Intro 3

 Thanks, Mayank! Based on your input and the NCERT content, here's a student-friendly, CBSE-aligned, high-impact teaching script for introducing the concept of chemical reactions using real-life situations and Activities 1.1 to 1.3. This version is ideal for classroom delivery and includes real-life relevance, safety notes, student engagement, and exam relevance.

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🧪 Introduction to Chemical Reactions

Chapter 1 – Chemical Reactions and Equations
(Class 10 Science – CBSE)

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🎯 Learning Objective:

To understand what a chemical reaction is and how to identify it using real-life clues and simple experiments.

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🌍 Start with Daily Life Situations

Begin by asking students:

“Have you ever noticed what happens when…”
✔ Milk is left outside in summer?
✔ An iron nail is kept in the open air for a week?
✔ Grapes are left in a closed container for a few days?
✔ We cook food, digest it, or simply breathe?

✅ In each of these cases, the original substance changes into something new — with a different look, smell, or property.

🧠 Conclusion:
These are all chemical reactions — the identity of the substance has changed.

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🧪 So What Is a Chemical Reaction?

📘 Definition:

A chemical reaction is a process where one or more substances (reactants) are converted into new substances (products) with different properties.

✅ A chemical change has occurred when the original substance is no longer the same.

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🔍 How Do You Know a Chemical Reaction Has Taken Place?

From everyday life and lab experiments, we identify chemical reactions using four signs:

🔬 Indicator	💡 What It Shows	🔥 Example
Change in state	Solid → liquid → gas	Magnesium burns to form ash
Change in colour	New colour appears	Lead nitrate + KI → yellow ppt
Gas is evolved	Bubbles or fizzing	Zinc + acid → hydrogen gas
Temperature changes	Heat is released or absorbed	Zinc + HCl → flask gets warm

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🔬 Let’s Prove It with Activities!

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✅ Activity 1.1 – Burning of Magnesium Ribbon

Materials:

• Magnesium ribbon (3–4 cm), tongs, spirit lamp, watch glass

Steps:

1. Rub ribbon with sandpaper (to remove oxide coating).

2. Hold with tongs and burn over flame.

3. Collect the white ash formed.

Observation:

✅ Dazzling white flame, white powder (magnesium oxide) is formed.

Reaction:

$$\text{2Mg} + \text{O}_2 \rightarrow \text{2MgO}$$

New substance formed → this is a chemical reaction.

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✅ Activity 1.2 – Lead Nitrate + Potassium Iodide

Materials:

• Test tube, lead nitrate solution, potassium iodide solution

Steps:

1. Mix both solutions in a test tube.

Observation:

✅ A bright yellow precipitate (lead iodide) forms immediately.

This shows a change in colour and state – another chemical reaction.

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✅ Activity 1.3 – Zinc + Acid Reaction

Materials:

• Zinc granules, dilute HCl or H₂SO₄, test tube/conical flask

Steps:

1. Add acid to zinc granules carefully.

Observation:

✅ Bubbles form (hydrogen gas), flask feels warm.

Reaction:

$$\text{Zn} + \text{H}_2\text{SO}_4 \rightarrow \text{ZnSO}_4 + \text{H}_2 \uparrow$$

Gas is evolved and temperature rises → clear signs of a chemical reaction.

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🧠 Conclusion from All 3 Activities:

Whenever we see any of these:

• A new substance is formed

• Heat is released or absorbed

• Gas is produced

• Colour or state changes

➡️ A chemical reaction has taken place.

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♻️ Why Should Students Care? (Environment Link)

• Rusting damages bridges and vehicles → we prevent it using galvanisation.

• Food spoilage happens due to unwanted chemical reactions → we preserve using low temperatures.

• Photosynthesis and respiration are vital chemical reactions for life.

✅ Chemical reactions are everywhere — in the kitchen, in our body, and in nature.

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📘 CBSE Exam Focus Tips:

📝 Frequently asked:

• Define chemical reaction (1 mark)

• List 2 signs of chemical reaction (2 marks)

• Write balanced equations for given changes (3 marks)

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💬 Ask Your Students:

1. Which changes in real life are chemical?

2. Can colour change alone confirm a chemical reaction?

3. What common feature did you notice in all 3 activities?

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🎤 Closing Line:

“Every time you burn a candle, digest food, or see rust — you’re watching chemistry at work. Understanding these reactions helps you understand how the world changes around you.”

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Would you like this turned into a student worksheet, lab sheet with observations, or flowchart summary for revision?