Chemical Changes: New Substances Formed

Active learning works because chemical changes are best observed through hands-on reactions where students can see, smell, and feel the evidence of new substances forming. When students mix, heat, or observe changes directly, they connect abstract concepts to real-world outcomes like bubbles, colour shifts, or temperature shifts.

• Class 7
• Science (EVS K-5)
• 4 activities
• 20 min–35 min

Learning Objectives

1. Identify at least three observable signs that indicate a chemical change has occurred.
2. Compare the properties of reactants before and products after a chemical change, such as burning paper to ash.
3. Classify given examples as either physical or chemical changes, providing justification.
4. Explain the difference between a physical change and a chemical change using examples like tearing versus burning paper.

Experiential Learning

⏱ 25 min·Pairs

Pairs Experiment: Vinegar and Baking Soda

Give pairs baking soda, vinegar, a test tube, and a balloon. Add baking soda to the tube, stretch balloon over top, pour in vinegar, and observe gas production inflating the balloon. Discuss how carbon dioxide gas is a new substance with different properties.

Prepare & details

Analyze the signs that indicate a chemical change has occurred.

Facilitation Tip: During the vinegar and baking soda experiment, ensure students hold the test tube gently and tilt it to observe gas bubbles rising, not just the fizzing at the surface.

Setup: Flexible classroom arrangement with desks pushed aside for activity space, or standard rows with group-work stations rotated in sequence. Works in standard Indian classrooms of 40–48 students with basic furniture and no specialist equipment.

Materials: Chart paper and sketch pens for group recording, Everyday household or locally available objects relevant to the concept, Printed reflection prompt cards (one set per group), NCERT textbook for connecting activity outcomes to chapter content, Student notebook for individual reflection journalling

• Apply
• Analyze
• Evaluate
• Self-Awareness
• Self-Management
• Social Awareness

Experiential Learning

⏱ 35 min·Small Groups

Small Groups: Iron Nail in Copper Sulphate

Provide small groups with copper sulphate solution, iron nails, and beakers. Place nail in solution for 10 minutes, note blue colour fading and reddish deposit on nail. Compare initial and final properties to confirm new substances formed.

Prepare & details

Compare the properties of reactants and products in a chemical change.

Facilitation Tip: When the iron nail is placed in copper sulphate solution, ask students to note the colour change in the solution and the deposition on the nail after 10 minutes.

Setup: Flexible classroom arrangement with desks pushed aside for activity space, or standard rows with group-work stations rotated in sequence. Works in standard Indian classrooms of 40–48 students with basic furniture and no specialist equipment.

Materials: Chart paper and sketch pens for group recording, Everyday household or locally available objects relevant to the concept, Printed reflection prompt cards (one set per group), NCERT textbook for connecting activity outcomes to chapter content, Student notebook for individual reflection journalling

• Apply
• Analyze
• Evaluate
• Self-Awareness
• Self-Management
• Social Awareness

Experiential Learning

⏱ 20 min·Whole Class

Whole Class Demo: Burning Magnesium Ribbon

Demonstrate safely with tongs: light magnesium ribbon, observe bright light and white ash. Students record signs like light and new powdery product. Follow with class discussion on why this differs from melting wax.

Prepare & details

Justify why burning paper is a chemical change, while tearing it is physical.

Facilitation Tip: For the burning magnesium ribbon demo, dim the classroom lights so students can clearly see the bright white flame and the white powdery ash formed.

Setup: Flexible classroom arrangement with desks pushed aside for activity space, or standard rows with group-work stations rotated in sequence. Works in standard Indian classrooms of 40–48 students with basic furniture and no specialist equipment.

Materials: Chart paper and sketch pens for group recording, Everyday household or locally available objects relevant to the concept, Printed reflection prompt cards (one set per group), NCERT textbook for connecting activity outcomes to chapter content, Student notebook for individual reflection journalling

• Apply
• Analyze
• Evaluate
• Self-Awareness
• Self-Management
• Social Awareness

Stations Rotation

⏱ 30 min·Small Groups

Stations Rotation: Curdling Milk

Set stations with milk and lemon juice. Groups add juice to milk, stir gently, watch lumps form. Filter and taste to note new solid (paneer-like) versus liquid whey, identifying precipitate as a chemical sign.

Prepare & details

Analyze the signs that indicate a chemical change has occurred.

Facilitation Tip: At the curdling milk station, have students add a few drops of lemon juice to warm milk and stir gently to observe the separation of curds and whey within 5 minutes.

Setup: Designate four to six fixed zones within the existing classroom layout — no furniture rearrangement required. Assign groups to zones using a rotation chart displayed on the blackboard. Each zone should have a laminated instruction card and all required materials pre-positioned before the period begins.

Materials: Laminated station instruction cards with must-do task and extension activity, NCERT-aligned task sheets or printed board-format practice questions, Visual rotation chart for the blackboard showing group assignments and timing, Individual exit ticket slips linked to the chapter objective

• Remember
• Understand
• Apply
• Analyze
• Self-Management
• Relationship Skills

Teaching This Topic

Start with simple, safe reactions like vinegar and baking soda to build confidence before moving to more complex setups such as the copper sulphate and iron nail. Avoid overloading students with too many reactions at once; allow time for observations and discussions after each experiment. Research shows that students grasp chemical changes better when they link observations to the particulate nature of matter—asking them to imagine how atoms rearrange helps bridge the gap between visible changes and unseen processes.

What to Expect

By the end of these activities, students should confidently identify chemical changes by observing signs such as gas bubbles, colour changes, or solid formation. They should explain why these signs indicate new substances have formed, using clear evidence from their experiments.

Watch Out for These Misconceptions

Common Misconception

During the vinegar and baking soda experiment, some students may think the fizzing indicates a new substance is forming, even though no new substance is permanent.

What to Teach Instead

Ask students to collect the gas in a balloon and observe that it does not behave like air or vinegar. Then, have them weigh the reactants before and after the reaction to see if mass is conserved, reinforcing that no new substance remains.

Common Misconception

During the iron nail in copper sulphate activity, students might believe the brown coating on the nail is rust rather than a new substance.

What to Teach Instead

Show students the original copper sulphate solution is blue and the deposited layer is reddish-brown. Ask them to compare the properties of the coating (shiny, conducts electricity) to rust (dull, does not conduct) to highlight it is copper, a new substance.

Common Misconception

During the burning paper activity, students may think tearing paper is similar to burning because both change the paper's shape.

What to Teach Instead

Have students burn a small piece of torn paper and compare the ash to that of an intact piece. Point out that both produce the same ash, showing no new substance forms when tearing, only when burning.

Assessment Ideas

Exit Ticket

After the vinegar and baking soda experiment, provide students with a list of scenarios including rusting iron, dissolving salt, and baking a cake. Ask them to circle chemical changes and write one sentence for each, referencing the formation of a new substance and linking it to signs they observed.

Discussion Prompt

During the iron nail in copper sulphate activity, ask students to imagine they are jewellery makers. What chemical changes would they want to avoid when cleaning metal jewellery? What would they look for to confirm no chemical change occurred?

Quick Check

After the burning magnesium ribbon demo, show students a piece of magnesium ribbon and the white ash formed. Ask: ‘What signs suggest a chemical change occurred here? What are the reactants and what are the products?’ Have students sketch the reaction and label the changes.

Extensions & Scaffolding

• Challenge students to design a small experiment using household items to test for gas production, such as mixing baking soda with lemon juice in a balloon to capture the gas.
• For students who struggle, provide pre-measured materials and a step-by-step observation sheet with space to record colour, temperature, and smell changes.
• Ask advanced students to research and explain why the reaction between magnesium and oxygen during burning is considered a chemical change, linking it to the properties of the new substance formed (magnesium oxide).

Key Vocabulary

Chemical Change	A process where one or more substances are transformed into new substances with different chemical properties. This often involves the breaking and forming of chemical bonds.
Physical Change	A change in the form of a substance that does not alter its chemical composition. Examples include changes in shape, size, or state.
Reactant	The starting substance(s) that undergo a chemical change. These are the materials that react together.
Product	The new substance(s) formed as a result of a chemical change. These have different properties from the reactants.
Formation of Gas	An observable sign of a chemical change where bubbles of gas are produced, indicating a new substance has formed.
Formation of Precipitate	An observable sign of a chemical change where a solid forms and separates from a liquid solution.