Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: First Term
Week: 7
Age: 15 years
Duration: 45 minutes
Subject: Chemistry
Curriculum Theme: Chemistry
Previous Lesson: Standard Separation Techniques.
Topic: STANDARD SEPARATION TECHNIQUES FOR MIXTURES
Subject Matter: chromatography and separation of coloured substances, sublimation as a separation method, pure and impure substances and simple tests such as melting and boiling points

Specific Objectives

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

Cognitive Domain:

Define chromatography and sublimation.
Explain the principle behind chromatography.
Differentiate between pure and impure substances.
State how melting and boiling points are used to determine purity.

Affective Domain:

Appreciate the importance of separation techniques in everyday life.
Show interest in performing practical chemistry experiments.
Value accuracy in determining the purity of substances.

Psychomotor Domain:

Perform a simple paper chromatography experiment to separate coloured substances.
Observe and describe the process of sublimation.
Identify pure and impure substances based on observed melting and boiling points.

Collaborate effectively with peers during group activities.
Communicate their observations clearly during practical sessions.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Chemistry.
State Unified Scheme of Work for Senior Secondary Schools.
New School Chemistry for Senior Secondary Schools by Osei Yaw Ababio.
Various online educational resources for Chemistry.

Instructional Materials

The teacher will teach this lesson with the aid of:

Ink (black or coloured marker ink)
Chromatography paper or filter paper
Beakers or jars
Solvent (e.g., water, ethanol)
Naphthalene or ammonium chloride (for sublimation)
Watch glass
Bunsen burner or spirit lamp
Tripod stand and gauze
Capillary tubes
Thermometer
Melting point apparatus or oil bath
Boiling tubes
Pure and impure samples of a substance (e.g., water, sugar)
Separating funnel
Cubes of sugar

Rationale for the Lesson

This lesson helps pupils understand how different substances in a mixture can be separated. It teaches practical skills for separating components and identifying pure substances, which is important for various applications in industries and for daily life activities like cooking and water purification.

Prerequisite/Previous Knowledge

Pupils should have prior knowledge of mixtures, types of mixtures, and basic laboratory apparatus from previous lessons.

Lesson Content/Board Summary

STANDARD SEPARATION TECHNIQUES FOR MIXTURES

Chromatography

Chromatography is a set of laboratory techniques used to separate mixtures of substances into their individual components. It works on the principle that components in a mixture have different affinities for a stationary phase and a mobile phase.

Types of chromatography include:

Paper chromatography
Thin-layer chromatography (TLC)
Column chromatography
Gas chromatography (GC)

Separation of Coloured Substances by Paper Chromatography:

This technique separates coloured components of an ink or dye. A spot of the mixture is applied to a strip of chromatography paper (stationary phase). One end of the paper is dipped into a solvent (mobile phase). The solvent moves up the paper by capillary action, carrying the components of the mixture at different rates, causing them to separate into distinct bands or spots.

Sublimation as a Separation Method

Sublimation is a physical process where a substance changes directly from a solid to a gas without passing through a liquid phase. This property can be used to separate a sublimable solid from a non-sublimable solid.

Common examples of substances that sublime are:

Naphthalene (mothballs)
Iodine
Ammonium chloride
Dry ice (solid carbon dioxide)

Procedure for Sublimation:

A mixture containing a sublimable solid is heated gently. The sublimable solid turns into a gas and then solidifies upon cooling on a cold surface, separating it from the non-sublimable components.

Pure and Impure Substances

A pure substance is a single substance that has a definite and constant composition and distinct chemical properties. An impure substance (mixture) consists of two or more pure substances physically combined, each retaining its own properties.

Examples of pure substances:

Distilled water
Table salt (sodium chloride)
Pure gold

Examples of impure substances:

Saltwater
Air
Tap water

Simple Tests for Purity: Melting and Boiling Points

Pure substances have sharp, constant melting and boiling points at standard pressure. Impure substances (mixtures) melt or boil over a range of temperatures.

Melting Point:

The melting point is the temperature at which a solid changes to a liquid at a specific pressure. A pure solid melts sharply at a specific temperature. The presence of impurities lowers the melting point and causes it to melt over a range of temperatures.

Boiling Point:

The boiling point is the temperature at which a liquid changes to a gas at a specific pressure. A pure liquid boils sharply at a specific temperature. The presence of impurities raises the boiling point and causes it to boil over a range of temperatures.

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 asks them to recall different types of mixtures and some simple separation techniques they already know (e.g., decantation, filtration). The teacher then introduces the topic: Standard Separation Techniques for Mixtures.
Pupils’ Activity: Pupils respond to questions and listen attentively.
Learning Point: Pupils recall prior knowledge of mixtures and separation, preparing them for new concepts.

Step 2: Chromatography

Time: 10 minutes
Teaching Skill: Demonstration/Explanation
Teacher’s Activity: The teacher defines chromatography and explains its principle. The teacher then demonstrates paper chromatography using ink and explains each step. While the separation is in progress, the teacher explains how it separates coloured substances.
Pupils’ Activity: Pupils observe the demonstration, ask questions, and take notes. Some pupils may assist in setting up the experiment.
Learning Point: Pupils understand the definition, principle, and application of chromatography in separating coloured substances.

Step 3: Sublimation as a Separation Method

Time: 10 minutes
Teaching Skill: Demonstration/Explanation
Teacher’s Activity: The teacher defines sublimation and lists common sublimable substances. The teacher then demonstrates the separation of a sublimable substance (e.g., naphthalene or ammonium chloride) from a non-sublimable substance by heating the mixture and collecting the sublimate on a cold surface (e.g., an inverted watch glass).
Pupils’ Activity: Pupils observe the sublimation demonstration, note the process, and identify the sublimable substance.
Learning Point: Pupils learn about sublimation as a separation technique and identify substances that undergo sublimation.

Step 4: Pure and Impure Substances

Time: 5 minutes
Teaching Skill: Explanation/Discussion
Teacher’s Activity: The teacher defines pure and impure substances, giving examples of each. The teacher leads a discussion on why it is important to distinguish between pure and impure substances.
Pupils’ Activity: Pupils participate in the discussion, contribute examples, and differentiate between pure and impure substances.
Learning Point: Pupils understand the definitions and differences between pure and impure substances.

Step 5: Simple Tests for Purity (Melting and Boiling Points)

Time: 5 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains how melting and boiling points are used to determine the purity of substances. The teacher explains that pure substances have sharp melting/boiling points, while impure substances have a range. The teacher briefly demonstrates or describes how melting and boiling points are determined in the laboratory.
Pupils’ Activity: Pupils listen, take notes, and ask questions about the determination of melting and boiling points.
Learning Point: Pupils learn how melting and boiling points serve as indicators of purity for substances.

Step 6: Practical Application Discussion

Time: 5 minutes
Teaching Skill: Discussion/Application
Teacher’s Activity: The teacher facilitates a discussion on the real-life applications of these separation techniques, such as drug testing (chromatography), purification of chemicals (sublimation), and quality control in industries (purity tests).
Pupils’ Activity: Pupils contribute ideas on where these techniques are applied in daily life and industry.
Learning Point: Pupils connect theoretical knowledge to practical, real-world applications.

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 chromatography.
Explain the principle of sublimation.
List two substances that can be separated by sublimation.
How do the melting points of pure and impure substances differ?

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 5 minutes
Teaching Skill: Summarization/Consolidation
Teacher’s Activity: The teacher summarizes the key learning points of the lesson, emphasizing the importance of standard separation techniques and purity tests. The teacher then assigns homework, which could include defining key terms or researching other separation methods.
Pupils’ Activity: Pupils listen to the summary and copy down the homework.
Learning Point: Pupils consolidate their understanding of the lesson and prepare for further study.

Lesson Keywords

Chromatography – A technique used to separate mixtures based on differential partitioning between a stationary phase and a mobile phase.
Sublimation – The process where a solid changes directly into a gas without passing through a liquid phase.
Pure substance – A substance consisting of only one type of matter, with a definite and constant composition.
Impure substance – A mixture of two or more pure substances that are physically combined.
Melting point – The temperature at which a solid changes to a liquid.
Boiling point – The temperature at which a liquid changes to a gas.

Differentiation

For pupils who grasp concepts quickly, the teacher can provide additional challenges, such as researching more complex chromatography techniques or designing an experiment to separate a specific mixture. For pupils who require more support, the teacher will provide simplified explanations, one-on-one guidance during practical activities, and visual aids to reinforce understanding.

Note for teachers using this lesson plan

Ensure all practical demonstrations are conducted safely, following laboratory safety guidelines. It is advisable to pre-test all materials for demonstrations. Encourage active participation and critical thinking throughout the lesson. Adjust the pace and depth of content based on the pupils’ prior knowledge and engagement levels.