Lesson video

Hello again.

How are you today? Are you excited for our lesson? Today we are going to learn about melting points and boiling points, and how we can use them to find out the state of matter of a substance at a particular temperature.

Ready? Let's go Today we are going to stop by recapping our previous knowledge.

We will then learn about how scientists measured temperature and two key temperatures for each substance, the melting point and the boiling point.

Finally, we will use our new understanding to predict the state of matter of a substance based on its melting point and its boiling point.

In this lesson, you will need an exercise book or paper and a pencil.

If you don't have one of these items, pause the video now and go and get them.

Press play when you're ready to start.

Let's start by recapping a previous knowledge.

Can you remember the three states of matter? Pause the video and write down the three states of matter.

The three states of matter are solids, liquids, and gases.

Pause the video and write down an example of a solid, a liquid, and a gas.

Can you remember the properties of solids? Pause the video and write down the three properties of solids.

Press play when you're ready to hear the answer.

Solid cannot be compressed, they do not flow, and they have a fixed shape.

Can you remember the properties of liquids? Pause the video and write down three properties of liquids.

Press play when you're ready to hear the answer.

Liquids cannot be compressed.

They can flow and they can take the shape of that container.

Can you remember the properties of gases? Pause the video and write down three properties of gases.

Press play when you're ready to hear the answer.

Gases can be compressed, they can flow, and they can ill the shape of their container.

Which of these diagrams shows a gas? The middle diagram shows a gas.

How does you know? The middle diagram shows a gas because the particles are far apart from each other and they're moving fast.

What is the difference between the particles in a solid and the particles in a liquid? Particles in a solid are in ordered rows, whereas the particles in a liquid are in a random arrangement.

Pause the video and match the description to the correct state of matter.

Press play when you're ready to find out the answer.

solid particles are touching and in ordered rows, liquid particles are touching in a random arrangement, and gas particles are far apart from each.

Pause the video and match the description to the correct state of matter.

Press play when you're ready to hear the answer.

Solid particles cannot move, but can vibrate, liquid particles slide past each other, and gas particles are moving constantly in all directions.

What happens to particles as they are heated? Pause the video and fill in the gaps on the bottom of the side.

When the temperature is increased, particles have more energy, and the substance expands.

What happens to popsicles as they're cooled? Pause the video and fill in the gaps in the sentence at the bottom.

Decreasing the temperature, particles have less energy, so the substance contracts.

What does each arrow represent? Pause the video and complete the diagram with the name of four state changes.

When a solid becomes a liquid, it's called melting.

When a liquid becomes a gas, it's called boiling.

When a gas becomes a liquid, it's called condensing.

And when a liquid becomes a solid is called freezing.

Now we're going to think about how scientists measure temperature.

Let's have a look at how I measured the temperature of water.

Can you remember the piece of equipment that we use to measure temperature? We use a thermometer to measure temperature.

I'm going to start by putting my thermometer in hot water.

Watch the moment to carefully.

What happens to the liquid in the thermometer when I put it in hot water? The liquid in the thermometer is rising because the liquid is expanding because it's getting hotter.

This thermometer has numbers on it.

The numbers represent temperature in degrees Celsius.

My turn, degrees Celsius.

Your turn.

Celsius is used to measure temperature.

I'm going to have a look, and I'm going to measure the temperature of my hot water.

My hot water is that 73 degree Celsius.

If you look carefully, you might be able to see how I got that number.

Now let's try to cold water.

Watch what happens to the thermometer when I put it in cold water? Can you see that the liquid is contracting because it is getting cooler? Again, I'm going to have a look at the numbers on my thermometer to work out the temperature.

This water is at 23 degrees Celsius.

What do we measure temperature in? Temperature is measured in degrees Celsius.

We measure temperature by placing the thermometer in water.

When I placed the thermometer in hot water, the liquid inside the thermometer expands.

When I placed my thermometer in cold water, the liquid inside the thermometer contracts.

Temperature is measured using a scale called the Celsius.

My turn, Celsius.

Your turn.

There are two important temperatures for a substance.

The temperature a substance melts and the temperature a substance boils.

Water always melts at zero degrees C.

This is called the melting point of water.

What do I mean by the melting point of water? I mean the temperature that water always melts.

What temperature does water melt at? Water melts at zero degrees C.

The temperature that water boils up is 100 degrees C.

What do I mean by the boiling point of water? The boiling point of water is the temperature that water boils at.

What temperature does water boil at? Water boils at 100 degrees C.

You are going to answer these three questions I'll read them to you.

Then you can pause the video to complete them in your notes.

Question one, what is temperature? Question two, what scale do we normally use to measure temperature? Question three, how did scientists decide what zero and 100 should mean in this scale? Pause the video and press play when you're ready to check your answers.

Temperature is a measure of how hot or cold a substance is.

We normally use a scale called Celsius, which is written as degrees C.

Zero degrees is the temperature the water melts and 100 degrees is the temperature the water boils.

Now we're going to think carefully about what to fixed point is.

A fixed point is the temperature that a state change happens for different substances.

Scientists most commonly used the melting point and the boiling point.

What is the melting point? The melting point is the temperature the substance melts at.

What is the pointing point? The boiling point is the temperature that's the substance boils at.

Let's have a look at some melting points.

Here I have two substances.

I have ice and I have candle wax.

Can you see that the ice is already melting? Can you remember the melting point of water? The melting point of water is zero degrees C.

So in this room, the ice is already starting to melt, but the candle is still a solid.

The candle has a much higher melting point than ice.

It requires a higher temperature to melt the candle than the ice.

I am going to light the candle using a match.

This is not something that you should try at home.

I need to light the candle with a match because the candle needs a higher temperature in order to melt.

Watch carefully to see what happens as I light the candle.

You should be able to see the wax around the candle starting to melt.

The wax around the candle starts to melt because the temperature gets high enough to reach the melting point of the wax.

Pause the video and write down the definition for melting point and boiling point.

Press play when you're ready to hear the answer.

The melting point is the temperature a substance melt sets, and the boiling point is the temperature a substance boils at.

We are going to use our new knowledge of melting points and boiling points to work out the states of matter of a substance at a given temperature.

We can use the melting point and the boiling point to identify if a substance is a solid, a liquid, or a gas.

If a substance is a solid, it means that it has not melted or boiled.

If a substance is a liquid, it means it has melted, but not boiled.

If a substance is a gas, it means that it has melted and boiled.

I'm going to show you how I work this out.

When I'm working this out, I draw myself a thermometer, and I say that the thermometer increases in temperature up the page.

When my substance gets to the melting point, what happens? At the melting point, the substance melts.

Before the melting point, the substance was just solid.

What happens to the solid at the melting point? At the melting point, the solid is going to become a liquid.

It's going to be a liquid until it reaches the boiling point.

What happens to a substance when it reaches the boiling point? When our substance reaches the boiling point, it's going to boil.

What happens when a substance boils? When a substance boils, it turns from a liquid into a gas.

Between the melting point and the boiling point, the substance is a liquid.

What states of matter is the substance after it has boiled? After it has boiled, the substance is a gas.

Let's look at a real example.

The melting point of water is naught degree C, and the boiling point of water is 100 degrees.

What's the melting point of water? The melting point of water is naught degree C.

What's the boiling point of water? The boiling point of water is 100 degrees C.

If the temperature is 25 degrees C, what's the temperature of water going to be? Sorry, what is the state of matter of water going to be? Let's have a look.

We need to go up our thermometer until we get to 25 degrees C.

25 degrees C is more than naught, but less than 100.

What states of matter will water be in at 25 degrees C? Water is going to be a liquid at 25 degrees Celsius.

What about if it was minus four degrees? Let's have a look at our thermometer.

Minus four degrees is less than zero degrees.

If it is less than the melting point, what state of matter will it be? At minus four degrees, our water is going to be a solid.

What about if the temperature was 150 degrees? 150 degrees is more than the melting point and more than the boiling point.

So if water has melted and boiled, what state of matter is it going to be? It's going to be a gas.

You're going to have a go at some other questions to work out what states of matter a substance is in at different temperatures.

Firstly, what state of matter is water in at 25 degrees C? Pause the video to work out the answer.

Press play when you're ready to continue.

Water is a liquid at 25 degrees C, because 25 is between the melting point and the boiling point.

What state of matter is aluminium in at 25 degrees C? Pause the video to work out your answer.

Press play when you're ready to continue.

Aluminium is a solid 25 degrees C, because 25 degrees C is less than the melting point.

It's chlorine a solid, a liquid, or a gas at 25 degrees C? Pause the video to work out your answer.

Chlorine is a gas at 25 degrees C, because 25 degrees C is more than the melting point and more than the boiling point.

Is iodine a solid, a liquid, or a gas at 100 degrees? Iodine is a solid at 100 degrees C, because it is less than the melting point and less than the boiling point.

Is oxygen a solid, a liquid or a gas at zero degrees C? Pause the video to work out your answer.

At zero degrees C, oxygen is a gas because it is higher than the melting point and higher than the boiling point.

You've worked so hard today, learning about how scientists measure temperature and how they use the fixed points, melting point and boiling point.

I am so impressed with all the work that you have done so far.

Make sure you do your quiz to show off your knowledge.

See you next time.

Bye.