Class: Senior Secondary School 2 (SS2 / SSS2)
Term: Second Term
Week: 2
Age: 16 years
Duration: 45 minutes
Subject: Chemistry
Curriculum Theme: Water and its properties
Previous Lesson: Water: Meaning, Structure and Solubility.
Topic: WATER
Subject Matter: Hardness of water (and removal of hardness), purification of water, municipal water supply, production of distilled water

Specific Objectives

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

Cognitive Domain:

Define hard water and soft water.
State the causes of water hardness.
Explain the various stages in water treatment for consumption.
Describe methods for removing water hardness.
Describe the steps in water purification.
Explain the process of producing distilled water.

Affective Domain:

Appreciate the importance of clean water for human health.
Develop interest in the processes of water purification and distillation.

Psychomotor Domain:

Sketch a simple distillation setup.
Identify the components of a water treatment plant (if an excursion is undertaken).

Participate in discussions about water quality and its impact on the community.

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

Instructional Materials

The teacher will teach this lesson with the aid of:

Weighing balance
Evaporating dish
Water bath
Distillation apparatus
Bath water
Charts showing water treatment stages
Diagrams of distillation setup

Rationale for the Lesson

This lesson enables pupils to understand the importance of water quality and the processes involved in making water safe for consumption. It helps them appreciate how water is treated for municipal supply and how pure water is obtained for laboratory use.

Prerequisite/Previous Knowledge

Pupils should have prior knowledge of water as a chemical compound, its physical and chemical properties, and its importance to life.

Lesson Content/Board Summary

WATER

Hardness of Water

Water hardness is caused by the presence of dissolved mineral salts, primarily bicarbonates, chlorides, and sulphates of calcium and magnesium.

Soft water: Lathers easily with soap because it contains very few dissolved mineral salts.
Hard water: Does not lather easily with soap because it contains significant amounts of dissolved mineral salts.

Types of Hardness

Temporary Hardness: Caused by dissolved bicarbonates of calcium and magnesium. It can be removed by boiling.
Permanent Hardness: Caused by dissolved chlorides and sulphates of calcium and magnesium. It cannot be removed by boiling.

Removal of Hardness

Removal of Temporary Hardness:
- Boiling: Heating causes the bicarbonates to decompose into insoluble carbonates, which settle out.
- Adding Slaked Lime (Clark’s Method): Adding calcium hydroxide precipitates calcium carbonate.
Removal of Permanent Hardness:
- Adding Washing Soda (Sodium Carbonate): Sodium carbonate reacts with calcium and magnesium salts to form insoluble carbonates.
- Ion Exchange Method: Hard water is passed through a resin column that exchanges calcium and magnesium ions for sodium ions.
- Distillation: This process removes all dissolved impurities, including those causing hardness.

Purification of Water / Municipal Water Supply

Municipal water treatment involves several stages to make water safe for drinking:

Screening: Large debris like leaves, sticks, and plastic are removed using screens.
Sedimentation (Coagulation): Chemicals like alum (aluminium sulphate) are added to coagulate small suspended particles into larger flocs, which then settle at the bottom of a sedimentation tank.
Filtration: Water is passed through layers of sand and gravel to remove remaining suspended particles and some microorganisms.
Chlorination (Disinfection): Chlorine gas or hypochlorite is added to kill harmful bacteria and other microorganisms.
Fluoridation (Optional): Fluoride may be added to help prevent tooth decay.
Storage and Distribution: Treated water is stored in reservoirs and then distributed to homes and businesses.

Production of Distilled Water

Distilled water is pure water obtained by heating water to produce steam, which is then condensed back into liquid form. This process removes dissolved solids, minerals, and many impurities.

Process (Simple Distillation):

Water is placed in a distillation flask and heated.
The water boils and turns into steam.
The steam rises and passes into a condenser, which is cooled by circulating cold water.
The steam condenses back into liquid water (distillate) and is collected in a receiving flask.

Uses of Distilled Water:

In laboratories for preparing solutions and experiments.
In car batteries and steam irons to prevent mineral buildup.
In medical applications.

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 asks pupils what they know about water and its importance, then introduces the topic of water quality and treatment.
Pupils’ Activity: Pupils respond to the teacher’s questions and listen attentively.
Learning Point: Pupils are engaged and the lesson topic is introduced.

Step 2: Hardness of Water

Time: 10 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher explains what hard and soft water are, stating the causes of hardness and distinguishing between temporary and permanent hardness.
Pupils’ Activity: Pupils listen, ask questions for clarification, and take notes.
Learning Point: Pupils understand the definitions and causes of water hardness.

Step 3: Removal of Hardness

Time: 10 minutes
Teaching Skill: Explanation/Elaboration
Teacher’s Activity: The teacher explains various methods for removing both temporary and permanent hardness from water, using examples.
Pupils’ Activity: Pupils listen, take notes, and contribute to discussions on practical applications.
Learning Point: Pupils learn how to remove different types of water hardness.

Step 4: Purification of Water / Municipal Water Supply

Time: 10 minutes
Teaching Skill: Description/Diagrammatic Representation
Teacher’s Activity: The teacher explains the various stages of municipal water treatment (screening, sedimentation, filtration, chlorination) using charts or diagrams.
Pupils’ Activity: Pupils observe the charts, describe the steps, and ask questions.
Learning Point: Pupils understand the process of making water safe for drinking.

Step 5: Production of Distilled Water

Time: 5 minutes
Teaching Skill: Demonstration/Practical Application
Teacher’s Activity: The teacher explains the concept of distilled water, demonstrates the laboratory distillation setup (if apparatus is available), and explains the process.
Pupils’ Activity: Pupils observe the setup, sketch the diagram, and note down the steps.
Learning Point: Pupils learn how distilled water is produced and its uses.

Step 6: Evaluation/Review

Time: 5 minutes
Teaching Skill: Questioning/Assessment
Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

Define hard water and soft water.
List two causes of water hardness.
State two methods for removing temporary hardness.
Describe two stages involved in municipal water purification.
What is distilled water and how is it produced?

Pupils’ Activity: Pupils answer orally and in writing.
Learning Point: Pupils demonstrate understanding of the lesson.

Step 7: Conclusion

Time: 1 minute
Teaching Skill: Summarization
Teacher’s Activity: The teacher briefly summarizes the key points of the lesson, emphasizing the importance of clean water.
Pupils’ Activity: Pupils listen and ask any final questions.
Learning Point: The lesson is brought to a logical close.

Lesson Keywords

Hard water – Water that contains dissolved mineral salts, preventing it from lathering easily with soap.
Soft water – Water that contains very few dissolved mineral salts, allowing it to lather easily with soap.
Temporary hardness – Water hardness caused by bicarbonates of calcium and magnesium, removable by boiling.
Permanent hardness – Water hardness caused by chlorides and sulphates of calcium and magnesium, not removable by boiling.
Distillation – A process of purifying water by heating it to steam and then condensing the steam.
Chlorination – The process of adding chlorine to water to kill harmful microorganisms.
Sedimentation – The process where suspended particles settle out of water, often aided by coagulation.
Filtration – The process of passing water through a filter medium to remove suspended impurities.
Alum – Aluminium sulphate, a chemical used as a coagulant in water purification.

Differentiation

For pupils who grasp concepts quickly, the teacher can encourage them to research advanced water purification methods like reverse osmosis. For those who need more support, the teacher can provide simplified diagrams and allow for peer tutoring during activity sessions.

Note for teachers using this lesson plan

Teachers should ensure that all instructional materials, especially the distillation apparatus, are available and in working condition for a practical demonstration. If an excursion to a water works is not feasible, detailed charts and videos can be used to illustrate the municipal water supply process. Emphasize the real-world application of water treatment to health and hygiene.