Science · Year 2 · Mixing and Moving Materials · Term 1

Dissolving Solids in Liquids

Students will experiment with dissolving various solids in water and other liquids, observing the changes.

• ACARA Content Descriptions
• AC9S2U04

About This Topic

Combining materials is a foundational chemistry concept where students explore the results of mixing different substances. They observe that some materials blend seamlessly, like salt in water, while others remain distinct, like oil and water or sand and pebbles. This topic introduces the idea of mixtures and the physical changes that occur during the mixing process.

In an Australian context, this can be linked to traditional practices such as mixing ochre with water or oils for painting, or the way different soils mix in a riverbed. Understanding these interactions helps students predict how materials will behave in everyday life and in industrial processes. Students grasp this concept faster through structured experimentation and peer explanation, where they can describe the 'disappearing' act of solutes or the layering of liquids.

Key Questions

1. Explain what happens to sugar when it dissolves in water.
2. Compare the dissolving rates of salt and sand in water.
3. Predict which common household solids will dissolve in water.

Learning Objectives

• Compare the dissolving rates of different solids in water.
• Explain the process of dissolving using the terms solute and solvent.
• Predict which common household solids will dissolve in water based on prior observations.
• Classify substances as soluble or insoluble in water.

Before You Start

Properties of Solids and Liquids

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

Observing and Recording Data

Why: Students must be able to carefully observe changes during an experiment and record their findings accurately.

Key Vocabulary

dissolve	When a solid breaks down into tiny particles and spreads evenly throughout a liquid, making it seem to disappear.
solute	The substance that dissolves in a liquid, for example, the sugar in sweetened tea.
solvent	The substance that dissolves another substance, for example, the water in sweetened tea.
soluble	A substance that can dissolve in a solvent, like salt in water.
insoluble	A substance that cannot dissolve in a solvent, like sand in water.

Watch Out for These Misconceptions

Common Misconception

Students often think that when sugar dissolves in water, it has completely disappeared or ceased to exist.

What to Teach Instead

Have students weigh the water and sugar before and after mixing to show the mass is still there. Tasting the water (if safe and hygienic) also proves the sugar is still present even if invisible.

Common Misconception

Children may believe that all liquids will mix together perfectly.

What to Teach Instead

Use an oil and water demonstration. Active observation of the layers forming helps students understand that some materials are 'immiscible' and will always stay separate.

Active Learning Ideas

Inquiry Circle: The Great Mix-Up

Groups are given clear jars of water and various solids (sugar, sand, glitter, flour). They predict what will happen, mix them, and then categorise the results as 'dissolved' or 'still there'.

45 min·Small Groups

Stations Rotation: Separation Challenge

Provide stations with pre-made mixtures like sand and water, or paperclips and rice. Students must use tools (sieves, magnets, filter paper) to separate the materials, recording which tool worked best for each mixture.

40 min·Small Groups

Think-Pair-Share: Why did it change?

Show a video of a chef mixing ingredients for a cake. Students think about which ingredients they can still see and which have 'hidden' away, then discuss with a partner why we mix things in the first place.

15 min·Pairs

Real-World Connections

• Bakers use dissolving to create smooth batters and doughs, ensuring ingredients like sugar and salt are evenly distributed for consistent texture and taste in cakes and bread.
• Chefs in restaurants prepare stocks and sauces by dissolving herbs, spices, and vegetables in water or broth, extracting flavors to create rich culinary bases.
• Pharmacists ensure medications dissolve properly in the body. They select the right form of a drug, like a tablet or liquid, so it can be absorbed and work effectively.

Assessment Ideas

Exit Ticket

Provide students with small cups of water, sugar, and sand. Ask them to record in their science notebooks what happens when they add sugar and stir, and what happens when they add sand and stir. Then, ask them to write one sentence explaining why one 'disappeared' and the other did not.

Discussion Prompt

Present students with a list of common household items (e.g., flour, oil, coffee grounds, Jell-O powder). Ask: 'Which of these do you predict will dissolve in water? Which will not? Explain your predictions using the words 'soluble' and 'insoluble'.

Quick Check

During the experiment, ask individual students: 'What is the solute in your cup?' and 'What is the solvent?' Observe their responses to gauge understanding of these key terms.

Frequently Asked Questions

What are some safe materials to use for mixing in Year 2?

Stick to kitchen staples: salt, sugar, flour, food colouring, vegetable oil, and cornflour. For solids, use sand, pebbles, and rice. These are non-toxic and easy to dispose of, making them perfect for hands-on classroom investigations.

How does this topic connect to Indigenous Australian culture?

You can discuss the preparation of traditional paints. Aboriginal artists mix natural pigments (ochre) with binders like water or egg yolk. This is a perfect example of combining materials to create something with a new purpose.

How can active learning help students understand mixtures?

Active learning turns students into 'scientists' rather than just observers. When they physically use a sieve to separate sand from rocks, they are using tactile feedback to understand particle size. This makes the properties of materials much more memorable than a diagram in a book.

What is the difference between a mixture and a solution for this age group?

At Year 2, you don't need to use the word 'solute' or 'solvent'. Focus on whether the materials can still be seen separately (like a fruit salad) or if they have blended so well they look like one thing (like salty water).