Grade by Grade
C. Matter and Energy · Properties of Liquids and Solids

Liquid Water and Solid Water

C2.3 C2.4 A1.2 A1.4 A1.5About 35 minutes
Learning goals
  • I can describe properties of liquid water and of ice.
  • I can explain that ice melts when it gets warmer than 0°C.
  • I can explain that water freezes when it gets to 0°C or colder.
  • I can observe that ice floats and that water takes up more space when it freezes.

Words to know

state
The form matter is in, like solid or liquid. Water can be in the solid state (ice) or the liquid state.
change of state
When matter changes from one state to another, like ice changing to water.
melt
To change from a solid to a liquid, like ice melting into water.
freeze
To change from a liquid to a solid, like water freezing into ice.
temperature
How hot or cold something is. We measure it with a thermometer, in degrees Celsius (°C).
0°C
Zero degrees Celsius: the temperature where water freezes and ice melts.
float
To stay at the top of a liquid instead of sinking.

A puzzle at the pond

In summer, you can swim in a pond. In winter, you might be able to skate on the same pond!

How can the same water be something you swim in and something you skate on? Let's find out.

A frozen pond surrounded by snowy evergreen trees, with a few skaters in the distance.
In winter the cold turns this pond's water into solid ice that people can skate on. In summer it will be liquid again. AI-generated image

Water has more than one state

Water is special. We see it every day as a liquid and as a solid.

  • Liquid water: rain, puddles, lakes, rivers, tap water, bath water.
  • Solid water: ice cubes, icicles, snow, frost, hail and the ice on a frozen lake.

Ice, snow and frost are all solid water. They are made of the same stuff as the water in your glass. Only the state is different.

Liquid waterSolid water (ice)
Shapetakes the shape of its containerkeeps its own shape
Feelwet, flows over your handhard, cold and slippery
Lookclear (clean water has no colour)clear or white
Can you pour it?yesno (ice cubes tumble out, but each cube keeps its shape)
Put it in waterit mixes with the waterit floats
Properties of liquid water and solid water

What makes water change?

The answer is temperature: how hot or cold it is.

  • Remember from Grade 1: water freezes at 0°C (zero degrees Celsius). When liquid water gets cold enough (0°C or colder), it freezes into ice.
  • When ice gets warmer than 0°C, it melts into liquid water.

Melting and freezing are changes of state. The water is still water. It only changed from one state to the other. And it can change back again!

SOLIDiceLIQUIDwaterwarm it up: MELTINGcool it down: FREEZING
Warm ice and it melts into liquid water. Cool water to 0°C or colder and it freezes into ice.

Two surprises about ice

  1. Ice floats. Drop an ice cube in a glass of water. It floats, with most of the cube under the water. That is why ice forms on the top of a lake in winter.
  2. Water takes up more space when it freezes. If you fill a plastic cup with water to a line and freeze it, the ice will be a little higher than the line. Frozen water pushes outward. That is why a water bottle filled to the very top can bulge or crack in the freezer.
Worked example

Let's think about a puddle

On a December morning the thermometer says −5°C. The puddle on the driveway is hard ice. In the afternoon the thermometer says 4°C. What happens to the puddle?

  1. In the morning it is −5°C. That is colder than 0°C, so the puddle water is frozen into ice.
  2. In the afternoon it is 4°C. That is warmer than 0°C.
  3. When ice gets warmer than 0°C, it melts.
  4. So the ice slowly changes back into liquid water.

The puddle melts in the afternoon, because the temperature went above 0°C. If it gets cold again at night, it will freeze again.

−10°C−5°C0°C5°C10°Cmorning: −5°C−10°C−5°C0°C5°C10°Cafternoon: 4°C0°C: freezing pointhard ice(colder than 0°C)melting into water(warmer than 0°C)
The 0°C line is the key. Below it, the puddle is frozen solid. Above it, the ice melts into liquid water.
Worked example

Let's observe: Does water grow when it freezes?

We fill a plastic cup halfway with water and draw a line at the top of the water. We put it in the freezer overnight. What will we see?

  1. Predict: I think the ice will be at the same line.
  2. Test: Leave the cup in the freezer overnight. Use a plastic cup, not glass, because glass can crack.
  3. Observe: In the morning, the water has frozen. The top of the ice is a little above the line. The top may even bump up in the middle.
  4. Think: The water took up more space when it froze.

The ice is higher than the line. Water takes up more space when it freezes into ice. Our prediction was not right, and that is okay. We learned something new!

Just for fun

What did the pond say to the skater in January?

"Don't worry, I've got a solid plan for winter!"

Safety for ice experiments

  • Use plastic cups, not glass, in the freezer.
  • Do not put ice or frozen metal on your tongue or lips.
  • Hold ice for only a short time. Very cold things can hurt your skin.
  • Wipe up melted water so no one slips.
Hands-on activity

Ice investigation

You need: 2 clear plastic cups, water, a marker, a freezer, a glass of water and a thermometer if you have one.

Day 1

  1. Fill one plastic cup halfway with water. Draw a line at the top of the water with the marker.
  2. Predict: Will the ice be above, below or at the line? Draw your prediction.
  3. Put the cup in the freezer overnight.

Day 2

  1. Take out the cup. Where is the top of the ice? Draw what you see.
  2. Pop the ice out and use your senses (no tasting): How does it feel? What colour is it? Does it keep its shape?
  3. Drop the ice into a glass of water. Does it float or sink? How much is under the water?
  4. Leave the ice on a plate. Check it every 10 minutes. Draw what happens.

Share: Tell a grown-up what you found. Use the words melt, freeze, solid and liquid.

Your turn

1

Name two kinds of solid water.

2

What happens to ice when it gets warmer than 0°C?

3

What happens to water when it gets to 0°C or colder?

4

Does an ice cube float or sink in water?

5

Is a puddle a solid or a liquid when it is 10°C outside?

6

Name one property of ice.

More practice: warm-up

1

Is snow liquid water or solid water?

2

Is rain liquid water or solid water?

3

What do we use to measure temperature?

4

What is it called when water turns into ice?

5

What is it called when ice turns into water?

More practice: on your own

1

The thermometer says −10°C. Will the pond be frozen or liquid on top? Explain.

2

Why does ice form on the top of a lake and not the bottom?

3

Ava filled a plastic bottle to the very top with water and put it in the freezer. The next day it was bulging. Why?

4

Is the water in an ice cube the same stuff as the water in a glass? Explain.

5

It is 2°C outside and snowing. Will the snow on the ground melt or stay frozen?

Challenge

1

Ice melts into water. Can that water become ice again? How?

2

Why should you not put a full glass jar of water in the freezer?

3

In the morning it is −3°C and in the afternoon it is 6°C. In the evening it is −2°C. What happens to a puddle during the day?

Check your understanding

Quiz

1.

Which one is solid water?

2.

Water freezes at...

3.

An ice cube is left on the kitchen counter. It will...

4.

What happens when you put an ice cube in a glass of water?

5.

When water freezes, it takes up...

6.

It is −8°C outside. A bucket of water is left outside all night. In the morning the water is...

For parents and teachers

Big idea: Water can be a solid (ice, snow, frost) or a liquid. Temperature makes it change: at 0°C or colder, liquid water freezes; above 0°C, ice melts (C2.3). Ice floats, and water expands a little when it freezes.

How to help: Check an outdoor thermometer or the weather app together on winter mornings. Ask, "Will the puddles be frozen today? How do you know?" Point out frost, icicles and slush, and name the state.

About the experiment (Strand A): Your child predicts, observes over two days and records with drawings. Help them write the date on each drawing.

Common difficulties:

  • Thinking ice and water are different materials. Melt an ice cube in a cup to show it becomes the same water.
  • Reading negative temperatures. Just say, "Minus means colder than zero, so water freezes."
  • Expecting ice to sink because it is hard. Let them test it; the result is memorable.

Safety: Use plastic, not glass, in the freezer. Do not let children put very cold items on their tongue or lips.