Science · Grade 2 · Properties of Liquids and Solids · Term 2

The Science of Dissolving

Students will investigate which solids dissolve in water and which do not, and explore factors affecting dissolving.

• Ontario Curriculum Expectations
• 2-PS1-2

About This Topic

Students investigate dissolving by testing solids such as salt, sugar, sand, and chalk in water. They record observations to classify materials as soluble or insoluble and explore factors like water temperature, stirring, and particle size that influence dissolving rates. Through structured tests, they compare how sugar dissolves faster than salt under certain conditions and predict outcomes for new substances based on visible properties like graininess or color.

This topic fits within the Ontario Grade 2 science curriculum's focus on properties of liquids and solids. It develops key skills in fair testing, data collection, and pattern recognition, while connecting to everyday experiences like making lemonade or ocean salinity. Students build foundational understanding of solutions versus mixtures, preparing them for later topics in chemical changes.

Active learning excels with dissolving because safe, everyday materials allow quick experiments that reveal immediate results. Students predict, test variables, and discuss discrepancies in small groups, turning abstract particle movement into visible changes they control and explain.

Key Questions

1. Analyze why some solids disappear in water while others do not.
2. Compare the dissolving rates of sugar and salt in water.
3. Predict if a new substance will dissolve in water based on its properties.

Learning Objectives

• Classify given solids as soluble or insoluble in water based on experimental results.
• Compare the dissolving rates of two different substances (e.g., sugar and salt) in water under controlled conditions.
• Explain how temperature affects the rate at which a solid dissolves in water.
• Predict whether a new, untested solid will dissolve in water, justifying the prediction based on observable properties.

Before You Start

Properties of Solids and Liquids

Why: Students need to be able to identify and describe basic properties of solids and liquids before investigating how they interact.

Observation and Recording Data

Why: This topic requires students to carefully observe changes and record their findings accurately, skills developed in earlier units.

Key Vocabulary

dissolve	When a solid mixes completely into a liquid, disappearing to form a clear solution.
soluble	A substance that can dissolve in a particular liquid, like water.
insoluble	A substance that cannot dissolve in a particular liquid, like water.
solution	A mixture where one substance dissolves completely into another, forming a clear liquid.
rate of dissolving	How quickly a solid dissolves into a liquid.

Watch Out for These Misconceptions

Common Misconception

All solids dissolve in water.

What to Teach Instead

Testing various materials shows sand and chalk remain visible. Hands-on station rotations let students compare results directly, building evidence against the idea through shared class data and discussion.

Common Misconception

Dissolved solids disappear forever.

What to Teach Instead

Evaporating the water reveals the solid returns unchanged. Simple evaporation demos in pairs help students observe this cycle, reinforcing that dissolving is a physical change via direct experimentation.

Common Misconception

Larger solid pieces dissolve faster.

What to Teach Instead

Breaking sugar into smaller bits speeds dissolving. Prediction and testing activities with crushed versus whole crystals allow students to discover particle size effects through trial and observation.

Active Learning Ideas

Testing Stations: Soluble or Not

Prepare stations with cups of room-temperature water and solids like salt, sugar, sand, and flour. Students predict solubility, add a teaspoon of each solid, stir for one minute, and record if it dissolves or leaves residue. Groups rotate stations and share findings on a class chart.

45 min·Small Groups

Hot vs Cold: Temperature Test

Provide pairs with hot and cold water in clear cups, plus sugar cubes. Students time how long it takes for the sugar to dissolve in each, stirring consistently, then graph results. Discuss why heat speeds dissolving.

30 min·Pairs

Stirring Challenge: Rate Comparison

In small groups, students dissolve equal amounts of salt and sugar in water: one cup stirred vigorously, one undisturbed. They observe and time differences, then predict outcomes for larger crystals. Record data in simple tables.

35 min·Small Groups

Prediction Walk: Classroom Hunt

Students walk the room to select safe solids, predict if they dissolve based on prior tests, then test individually in small dishes of water. They justify predictions with properties like texture and share results whole class.

25 min·Individual

Real-World Connections

• Bakers use their understanding of dissolving to create recipes. For example, they know that sugar dissolves in liquids to make cakes and cookies sweet, and that the temperature of the liquid can affect how quickly it dissolves.
• Chefs preparing sports drinks or flavored waters need to understand dissolving. They ensure that powders like drink mixes dissolve completely to create a uniform taste and appearance for consumers.
• Pharmacists measure precise amounts of active ingredients that need to dissolve in liquids to create liquid medicines. They must ensure the medication dissolves properly for the body to absorb it.

Assessment Ideas

Exit Ticket

Provide students with three small cups of water, each with a different solid (e.g., salt, sand, baking soda). Ask them to record which solids dissolved and which did not. Then, ask them to write one sentence explaining why they think one dissolved and another did not.

Quick Check

During an experiment comparing dissolving rates, ask students: 'Which substance do you predict will dissolve faster, and why?' Observe their responses and listen for reasoning based on prior knowledge or visible properties of the substances.

Discussion Prompt

Pose the question: 'Imagine you have a cup of cold water and a cup of hot water. If you add the same amount of sugar to both, what do you think will happen? How will the dissolving be different?' Facilitate a brief class discussion, encouraging students to share their predictions and reasoning.

Frequently Asked Questions

How do I teach dissolving factors to Grade 2 students?

Start with clear tests of temperature, stirring, and particle size using sugar and salt. Provide timers and charts for recording. Guide predictions first, then observations, to show patterns like hot water dissolving faster. Relate to real life, such as instant coffee, for relevance. This builds fair testing skills over 3-4 lessons.

What are common materials for dissolving experiments?

Use safe, accessible items: salt, sugar, baking soda for solubles; sand, flour, chalk for insolubles. Test in clear cups with room-temp, hot, and cold water. Measure equal amounts with spoons for fairness. These let students see clear differences and predict for new items like rice or gelatin.

How can active learning help students understand dissolving?

Active approaches like station rotations and variable tests give direct experience with changes, making particle ideas tangible. Students predict, observe fast results, and adjust in pairs or groups, which corrects misconceptions through evidence. Collaborative charting reveals class patterns, boosting engagement and retention over passive explanations.

Why compare sugar and salt dissolving rates?

Both dissolve but at different speeds, highlighting factors without overwhelming beginners. Students time stirred versus un-stirred trials, graphing simple bars. This teaches controlled variables and prediction, aligning with curriculum expectations for data analysis in properties of matter.