Decomposition Reactions

Curriculum Area: Science – Chemistry (Level 6, Year 11)

This lesson aligns with the New Zealand Curriculum and NCEA Science Achievement Standards. It specifically addresses chemical reactions, with a focus on decomposition reactions and balancing chemical equations. The lesson includes hands-on practical work to support student engagement with key scientific concepts.

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Lesson Duration: 50 minutes

Class Size: 25 students

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Learning Intentions

By the end of this lesson, students will be able to:

• Explain decomposition reactions and identify their types.
• Observe and analyse the decomposition of copper carbonate (CuCO₃).
• Write a balanced chemical equation for the reaction.
• Understand the role of decomposition reactions in real-world applications.

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Success Criteria

• Students can define thermal decomposition and explain how it differs from other decomposition reactions.
• They can accurately write and balance the decomposition reaction of copper carbonate.
• Students can make detailed observations and explain their significance.
• Students follow all safety protocols when conducting the experiment.

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Lesson Structure

1. Introduction & Engagement (10 minutes)

Begin by engaging students with a quick scenario-based discussion:

• Question: "What happens when you heat sugar in a pan for too long?" (Students to describe – sugar breaks down, changes colour, and produces a gas.)
• Link this to decomposition reactions: "Just like sugar, some compounds break down when heated, producing simpler substances. Today, we’ll explore this with a metal carbonate."

Key Concept Exploration:

• Explain that decomposition reactions involve a single reactant breaking down into two or more simpler products.
• Three main types of decomposition reactions:
  • Thermal decomposition (heat-driven)
  • Electrolytic decomposition (electricity-driven)
  • Photolytic decomposition (light-driven)
• Real-world applications: decomposition of baking soda in cooking, corrosion of materials, and the role of decomposition in the environment.

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2. Hands-on Experiment: Decomposition of Copper Carbonate (20 minutes)

Before starting, briefly go over lab safety:

• Wear safety goggles and gloves.
• Use tongs when handling hot equipment.
• Work in a well-ventilated space or fume hood.

Materials per group (five groups of five students):

• Copper carbonate (CuCO₃)
• Test tube
• Bunsen burner
• Tongs
• Limewater (Ca(OH)₂ solution)
• Splint

Step-by-step procedure:

1. Place a small amount of CuCO₃ in a dry test tube.
2. Heat the test tube gently over a Bunsen burner (observe colour change during heating).
3. Hold the open end of the test tube near a test tube containing limewater to detect CO₂ production (limewater will turn cloudy).
4. Once the reaction completes, observe the residue inside the test tube.
5. Use a glowing splint to test for gas presence near the test tube.

Observations students should make:

• Before heating: Green solid (copper carbonate).
• During heating: Green solid turns black (indicates formation of copper oxide).
• Gas production: Limewater turns milky, indicating CO₂.

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3. Discussion: Chemical Equation & Analysis (10 minutes)

Write the word equation on the board:
Copper carbonate → Copper oxide + Carbon dioxide

Balanced chemical equation:
CuCO₃ (s) → CuO (s) + CO₂ (g)

Have students explore the following:

• Why is this considered a decomposition reaction?
• How does heating assist in breaking the bonds in CuCO₃?
• What practical applications does this reaction have in industry?
• What evidence confirms that gas was released during heating?

Quick quiz (turn-and-talk pairs):

1. What type of reaction is this?
2. Name another example of thermal decomposition.
3. Why does limewater turn milky?

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4. Reflection & Wrap-Up (10 minutes)

• Mini whiteboard challenge: Groups write a correct decomposition reaction equation for a given compound (e.g., calcium carbonate, potassium chlorate).
• Open the floor for students to share their learnings and real-life applications of decomposition reactions.
• Link to future lessons: “Next class, we’ll explore how decomposition reactions play a role in environmental chemistry and industry!”

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Assessment & Homework

• Exit Ticket: Before leaving, students write one key learning from today’s lesson and one question they still have.
• Home Task: Research and bring an example of a decomposition reaction they encounter in daily life.

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Teacher Reflection (Post-Lesson)

• What went well?
• Did students grasp the concept of balancing chemical equations?
• Were students actively engaged in the experiment and discussion?
• Any adjustments needed for next time?

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Extra Notes for Teachers:

• Mātauranga Māori Connection: If possible, discuss natural thermal decomposition processes in Aotearoa (e.g., geothermal activity and mineral changes).
• Differentiation Strategies: Pair students with mixed abilities for the experiment and allow early finishers to research related decomposition reactions.

This lesson ensures direct engagement with NCEA Science standards, reinforcing both observation and analysis skills in chemistry. 🎯 An interactive, hands-on approach makes decomposition reactions memorable! 🚀