Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: 1st Term
Week: 5
Age: 15 years
Duration: 45 minutes
Subject: Chemistry
Curriculum Theme: Chemistry
Previous Lesson: Chemical Industries: Excursion, Processes and Environmental Effects.
Topic: STANDARD SEPARATION TECHNIQUES FOR MIXTURES
Subject Matter: classification of substances, filtration, evaporation, decantation, floatation and froth flotation, crystallization and fractional crystallization

Specific Objectives

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

Cognitive Domain:

Define pure substances and mixtures.
Classify various substances as pure or mixtures.
State the principles behind different separation techniques.

Affective Domain:

Appreciate the importance of separation techniques in daily life.
Develop an interest in carrying out practical chemistry experiments.

Psychomotor Domain:

Demonstrate the processes of filtration, evaporation, and decantation.
Observe and describe the process of crystallization from a solution.
Record observations accurately from separation experiments.

Work cooperatively in groups during practical activities.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic 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:

Water
Sand
Common salt
Filter paper
Evaporation dish
Beakers
Funnel
Tripod stand
Bunsen burner
Spatula

Rationale for the Lesson

This lesson helps pupils understand how to separate different components from a mixture. This knowledge is important for daily activities like purifying water or separating ingredients in cooking, and it forms a fundamental basis for further studies in chemistry.

Prerequisite/Previous Knowledge

Pupils have a basic understanding of matter and its states (solids, liquids, gases) from previous lessons.

Lesson Content/Board Summary

STANDARD SEPARATION TECHNIQUES FOR MIXTURES

Classification of Substances

Substances can be broadly classified into pure substances and mixtures.

Pure Substances: These are substances that contain only one type of particle and have fixed chemical properties. They cannot be separated into simpler substances by physical means.

The following are examples of pure substances:

Water (H₂O)
Common salt (NaCl)
Oxygen (O₂)
Iron (Fe)

Mixtures: These are substances formed when two or more pure substances are physically combined, and their individual properties are retained. They can be separated into their components by physical methods.

The following are examples of mixtures:

Salt solution (salt + water)
Sand and water
Air (nitrogen, oxygen, carbon dioxide, etc.)
Brass (copper + zinc)

Filtration

Filtration is a separation technique used to separate insoluble solid particles from a liquid or gas.

Principle: It works on the principle that solid particles are too large to pass through a filter medium, while the liquid or gas particles are small enough to pass through.

The following are examples of mixtures separated by filtration:

Sand and water
Chalk powder and water
Muddy water

Evaporation

Evaporation is a separation technique used to separate a soluble solid from its solvent by heating the solution, causing the solvent to turn into a gas and leave the solid behind.

Principle: It relies on the difference in boiling points between the solid and the solvent, where the solvent has a lower boiling point and evaporates away.

The following are examples of mixtures separated by evaporation:

Salt from salt solution
Sugar from sugar solution

Decantation

Decantation is a separation technique used to separate immiscible liquids or a liquid from a solid that has settled at the bottom.

Principle: It works by carefully pouring off the top layer of liquid, leaving the heavier liquid or solid behind.

The following are examples of mixtures separated by decantation:

Oil and water
Sand and water (after sand has settled)

Floatation and Froth Flotation

Floatation is a separation technique used to separate components of a mixture based on differences in density, where one component floats on the surface of a liquid.

Froth Flotation: This is a specialized floatation technique used to separate hydrophobic materials (like minerals) from hydrophilic materials. Air bubbles are introduced into a slurry, and the hydrophobic particles attach to the bubbles and float to the surface as froth.

The following are examples of mixtures separated by floatation/froth flotation:

Sawdust and sand (using water for floatation)
Sulphide ores from gangue (froth flotation)

Crystallization and Fractional Crystallization

Crystallization is a separation technique used to obtain a pure solid in crystalline form from a solution.

Principle: It involves dissolving the solid in a suitable solvent, forming a saturated solution, and then allowing the solvent to slowly evaporate or cool, causing the solute to form crystals.

The following are examples of substances obtained by crystallization:

Pure sugar from sugar solution
Copper (II) sulphate crystals from its solution

Fractional Crystallization: This is a technique used to separate two or more soluble solids with different solubilities in the same solvent. The solution is cooled, and the substance with lower solubility crystallizes out first.

The following are examples of mixtures separated by fractional crystallization:

Separation of potassium nitrate and sodium chloride from their mixture.

Teaching Methods/Instructional Techniques

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

Instructional Procedures

Step 1: Introduction

Time: 3 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils and asks them to recall what they know about matter and its forms. The teacher then introduces the topic by asking how they would separate sand from water or salt from water.
Pupils’ Activity: Pupils respond to the questions and listen attentively to the introduction.
Learning Point: Pupils are prepared for the lesson and connect to prior knowledge.

Step 2: Classification of Substances

Time: 7 minutes
Teaching Skill: Explanation/Discussion
Teacher’s Activity: The teacher defines pure substances and mixtures, providing examples for each. The teacher guides pupils to classify given items as pure substances or mixtures.
Pupils’ Activity: Pupils participate in the discussion, classify substances, and take notes.
Learning Point: Pupils understand the difference between pure substances and mixtures.

Step 3: Filtration, Evaporation, and Decantation (Explanation & Demonstration)

Time: 7 minutes
Teaching Skill: Demonstration/Explanation
Teacher’s Activity: The teacher explains the principles of filtration, evaporation, and decantation. Using simple mixtures like sand and water, and salt solution, the teacher briefly demonstrates each technique, explaining the steps involved.
Pupils’ Activity: Pupils observe the demonstrations carefully, ask questions, and listen to the explanations.
Learning Point: Pupils observe the practical application of these separation techniques.

Step 4: Practical Activity – Filtration, Evaporation, and Decantation

Time: 10 minutes
Teaching Skill: Practical Application
Teacher’s Activity: The teacher divides pupils into small groups and provides them with materials (water, sand, common salt, filter paper, funnels, beakers, evaporation dishes, Bunsen burner). The teacher guides them to perform filtration of sand from water, decantation of sand from water (after settling), and evaporation of salt from salt solution.
Pupils’ Activity: Pupils work in groups to carry out the separation techniques, record their observations, and discuss their findings.
Learning Point: Pupils gain hands-on experience in performing basic separation techniques.

Step 5: Floatation and Froth Flotation

Time: 5 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher explains the concept of floatation and then elaborates on froth flotation as a specialized technique, discussing its principle and applications, especially in mining.
Pupils’ Activity: Pupils listen, ask questions for clarification, and take notes.
Learning Point: Pupils understand how floatation methods are used for separation.

Step 6: Crystallization and Fractional Crystallization

Time: 7 minutes
Teaching Skill: Explanation/Illustration
Teacher’s Activity: The teacher explains crystallization as a method to obtain pure solids from solutions, describing the process. The teacher then introduces fractional crystallization for separating mixtures of soluble solids with different solubilities. If possible, the teacher shows a pre-prepared crystal or an image.
Pupils’ Activity: Pupils observe, listen to the explanation, and take notes on the processes.
Learning Point: Pupils understand the principles and applications of crystallization techniques.

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 pure substances and mixtures, giving one example for each.
State the principle behind filtration.
Mention two mixtures that can be separated by decantation.
Describe briefly how you would obtain salt from a salt solution.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 1 minute
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key separation techniques discussed and assigns homework: “Explain how fractional crystallization differs from simple crystallization.”
Pupils’ Activity: Pupils listen to the summary and copy the homework.
Learning Point: Pupils consolidate their learning and prepare for further study.

Lesson Keywords

Pure Substance – A substance containing only one type of particle.
Mixture – A substance formed from two or more pure substances physically combined.
Filtration – Separating insoluble solids from liquids using a filter.
Evaporation – Separating a soluble solid from a liquid by heating the liquid away.
Decantation – Separating immiscible liquids or a liquid from a settled solid by pouring.
Crystallization – Obtaining pure solid crystals from a solution.
Floatation – Separating components based on density differences, where one floats.
Froth Flotation – A specialized floatation method for separating minerals using air bubbles.

Differentiation

For pupils who grasp concepts quickly, the teacher will encourage them to research other separation techniques like distillation or chromatography. For pupils requiring more support, the teacher will provide additional one-on-one guidance during practical activities and simplify explanations with more visual aids.

Note for teachers using this lesson plan

Ensure all practical materials are ready before the lesson. Emphasize safety precautions during demonstrations and practical activities, especially when using heat. Encourage pupils to record observations accurately and discuss their findings within groups.