Dissolving and Solutions

Overview

This 60-minute lesson introduces year 7 students (ages 11-12) to fundamental concepts of dissolving, focusing on solute, solvent, and solution. It integrates a practical investigation to solidify understanding of solubility, conservation of mass, and properties of solutions, adhering closely to the national curriculum for England’s science programme of study for KS3 (Key Stage 3).

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National Curriculum Links

• Year 7 Programme of Study: Chemistry – States of Matter and Mixtures

• Pupils should be taught to describe how mixtures, including solutions, can be separated by filtering, evaporating, and dissolving, and understand the concept of solubility.

• Understand that in a solution, the solute dissolves in the solvent to make a solution.

• Recognise that dissolving is a physical change and that mass is conserved in dissolving processes.

• Working Scientifically

• Plan and carry out investigations, including measuring accurately.

• Record data and results of increasing complexity using scientific diagrams and labels, classification keys, tables, and bar and line graphs.

• Use relevant scientific language, conventions, and symbols.

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Learning Objectives

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

1. Define and identify the solute, solvent, and solution in a dissolving process.
2. Conduct a fair test to investigate how sugar dissolves in water and measure the solubility limit.
3. Explain the concepts of solubility and distinguish between soluble and insoluble substances.
4. Understand and demonstrate the conservation of mass in dissolving processes.
5. Accurately record observations and present results using appropriate scientific vocabulary and representations.

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Resources

• Granulated sugar (solute)
• Water (solvent)
• Clear plastic cups or beakers (one per pair)
• Digital scales (accuracy to at least 0.1 g)
• Measuring cylinders (50 ml)
• Stirring rods or spoons
• Whiteboards and markers or exercise books
• Labels and sticky notes
• Stopwatch or timer
• Worksheet with data tables and guided questions

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Lesson Structure

1. Starter (10 minutes)

• Engagement Question: Write “What is dissolving?” on the board. Ask students to discuss in pairs and share examples of dissolving they see in everyday life.
• Concept Introduction: Teacher explains dissolving as a physical process where a solute (solid) disappears in a solvent (liquid) to form a solution. Define key terms clearly with examples.
• Visual Aid: Use a simple diagram to label solute, solvent, and solution.

2. Main Activity - Practical Investigation (30 minutes)

Setup

• Students work in pairs to ensure safety and engagement.
• Provide each pair with 50 ml of water in a beaker and digital scale.

Steps:

1. Weigh the empty beaker and record the mass.
2. Pour 50 ml of water into the beaker; weigh and record the mass (mass of water + beaker).
3. Gradually add sugar (e.g., increments of 5g), stirring continuously until no more dissolves (saturation point).
4. Note the mass after each increment and observe if sugar dissolves fully or settles at the bottom.
5. Stop when sugar stops dissolving – mark this point as the maximum solubility under the conditions.

Scientific Focus

• Guide students to observe and record what happens when sugar dissolves vs when it does not dissolve.
• Encourage predicting what effect increasing temperature would have (optional extension).
• Discuss the role of ‘stirring’ in speeding up dissolving (prediction and observation).

3. Discussion and Concept Reinforcement (10 minutes)

• Recap observations: How much sugar dissolved, what the beaker looked like.
• Discuss why sugar stops dissolving (solubility limit).
• Introduce insoluble substances briefly (e.g., sand in water) and compare.
• Demonstrate and explain how total mass is conserved before and after dissolving (using recorded data).
• Highlight dissolving as a physical change (no new substance formed).

4. Plenary and Assessment (10 minutes)

• Ask students to complete a worksheet with:
• Definitions of solute, solvent, solution.
• Draw and label a diagram of the experiment.
• Short answers explaining solubility and why sugar dissolves.
• Interpretation of their data: What was the maximum mass of sugar that dissolved?
• Conduct a quick Q&A session to check understanding and clarify misconceptions.
• Invite a few pairs to share results and reasoning in a brief class discussion.

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Differentiation

• Support: Provide a partially completed worksheet and sentence starters for EAL or SEND pupils.
• Extension: Challenge more able students to think about factors affecting solubility (temperature, stirring speed) and how to investigate them.
• Use questioning to scaffold scientific explanations at varying cognitive levels.

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Assessment Opportunities

• Formative assessment through observation of practical skills and contributions during discussions.
• Review of worksheet answers to check understanding of key concepts and scientific vocabulary.
• Anecdotal assessment during Q&A to identify misconceptions and gaps.

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Cross-Curricular Links

• Math: Measuring, recording masses, interpreting data tables.
• Literacy: Using scientific terminology correctly, writing explanations, and note-taking.
• PSHE/Science attitudes: Working cooperatively during practical investigations, developing enquiry skills.

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Teacher Notes

• Ensure safety by reminding students about careful use of scales and no tasting the materials.
• Demonstrate the dissolving process first if possible to model expectations.
• Prepare all materials prior to lesson to maximise practical time.
• Use real-life examples (e.g., making tea or squash) to contextualise dissolving.
• Encourage scientific curiosity and questioning throughout.

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This lesson provides a stimulating and interactive introduction to dissolving, balancing practical investigation with conceptual understanding, aligned carefully with the national curriculum to support development of enquiry skills and science literacy at KS3.