Lesson video

Hi, I'm Miss Miah.

Thank you so much for joining me in this lesson.

Let's get started.

In this lesson, you will be able to measure the melting point and freezing point of a substance.

Your keywords are on the screen now.

Let's go through them.

Liquid state, solid state, melting point, freezing point.

Now let's find out what these keywords mean.

Substances in the liquid state will take the shape of their container.

Particles in a substance in a solid state are in a fixed position and can only vibrate.

The melting point of a substance is the temperature at which it changes from a solid state to a liquid state.

The freezing point is the temperature at which a substance changes from a liquid state to a solid state.

So this lesson is all about Melting: melting and freezing points.

We have three lesson cycles today, and our first lesson cycle is to do with freezing.

We're then gonna be at the freezing point.

And lastly, we'll be comparing melting and freezing.

Let's begin Melting.

When a substance in the solid state is melted, it changes into a liquid state.

Freezing.

When a substance in the liquid state is cooled, it will change into a solid state.

This is called freezing.

Over to you.

Identify the substance that has frozen.

Is it A, B, or C?

You can pause the video here and click play when you've got the answer.

So what did you get?

If you got A, you are correct.

We can see that the water has frozen into ice.

Onto Task A.

I'd like you to explain why the substance is frozen or not frozen for each substance.

Have a look.

So we've got one, unlit candle, two, orange juice, three, ice lolly, four, fudge, five, plastic blocks, and six, black treacle.

You can pause the video here and click play once you've completed this task.

So what did you get?

Well, so an unlit candle, it's frozen.

Wax is in a solid state.

For two, not frozen.

Juice is in a liquid state.

And for three, the ice lolly is in a solid state.

It's frozen.

Fudge, frozen.

The fudge is in a solid state.

And five, it's frozen.

Plastic is in a solid state.

And lastly, six, black treacle.

It's not frozen.

Treacle is in a liquid state.

Well done if you managed to get those correct.

Let's move on.

Now we're going to be looking at the freezing point.

The temperature that a substance changes from a liquid state to a solid state is known as the freezing point.

The temperature that a substance changes from a solid state to a liquid state is known as the melting point.

The melting point and freezing point are the same temperature for a substance.

Melting point for ice equals zero degrees.

Freezing point for ice is also zero degrees.

Melting point for chocolate is equal to 30 degrees and the freezing point for chocolate is also equal to 30 degrees.

The melting point for silver is 962 degrees.

So I think you've guessed it.

The freezing point for silver is also 962 degrees.

Over to you.

True or false?

The freezing point and melting point are the same temperature for a substance.

Is this true or is this false?

And can you justify your answer?

Is it because A: water becomes ice at zero degrees and melts at zero degrees?

Or B: silver melts at a different temperature than it freezes at?

What do you think?

You can pause the video here and click play when you've got the answer.

So what did you get?

If you got true, you are correct.

Why is this?

Can you justify your answer?

So what did you get?

Well, water becomes ice at zero degrees and it melts at zero degrees.

That's because the freezing and melting point have the same temperature for every substance.

At temperatures below its melting point, a substance is in its solid state.

So here we've got an example of a melting point.

So anything below its melting point, the substance will be in solid form.

At temperatures above its freezing point, a substance is in its liquid state.

So here we have the freezing point this time and anything above this, it's in its liquid state.

Water has a freezing point of zero degrees Celsius.

Below zero degrees Celsius, water is frozen as ice in the solid state.

Above zero degrees Celsius, water is melted and in the liquid state.

Room temperature is 20 degrees Celsius, water would be in the liquid state.

So zero degrees Celsius, melting point of water, Below zero degrees, water is frozen as ice in the solid state.

Above it, it's melted and in liquid state.

And room temperature is 20 degrees here.

Over to you.

Paraffin has a melting point of 67 degrees Celsius.

What state of matter is paraffin in at room temperature?

What do you think?

You can pause the video here and click play when you've got the answer.

So what did you get?

Well, 40 degrees is there, 60 degrees is there.

And then we've got 80 degrees Celsius there.

The melting point of paraffin is 67 degrees Celsius.

So anything below that, paraffin is at solid state.

Anything above that, paraffin will be at liquid state.

So that means the state of matter for paraffin at room temperature is solid.

Well done if you got that correct.

Let's move on.

Back to you.

The freezing point of substance A is 15 degrees Celsius.

The room temperature is 20 degrees Celsius.

What state of matter is substance A at room temperature?

A: solid state, B: liquid state, or C: neither liquid state or solid state?

What do you think?

You can pause the video here and click play when you've got the answer.

So what did you get?

If you got B, liquid state, you are correct.

Back to you.

The freezing point of substance B is 30 degrees Celsius.

The room temperature is 20 degrees Celsius.

Which state of matter is substance B at room temperature?

Is it A: solid state, B: liquid state, or C: neither liquid state or solid state?

What do you think?

You can pause the video here and click play when you've got the answer.

So what did you get?

If you got A, solid state, you are correct.

Well done.

Let's move on.

Task B.

At a room temperature of 20 degrees Celsius, would the following substances be in a solid state or a liquid state?

One: Gallium has a freezing point of 30 degrees Celsius.

Two: Substance B has a melting point of 45 degrees Celsius.

Three: Substance D has a melting point of 19 degrees Celsius.

Four: Substance E has a freezing point of 21 degrees Celsius.

Five: Iron has a melting point of 1003 degrees Celsius.

Six: Ice cream has a freezing point of minus three degrees Celsius.

You can pause the video now and complete the task.

Click play when you're ready to rejoin us.

So, what did you get?

Well, one, gallium has a freezing point of 30 degrees Celsius, so that means it'll be solid.

Two, substance C has a melting point of 45 degrees Celsius, so it will also be solid.

Substance D has a melting point of 19 degrees Celsius, so that means it will be liquid.

Substance E has a freezing point of 21 degrees Celsius, so that means it will be a solid.

Because iron has a melting point of 1003 degrees Celsius, with a room temperature at 20 degrees Celsius, it will be solid.

And lastly, ice cream will become liquid if the room temperature is 20 Celsius.

Well done if you managed to get all of those correct.

Super work.

Let's move on.

Lesson cycle three: Comparing melting and freezing.

Let's begin.

When a substance melts, the substance changes from a solid state to a liquid state.

It is the reverse for freezing.

So for a solid state, once it melts, it changes into a liquid state.

And from liquid state, if we freeze it, it turns into a solid state.

Melting.

When a substance melts, the particles go from being in fixed positions in a regular arrangement to being in a random arrangement with the particles sliding past each other.

Freezing.

When a substance freezes, the particles go from sliding past each other in a random arrangement to being in fixed positions in a regular arrangement.

And we can see this here in the animations.

A substance is in a solid state below its freezing or melting point and in a liquid state above its freezing or melting point.

So here we've got temperature and then we've got melting point and freezing point.

So anything below its freezing or melting point, it will be solid.

And anything above its melting or freezing point, it will be liquid.

Over to you.

When melting occurs, the change of state is.

A: from solid state to liquid state, B: from liquid state to solid state, or C: non-existent?

What do you think?

You can pause the video here and click play when you've got the answer.

So what did you get?

If you got A, you are correct.

When melting occurs, the change of state is from solid state to liquid state.

Back to you.

After a substance has melted, the particles are randomly arranged.

What do you think?

Is this true or is this false?

And you can pause the video here for this first part.

So what did you get?

If you got true, you are correct.

Can you justify your answer why?

Is it A: particles in a solid state can only vibrate but are fixed in position, or B: particles in a liquid state can slide past their neighboring particles?

What do you think?

You can pause the video here and click play when you've got the answer.

So what did you get?

If you got B, you are correct.

After a substance has melted, the particles are randomly arranged.

Particles in a liquid state can slide past their neighboring particles.

Well done if you got that correct.

Let's move on.

Task C.

Help Alex sort the statements into a table.

With the headings of melting and freezing.

Solid state to liquid state.

Particles become fixed into position.

Liquid state to solid state.

Particles become free to slide over and around each other.

Particles end up in a regular arrangement.

Particles end up in a random arrangement.

You can pause the video here and click play once you've completed this table.

So how did it go?

Well, this is what you should have got.

Melting: solid state to liquid state.

Freezing: liquid state to solid state, particles become free to move over and around each other.

Freezing: particles become fixed into position.

Melting: particles end up in a random arrangement.

Freezing: particles end up in a regular arrangement.

Well done if you got that correct.

Super work.

Let's move on.

We made it to the end of the lesson.

Let's summarize our learning.

So this lesson was all about melting, and in particular melting and freezing points.

You now understand that when it melts, a substance changes from solid state to the liquid state.

When it freezes, a substance changes from the liquid state to the solid state.

At temperatures below its melting point, a substance is in its solid state.

At temperatures above its freezing point, a substance is in its liquid state.

Thank you so much for joining me in this lesson.

I hope you enjoyed it.

Bye.