Class: Senior Secondary School 1 (SS1 / SSS 1)
Term: Second Term
Week: 10
Age: 15 years
Duration: 45 minutes
Subject: Refrigeration And Air Conditioning
Curriculum Theme: Trade
Previous Lesson: Refrigerants: Types of Refrigerants and Examples.
Topic: Refrigerant Chemical Names and Formulae
Subject Matter: Chemical names, chemical formulae, refrigerant identification

Specific Objectives

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

Cognitive Domain:

Define what a refrigerant is.
State the chemical names and formulae of common refrigerants.
Identify different refrigerants based on their chemical composition and ASHRAE numbering.

Affective Domain:

Appreciate the importance of knowing refrigerant chemical names for safety and proper handling.
Develop an interest in understanding the properties of various refrigerants.

Psychomotor Domain:

Write the chemical formulae for common refrigerants when given their names.
Properly identify refrigerants using labels and chemical charts.

Share information about refrigerant identification with peers.
Collaborate with classmates to understand complex chemical formulae.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Technical Vocational Education.
State Unified Scheme of Work for Senior Secondary Schools.
Refrigeration and Air Conditioning Technology by Billy C. Langley.

Instructional Materials

The teacher will teach this lesson with the aid of:

Chemical charts showing elements and compounds.
Sample refrigerant labels.
Tables listing common refrigerants with their chemical names and formulae.
Whiteboard and markers.

Rationale for the Lesson

This lesson helps pupils to understand the fundamental chemical composition of refrigerants, which is important for their safe handling and proper application in refrigeration and air conditioning systems. Knowing the chemical names and formulae enables pupils to differentiate between various refrigerants and understand their properties.

Prerequisite/Previous Knowledge

Pupils have a basic understanding of refrigeration and air conditioning principles and some fundamental concepts of chemistry, including elements and simple compounds.

Lesson Content/Board Summary

Refrigerant Chemical Names and Formulae

Definition of Refrigerant

A refrigerant is a substance used in a heat pump and refrigeration cycle. It undergoes phase transitions from a liquid to a gas and back to a liquid, absorbing and releasing heat in the process. This allows it to cool a space or substance.

Importance of Knowing Refrigerant Chemical Names and Formulae

It is important to know refrigerant chemical names and formulae for the following reasons:

Safety: To understand potential hazards like flammability or toxicity.
Identification: To correctly identify refrigerants and avoid mixing incompatible types.
Environmental Impact: To understand their Ozone Depletion Potential (ODP) and Global Warming Potential (GWP).
System Compatibility: To ensure the correct refrigerant is used for a specific system design.
Legislation and Regulations: To comply with laws regarding refrigerant use and handling.

Common Refrigerants: Chemical Names and Formulae

Refrigerants are often identified by an R-number (ASHRAE designation). The following are examples of common refrigerants with their chemical names and formulae:

R-11: Trichlorofluoromethane (CCl₃F)
R-12: Dichlorodifluoromethane (CCl₂F₂)
R-22: Chlorodifluoromethane (CHClF₂)
R-134a: 1,1,1,2-Tetrafluoroethane (CH₂FCF₃)
R-410A: A blend of Difluoromethane (CH₂F₂) and Pentafluoroethane (CHF₂CF₃)
R-717: Ammonia (NH₃)

Refrigerant Identification

Refrigerants can be identified through various means:

ASHRAE Number: The most common method, e.g., R-12, R-134a.
Chemical Name: The systematic name based on chemical composition.
Chemical Formula: Shows the types and number of atoms in a molecule.
Product Labels: Refrigerant cylinders and containers have labels indicating the R-number, chemical name, and safety information.
Colour Coding: Some refrigerant cylinders are colour-coded, though this is not a universal standard.

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 greets the pupils and introduces the topic by asking pupils to mention some common substances they know that have chemical names and formulae (e.g., water, salt). The teacher then links this to the importance of knowing the chemical names and formulae of refrigerants.
Pupils’ Activity: Pupils respond to the teacher’s questions and listen attentively.
Learning Point: Pupils are prepared for the lesson and understand the relevance of the topic.

Step 2: Definition of Refrigerant

Time: 8 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines what a refrigerant is, explaining its role in the refrigeration cycle. The definition is written on the board.
Pupils’ Activity: Pupils listen, ask questions for clarity, and copy the definition into their notebooks.
Learning Point: Pupils understand the basic function of a refrigerant.

Step 3: Importance of Knowing Refrigerant Chemical Names and Formulae

Time: 7 minutes
Teaching Skill: Elucidation/Discussion
Teacher’s Activity: The teacher discusses why it is important for technicians and users to know the chemical names and formulae of refrigerants, highlighting aspects like safety, environmental impact, and system compatibility. The points are listed on the board.
Pupils’ Activity: Pupils contribute to the discussion, ask questions, and note the key importance points.
Learning Point: Pupils understand the practical significance of refrigerant identification.

Step 4: Common Refrigerants: Chemical Names and Formulae

Time: 10 minutes
Teaching Skill: Demonstration/Listing
Teacher’s Activity: The teacher presents examples of common refrigerants, showing their ASHRAE numbers, chemical names, and chemical formulae using chemical charts and formula tables. The teacher explains the components of the formulae.
Pupils’ Activity: Pupils observe the charts, listen to the explanations, and copy the examples into their notebooks.
Learning Point: Pupils learn to associate common refrigerants with their chemical identities.

Step 5: Refrigerant Identification

Time: 5 minutes
Teaching Skill: Demonstration/Visualisation
Teacher’s Activity: The teacher uses sample refrigerant labels and charts to demonstrate how refrigerants are identified. The teacher explains how to read the R-number, chemical name, and other information on a label.
Pupils’ Activity: Pupils observe the labels and charts, and ask questions about identification methods.
Learning Point: Pupils understand practical methods for identifying refrigerants.

Step 6: Class Activity/Practice

Time: 5 minutes
Teaching Skill: Application/Guided Practice
Teacher’s Activity: The teacher writes a few refrigerant names on the board and asks pupils to attempt writing their chemical formulae, or provides a formula and asks for the name. The teacher guides them as needed.
Pupils’ Activity: Pupils attempt the practice questions in their notebooks, applying what they have learned.
Learning Point: Pupils practice applying their knowledge of refrigerant names and formulae.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

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

Define a refrigerant.
State two reasons why it is important to know the chemical names and formulae of refrigerants.
Mention the chemical name and formula for R-22.
How can refrigerants be identified on a container?

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 2 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson, reinforcing the importance of knowing refrigerant chemical names and formulae for safety and proper application. The teacher assigns homework: research two other common refrigerants and their chemical names/formulae.
Pupils’ Activity: Pupils listen to the summary and copy down the homework.
Learning Point: Pupils consolidate their learning and prepare for further study.

Lesson Keywords

Refrigerant – A substance used in a refrigeration cycle to absorb and release heat.
Chemical Formula – A way of expressing information about the proportions of atoms that constitute a particular chemical compound or molecule.
ASHRAE – American Society of Heating, Refrigerating and Air-Conditioning Engineers, which assigns R-numbers to refrigerants.
CFC – Chlorofluorocarbon, a type of refrigerant known for ozone depletion.
HCFC – Hydrochlorofluorocarbon, a type of refrigerant with less ozone depletion potential than CFCs.
HFC – Hydrofluorocarbon, a type of refrigerant with no ozone depletion potential, but often high global warming potential.

Differentiation

For pupils who grasp concepts quickly, the teacher can challenge them to research the environmental impact (ODP and GWP) of different refrigerant types. For pupils who require more support, the teacher can provide simplified charts or flashcards with the most common refrigerants and their formulae, offering individual guidance during the practice activity.

Note for teachers using this lesson plan

Ensure that actual refrigerant labels or clear visual aids are available for demonstration. Emphasize safety precautions related to handling refrigerants, even when discussing them theoretically. Encourage pupils to ask questions, especially regarding the chemical composition, as this can be a complex topic for some.