Hello scientists, my name is Mr. Wilshire.

In this lesson, we're going to be looking at removing salt from seawater.

The outcome for this lesson is I can investigate ways of making seawater safe to drink.

There are some keywords to think about as we progress our way through this lesson.

The first is seawater.

Then, it's solution.

Next up, evaporation.

After that, condensation.

And finally, desalination.

Don't worry if you're not too sure what some of these words mean.

You can have a look at the definitions that have appeared on the screen for you now.

If you need to, you can pause the video, have a look, and restart when you're ready.

The first part of this lesson is called "Evaporation and condensation." Aisha says, "I think people who live near the coast must have all the drinking water that they need." Here you can see a picture of a town that's next to the seaside.

I wonder, though, do you agree with Aisha? What do you think? Pause the video and discuss.

Restart when you've done that.

So what did you think? Do people who live by the sea have all the drinking water that they need? Unfortunately, we cannot drink seawater.

It's not very good for humans to drink.

I wonder if you know why, though.

Have a quick discussion again.

Restart the video when you've done that.

So why is seawater so unsafe for people to drink? Why is it not a good idea to do that? Let's find out more.

Well, we can start here by looking at a lake.

Here you can see that the water in this lake is freshwater.

Freshwater is a type of water that's made safe to drink.

It comes through our taps.

It'd need to go through a lot of filtration processes before it reaches us in our homes, though.

The water in our seas and our oceans is very different to the freshwater found in raindrops, lakes, and rivers.

The water in our seas and oceans contains salt.

The salt not only makes the water taste bad, but the salt in it would also make us very ill if we drank a lot of it.

This is why if you've ever been in the ocean swimming and your tummy has felt a little bit funny after going in, this could be the reason why it felt bad.

Maybe you drank a little bit too much of the seawater that was there.

If you're swimming in the sea, it's a very hard thing not to get some of the water in your mouth, so sometimes it's a taste that you really get used to.

But if you drink too much of it, it is definitely going to make your stomach turn a little bit.

Is it possible, though, to make seawater suitable for drinking? Have a think and discuss.

Restart the video when you've done that.

So what do you think? Is it possible to actually drink seawater? Is there a way of making it safe? Let's find out more.

But first, let's stop and think.

Is this true or false? Seawater is safe for drinking.

The answer here, it's false.

It is not safe for drinking.

I wonder if you can tell me why.

Have a think about why this is.

So why is seawater not safe for drinking? Well, the water in our seas and oceans contains salt and so is not safe for drinking.

If you drink too much salty water, it's definitely gonna make your stomach feel rather bad.

Salt is soluble in water.

That means that it dissolves.

When salt dissolves in water, it makes a salt solution.

Aisha says, "In school we've been learning how to separate salt from a salt solution." Can you remember which process you can use to do this? Is this the way that we're going to be able to make seawater safe for drinking? Have a think there.

Can you remember the process that you can use to dissolve water to make a solution? Pause the video here and answer the question.

Restart when you've done that.

So which process can you use to separate salt from a salt solution? Evaporation; evaporation can be used to remove the water from a salt solution.

There you can see an image that you might recognise of some salt on a saucer.

This is after all of the water has evaporated and it's left the salt behind.

Aisha knows that the rate of evaporation increases as the temperature increases.

Oh, yes, you can speed things up by warming things up, can't you? So to make the water evaporate quickly, Aisha could heat a sample of seawater, which is also known as a salt solution.

Stop and think.

What's the name of the process used to remove water from a salt solution? Is it filtering? Is it evaporating? Or is it melting? You can use the image there of the oil burner and the candle providing heat to help you.

The correct answer here is evaporating.

You put the water, the salt solution in the well there.

You put a candle underneath and that starts to heat things up, and then you can see the water vapour rising as the water starts to evaporate.

By heating something, you can speed up this process.

Now, Alex knows that during evaporation, the liquid in a solution evaporates and the original solid is left behind.

He says, "When we evaporated the water from our salt solution, we were left with the salt.

This time, though, we want to collect the water in a salt solution to investigate if it could be safe to drink." So what could the children do here? How are they going to do this? Have a quick discussion and decide.

Restart the video when you've done that.

How did you get on? Were you able to decide how you could collect water in a salt solution to investigate if it could be safe to drink? Let's find out more.

When a substance changes from a liquid state to a gas state, often it can't be seen, but it still exists as invisible vapour in the air.

Here you can see steam rising out of a cup as boiling water is poured from a kettle.

Now scientists can collect this gas.

They can then cool it down so that it changes state back into a liquid.

Do you know the name of this process? So the water evaporates and then something happens.

What's the name of that process? Pause the video and discuss, restart when you've done that.

So what's the name of this process? Well, it's called condensation.

Did you get that right? Well done if you did.

Condensation occurs when water vapour, which is very warm, hits a colder surface like a window in winter or a cold bathroom wall.

Here you can see the droplets on a window that form and the water droplets on a bathroom wall.

You may have spotted this when you have a shower or a bath.

So stop and think, which of these describes condensation? Is it the water in the liquid state is heated and changes to water in the gas state? Is it that water in the gas state is cooled and changes to water in the liquid state? Is it water in the liquid state is heated and changes to water in the solid state? The correct answer here is B.

Condensation is water in the gas state is cooled and changes to water in the liquid state.

Here is Task A.

You need to take a closer look at evaporation and condensation.

Step one is to ask an adult to half fill a mug with some hot water.

You need to be very careful here because it's hot, isn't it? Step two is to take a cold plate and place it on top of the mug.

Step three, wait for a few minutes then carefully remove the plate from the mug.

Step four, explain to a partner what you observe on the underside of the plate.

So you really need to be using some keen observation skills here.

Best of luck with your task, follow those instructions, restart the video when you've done that.

How did you get on? Maybe you found something very similar to this when you followed those steps.

Some of the hot water evaporated and became water in a gas state, which is water vapour.

The water vapour hits the cold plate and it was suddenly cooled.

This made the water vapour change back to a liquid state.

The liquid was observed as tiny droplets of water on the underside of the plate.

Well done for completing that task.

Hopefully you observed something similar to this too.

I wonder if there's anywhere else that you've spotted this kind of condensation before.

The last part of this lesson is called "Removing salt from seawater." Scientists and engineers investigate ways of removing salt from seawater using evaporation and condensation.

The process is called desalination, which means removing salt.

One way to do this is to heat the seawater.

You can see there a scientist using a Bunsen burner to heat up a container, and that is then feeding through to a beaker.

The water evaporates from the salt solution.

It rises up the spout, and then the water vapour moves away into a cooling tube.

In the cooling tube, it condenses back into water and is collected.

So that vapour rises, passes down the tube, and ends up there.

Maria Telkes was a Hungarian engineer.

She was born in 1900.

That's quite a long time ago now, isn't it? She was interested in developing technology which needed sunlight to work.

So during World War II, she developed the very first solar-powered water desalination system.

It was designed to help soldiers produce drinking water in very difficult locations.

Wow, how clever and how useful.

This was called a solar still.

It worked like this.

Step one is the unclean, salty water is held within a shallow bowl covered by a sloped roof.

There you can see the unclean water sitting in a container.

Step two, the sunlight heats the water, causing it to evaporate.

Sunlight shines down onto the container there, the water vapour rises from the unclean water.

Step three, the water vapour then condenses on a plastic roof and flows down into a collection container.

Can you see how it's a slightly slanted roof there, so the water vapour rises up, it condensates onto the roof there, turns into liquid again, and then it drips down into the container.

Now, many boats still carry solar stills to allow them to produce drinking water just in case of emergencies.

Let's stop and think.

Which professionals would investigate ways of removing salts from seawater using evaporation and condensation? Is it electricians and electrical engineers? Is it teachers and teaching assistants? Is it scientists and engineers? Or is it doctors and nurses? The correct answer here is scientists and engineers.

Now, desalination is an important area of scientific research and engineering.

This is especially true where populations are growing and there's very limited freshwater.

Aisha says, "Well, there is desalination plants just like this all around the world.

They are factories where salt is removed from seawater to make the water suitable for drinking." Here you can see an example of a modern desalination plant.

Wow, it's a very big type of area, isn't it? Lots of warehouses there and obviously lots of people doing very important work.

Now, some modern desalination systems use processes other than evaporation and condensation.

This helps them to remove the salt from seawater in different ways.

Scientists are working to reduce the amount of greenhouse gases produced during desalination.

This then makes the process much more sustainable.

There you can see a scientist carrying out some research.

A very important thing to do.

After the seawater has undergone desalination, microorganisms must be removed from it.

Microorganisms are very, very tiny living things which are so small that we can't see them without using a special microscope.

There's no way of telling if they're in the water or not, so it's better to use a microscope to investigate and have a look inside first.

If we drink water containing these microorganisms, we can become ill, which wouldn't be very good for us, and that would mean that the desalination process isn't making it any safer for us, is it? Microorganisms can also be present in freshwater as well.

It's always a good idea to make sure that you drink carefully-processed water to ensure that you're not going to drink anything that's going to upset your stomach.

Stop and think, is this true or false? Microorganisms are not usually removed from water to make it safe to drink.

The answer is false.

Can we justify our answer? Have a look at the two statements and decide which one best fits.

The correct answer here is A.

Microorganisms must be removed from water to make it safe to drink.

Otherwise, we're going to end up drinking it and that's not gonna make our stomachs feel very good, is it? Here is Task B.

As a class, follow the instructions on the worksheet to make your own mini-desalination plant.

There you can see a mini-desalination plant that's been made for you already.

So you can use the sun.

Or if it's cloudy, you could use a desk lamp.

This will then represent the sun.

So you can have a go at making this yourself.

After 24 hours, observe what has happened.

You need to leave this for a little while so you can collect some water and see then if it's safe to do so.

You can collect some water and see if it's safe to drink.

Best of luck with that task in creating your very own desalination plant.

Remember, you do need somewhere warm to help that water to evaporate and condensate on a slightly pitched roof.

Best of luck with your task.

Reset the video when you've done that.

How did you get on? As a class, you might have done something similar to this.

Step one here was that they poured 200 millilitres of salt solution into a big bowl.

They then placed a smaller empty bowl into the big bowl.

They then covered the top of the big bowl with a clear recycled plastic bag, held it on with an elastic band.

Step three, they placed a very small weight, which was a pile of coins in this case, just in the middle of the plastic bag to make sure that the lowest part of the bag was above the collection bowl.

Remember, that roof needs to be slightly pitched in, doesn't it? Step four, as it was winter, we used a desk lamp to represent the sun.

Step five, we left it for 12 to 24 hours and then observed what had happened.

These are the things that they found out.

Your results might have been similar.

"After 24 hours, there was a pool of water in the small bowl and the level of the salt solution had gone down.

We observed lots of drops of condensation on the plastic bag." So they have created their very own desalination plant.

I wonder if you found very similar things as well.

I wonder if there's any difference between using it under a lamp and doing this experiment under the sun.

Let's summarise our lesson.

The water in our seas and oceans contains salt.

This water is not safe for drinking.

Evaporation can be used to remove the water from a salt solution.

Condensation is when a water in a gas state, water vapour, is cooled so that it changes to water in the liquid state.

Scientists and engineers investigate ways of making water safe to drink using evaporation and condensation.

Microorganisms must also be removed from saltwater to make it safe to drink.

Hopefully, you could go on too using this kind of knowledge in an emergency situation of your own.

Hopefully it's not a real emergency, but at least you would know how to survive on saltwater when you are able to evaporate it and get rid of all that nasty salt.

Well done for completing that task.

I've been Mr. Wilshire, thank you very much for listening.