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Subject: Chemistry
Semester: 1
Period: 1
Week: 3
School Name:
Teacher’s Name:
Subject: Chemistry
Grade Level: Grade 11
Week & Period: Week 3, Period I
Date:
Topic: Solutions (continued)
Sub-topic: Colligative Properties, Colloids, Factors Affecting Solubility
Learning Objectives
By the end of the lesson, learners should be able to:
- Describe the four main colligative properties of solutions
- Discuss the nature of colloids and their differences from true solutions
- Identify and explain factors affecting the solubility of substances in solvents
Previous Knowledge
Learners already understand the idea of solution concentration and saturation, and have been introduced to solute-solvent interactions.
Instructional Materials
- Salt and sugar for solute demos
- Water and thermometer
- Ice and stove or burner (for temperature demo)
- Diagrams illustrating boiling point elevation and freezing point depression
- Sample colloids: milk, starch solution, fog-in-a-bottle
Anticipation (Warm-Up) – 5 minutes
Ask:
- “Why does adding salt make water boil slower?”
- “Why doesn’t milk look as clear as saltwater?”
Guide the discussion toward the effect of dissolved particles and particle size in mixtures.
Building Knowledge (Main Lesson) – 25 minutes
- Colligative Properties
These depend on the number of solute particles in a solvent, not their type:- Vapor pressure lowering: Solute particles prevent solvent molecules from escaping into the air, reducing vapor pressure.
- Boiling point elevation: Solutions boil at higher temperatures than pure solvents. More energy is needed to overcome the lower vapor pressure.
- Freezing point depression: Solutions freeze at lower temperatures because solute particles disrupt crystal formation.
- Osmotic pressure: The pressure needed to stop water from passing through a membrane from a less concentrated solution to a more concentrated one.
- Colloids
- Colloids are mixtures where the particles are larger than those in true solutions but smaller than in suspensions.
- Examples include milk, fog, paint, and gelatin.
- Colloids show the Tyndall effect – they scatter light, unlike true solutions.
- Factors Affecting Solubility
- Temperature: Solids usually dissolve better in hot solvents; gases dissolve better in cold ones.
- Pressure: Only affects gases. Higher pressure increases gas solubility in liquids (e.g., soda bottles).
- Nature of solute and solvent: Polar solutes dissolve in polar solvents; non-polar in non-polar. ("Like dissolves like.")
Learners’ Activities
- Group demonstration: Add salt to boiling water and observe delay in boiling
- Use fog-in-a-bottle or starch-water mix to see Tyndall effect
- Match real-life examples to colligative properties (e.g., antifreeze, salted roads, rehydration salts)
- Answer practice questions on solubility changes with temperature and pressure
Consolidation (Review and Assessment) – 10 minutes
Ask:
- “Why does adding solute lower the freezing point of water?”
- “How does a colloid differ from a true solution?”
- “What are two things that affect how well something dissolves?”
Homework / Assignment
- Define and give examples of all four colligative properties
- List five common colloids and describe their dispersed and continuous phases
- Research: Why do cold soft drinks lose fizz faster when opened?
Notes – Detailed and Explained
Colligative Properties of Solutions
Colligative properties are physical changes in a solvent that depend on the number of solute particles, not their type.
- Vapor Pressure Lowering
Non-volatile solutes reduce the escaping tendency of solvent particles. Fewer particles at the surface means fewer escape, thus vapor pressure drops. - Boiling Point Elevation
Since vapor pressure is lowered, the liquid must be heated more to boil. The boiling point of a solution is therefore higher than that of the pure solvent. - Freezing Point Depression
Solute particles interfere with the orderly formation of the solid phase, so more cooling is needed to freeze the solution. This is used in de-icing roads and making ice cream. - Osmotic Pressure
In biological systems, water moves from dilute to concentrated solutions across membranes. This is important in kidney function and IV fluids.
Colloids
Colloids are between solutions and suspensions. The particles don’t settle, but are large enough to scatter light (Tyndall effect).
Examples:
- Milk (liquid in liquid)
- Fog (liquid in gas)
- Foam (gas in solid, e.g., marshmallow)
Colloids are stable and useful in food, cosmetics, and medicine.
Factors Affecting Solubility
- Temperature: Increasing temperature usually increases solubility of solids, but decreases solubility of gases (e.g., oxygen in water).
- Pressure: Has little effect on solids/liquids, but increases gas solubility in liquids.
- Nature of solute/solvent: Substances with similar intermolecular forces dissolve in each other. Polar dissolves polar, non-polar dissolves non-polar.
Expanded Notes / Instructions
- Emphasize real-life relevance: salt on icy roads, preserving fish in cold brine, pressure in soda cans
- Use animations or flashcards to help remember the four colligative properties
- Offer support for students who find these properties abstract by using stories or metaphors (e.g., “crowded dance floor” for vapor pressure lowering)
Inclusive / Differentiation
- Use multimedia and real objects for learners who are visual and tactile
- Give stronger students a challenge: relate colligative properties to ionic vs molecular solutes
- Provide step-by-step problem-solving guides to learners needing support with calculations
Teacher’s Reflection (Post-Lesson Questions)
- Did learners connect the four colligative properties with real-world examples?
- Were they able to explain the difference between solutions and colloids clearly?
- Did students demonstrate understanding of solubility factors with confidence?
- Should a short lab or video demo be repeated to reinforce learning?