Observing Chemical Changes: Bubbles and Colour

Active learning helps students connect abstract chemical reactions to concrete observations they can see, touch, and discuss. Hands-on stations and experiments give every learner a chance to test ideas, debate findings, and build shared understanding of how reactions reveal themselves through bubbles, colour, and other signs.

• 6th Year
• Advanced Chemical Principles and Molecular Dynamics
• 4 activities
• 20 min–45 min

Learning Objectives

1. Identify at least three observable signs of a chemical change, such as gas production, color change, or odor formation.
2. Compare and contrast physical changes with chemical changes, providing specific examples for each.
3. Explain the formation of new substances during a chemical reaction using the baking soda and vinegar example.
4. Classify reactions based on observable evidence, distinguishing between reactions that produce gas and those that produce a color change.

Stations Rotation

⏱ 45 min·Small Groups

Stations Rotation: Reaction Signs Stations

Prepare four stations: 1) baking soda-vinegar for bubbles, 2) iodine-starch for colour change, 3) Alka-Seltzer in water for fizz and smell, 4) control station with physical mixing like sand-water. Groups rotate every 10 minutes, draw observations, and note differences from physical changes.

Prepare & details

How can we tell if a new substance has been made?

Facilitation Tip: At the Reaction Signs Stations, place a small dish of vinegar next to baking soda so students can test both substances individually before mixing to control variables.

Setup: Tables/desks arranged in 4-6 distinct stations around room

Materials: Station instruction cards, Different materials per station, Rotation timer

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

⏱ 30 min·Pairs

Pairs: Indicator Colour Changes

Pairs test red cabbage indicator with vinegar, baking soda solution, and water. They predict colour outcomes, mix solutions, observe shifts, and discuss why pink or green appears. Record results in a shared class chart.

Prepare & details

What happens when we mix baking soda and vinegar?

Facilitation Tip: During the Indicator Colour Changes activity, provide each pair with a set of pre-marked droppers to ensure consistent amounts of indicator and solutions.

⏱ 25 min·Whole Class

Whole Class: Prediction Demo

Project a baking soda-vinegar setup. Class predicts signs before mixing, then observes live. Follow with vote on 'new substance formed?' and explain evidence. Students replicate in mini versions.

Prepare & details

Are all changes to materials easy to see?

Facilitation Tip: For the Prediction Demo, ask students to write their predictions on whiteboards before the reaction starts, then revisit them afterward to compare predictions with observations.

⏱ 20 min·Individual

Individual: Observation Logs

Students watch teacher demos of three reactions, log signs in tables (bubbles/colour/smell yes/no), classify as chemical or physical, and justify with evidence from their senses.

Prepare & details

How can we tell if a new substance has been made?

Facilitation Tip: When students complete Observation Logs, model how to use a two-column format: one side for observations, the other for inferences about what those observations mean.

Teaching This Topic

Teachers succeed when they balance hands-on exploration with structured reflection, ensuring students connect what they see to what they know. Avoid rushing through observations; give students time to notice details and ask questions. Research shows that guided inquiry, where students generate questions and test ideas, leads to deeper understanding of chemical processes than direct instruction alone.

What to Expect

By the end of these activities, students should confidently identify chemical changes by their observable signs and explain why those signs matter. They will use evidence from experiments to support claims, record detailed observations, and correct common misconceptions through peer discussion and teacher guidance.

Watch Out for These Misconceptions

Common Misconception

During the Reaction Signs Stations, watch for students who assume bubbles always mean boiling or trapped air is escaping.

What to Teach Instead

Set up a control station with plain water heated to the same temperature as the reaction mixture. Have students compare bubbles in both, then use a simple gas test (like relighting a glowing splint) to show carbon dioxide is produced in the vinegar-baking soda reaction.

Common Misconception

During the Indicator Colour Changes activity, watch for students who describe colour shifts as simple mixing or dye blending.

What to Teach Instead

Provide vials of phenolphthalein and sodium hydroxide solution. Have students test small amounts and observe that the pink colour does not fade when diluted, unlike a physical dye blend. Ask them to compare this to a control of food colouring in water to highlight the irreversible change.

Common Misconception

During the Prediction Demo, watch for students who assume products of a reaction are the same as the reactants.

What to Teach Instead

After mixing baking soda and vinegar, let the mixture dry overnight. Have students compare the solid residue to the original powders and discuss why the new substance feels different and has a distinct texture, reinforcing the idea of new molecular arrangements.

Assessment Ideas

Exit Ticket

After the Reaction Signs Stations, provide students with three scenarios: 1. Water boiling, 2. A leaf changing color in autumn, 3. Alka-Seltzer dissolving in water. Ask them to identify which scenario represents a chemical change and list at least two observable signs that support their answer.

Quick Check

During the Prediction Demo of mixing baking soda and vinegar, ask students to observe carefully. Then pose questions like: 'What did you see happening?' (looking for 'bubbles' or 'fizzing') and 'What does this tell us about what is being made?' (looking for 'a new substance' or 'gas').

Discussion Prompt

After the Indicator Colour Changes activity, pose the question: 'Imagine you mix two clear liquids, and the mixture turns bright blue. Is this likely a physical or chemical change? Explain your reasoning, referring to the signs of chemical change we discussed.' Have students discuss in pairs before sharing with the class.

Extensions & Scaffolding

• Challenge students to design their own experiment using household items to produce a chemical change with at least two observable signs.
• For students who struggle, provide a partially completed Observation Log template with key terms filled in to model expected responses.
• Deeper exploration: Ask students to research how chemical reactions in fireworks produce their colours and present findings to the class with visuals of the compounds involved.

Key Vocabulary

Chemical Change	A process where one or more substances are transformed into new substances with different properties. Evidence includes gas bubbles, color change, or new smells.
Physical Change	A change in the form of a substance but not its chemical composition. Examples include melting ice or cutting paper; no new substances are formed.
Reactants	The starting substances in a chemical reaction that are mixed together. In the baking soda and vinegar reaction, these are sodium bicarbonate and acetic acid.
Products	The new substances formed as a result of a chemical reaction. For baking soda and vinegar, these include carbon dioxide gas, water, and sodium acetate.
Gas Production	The formation of a gas during a chemical reaction, often observed as bubbles or fizzing. This indicates a new substance has been created.