What Is a Liquid — Chemistry (Grade 7)

Define and explain What Is a Liquid in your own words
Use key terms such as liquid accurately
Apply what you have learned to new examples and questions
Avoid the common mistakes learners make with this topic

This lesson focuses on What Is a Liquid: see how liquids flow and take the shape of their container.

Definition: What Is a Liquid

See how liquids flow and take the shape of their container.

Key ideas

Liquids take the shape of their container

Pour water into a tall glass and it becomes tall and thin; pour the same water into a wide bowl and it becomes short and wide. The water flows because its shape is not fixed, but the amount of water stays the same. This is why we measure liquids by pouring them into measuring jugs.

Solids keep their shape

A solid holds its shape wherever you put it: a wooden block is still a block in your hand, in a box or on the table. You can often change a solid's shape by squashing, bending or cutting it, but it will not flow into a new shape on its own. That is why buildings, furniture and toys are mostly made from solids.

Key term — liquid: A material that flows and takes the shape of its container, like water or milk.

Is it a solid or a liquid?

You are given sand, honey, a marble and orange juice. Decide which are solids and which are liquids, and explain each choice.

Ask of each material: does it keep its own shape, or does it flow? The marble keeps its shape wherever it is put: solid. The orange juice flows and takes the shape of its cup: liquid. Honey flows very slowly when poured: it is a liquid, even though it is thick. Sand is trickier: each grain is a solid, and the grains pour like a liquid — but every single grain keeps its own shape, so sand is made of solids.

Answer: Solids: marble, sand (each grain keeps its shape). Liquids: orange juice, honey (both flow).

Common mistakes

Calling thick liquids solids Honey, treacle and paint pour slowly, but they still flow and take the shape of their container. Thickness does not make something a solid — flowing does make it a liquid.
Thinking melted ice has disappeared When ice melts, it turns into water — the material is still there, just in a different state. If you freeze the water, the ice comes back, which proves nothing was lost.

Practice

Sand pours like a liquid. Explain why scientists still call each grain a solid.

Look closely at a single grain.

Each grain keeps its own shape and does not flow; only the pile of grains moves.

Why is a chair a solid?

What happens to its shape when you move it?

It keeps its own shape wherever you put it and does not flow.

Name one solid and one liquid you used today.

Think about breakfast or getting dressed.

Any sensible pair, for example toast (solid) and milk (liquid).

Pour 100 ml of water from a beaker into a bottle. What changes and what stays the same?

Think about shape and amount.

The shape changes to fit the bottle, but the amount (volume) of water stays the same.

Quick check

What Is a Liquid — quick check

Which of these best defines "liquid"?

A material that flows and takes the shape of its container, like water or milk.

You warm some butter and it melts. How could you prove the melted butter is the same material?

Cool it down and it freezes back into solid butter, showing no new material was made.

Chocolate left in a warm car goes soft. What is this change called, and is it reversible?

Melting; yes, it is reversible because cooling the chocolate hardens it again.

Key takeaways

What Is a Liquid: see how liquids flow and take the shape of their container.
Liquids take the shape of their container: Pour water into a tall glass and it becomes tall and thin; pour the same water into a wide bowl and it becomes short and wide.
solid: A material that keeps its own shape, like a brick or an apple.
Watch out for: calling thick liquids solids

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