Physical and Chemical Changes; Mixtures

Grade 9 · General Science

Semester 1 | Period 1 | Week 4

Download the Lessonotes Mobile Liberia app for faster lesson access on Android and iPhone.

Get it on Google Play Get it on the Apple App Store

Subject: General Science

Semester: 1

Period: 1

Week: 4

School Name:
Teacher’s Name:
Subject: General Science
Grade Level: Grade 9
Date:
Lesson Duration: 45 minutes
Week & Period: Week 4, Period 1
Topic: Physical and Chemical Changes; Mixtures
Sub-topic: Changes in Matter and Separation Techniques
Learning Objectives
By the end of the lesson, students should be able to:

  1. Identify physical and chemical changes with examples
  2. Describe mixtures and explain separation methods
  3. Perform simple experiments to observe changes and separation techniques

Previous Knowledge
Students already know:
• Basic properties of matter
• Simple experiments involving water and solids
Instructional Materials
• Textbook: General science textbooks for Grade 9
• Teaching aids: Samples of sand, salt, water, seawater, and rusting iron; filtration and evaporation apparatus
• Students' notebooks and writing materials
Lesson Development – ABC Model
A – Anticipation (Warm-up / Starter)
Time: 5–10 minutes
Activity: The teacher will ask the class:
• Can you give examples of physical and chemical changes you have seen?
• How would you separate a mixture of sand and salt?
The teacher will record their responses on the board.
Teacher’s Role: Guide brainstorming, clarify misconceptions, and connect to local examples in Liberia.
Learner’s Role:
• Share examples of physical and chemical changes
• Suggest ways to separate mixtures and participate in discussion
B – Building Knowledge (Main Lesson Body – Expanded Version)

Time: 25–30 minutes

Teacher’s Role (Highly Expanded & Detailed):

  1. Explain Physical vs Chemical Changes:
    • Physical Changes: no new substance is formed; often reversible; examples: melting chocolate, cutting paper, dissolving sugar in water.
    • Chemical Changes: new substances are formed, often irreversible, usually involve energy change (heat, light, gas); examples: rusting of iron, burning wood, souring of milk.
    • Use local Liberian examples:
      • Rusting of iron roofing sheets
      • Burning firewood for cooking
      • Cooking oil turning brown on heating
      • Fermentation of cassava to produce garri
  1. Introduce Mixtures and Types:
    • Mixtures: combination of two or more substances not chemically bonded.
    • Homogeneous Mixtures: uniform composition throughout, e.g., sugar dissolved in water, salt water.
    • Heterogeneous Mixtures: non-uniform composition, e.g., sand in water, rice and beans.
    • Relate to daily life examples in Liberia, such as mixing sand and clay for brick-making or preparing pepper soup with multiple ingredients.
  2. Demonstrate Separation Methods:
    • Filtration: separate solid from liquid; example: sand from water
    • Evaporation: recover dissolved solids; example: salt from seawater
    • Distillation: separate liquid mixtures; example: purifying water
    • Chromatography: separate pigments; example: ink or leaf pigments
    • Conduct simple classroom experiments:
      • Dissolve salt in water and evaporate to retrieve salt
      • Mix sand and water and filter to retrieve sand
  1. Relate Changes and Separation to Local Applications:
    • Filtration of water in households or boreholes
    • Evaporation of salt from coastal areas
    • Distillation in local palm wine or essential oil extraction
    • Chromatography for educational or small-scale research purposes

 

Learners’ Activities (Expanded & Interactive):

  • Observe and record outcomes of classroom experiments.
  • Classify observed changes as physical or chemical, giving reasons.
  • Practice separating mixtures using filtration, evaporation, and simple distillation setups.
  • Discuss results in groups, connecting to everyday examples in Liberia, like food preparation or water purification.
  • Draw labeled diagrams of separation methods in notebooks.

 

Assessment Checks (Expanded):

  • Ask learners to classify each observed change as physical or chemical.
  • Evaluate accuracy and safety in using separation techniques.
  • Oral questions:
    • How can you tell a chemical change from a physical change?
    • Give an example of a homogeneous and a heterogeneous mixture from local life.
    • Explain how evaporation is used to obtain salt from seawater.
  • Review group discussions, diagrams, and written observations for understanding of concepts.

 

Notes (Highly Expanded & Detailed):

  • Emphasize the key differences between physical and chemical changes:
    • Reversibility, new substance formation, energy changes
  • Highlight practical applications of separation methods in local industries:
    • Filtration for clean drinking water
    • Evaporation for salt harvesting
    • Distillation for essential oil extraction or potable water
  • Encourage learners to observe everyday changes around them, such as cooking, rusting of metals, or dissolving sugar in water.

 

Optional Practical Extensions:

  • Assign a home experiment: separate mixtures such as sand and rice, sugar in water, or salt from seawater.
  • Have learners document their observations and methods in a mini-lab report.
  • Discuss how small-scale separation techniques are used in Liberian schools, households, and industries.
  • Encourage creative representation: draw stepwise diagrams of each separation technique.

C – Consolidation (Conclusion & Assessment)
Time: 5–10 minutes
Summary:
• The teacher will ask students to recall the differences between physical and chemical changes, types of mixtures, and separation methods
Evaluation Method (Expanded):
• Exit slip/quiz: Students will write short answers to:

Give one example each of physical and chemical change

Explain how to separate sand from salt

Name two mixtures in daily life
• Teacher will collect and quickly review for understanding
• Provide oral feedback before class ends
Assignment (Expanded): Follow-up Activity:
• Students will bring one example of a mixture from home, identify its type, and describe a method to separate its components
Differentiation / Inclusive Strategies
• Struggling Learners: Provide guided step-by-step demonstration and labeled diagrams
• Advanced Learners: Design experiments combining multiple mixtures and separation methods
• Students with Disabilities: Pair with peers for conducting experiments and observing results
Teacher’s Reflection (After Class)
• What worked well? ______________________________________________________
• What needs improvement? _________________________________________________
• Students’ engagement level: □ High □ Medium □ Low