Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: 2nd Term
Week: 5
Age: 15 years
Duration: 45 minutes
Subject: Chemistry
Curriculum Theme: Chemistry
Previous Lesson: Symbols,.
Topic: Symbols, Formulae and Equation
Subject Matter: Law of constant composition, law of multiple proportions, chemical equations, and reporting experiments correctly

Specific Objectives

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

Cognitive Domain:

define the law of constant composition (definite proportions).
define the law of multiple proportions.
state examples that illustrate the law of constant composition and the law of multiple proportions.
write and interpret simple chemical equations using correct symbols and formulae.
list the standard parts of a simple chemistry laboratory report.

Affective Domain:

show honesty in recording results exactly as observed.
demonstrate carefulness and responsibility when handling simple chemicals and apparatus.

Psychomotor Domain:

observe demonstrations and identify the law illustrated from the results.
write a short laboratory report using a guided template.
balance and write simple chemical equations using correct coefficients.

work in groups to compare observations and agree on correct conclusions.
present group findings politely and listen to others during class discussion.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum (NERDC).
State Unified Scheme of Work.
Ababio, O. Y. New School Chemistry for Senior Secondary Schools.
OpenStax Chemistry 2e: Early Ideas in Atomic Theory (law of definite proportions/constant composition).
Khan Academy: Law of Multiple Proportions.
Chem LibreTexts: Proust’s Law of Constant Proportion.
Phoenix College Library Guide: Lab Report Format.

Instructional Materials

The teacher will teach this lesson with the aid of:

Simple chemicals for demonstration (e.g., copper carbonate or copper hydroxide for preparing copper(II) oxide, dilute acid, water).
Basic apparatus for safe heating and weighing (e.g., crucible or test tube, tripod, wire gauze, burner/spirit lamp, tongs, balance).
Charts showing examples of constant composition and multiple proportions.
Lab report template (Aim, Objective, Apparatus/Materials, Method/Procedure, Diagram, Results/Observation, Discussion, Conclusion).
Whiteboard/marker or chalkboard/chalk.

Rationale for the Lesson

The laws of chemical combination help pupils to understand that compounds form in fixed mass ratios and that elements can form different compounds in simple ratios. Correct reporting of experiments helps pupils to present observations clearly and answer practical questions in tests and examinations.

Prerequisite/Previous Knowledge

Pupils have learned basic ideas of elements, compounds, symbols, simple formula writing, and the meaning of a chemical reaction.

Lesson Content/Board Summary

SYMBOLS, FORMULAE AND EQUATION

Law of Constant Composition (Law of Definite Proportions)

The law of constant composition states that a pure compound always contains the same elements combined in the same fixed proportion by mass, no matter the source or method of preparation.

The following are examples that illustrate the law of constant composition:

Water (H₂O) always contains hydrogen and oxygen in a fixed mass ratio.
Carbon(IV) oxide (CO₂) always contains carbon and oxygen in a fixed mass ratio.
Sodium chloride (NaCl) always contains sodium and chlorine in a fixed mass ratio.

Law of Multiple Proportions

The law of multiple proportions states that when two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other are in a ratio of small whole numbers.

The following are examples that illustrate the law of multiple proportions:

Carbon and oxygen form CO and CO₂.
Nitrogen and oxygen form NO and NO₂.
Sulfur and oxygen form SO₂ and SO₃.

Chemical Equations

A chemical equation is the representation of a chemical reaction using symbols and formulae to show reactants and products.

The following are features of a chemical equation:

Reactants are written on the left-hand side of the arrow.
Products are written on the right-hand side of the arrow.
The arrow (→) shows the direction of the reaction.
Coefficients are numbers placed before formulae to balance the equation.

The following are examples of balanced chemical equations:

2H₂ + O₂ → 2H₂O
2Mg + O₂ → 2MgO
Zn + 2HCl → ZnCl₂ + H₂

Reporting Experiments Correctly

A laboratory report is a written record of an experiment showing what was done, what was observed, and the conclusion.

The following are the standard parts of a simple chemistry laboratory report:

Aim: what the experiment is meant to show.
Objective: the specific outcome expected.
Apparatus/Materials: items used for the experiment.
Method/Procedure: step-by-step description of what was done.
Diagram: labelled drawing of the setup where necessary.
Results/Observation: measurements and observations recorded clearly.
Discussion: explanation of results and the law/principle illustrated.
Conclusion: final statement based on results.

Teaching Methods/Instructional Techniques

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

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher revises symbols, formulae, and simple equations from the previous lesson and writes two simple equations on the board for pupils to interpret. The teacher introduces the lesson focus: laws of chemical combination and correct experiment reporting.
Pupils’ Activity: Pupils interpret the equations, identify reactants and products, and respond to brief revision questions.
Learning Point: Chemical reactions can be represented using symbols, formulae, and equations.

Step 2: Law of Constant Composition Demonstration

Time: 8 minutes
Teaching Skill: Demonstration and Observation
Teacher’s Activity: The teacher performs a simple demonstration showing that a compound produced by a given process has a fixed composition (e.g., preparing copper(II) oxide by heating a copper compound and relating it to fixed composition of the product). The teacher guides pupils to identify the law illustrated and records key observations on the board.
Pupils’ Activity: Pupils observe, record observations, and state the law illustrated from the demonstration results.
Learning Point: A pure compound has a fixed composition by mass.

Step 3: Law of Constant Composition Explanation and Examples

Time: 6 minutes
Teaching Skill: Explanation and Questioning
Teacher’s Activity: The teacher defines the law of constant composition and presents examples using charts (water, carbon(IV) oxide, sodium chloride). The teacher asks pupils to mention two compounds and their constituent elements.
Pupils’ Activity: Pupils copy the definition, list examples, and answer questions on elements present in given compounds.
Learning Point: The elements in a compound are combined in fixed proportions by mass.

Step 4: Law of Multiple Proportions Demonstration

Time: 7 minutes
Teaching Skill: Demonstration and Guided Discovery
Teacher’s Activity: The teacher uses charts/data to illustrate that the same two elements can form more than one compound in simple whole-number ratios (e.g., CO and CO₂, NO and NO₂). Where feasible, the teacher performs a simple demonstration or shows prepared samples/data to support the idea of multiple compounds from the same elements.
Pupils’ Activity: Pupils observe, compare examples, and state the law of multiple proportions in their own words.
Learning Point: Two elements can form different compounds in simple mass ratios.

Step 5: Writing and Interpreting Chemical Equations

Time: 6 minutes
Teaching Skill: Board Work and Guided Practice
Teacher’s Activity: The teacher guides pupils to write and balance simple chemical equations, stressing correct symbols, formulae, and coefficients. The teacher gives classwork examples for pupils to balance.
Pupils’ Activity: Pupils balance given equations and interpret them by stating reactants and products.
Learning Point: Balanced equations show correct reactant-product relationships in a reaction.

Step 6: Laboratory Report Writing (Format and Practice)

Time: 8 minutes
Teaching Skill: Explanation and Writing Skill Development
Teacher’s Activity: The teacher presents the correct format of a laboratory report using a template (Aim, Objective, Method, Diagram, Result, Discussion, Conclusion). The teacher guides pupils to write a short report on one of the demonstrations carried out in class.
Pupils’ Activity: Pupils write short lab reports using the template and submit for quick check or peer review.
Learning Point: Correct lab reports present experiments clearly and logically.

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 the law of constant composition (definite proportions).
Define the law of multiple proportions.
State two examples that illustrate the law of multiple proportions.
List four parts of a simple laboratory report.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 5 minutes
Teaching Skill: Summary and Reinforcement
Teacher’s Activity: The teacher summarizes the two laws, correct use of chemical equations, and the proper format for reporting experiments. The teacher gives an assignment: write one balanced equation and a short lab report outline for a given practical scenario.
Pupils’ Activity: Pupils copy the summary points and assignment and ask questions where necessary.
Learning Point: Laws of chemical combination and correct reporting support understanding of chemical reactions and practical work.

Lesson Keywords

Constant composition – a law stating that a pure compound has fixed proportions of elements by mass.
Definite proportions – another name for the law of constant composition.
Multiple proportions – a law stating that two elements can form more than one compound in small whole-number mass ratios.
Chemical equation – a representation of a reaction using symbols and formulae.
Coefficient – a number placed before a formula in an equation to balance atoms.
Laboratory report – a written record of an experiment with aim, method, results, and conclusion.

Differentiation

Pupils who need support will use a guided report template with sentence starters and a checklist for each section. Pupils who learn faster will solve additional equation-balancing exercises and write fuller discussions linking observations to the laws.

Note for teachers using this lesson plan

Ensure safety rules are followed during demonstrations and use clear, simple examples that pupils can relate to. Emphasize neatness, correct headings, and accurate recording in lab reports. Provide quick feedback on report structure so pupils improve before practical examinations.

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