Chapter 3 of 7

All 7 chapters
  1. 1Solids, liquids and gases, readunderstood
  2. 2Air is all around us, readunderstood
  3. 3Melting and freezing, readunderstood
  4. 4Evaporation and drying, readunderstood
  5. 5Condensation, readunderstood
  6. 6The water cycle, readunderstood
  7. 7Clean water, readunderstood

S2.4.3 Chapter 3

Melting and freezing

Where does my ice go when I leave it in the sun?

Your guess

Pick one before you read on. It is fine to be wrong.

Your guess

  • You picked A. Read on. At the end, the chapter comes back to your guess.

  • You picked B. Read on. At the end, the chapter comes back to your guess.

  • You picked C. Read on. At the end, the chapter comes back to your guess.

By the end you can

  • Explain melting and freezing as changes caused by heating and cooling
  • Compare how fast butter melts in sun and shade

Ice is hard. A puddle of water is not. But ice and water are the same material.

Draw it first

Draw ice melting and freezing

  1. On the left, a box of dots in neat rows, labelled ice. On the right, a box of jumbled dots filling the bottom, labelled water. An arrow points from the ice to the water and is labelled heat. A second arrow points back from the water to the ice and is labelled cool. Labels: ice, water, heat, cool.ice

    1 Draw a box of dots in neat rows. Write ice.

  2. On the left, a box of dots in neat rows, labelled ice. On the right, a box of jumbled dots filling the bottom, labelled water. An arrow points from the ice to the water and is labelled heat. A second arrow points back from the water to the ice and is labelled cool. Labels: ice, water, heat, cool.icewaterheat

    2 Draw an arrow to the right, marked heat. Draw a box of loose dots, marked water.

  3. On the left, a box of dots in neat rows, labelled ice. On the right, a box of jumbled dots filling the bottom, labelled water. An arrow points from the ice to the water and is labelled heat. A second arrow points back from the water to the ice and is labelled cool. Labels: ice, water, heat, cool.icewaterheatcool

    3 Draw an arrow back to the left. Write cool.

Melting is when a solid turns into a liquid. Heat makes things melt. Ice melts into water. Butter and wax melt too.

Freezing is when a liquid turns into a solid. Cooling makes things freeze. Water freezes into ice. Melted wax freezes back into hard wax.

You can undo both changes. Heat ice and it melts. Cool the water and it freezes again.

Melting does not change how much water there is. The water weighs the same as the ice did.

Temperature tells how hot or cold something is. We measure it in degrees Celsius, or °C. Pure water freezes at 0 °C. Ice melts at the same temperature.

A thermometer with a scale from -10 to 10 °C. The liquid stands at 0 °C, marked by a pointer labelled 0 °C. Beside it, a hatched block labelled ice melts at 0 °C, and a dotted block labelled water freezes at 0 °C. Labels: 0 °C, ice melts, at 0 °C, water freezes, -10, -5, 0, 5, 10, °C.-10-50510°C0 °Cice meltsat 0 °Cwater freezesat 0 °C
Ice melts at 0 °C. Water freezes at 0 °C.

Other materials melt at other temperatures. Butter melts on a warm day. Wax needs more heat. A stone does not melt in the sun.

A cup of water with a cube of ice, labelled ice, in it. The ice floats. Most of the cube is under the water, and a small part sticks up above it. The cup is labelled water. Labels: ice, water.icewater
Ice floats. Most of it is under the water.

See it three ways

As a picture

Two boxes side by side. The first box is hatched, to show ice. It is labelled ice, and below it, below 0 °C. The second box is dotted, to show water. It is labelled water, and below it, above 0 °C. Labels: ice, below 0 °C, water, above 0 °C.icebelow 0 °Cwaterabove 0 °C

In words

Heat turns ice into water. Cooling turns water into ice. Both changes can be undone.

In symbols

Pure water freezes at 0 °C. Ice melts at 0 °C. Below 0 °C, water becomes ice. Above 0 °C, ice becomes water.

Try it

Sun or shade: which melts butter faster?

You need: two saucers, butter or a hard cooking fat, a knife, a sunny place, a shady place, a clock or a watch.

Be safe: Do not eat the butter. Do not look at the Sun. A saucer in the sun can get hot.

  1. Cut two pieces of butter the same size. Put one on each saucer.
  2. Put one saucer in the sun. Put the other in the shade.
  3. Look at both every few minutes. Note the time.
  4. Which one gets soft and flat first?

What you will see: The piece in the sun melts first. The piece in the shade melts later. In a cool place it may only get soft.

If you cannot try it, this is what happens.
Two pictures side by side, each with a saucer and butter on it. On the left, the Sun is above. The butter has melted into a flat dotted pool. It is labelled sun. On the right, a tree gives shade above. The butter is still a hatched lump. It is labelled shade. Labels: sun, shade.sunshade

A wrong idea many people have

When a thing melts, it is gone for good.

Why it feels right: A puddle does not look like ice any more.

The test that breaks it: A grown up warms a little candle wax in a tin. Stand the tin in a bowl of hot water. The wax melts. The grown up lifts the tin out. Wait. The wax goes hard again. Never touch hot wax or hot water.

What is true: Melting can be undone. Cool the liquid and it freezes again. It is the same material.

Three tins in a row. The first tin holds a hard lump of wax, labelled hard wax. An arrow labelled heat points to the second tin, which holds flat melted wax, labelled melted. An arrow labelled cool points to the third tin, which holds flat hard wax, labelled hard again. Labels: hard wax, heat, melted, cool, hard again.heatcoolhard waxmeltedhard again
Heat melts wax. Cooling makes it hard again.

Key words

melting
a solid turning into a liquid. Heat makes it happen.
freezing
a liquid turning into a solid. Cooling makes it happen.
temperature
how hot or cold something is.

Back to your guess

The answer is B: It turns into water.

The ice melts. It turns into water. Nothing has gone.

Check yourself

Try each one before you look. A wrong answer tells you where to go next.

  1. What turns ice into water?

    Tap your answer.

    1. Yes, that is right. Heat makes a solid melt into a liquid. Ice melts into water.

    2. Not this one. Cooling makes water freeze into ice. Heat makes ice melt. Try another.

    3. Not this one. Shaking does not change ice. It melts when it is heated. Try another.

    See the answer

    Heat

    Heat makes a solid melt into a liquid. Ice melts into water.

    • If you chose B: Cooling makes water freeze into ice. Heat makes ice melt.
    • If you chose C: Shaking does not change ice. It melts when it is heated.

  2. At what temperature does pure water freeze?

    Tap your answer.

    1. Not this one. That is very hot. Water freezes when it is cooled to 0 °C. Try another.

    2. Not this one. At 10 °C, ice melts. Water freezes at 0 °C. Try another.

    3. Not this one. Pure water freezes at 0 °C. It does not need to get colder. Try another.

    4. Yes, that is right. Pure water freezes at 0 °C, and ice melts at 0 °C.

    See the answer

    0 °C

    Pure water freezes at 0 °C, and ice melts at 0 °C.

    • If you chose A: That is very hot. Water freezes when it is cooled to 0 °C.
    • If you chose B: At 10 °C, ice melts. Water freezes at 0 °C.
    • If you chose C: Pure water freezes at 0 °C. It does not need to get colder.

  3. An ice cube is put in a glass of water. What does it do?

    Tap your answer.

    1. Not this one. Ice floats on water. Most of it is under the water, but it does not sink. Try another.

    2. Not this one. Most of an ice cube is under the water. Only a small part sticks up. Try another.

    3. Yes, that is right. Ice floats on water. Most of the cube is under the water. A small part is above it.

    See the answer

    It floats with most of the cube under the water.

    Ice floats on water. Most of the cube is under the water. A small part is above it.

    • If you chose A: Ice floats on water. Most of it is under the water, but it does not sink.
    • If you chose B: Most of an ice cube is under the water. Only a small part sticks up.

  4. Ravi puts butter in the sun and butter in the shade. Which melts first, and why?

    Tap your answer.

    1. Not this one. The shade is cooler. The sun gives the butter more heat, so that piece melts first. Try another.

    2. Not this one. The pieces are the same, but the sun heats one more. That piece melts first. Try another.

    3. Yes, that is right. Heat makes butter melt. The sun heats it more than the shade does. So it melts faster.

    See the answer

    The butter in the sun. The Sun heats it more.

    Heat makes butter melt. The sun heats it more than the shade does. So it melts faster.

    • If you chose A: The shade is cooler. The sun gives the butter more heat, so that piece melts first.
    • If you chose B: The pieces are the same, but the sun heats one more. That piece melts first.

  5. From an earlier chapter

    Ice is a solid and water is a liquid. Which keeps its shape in a cup?

    Tap your answer.

    1. Not this one. Ice and water are the same material. But only the ice keeps its shape. Water takes the shape of the cup. Go to S2.4.1. Try another.

    2. Yes, that is right. Ice is a solid. A solid keeps its own shape.

    3. Not this one. Water takes the shape of its cup. It is a liquid. Go to S2.4.1. Try another.

    See the answer

    Ice

    Ice is a solid. A solid keeps its own shape.

    • If you chose A: Ice and water are the same material. But only the ice keeps its shape. Water takes the shape of the cup. Go to S2.4.1.
    • If you chose C: Water takes the shape of its cup. It is a liquid. Go to S2.4.1.

  6. Two jars of pure water stand outside all night. Each thermometer shows the air by its jar. In which jar will the water freeze?

    Two thermometers with scales from -10 to 10 °C. The thermometer labelled jar A shows the air by jar A and stands at -5 °C. The thermometer labelled jar B shows the air by jar B and stands at 5 °C. Labels: jar A, jar B, -10, -5, 0, 5, 10, °C.-10-50510°Cjar A-10-50510°Cjar B
    Tap your answer.

    1. Yes, that is right. Jar A is below 0 °C. Pure water freezes when it is cooled to 0 °C or below.

    2. Not this one. Jar B is above 0 °C. Water does not freeze there. Try another.

    3. Not this one. Both are cold, but only one is below 0 °C. Water freezes below 0 °C. Try another.

    4. Not this one. Water freezes anywhere that is cooled to 0 °C or below. It does not need a freezer. Try another.

    See the answer

    Jar A

    Jar A is below 0 °C. Pure water freezes when it is cooled to 0 °C or below.

    • If you chose B: Jar B is above 0 °C. Water does not freeze there.
    • If you chose C: Both are cold, but only one is below 0 °C. Water freezes below 0 °C.
    • If you chose D: Water freezes anywhere that is cooled to 0 °C or below. It does not need a freezer.

  7. A grown up warms wax until it melts. Then it cools and goes hard again. What does this show?

    Tap your answer.

    1. Not this one. Cooling the melted wax made it hard again. Melting can be undone. Try another.

    2. Not this one. It is the same wax. It melted, and then it froze again. Try another.

    3. Yes, that is right. Heat melts wax and cooling sets it. The wax is the same material all the way through.

    See the answer

    Melting can be undone by cooling.

    Heat melts wax and cooling sets it. The wax is the same material all the way through.

    • If you chose A: Cooling the melted wax made it hard again. Melting can be undone.
    • If you chose B: It is the same wax. It melted, and then it froze again.

Keep it

Copy this into your exercise book.

Heat makes a solid melt into a liquid. Cooling makes a liquid freeze into a solid. Pure water freezes and ice melts at 0 °C. Ice floats. Butter melts faster in the sun than in the shade.

Draw: Draw a box of ice and a box of water. Draw an arrow marked heat. Draw an arrow back marked cool.

Reading with a child? A short page for the adult: what this chapter teaches and three questions to ask.

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