# Lesson video

In progress...

Hello again.

How are you? My name is Ms. Couves, and this is our last lesson in our unit on separating mixtures.

We have been working so hard in this unit, and we have learnt so much.

Today, we are going to be thinking about a big problem that scientists have.

How can we make water safe to drink? Why do you think it's important to scientists to know how to make water that is safe to drink? Today, we are going to think about river water and how we can separate it into separate substances.

Here I have my own sample of river water.

You should be able to see that there's some stones, some soil, and some water.

We're going to think about how we can separate it.

Today, we will start by recapping our knowledge from this unit.

Then we will think about the job of an environmental scientist.

Then we will plan an investigation to separate a sample of river water.

And then we will evaluate our investigation.

For this lesson, you will need an exercise book and paper and a pencil.

If you don't have one of these items, pause the video now and go and get them.

Press play when you're ready to continue.

Let's recap our knowledge.

Can you remember which of the states of matter these diagrams represent? Pause the video now and write them down.

Can you annotate your diagram with how the particles behave? Press play when you're ready to continue.

The particles in a solid are in ordered rows.

They're also touching.

Particles in a solid vibrate on the spot.

Show me a solid particle.

Great.

Particles in a liquid are touching, and they are randomly arranged.

Particles in a liquid can slide past each other.

Show me particles in a liquid.

Great.

Particles in a gas are moving fast in all directions.

Show me particles in a gas.

Great.

Which diagram shows an impure gas? The diagram on the right shows an impure gaps because there are two types of particle.

How do I know that there are two different types of particle? Because there are two different colours.

Pause the video to complete this slide to identify which samples are pure metals and which one is an alloy.

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

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

How do we know that? We know that the diagrams on the left show pure substances because they only contain one type of particle.

The diagram on the right shows a mixture.

How do we know the diagram on the right shows a mixture? We know that the diagram on the right shows a mixture because there are more than one type of particle.

The diagram on the right shows an alloy.

Can you remember an example of an alloy? Bronze is an alloy of tin and copper.

And steel is an alloy of carbon and zinc.

Salt dissolves in water.

Is salt soluble or insoluble? Salt is soluble because it dissolves in water.

When salt dissolves in water, the salt crystals are broken apart into tiny particles, which are surrounded by water particles.

So we can't see them anymore.

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

The particles collect at the bottom of the container.

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

Examples are sugar and salt.

And we separate soluble solids using evaporation.

Insoluble solids cannot dissolve in water to form a solution.

They include rocks and sand.

We separate insoluble solids by using filtration or sieving.

Now we're going to learn about environmental scientists.

An environmental scientist works to protect the environment and human health.

They measure the amount of pollution in the air and in rivers.

Pause the video and write down what an environmental scientist does.

An environmental scientist works to protect the environment and human health.

They measure the amount of pollution in rivers and in the air.

I have a sample of river water.

In our investigation today, we are going to be environmental scientists and plan how to make this river water pure.

River water is made up of soil, gravel, and water.

Have a look at my sample.

Can you see the gravel and the soil? What states of matter are these substances in? The soil and the gravel are solids, and the water is a liquid.

Is this sample pure or impure? The sample is impure because there is more than one type of particle.

What types of particle do we have? We have gravel particles, water particles, and soil particles.

Are the solids soluble or insoluble? We've got two insoluble solids: soil particles and gravel particles.

What's the difference between the two insoluble solids? One of the solids is very big.

And one of the solids is very small.

That will help us to separate them.

How do we separate insoluble solids from a liquid? We separate insoluble solids from a liquid using sieving or filtration.

What do you notice about the size of gravel compared to soil? The soil is much smaller than the gravel particles.

Now we're going to plan our experiment.

Which techniques do we need to use in order to separate our river water? Filtration, sieving, or evaporation? What do you think? We need to use filtration and sieving.

We don't need to use evaporation, because we don't have a soluble solid.

Which particle is going to be removed by sieving? The gravel particles are going to be removed by sieving.

Which particle is going to be removed by filtration? The soil particles are going to be removed by filtration.

Write a list of all the equipment that you will need.

Then number your steps in your method, and start each step with a verb.

For example, place the filter paper in a funnel and place the funnel into a cup.

Pause the video and write the method for the filtration and sieving.

Press play when you're ready to see my method.

We're going to place the filter paper into the funnel and place the funnel into the cup.

Pour the river water sample into the filter paper, and then place the insoluble sample into a sieve.

We'll shake the sieve until the sand particles and gravel particles are separated.

While we're doing our experiment, I want to think about how we can make it better.

We're going to write down next to our method if we think of something that can make it better.

Right, let's have a go at our experiment.

What was the first step in my method? The first step in my method was to place the filter paper into the funnel.

So I put my funnel into a cup, and I'm putting my filter paper into my funnel.

This is not an experiment that you should try at home.

I'm now going to pour my river water sample into the funnel.

I poured a little bit too much in there and some of the soil has ended up in the sample underneath.

I might need to add to my method, pour the river water slowly into the filter paper to improve it.

When I had filtered all of the sample, I placed my insoluble solids into the sieve, and I'm going to shake my sieve until the soil particles and gravel particles are separated.

Here is my pure gravel sample after the sieving.

Can you see that there are still some bits of soil in my sample? Why do you think there are still some bits of soil in my sample? These bits of soil are too big to fit through the holes in the sieve.

So I need to use a sieve with bigger holes.

That's two improvements we could make to this method.

Have you written them down? Firstly, we needed to pour the river water in slowly to prevent overflowing the filter paper.

And secondly, we needed to use a sieve with bigger holes.

Now we're going to evaluate our investigation.

We need to evaluate our method by saying two things that went well and one thing that we could have done better.

Pause the video and write down two things that went well in our experiment and one thing that could have gone better.

Two things that went well in our experiment were that we did manage to separate the water from the soil and we did manage to separate the gravel from most of the soil particles.

One thing that could have gone better is that we could have used a sieve with bigger holes to separate the soil and the gravel.

Pause the video and redraft your method to make it better.

Press play when you're ready to continue.