Lesson video

Hi, I'm Miss Mia, and I'm really looking forward to teaching you this lesson today.

In this lesson, you'll be able to describe the difference between a pure substance and a mixture.

Your key words will appear on the screen now.

Pure substance.

Mixture.

Impurity.

Let's find out what these keywords mean.

A pure substance contains only one type of chemical.

A mixture is a material that contains two or more different substances, which can be physically separated.

And impurity is a chemical that is found in a material in very small amounts, but can change the materials properties.

So those are our key Words for this lesson.

Let's move on.

So this lesson is all about PUre substances.

We have three lesson cycles in today's lesson.

Our first lesson cycle is to do with pure substances.

We're then gonna move on to looking at mixtures.

And then lastly, we're gonna find out how to identify pure substances and mixtures.

I'm super excited about this lesson.

I hope you're too.

Let's begin.

In everyday usage, the word pure can be found or used in different ways.

So here we have some examples.

Blessed are the pure of heart,.

Pure orange juice.

And pure can be described as something that looks clean.

In science, pure refers to a substance that is composed or made up of only one type of chemical.

So here are particles in pure solid carbon.

Particles in pure liquid bromine.

Particles in pure oxygen gas.

Hmm, I wonder what you notice.

The chemical of pure can be composed of different particles.

So here we have an example of pure carbon dioxide, and here we have an example of pure water.

Over to you, true or false, a material that contains one type of substance is pure.

Is this true or is this false?

You can pause the video here for this first part and then click play when you've got the answer.

So what did you get?

If you got true, well done.

I'd like you to justify your answer.

So is it A, because pure materials contain different chemicals.

Or B, because pure materials are composed of only one type of chemical.

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.

A material that contains one type of substance is pure.

Pure materials are composed of only one type of chemical.

Back to you.

What do you think about each of these substances?

We've got three examples here.

A, fresh orange juice is pure.

B, orange squash is pure.

C, water is pure.

What do you think?

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

So what did you get?

Well, fresh orange juice is not pure.

Orange squash is not pure either.

Water is pure.

Well done if you manage to get those correct.

Let's move on.

Task A, I'd like you to look carefully at the pictures.

One, is the term pure being used scientifically?

Pure orange juice.

And two, justify your answer.

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

So what did you get?

Let's have a look.

For question one this is what you should have got, no, pure is not being used scientifically with reference to this juice.

So your answer might include an orange contains several chemicals, for example, carbohydrates, proteins, vitamin C and potassium.

Well done if you manage to include some of those key points and get the answer correct.

Three, discuss who is correctly describing a pure substance.

Explain your answer using a because clause.

Aisha says, "A sample of gas that only contains oxygen.

" Andeep says, "Asprin contains a drug to stop pain and sugar to help the tablet taste better.

" Sam says, "My gold earring is made up of lots of gold particles joined together.

" You can pause the Video here and click play when you've got the answers.

So what did you get?

Both Aisha and Sam correctly described a pure substance.

This is because both of their statements refer to only one chemical.

Well done if you managed to get that correct.

Lets move on.

So our second lesson is to do with mixtures.

Let's begin.

Many of the starting materials that scientists work with are found in nature and exist as mixtures, including: rocks, sea water, air.

A mixture is a material that contains two or more different substances which can be physically separated.

Rocks are mixtures of many minerals including useful metals.

So here we have a photograph of some rocks and we can see here the composition of that.

So we've got metals and different minerals.

Sea water is mainly a mixture of salt and water, but also contains some gases.

So here we've got a photograph of sea water.

And then here we can see the composition of the water and salt molecules.

Air is a mixture of gases including nitrogen, oxygen, carbon dioxide, water vapor, and argon.

And here we have a photograph of air.

And then we can see here the nitrogen and carbon dioxide.

Over to you.

Which of the diagrams below show a mixture?

Is it A, B, C, or D?

You can pause the video Here and click play when you've got the answers.

So what did you get?

If you got B, C, and D you are correct.

Well done.

Let's move on.

It doesn't matter how much of one substance is mixed with another.

The result is referred to as a mixture.

So here we have an example of pure sample, and here we have a mixture.

Some mixtures contain small amounts of chemicals known as impurities.

These can alter a material's properties.

Impurity.

Sometimes impurities are useful.

Mineral impurities give water its flavor.

Lightweight impurities lessen the mass of otherwise heavy objects.

Sometimes impurities are not helpful.

Metals for electronics that contain impurities conduct electricity less well.

Impurities in a medicine could be harmful.

Over to you, true or false?

Mixtures do not contain impurities.

What do you think?

Is this true or is this false?

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

So what did you get?

If you got false, well done.

I'd like you to justify why.

Is it because A, a mixture contains two or more substances joined together?

Or B, an impurity is a chemical found in a mixture in very small amounts.

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, if you got B, you are correct.

An impurity is a chemical found in a mixture in very small amounts.

Let's move on.

sometimes substances are mixed together but cannot be physically separated once mixed.

For example, mixing cake batter.

Or mixing cement.

In science a key feature of a mixture is that it's different substances can be physically separated from each other.

Can you think of any other mixtures that cannot be physically separated from each other?

Some models to show how a mixture can be physically separated include sweets Can be separated or grouped by color or flavor, Wooden blocks can be grouped by color or size.

Money can be grouped by denomination or country of origin.

Over to you.

Which of these pictures show a model of a mixture and why do you think that?

Is it A or B?

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

So what did you get?

If you got A, you while correct.

The sweets in picture A can be physically separated.

Back to you.

This is our task.

I'd like you to use the words pure, mixture or impurity to write a sentence describing each model shown.

So you've got A, B, C, and D.

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

So how did it go?

So your answers may be similar to these.

A, jar A is a model of a pure material because it only contains one grain, popcorn kernels.

Jar B is a model of a mixture because it contains two grains, lentils and rice, which can be separated.

Jar C is a model of a mixture because it contains three substances, brown rice, black beans, and white beans, which can be separated.

Jar D is a model of a mixture because it contains two which can be separated.

However, it appears to have an impurity of a few darker grains.

Well done if you manage to get that correct.

Let's move on.

Lesson cycle three, how to identify pure substances and mixtures.

Let's get started.

Scientists use properties to tell the difference between pure substances and mixtures.

Here we have pure iron.

Very soft, not used for building.

Steel has iron and carbon.

It's hard and strong and used for building.

The properties most often used to tell the differences between a pure substance and a mixture are melting points and boiling points.

A pure substance changes its state of matter at a definite temperature.

For example, pure water boils at exactly a 100 degrees Celsius.

Sea water, the boiling point is anywhere between 102 degrees Celsius and 123 degrees Celsius.

Mixtures change state of matter over a range of temperatures.

24 pure gold, its melting point is 1,064 degrees Celsius.

Rose gold is a mixture of gold and copper.

Its melting point is different.

So it melts anywhere between a 1,000 degrees Celsius and 1,100 degrees Celsius.

Over to you.

Two different sized cubes of the same pure wax are being heated.

Which student do you think is correct about what will happen?

Laura says, "The smaller cube will melt at a much lower temperature.

" Lucas says, "Both wax cubes will melt at the same temperature.

" And lastly, Jacob says, "The larger cube will need to reach a higher temperature before it melts" What do you think?

You pause the video here and click play once you have completed this check for understanding.

So what did you get?

Well, Lucas is correct.

Both wax cubes will melt at the same temperature.

Well done if you manage to get that.

Let's move on.

Back to you again.

What does a scientist need to know in order to decide if a sample is a pure substance or a mixture?

Is it A, if things were mixed to make it?

B, if it is natural or has been manmade.

C, what happens when it is added to water.

Or D, the temperature at which it melts.

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, if you got D, you are correct.

A scientist needs to know the melting point to decide if a sample is a pure substance or a mixture.

Fantastic.

Let's move on.

Task C.

A lab technician Has two jars of steric acid, which is a waxy solid at room temperature.

She suspects that steric acid in one of the jars is contaminated with impurity.

One, I'd like you to describe an experiment you could perform to decide if one of the jars is contaminated.

She can let you have two grams from each jar.

Two, what result would you expect if the sample is pure?

And three, what result would you expect for a contaminated sample?

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

So what did you get?

Well, you may have said something along these Lines.

You could heat the steric acid sample until it melts and measure the temperature or temperature range at which this happens.

And here we can see that this is happening in the diagram.

The pure sample will melt at a specific temperature.

The contaminated sample will melt over a range of temperatures because it's a mixture, steric acid and an impurity.

We're now at the end of our lesson.

Let's summarize our learning.

So this lesson was to do with pure substances.

You now understand that a pure sample of a substance is made up of only one type of chemical.

It changes state at a single distinct temperature.

A mixture is made up of different substances that can be physically separated.

It changes state over a range of temperatures.

Lastly, an impurity is a small amount of a substance in a mixture.

It changes the properties of a material including its melting point and boiling point.

Thank you so much for joining me in this lesson and I hope you really enjoyed it.

Bye.