Lesson video

Hello again.

My name's Ms. Couves and I am really excited to be your science teacher today.

Today, we're going to be investigating seawater.

Have you ever been to the beach? What was it like? Did you go in the sea? Did you accidentally taste the seawater? What did it taste of? Did it taste salty? That's because seawater contains a lot of salt.

We're going to look closely at the particles in seawater together.

Let's get started.

Today, we will start by recapping our knowledge so far.

Then we will talk about dissolving and soluble and insoluble solids.

We are then going to make our own seawater sample and plan how we can separate it.

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.

If you would like to make your own sample of seawater, you will also need some salt, some sand, some water, and a spoon.

You'll also need an adult to help you.

Right, let's recap our knowledge.

Pause the video and complete the slide to say which state of matter each diagram represents.

Underneath the diagram, you can write a description of the arrangement of particles in solids, liquids, and gases.

Pause the video and press play when you're ready to continue.

The particles in a solid, which is the left-hand diagram, are arranged in ordered rows.

They are touching and their particles vibrate on the spot.

Particles in a liquid are touching each other but are arranged randomly.

Particles in a gas are far apart and moving really fast.

Point to the diagram which shows a pure gas.

The diagram on the left shows a pure gas.

How do we know that this is a pure gas? We know that it's a pure gas because it only contains one type of particle.

Pause the video and complete this slide.

Press play when you're ready to continue.

What is an alloy? An alloy is a mixture of metals.

The two diagrams on the left-hand side show the particles in a pure metal.

How do we know that these are pure metals? We know that they're pure because they only contain one type of atom.

The diagram on the right shows an alloy.

How do we know that this is a mixture? We know this is a mixture because it contains more than one type of particle.

Can you remember an example of an alloy? Bronze is an alloy of tin and copper, and steel is an alloy of carbon and iron.

Can you remember the definition of a formulation? A formulation is a mixture made with a specific ratio of substances.

Is a cake a formulation? A cake is an example of a formulation.

If you were to use a different ratio of ingredients, it wouldn't taste the same.

If I wanted to make four cakes, what do I need to do differently? I need to multiply all the ingredients in my recipe for one cake by four.

This keeps the ratio the same, but makes more cake.

We're now going to learn about dissolving.

I am going to dissolve some salt in water to make salty water.

Watch carefully to see what happens.

Here are my large particles of salt.

When put them in and I stir, the particles are going to break down and get smaller and smaller and smaller, and then they're going to be surrounded by water particles, which means we'll no longer be able to see them.

The solid that are, is dissolved in a liquid is called a solute.

Solid that can dissolve in a liquid is called a solute.

What was the solute in our experiment? The solute in our experiment was salt because salt was dissolved in water.

A solvent is a liquid a solid dissolves in.

What was the liquid a solid dissolved in in our experiment? Water.

Water is an example of a solvent because the solute, such as salt, can be dissolved in it.

The solution we have now is made of salt particles and water particles.

When a solute has been dissolved in a solvent, it's called a solution.

What two particles are in our solution? The two particles in our solution are salt particles and water particles.

Have a go at drawing the particle diagram for saltwater.

Press play when you're ready to continue.

Check your answer against my answer.

Your particle diagram should have two different types of particles, salt particles and water particles.

Salt dissolves in water.

Salt is called, option one, a solution, option two, a solvent, option three, a solute, or option four, a formulation.

What do you think? Salt is an example of a solute.

Salt dissolves in water.

Water is called a solution, option two, a solvent, option three, a solute, or option four, a formulation.

What do you think? Option two, salt is a salt, sorry, water is a solvent, salt is a solute.

Salt dissolves in water.

The mixture produced is called, option one, a solution, option two, a solvent, option three, a solute, or option four, a formulation.

What do you think? The mixture produced is called a solution.

A soluble solid dissolves in water.

My turn, soluble, your turn.

An insoluble solid does not dissolve in water.

My turn, insoluble, your turn.

We know that salt is soluble in water because it forms a solution.

Let's see if sand is soluble or insoluble.

What happens when I add sand to water? This is the cup that I placed my salt into.

We can see that salt has formed a solution because we can no longer see the salt.

I'm going to add sand to this cup of water.

What do you think is going to happen? Sand does not dissolve in water.

Is it soluble or insoluble? Sand is insoluble because it does not dissolve in water.

A soluble solid is a solid that can dissolve in a liquid to form a solution.

Examples are sugar and salt.

An insoluble solid is a solid that cannot dissolve in liquid to form a solution.

Examples include rocks and sand.

Pause the video and write down the definition of soluble and insoluble.

Press play when you're ready to continue.

A soluble solid can be separated by evaporation.

My turn, soluble solids are separated by evaporation.

Your turn.

An insoluble solid is separated by filtration or sieving.

My turn, an insoluble solid is separated by filtration or sieving.

Your turn.

When would I use filtration instead of sieving? I'd use filtration instead of sieving if the particles of solids were very small, like sand, because the particles of sand could pass through the holes in the sieve.

Let's recap our knowledge.

I'm going to read the four questions to you and then give you a chance to pause the video and answer them in full sentences.

Sugar is soluble in water.

Will sugar dissolve in water? Question two, give two examples of insoluble solids.

Question three, how can a soluble solid be separated from a liquid? Question four, how can an insoluble solid be separated from a liquid? Pause the video now and answer the questions in full sentences.

Press play when you're ready to continue.

Question one, sugar will dissolve in water because it is soluble.

Question two, two examples of insoluble solids are rocks and sand.

Question three, a soluble solid is separated from a liquid using evaporation.

Question four, an insoluble solid is separated from a liquid using filtration or sieving, depending on how big the particles are.

Pause the video to tick or fix your answers.

Press play when you're ready to move on.

Now we're going to make some seawater.

If you would like to have a go at making some seawater, you need to get some salt, some sand, some water, a spoon, and an adult to help you.

Pause the video and go and get them now.

Alternatively, you can watch me do the experiment.

Press play when you're ready to start.

Seawater is a mixture of sand, salt, and water.

We are going to make our own sample of seawater by adding sand, salt, and water.

We're going to start by adding salt.

Here is my water.

I'm going to add salt.

Is salt soluble or insoluble? Salt is soluble.

Does that mean it will dissolve or it won't dissolve? It will dissolve.

Let's watch.

Can you see how the particles are being broken apart and surrounded by water molecules? What do I need to add to my seawater now? I need to add some sand.

Is sand soluble or insoluble? Sand is insoluble.

Does that mean it will dissolve in water or it won't dissolve in water? Let's see.

Sand is insoluble, so it doesn't float, doesn't dissolve in water.

It sinks to the bottom.

Can you see the sand? Here we have our seawater.

It contains three types of particles.

What are they? The three types of particles in our seawater are sand, water, and salt.

Now let's imagine we've taken our sample of seawater from the sea and we want to separate it into pure water, pure salt, and pure sand.

What could we do? Have a think.

Which solid is soluble? Which solid is insoluble? How can I separate sand? How can I separate salt? In step one, we're going to remove the sand.

Is sand soluble or insoluble? Sand is insoluble.

How do we remove an insoluble solid from a liquid? We use filtration to remove an insoluble solid from a liquid, so our step one will be filtration.

In step two, we are going to remove salt.

How do we remove a soluble solid from a liquid? To remove a soluble solid from a liquid, we use evaporation.

Let's test our knowledge.

I'm going to read you the six questions, then you can pause the video and answer them in full sentences.

Question one, which solid in the seawater mixture was insoluble? Question two, how was the insoluble solid separated? Question three, draw a particle diagram to represent the pure sand that was separated.

Question four, which solid in the seawater mixture was soluble? Question five, how was the soluble solid separated? And question six, draw a particle diagram to represent the pure salt that was separated.

Press play when you're ready to continue.

The insoluble solid in seawater is sand.

The insoluble solid, sand, was separated by filtration.

Number four, the soluble solid in seawater is salt.

Five, the soluble solid, salt, was separated by evaporation.

Pause the video to tick or fix your answer.

Well done today, you've done so much learning.

We made our own seawater solution and worked out how we could make it back into pure substances.

Make sure you have a go at the quiz to check your knowledge.

See you next time.