Lesson video

Hello again, are you excited for our lesson today? I am so excited, as today we're going to be looking at how we can convert mixtures into pure substances.

I'm going to be showing you so many ways of separating mixtures that I've decided to wear my lab coat for the whole time.

This is such an important skill for scientists.

And at the end, you're going to be an expert.

Are you ready to get started? Right, let's go.

Today, we're going to start by recapping our knowledge of mixtures so far.

Then we're going to think about how we can separate mixtures of solids, mixtures of solids and liquids and mixtures of solids and liquids, where the solid is soft.

We are going to make our own mixture and think about how we could get pure substances back.

For this lesson, you're going to 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.

If you would like to have a go at our experiment, you will also need some salt, some water and a spoon and an adult to help you.

Ready? Let's start by recapping our knowledge.

First, we learned about how particles are arranged in solids, liquids and gases.

Can you remember how they are arranged? Pause the video now and draw a diagram to represent the particles in each of the three states of matter.

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

The particles in a solid are arranged in ordered rows and touching.

Can you remember how the particles in a solid move? They vibrate on the spot.

Show me the particles in a solid.

Great, they vibrate on the spot.

The particles in a liquid are touching, but in a random arrangement.

How did the particles in a liquid behave? The particles in a liquid can slide past each other.

Show me the particles in a liquid.

Right.

The particles in a gas are really far apart and moving really fast.

Show me the particles in a gas.

The particles in a gas are moving really, really fast and they're not touching.

Point to the diagram that represents an impure gas.

How'd you know? The diagram on the right shows an impure gas, because an impure gas has more than one type of particle.

The particle on the diagram on the right has more than one type of particle, because there are two different coloured particles in the diagram.

Point to the diagram that represents a pure metal.

How do you know? The two diagrams on the left of the screen represent a pure metal, because they only contain one type of particle.

Point to the diagram that represents an alloy.

How do you know this is an alloy? This diagram contains two different types of particles.

Therefore, we know that it's a mixture.

An alloy is a mixture made up of metals.

Now, we're going to think about how we can separate solids.

We're going to start with a experiment where we separate sand and iron into sand particles and iron particles.

So, I have my sand particles, I have my iron particles.

I'm going to mix them together.

Here's my sheet of paper.

I'm going to mix my sand particles with my iron particles.

Can you see that they're mixed together? Now, I want to separate my sand particles and my iron particles.

How can I separate my sand particles from my iron particles? I'm going to use a magnet.

I can use a magnet, because iron is magnetic, but sand isn't.

Let's have a go.

I'm going to put my magnet underneath.

Can you see how it's picked up the iron particles and is pulling them out? There, can you see that it's collecting the iron particles only and leaving the sand particles behind? If I keep doing this, I can collect all of the iron particles in the mixture and separate them from the sand particles so that I have a sample of pure sand and a sample of pure iron.

So here I have my iron particles and here I have my sand particles, they're separate.

Why could I use a magnet to separate iron and sand? You could use a magnet to separate iron and sand, because the iron is magnetic and the sand isn't.

Which two particles are present in the mixture? In the mixture there were sand particles and iron particles.

Now we have pure sand and pure iron.

How many particles are there in the pure sand? How many types of particles are there in the pure sand sample? There's only one type of particle, sand particles.

How many particles are there, types of particles are there in the pure iron sample? Just one, iron particles.

After using the magnetic to separate the iron and the sand, we have pure sand and pure iron.

Pause the video and have a go at drawing all three particle diagrams to represent the mixture, pure iron and pure sand.

Press Play when you're ready to continue.

For the mixture of sand and iron there were two types of particles, sand particles and iron particles.

So we had two different coloured particles in our diagram.

For our pure samples, we only had one type of particle.

Throughout our experiment, everything was a solid, so we've arranged our particles so that they're touching and in ordered rows.

Let's test our knowledge.

I'm going to read you all three questions and then give you a chance to write the answers down.

Number 1, why is the mixture of sand and iron impure? Number 2, why was the sand sample at the end pure? Number 3, why could we use a magnet to separate sand and iron? Pause the video and complete the questions.

Press Play, when you're ready to continue.

Number 1, the mixture of sand and iron contain two different types of substance and a pure substance can only contain one.

the sand sample at the end was pure, because it only contained sand particles and the iron particles had been removed.

Number 3, a magnet can be used to separate iron and sand, because iron is magnetic and sand is not.

Pause the video to tick or fix your answers? Press Play, when you're ready to continue.

Now, we're going to think about separating a solid and a liquid.

In this experiment, we're going to look at pasta and water.

Here I have my mixture of pasta and water.

Can you see the pasta at the bottom and the water at the top? I want to separate my mixture of pasta and water.

What do you think I could use to separate a mixture of pasta and water? I'm going to use a sieve to separate my pasta and my water.

The sieve can be used to separate pasta and water, because the holes in the sieve are small enough for the water to go through, but big enough.

Sorry, big enough for the water to go through, but small enough to stop the pasta from going through.

Let's watch.

So I'm going to pour my liquid through.

Can you see that the water is now in the jug below and my pasta is being stayed in the sieve? That's because the pasta is too big to fit through the tiny holes in the sieve, but the water can fit through.

So now we have a pure sample of pasta and a pure sample of water.

Let's have a look at another solid.

This time, I have a mixture of sand and water.

Can you see the sand is collecting at the bottom? Particles are much smaller than the pasta particles.

Do you think that the sand particles will be small enough to fit through the sieve? The sand particles are small enough to fit through the sieve.

So we need to use something different.

We need to use filter paper and a funnel.

This is a funnel, and this is a piece of filter paper.

The filter paper has really tiny holes.

The holes are so small that the water particles can fit through, but the sand particles will get trapped.

Why can filter paper be used to separate sand and water? Filter paper can be used to separate sand and water, because the water particles can fit through the filter paper, but the sand particles can't.

So I've just placed my filter paper in the bottom of my funnel and I'm going to pour my sand and water mixture into the filter paper.

Remember, we're expecting the water particles to go through and the sand particles to not.

Poured too much in.

So we can see that the water is going through.

Can you see it dripping out the bottom? The water particles are small enough to fit through the tiny holes in the filter paper.

Let's see what happens when the sand particles are there.

Okay, so now I've got sand particles in the filter paper and water particles dropping through.

Why can't the sand particles pass through the filter paper? The sand particles can't pass through the filter paper because the sand particles are too big to fit through.

The water particles can fit through the filter paper because they are small enough to fit through the tiny holes in the filter paper.

So when this is finished, we'll have all of our sand particles in the filter paper and all of our water particles in the jug below.

So now we have a pure sample of sand and a pure sample of water.

How many particles are there in the pure sample of sand? There's one type of particle in the pure sample of sand.

How many types of particles are there in the pure sample of water? There is one type of particle in the pure substance of water.

So now we've learned how to separate sand and water and pasta and water.

Let's have a go at recapping our knowledge.

I'm going to read you these four questions, then I'm going to give you some time to pause the video and answer them.

Why was the mixture of sand and water impure? 2, why could pasta be removed from the water using a sieve? 3, why could sand not be removed from the water using a sieve? Number 4, why was the filter paper better for removing sand from water? Number 5, why was the sieve better for removing pasta from water? Pause the video now to complete the questions.

Press Play when you're ready to continue.

Question 1, the mixture of sand and water was impure, because it contained two different types of substance.

Number 2, the pasta could be removed from the water with using a sieve, because the pasta was too big to fit through the holes in the sieve.

Number 3, sand could not be removed from the water using a sieve, because it was small enough to fit through the holes in the sieve.

4, filter paper was better for moving sand, because the sand could not fit through the holes in the filter paper.

Number 5, the sieve was better for removing pasta from water, because the water could pass through faster.

Pause the video now to tick and fix your answers.

Now, we're going to make a solution together.

A solution is a mixture of a liquid where the solid dissolves.

If you would like to have a good making a solution, you need to get yourself some salt, some water and a spoon.

You also need an adult to help you.

Pause the video and go and get them if you would like to have a go.

If not, you can watch me do the experiment.

I'm going to make a solution of salt and water.

When we mix salt and water, the salt dissolves.

My turn, dissolves.

Your turn.

Great.

We can see the salt has dissolved, because we won't be able to see it anymore.

Here I have some salt.

Salt is a white solid.

I also have some water.

I'm going to add my salt to the water and see what happens.

When I add my salt to the water and stir, it looks like the salt disappears.

Actually, what's happening is the salt is breaking down into tiny, tiny, tiny particles and the water is surrounding it so that we can no longer see it.

If we keep mixing all of the salt will dissolve.

Now my particles are well and truly mixed up.

The salt has dissolved.

If a solid can dissolve in a liquid, it is called soluble.

My turn, soluble.

Your turn.

Is salt a soluble solid? Salt is a soluble solid, because all of my salt has dissolved.

Now, how do I get my salt back? Can I use a magnet? I can't use a magnet, because salt and water are not magnetic.

Can I use a sieve? I can't use a sieve, because the salt particles are really, really tiny.

What about filter paper? I can't use filter paper, because again, I can't see the solid, the particles are really tiny.

I need to use something different I need to use evaporation.

My turn, evaporation.

Your turn.

Great, we need to use evaporation.

I'm going to heat the water up, so that it evaporates.

You shouldn't do this at home, because it can be a bit dangerous.

So just watch me.

I've poured my salty water into a glass bowl and I'm putting my glass bowl on top of some boiling water.

I'm doing that so that I can heat the water in my salt water solution slowly so that I can evaporate it, leaving behind salt particles.

Can you see the water boiling? The reason we can use evaporation to separate salt and water is because water evaporates at a much lower temperature than salt.

Water has a low boiling point and salt has a high boiling point.

So when we heat the water, all of the water will evaporate leaving behind the salt.

Why can we use evaporation to separate salt and water? We can use evaporation to separate salt and water, because salt has a much higher boiling point than water.

So all of the water will evaporate leaving behind the salt.

If you watch carefully, around the edge, you'll see the salt starting to form.

Look it's boiling really vigorously now.

We should be able to start seeing some salt soon.

Can you see the salt that is formed now the water has evaporated? We're left with these crystals of salt in our bowl.

Why could we use evaporation to separate salt and water? We could use evaporation to separate salt and water, because salt has a much higher boiling point than water.

Let's have a go at drawing the particle diagrams for salty water, the solution of salt and water, salt and water.

Have a think.

How many different types of particles are there in salty water? How were the particles arranged? Pause the video and draw the diagrams. Press Play, when you're ready to continue.

The salty water has two types of particles, salt particles and water particles.

Pure salt has got just salt particles and water has got just water particles.

Let's test our knowledge.

Question 1, why was the mixture of salt and water impure? Question 2, why could we not use filtration to separate salt and water? Question 3, why could we use evaporation to separate salt and water? Pause the video now and answer the questions in full sentences.

Press Play when you're ready to continue.

The mixture of salt and water was impure, because it contained two different substances.

Filtration could not be used to separate salt and water because when the salt particles dissolve, they are small enough to fit through the holes in the filter paper.

Evaporation could be used to separate salt and water because salt has a much higher boiling point than water.

So the water evaporates leaving behind the salt.

Pause the video to tick and fix your answers.

Press Play when you're ready to continue.

How can we separate sugar and water? Sugar dissolves in water, it is soluble.

Option 1, using a magnet, option 2, using a sieve, option 3, using filter paper, or option 4, evaporation.

What do you think? We need to use evaporation to separate sugar and water, because sugar dissolves in water.

How could we separate iron and wood chips? Iron and wood chips are both solids.

Iron is magnetic.

Option 1, use a magnet, option 2, use a sieve, option 3, use filter paper, or option 4, evaporation.

We can use option 1, a magnet, because iron is magnetic and wood chips are not.

Last question.

How could we separate pebbles and water? Option 1, using a magnet, option 2, using a sieve, option 3, filter paper, or option 4, evaporation.

We would separate pebbles and water using a sieve, because the pebbles would be too big to fit through the tiny holes in the sieve.

You've done an excellent job in our lesson today, we have learnt so much about separation.

Make sure you do the quiz to show all that you have learned.

See you next time.