Pure and Impure Water, Water Contaminants and Purification for SS 1

Class: SS 1
Term: Third Term
Week: 7
Age: 15 years
Duration: 60 minutes
Subject: Chemistry
Curriculum Theme: Chemistry and the environment
Focal competence: Demonstrating water purification using filtration and distillation methods
Key competencies/values: Collaboration; Responsibility
Skills:

• Using filtration and distillation methods to purify water

Previous Lesson: Water, Structure,
Topic: Water: Pure And Impure Water
Subject Matter: Pure and impure water, Substances that contaminate water. Purification of water

Specific Objectives

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

Cognitive Domain

• Distinguish between pure and impure water.
• Identify substances that contaminate water.
• Write the chemical formula of water.

Affective Domain

• Appreciate the importance of clean water for health.
• Collaborate effectively with peers during group activities.
• Demonstrate responsibility in handling laboratory apparatus.

Psychomotor Domain

• Use filtration method to purify water.
• Use distillation method to purify water.

Social Domain

• Work cooperatively in groups to purify water samples.

Reference Materials

The following resources were used in planning this lesson:

• 2025 New Revised Senior Secondary Education Curriculum (SSEC)
• Relevant State Unified Scheme of Work
• The HeadTeacher Scheme of work For The New Revised Senior Secondary Education Curriculum (SSEC)
• A suitable Senior Secondary Chemistry textbook for SS 1

Instructional Materials

The teacher will teach this lesson with the aid of:

• Charts on the structure and sources of water.
• Samples of pure water (distilled water) and impure water (e.g., muddy water, tap water).
• The Periodic Table.
• Markers and cardboard papers.
• Plastic buckets or containers.
• Filtration apparatus: filter funnel, filter paper, beaker, retort stand.
• Distillation apparatus: round-bottom flask, condenser, receiving beaker, heat source (Bunsen burner), thermometer, retort stands.

Rationale for the Lesson

This lesson is important as it provides students with fundamental knowledge about water quality, its contaminants, and practical methods for purification. Understanding these concepts helps students appreciate the significance of clean water for health and the environment. It also equips them with basic scientific skills in water treatment, which has direct applications in daily life and various industries.

Prerequisite/Previous Knowledge

Students should have a basic understanding of matter, mixtures, and simple separation techniques from their Junior Secondary Science lessons.

Lesson Content/Board Summary

Water: Pure And Impure Water

Pure Water

Pure water is chemically defined as a substance containing only hydrogen and oxygen atoms bonded together in a specific ratio, represented by the chemical formula (H_2O). It is free from any dissolved minerals, salts, gases, or biological contaminants. Distilled water is an example of pure water.

Characteristics of pure water:

1. It boils at exactly (100^circ C) at standard atmospheric pressure.
2. It freezes at exactly (0^circ C) at standard atmospheric pressure.
3. It is tasteless, odourless, and colourless.
4. It does not conduct electricity (as it lacks dissolved ions).
5. It has a neutral pH of 7.

Impure Water

Impure water, also known as natural water or contaminated water, contains dissolved or suspended substances other than (H_2O). These impurities can be minerals, salts, gases, organic matter, microorganisms, or pollutants.

Characteristics of impure water:

1. Its boiling point is usually above (100^circ C).
2. Its freezing point is usually below (0^circ C).
3. It may have a taste, odour, or colour depending on the impurities.
4. It conducts electricity due to the presence of dissolved ions.
5. Its pH can vary depending on the nature of the dissolved substances.

Distinction Between Pure and Impure Water

The key differences between pure and impure water are summarised below:

1. Composition: Pure water contains only (H_2O) molecules, while impure water contains (H_2O) plus other dissolved or suspended substances.
2. Boiling Point: Pure water boils at a fixed temperature ((100^circ C)), whereas impure water boils over a range of temperatures, typically above (100^circ C).
3. Freezing Point: Pure water freezes at a fixed temperature ((0^circ C)), while impure water freezes below (0^circ C).
4. Conductivity: Pure water is a poor conductor of electricity, while impure water conducts electricity due to dissolved ions.
5. Taste/Odour: Pure water is tasteless and odourless, while impure water may have a taste or odour from impurities.

Substances that Contaminate Water

Water can be contaminated by various substances, which can be broadly classified into physical, chemical, and biological contaminants.

1. Physical Contaminants: These are visible impurities that affect the physical appearance of water.
   • Sand, silt, clay, and other suspended solids.
   • Dust particles.
   • Organic debris (e.g., leaves, twigs).
2. Chemical Contaminants: These are dissolved chemical substances, often invisible, that can be harmful.
   • Industrial waste (e.g., heavy metals like lead, mercury; acids, alkalis).
   • Agricultural runoff (e.g., pesticides, herbicides, fertilisers containing nitrates and phosphates).
   • Household chemicals (e.g., detergents, cleaning agents).
   • Dissolved salts (e.g., calcium, magnesium, sodium chlorides).
3. Biological Contaminants: These are living organisms that can cause diseases.
   • Bacteria (e.g., E. coli, cholera bacteria).
   • Viruses (e.g., hepatitis A, rotavirus).
   • Protozoa (e.g., Giardia, Cryptosporidium).
   • Algae and fungi.

Purification of Water

Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from water to make it suitable for a specific purpose, such as drinking or industrial use.

Methods of Water Purification

1. Filtration: This is a physical process that separates insoluble solid impurities from a liquid by passing the mixture through a filter medium.
   • Principle: The filter medium (e.g., filter paper, sand, gravel) has pores that are large enough for water molecules to pass through but too small for solid particles.
   • Process: Impure water is poured through a filter funnel lined with filter paper. The solid impurities (residue) are retained on the filter paper, while the clear water (filtrate) passes through into a collecting beaker.
   • What it removes: Suspended solids like sand, mud, and other particulate matter. It does not remove dissolved substances or microorganisms.
2. Distillation: This is a process that involves heating water to its boiling point to form steam, then cooling the steam to condense it back into liquid water.
   • Principle: Water has a lower boiling point than most dissolved solids and a higher boiling point than dissolved gases. By boiling and condensing, water is separated from these impurities.
   • Process: Impure water is heated in a distillation flask until it boils, producing steam. The steam rises and passes into a condenser, where it is cooled by circulating cold water. The cooled steam condenses into pure liquid water (distillate) which is collected in a receiving beaker. Non-volatile impurities remain in the distillation flask.
   • What it removes: Dissolved salts, non-volatile organic compounds, and most microorganisms. It produces highly pure water.

Teaching Methods/Instructional Techniques

Discussion, Demonstration, Guided Practice, Question and Answer, Explanation, Group Work, Practical Activity.

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Questioning/Activating Prior Knowledge

Teacher’s Activity: The teacher greets the students and asks them to state various sources of water they know and discuss the importance of water. The teacher then introduces the topic: “Water: Pure and Impure Water.”

Pupils’ Activity: Pupils respond by naming sources of water (e.g., rain, rivers, wells, taps) and discussing its importance (e.g., drinking, cooking, washing).

Learning Point: Importance of water

Step 2: Pure and Impure Water

Time: 10 minutes

Teaching Skill: Explanation/Demonstration

Teacher’s Activity: The teacher explains the concepts of pure and impure water, highlighting their chemical compositions and observable properties. The teacher shows samples of distilled water (pure) and tap/muddy water (impure) and asks students to observe their differences. The chemical formula of water ((H_2O)) is written on the board.

Pupils’ Activity: Pupils observe the water samples, listen to the explanation, and copy the chemical formula of water.

Learning Point: Pure and impure water

Step 3: Distinguishing Water Types

Time: 10 minutes

Teaching Skill: Discussion/Comparison

Teacher’s Activity: The teacher guides a discussion on how to distinguish between pure and impure water based on properties like boiling point, freezing point, taste, and electrical conductivity. The teacher uses a chart to summarise these distinctions.

Pupils’ Activity: Pupils participate in the discussion, contributing ideas and noting the distinguishing characteristics.

Learning Point: Distinguishing water types

Step 4: Water Contaminants

Time: 5 minutes

Teaching Skill: Explanation/Identification

Teacher’s Activity: The teacher explains that water can be contaminated by physical, chemical, and biological substances. The teacher asks students to brainstorm examples of each type of contaminant.

Pupils’ Activity: Pupils identify various substances that contaminate water, such as sand, industrial waste, and bacteria.

Learning Point: Types of contaminants

Step 5: Water Purification – Filtration

Time: 10 minutes

Teaching Skill: Demonstration/Guided Practice

Teacher’s Activity: The teacher demonstrates the filtration method using muddy water, a filter funnel, filter paper, and a beaker. The teacher explains the process and what filtration removes. Students are guided to work in groups to set up their own filtration apparatus.

Pupils’ Activity: Pupils observe the demonstration, ask questions, and then set up and perform simple filtration in their groups.

Learning Point: Filtration method demonstrated

Step 6: Water Purification – Distillation

Time: 10 minutes

Teaching Skill: Demonstration/Explanation

Teacher’s Activity: The teacher demonstrates the distillation method using a complete distillation apparatus (if available, or a simplified setup). The teacher explains the principle, process, and what distillation removes to produce pure water. Safety precautions for heating are highlighted.

Pupils’ Activity: Pupils observe the distillation demonstration, paying attention to the setup and process, and note the safety precautions.

Learning Point: Distillation method demonstrated

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

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

1. State two differences between pure and impure water.
2. Name three substances that can contaminate water.
3. What is the chemical formula of water?
4. Briefly describe how filtration is used to purify water.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Understanding water purification

Step 8: Note-Taking

Time: 10 minutes

Teaching Skill: Guided Writing

Teacher’s Activity: The teacher guides pupils/students to copy the essential Board Summary notes on pure/impure water, contaminants, and purification methods into their notebooks.

Pupils’ Activity: Pupils/students copy the notes carefully into their notebooks.

Learning Point: Recording lesson notes

Step 9: Conclusion

Time: 5 minutes

Teaching Skill: Summarisation

Teacher’s Activity: The teacher summarises the main points of the lesson, reiterating the importance of clean water and the methods used to achieve it. The teacher encourages students to apply this knowledge in their daily lives.

Pupils’ Activity: Pupils listen attentively and ask any final clarifying questions.

Learning Point: Lesson consolidation

Continuous Assessment/Further Study

Type: Homework

Instruction: Answer the following questions in your notebook.

1. Explain why distilled water is considered pure water.
2. List two physical, two chemical, and two biological contaminants of water.
3. Draw a labelled diagram of the apparatus used for simple distillation.
4. Research and write a short paragraph on one other method of water purification not discussed in class.

Lesson Keywords

• Pure water – Water containing only (H_2O) molecules, free from impurities.
• Impure water – Water containing dissolved or suspended substances in addition to (H_2O).
• Contaminants – Substances that make water impure or unsafe.
• Filtration – A physical method to separate insoluble solids from a liquid.
• Distillation – A process involving boiling and condensation to purify water from dissolved impurities.
• (H_2O) – The chemical formula for water.

Differentiation

For learners needing support: Provide pre-drawn diagrams of the filtration and distillation apparatus. Pair them with more capable students during group activities. Simplify explanations and provide clear, concise definitions for key terms. Focus on identifying contaminants and the basic steps of filtration.

For advanced learners: Challenge them to research and present on the industrial applications of water purification or the chemical processes involved in water treatment plants. Ask them to explain why different types of impurities require different purification methods.

Suggested Lesson Videos

For further understanding, search on YouTube for:

• “Pure and Impure Water Chemistry SS1”
• “Water Purification Methods for Senior Secondary School”
• “Filtration and Distillation Experiment Chemistry”