations. Practical demonstrations using a simple electrolytic cell, if available, can greatly enhance understanding.