Hello, my name's Mrs. Nevin, and today we're going to be talking about separating liquids in a mixture as part of our topic on separation techniques.

Now, you may have had some experience of this before if you've ever helped perhaps make the gravy using the juices from a roast dinner or something along those lines, but this is really gonna help us moving forward as well in our journey through science, because it will help us to consider how we can separate different types of mixtures than things that are composed of simply solids and liquids.

So this will be really useful.

It will also help us to explore a little bit more on that big question, how can we explain how substances behave? So by the end of today's lesson, you should be able to describe a few different ways that we could decide how to best separate a mixture that is composed or made up of at least two different liquids.

We'll be using a few keywords throughout today's lesson, and those will include density, boiling point, immiscible, miscible, and decanting.

Now the definitions for these keywords are given in sentence form on the next slide, and you may wish to pause the video here so you can read through them or jot them down a little bit for reference later on in the lesson.

We'll be looking at a few different aspects through today's lesson.

We'll firstly start off by talking about the physical properties of liquids.

Then we'll look at the different ways that we can separate an immiscible liquid, and finish up by looking at how we could separate miscible liquids.

So let's get started by looking at the physical properties of liquids.

Now there are multiple mixtures that exist in the world that are made up of two or more substances in the liquid state.

And as we go through today's lesson, sometimes it's useful to have some examples in the back of your head of things that you might be familiar with to help you think about what might be the best technique to separate when looking at mixtures of those compositions.

So some examples might be things like vegetable oil and vinegar that's used commonly as a salad dressing, maybe some ink in water.

You could think about any kind of essential oils that might be used for things like a reed diffuser, or perfumes, things like that.

You could also think about something you might see perhaps on your walk to school in the morning if there's some motor oil that has mixed with water on the road.

So all of these are examples of mixtures that are composed of at least two or more substances in the liquid state.

So if we're going to consider the best way to separate out a mixture that contains multiple liquids in it, we need to consider the physical properties of the liquids within the mixture.

So we'll need to think about things like, do the liquids actually mix together? Do they perhaps have different densities, and do they perhaps have different boiling points? Because all of these physical features of the liquids in the mixture could be used to decide what's the best separation technique to use on that particular mixture.

So the first question we wanna ask about a mixture containing substances in the liquid state is, are they mixing together or not? And if we look at our example here, we have vegetable oil and water, and it's clear that they are not mixing.

We've got kind of little globules of vegetable oil floating around in the water, and we would describe those two substances then as immiscible.

Now if we pull that word apart, we've got the prefix of im, meaning not, so similar to impossible, not possible.

Mis then is the next bit, and that means mix essentially.

And then the last bit of ible, the suffix, means essentially able.

So if we bring all those pieces together, immiscible simply means not able to mix together.

What do you think we might call a substance that does mix together? Well, if you thought miscible, able to be mixed, you'd be exactly right.

So liquids that are able to mix together would be called miscible.

And a good example of that are things like alcohol and water, which we can find here in the example of the hand sanitizer.

Now the thing that we need to remember as well is that pure substances have a very specific density.

Now density is a measure of a substance's particles and how tightly packed they are.

So we're looking at the mass of each individual particle of that particular pure substance, and how tightly those particles are packed together in a very specific space.

Now because of that, the units that we use for density is grammes per centimetre cube.

So we're looking at comparing the mass per unit volume, so the mass of the particles per unit of space that those particles are packed into, grammes per centimetre cubed.

Now when we compare some units then, or different examples really, we can look at gold.

Now the density of gold is ridiculously high.

It is 19.

3 grammes per centimetre cubed.

So when you're seeing people throwing gold bars around in the movies, absolutely not.

It's far heavier than that.

Now olive oil on the other hand has a density of not 0.

9 grammes per centimetre cubed, and that is quite low when you compare it to gold.

So why do we care? Because when we are looking at the density of liquids for instance, the denser substances tend to settle in a container.

So a dense material will fall to the bottom of a container, whereas a less dense substance would tend to float on another substance, or a substance that has a higher density.

So we might be able to use this difference in densities to separate out pure substances that are found within a mixture if they are immiscible liquids or miscible liquids, we need to check that out.

<v ->Another property of a pure substance</v> that we might be able to use in our separation techniques is the fact that pure substances have a very unique boiling point, a very specific temperature, at which all of the particles in that substance have enough energy to change from the liquid state into the gas state.

So for instance, if we compare water and olive oil, water will boil at 100 degrees Celsius, whereas olive oil tends to boil at 299 degrees Celsius.

Let's pause here for a quick check.

Which of the following is not a property of liquids? Well done if you said strength.

Strength tends to be a property that we are looking at using to describe substances in the solid state, not the liquid state, but very well done if you manage to choose strength.

Time for our first task, we've gone through quite a few key terms up to this point.

So what I'd like you to do in this first part is to match up the term to the correct definition.

You may wish to pause the video here and come back when you're ready to check your answers.

Let's see how you got on.

So boiling point I remember is a temperature, and it's definitely changing from a liquid into a gas.

So when I skim those definitions on the right hand side, I can see that the third definition is correct.

So the boiling point is the temperature at which a substance changes from the liquid and gas states.

And miscible, remember we pulled that word apart, mis means mix and ible means able, so able to mix together.

So that is the bottom definition, Miscible is a liquid that does mix with another specific liquid, and immiscible, that prefix meaning im, meaning not, means it will not mix with another specific liquid, so that's the top definition.

And the last one of density is really the last one that's there.

But even if you'd done that first, the units, that very last bit where it says grammes per centimetres cubed is the specific units that we use for density, and that might've helped you decide that that was the definition.

So very well done if you managed to match those up correctly.

Okay, for this next part of the task, what I'd like you to do is to read these sentences carefully, and then within the brackets, choose one word from each pairing that you think will correctly complete each of those sentences.

You want to pause the video here and come back when you're ready to check your answers.

Okay, let's see how you guys got on then.

So for A, it should read water and ethanol are two liquids which mix together, they are miscible.

<v ->For B, a liquid's density is the property that helps</v> to decide if it will sink or float in another substance.

For C, oil floats on water.

So oil is less dense than water because it floats on top.

For D, petrol does not mix with water.

They are immiscible E, iron floats on mercury, so mercury is more dense than iron.

You should find it below the iron, it sunk.

And for F, the boiling point of a substance is the temperature at which it changes from a liquid state into the gas state.

That was a tricky task.

You might've had to have a few chats with the people nearest you, but you've done an excellent job.

Great start to the lesson guys.

Now that we're feeling a little more confident talking about the physical properties of liquids, let's look at how we might be able to separate immiscible liquids in a mixture.

So the thing that we need to remember about immiscible liquids is that they don't actually mix together.

You can stir them together, but essentially what happens is, they will form layers one on top of the other according to their relative densities.

So how one compares to the other, the lighter or less dense substance will float then on the more dense substance.

And if we leave them to rest a little bit, they might look a little bit like this.

You'll be able to see the layers a little bit more clearly.

Now the great thing about trying to separate immiscible liquids in a mixture is that because they form those layers, they're actually really easy to separate, and you have a few options open to you.

The first one is decanting.

Now decanting is simply the process of pouring off the less dense liquid into another container.

And there are some pros and cons to this method.

The first one is that it's very quick and very, very easy.

You literally need to just pour it off into another container.

And if you don't wanna keep that top layer, you can literally pour it down the drain, so it's fine.

The problem is, it doesn't fully separate.

It's very, very difficult to get the technique right where you're able to pour off every single particle of that less dense substance that's floating on top without accidentally getting some of that bottom or more dense layer to go with it, or some of the top layer being left behind, so it doesn't fully separate.

So we have another option here, and that is using something called a separating funnel.

Now this one actually taps off the more dense liquid.

So if you want the bottom layer, the separating funnel's very useful, and you can see that there's a really, really light control at the back that can be turned.

So you can control just how much is tapped off at any one point.

So we've got full separation that takes place here.

The problem is, you need specialist equipment and you need to know how to use it in order to get that full separation.

But it can be done.

Let's pause again for a quick check.

True or false? Immiscible liquids have similar densities.

Well done if you said false, but which of these sentences justifies that choice? Well done if you said A, immiscible liquids form layers, and they form layers because they have different densities.

Immiscible liquids won't really form a solution, because a solution means that they have dissolved into each other, in which case you would call them miscible liquids.

So that's a false statement there.

Well done if you managed to say that they don't have the same densities if they're immiscible liquids, and as a result, they form layers.

Well done.

Let's move on now to our next task.

Now, petrol and water are described as immiscible in each other, and some students are discussing ways in which a sample of petrol and water could be separated.

And I want you to discuss their suggestions.

So first of all, we have Lucas, who thinks that filtering will work because petrol is insoluble in the water.

Then Alex thinks that if petrol is immiscible in the water, then maybe you could just evaporate the water away.

Whereas Izzy reckons that layers of petrol and water will form, so they could just be decanted one layer off the other.

So take some time to discuss their suggestions and come back when you were ready to check your thoughts.

Okay, let's see how you got on.

So Lucas thought that filtering would work because the petrol was insoluble in the water.

The problem is filtering only works if you have an insoluble solid.

In fact, the petrol is an insoluble liquid in the water, so filtering wouldn't work.

Alex said that if the petrol is immiscible in the water, then you could simply evaporate off the water layer.

The problem is the petrol could also evaporate, so that really wouldn't separate the substances into two different things.

You'd end up losing both of the substances into the surroundings, because both of them might evaporate at the same time.

Now, Izzy said that layers would form if they're immiscible, and she's exactly right, and because of that, decanting one layer off would actually work.

So well done if you've got any of those ideas and discussing the pros and cons or the ins and outs of each of those suggestions on how that might be able to separate the immiscible mixture of petrol and water, not an easy thing to do.

So very well done for having a go.

Let's now move on to the last topic for today's lesson, separating miscible liquids.

Now, when miscible liquids are put together and mixed, what really happens here is one liquid is essentially dissolving into the other liquid.

And an example here is ethanol in water or ink in water, or we could have essential oils with the water and the ethanol that helps that mixing and dissolving to happen a bit better.

Now the problem we have with miscible liquids is that because they are miscible, they mix together and dissolve together, the layers don't form.

So the methods that we might use for immiscible liquids with the layers, so using decanting or a separating funnel, just aren't going to work in a situation where we have a mixture containing miscible liquids.

Now while we might not have layers, what we do have is a miscible liquid that will boil at a unique temperature.

So what that means that is if we were to apply some heat to a mixture that contains miscible liquids, then that would cause the liquid with the lower boiling point to change from the liquid state into the gas state.

So if we look at our diagram here, we've got some heat that's being applied to a mixture in an evaporation dish, and what the bubbles represent then is the liquid with the lower boiling point that has changed now into the gas state and is leaving the mixture, and we're left then with the substance in the evaporation dish that has the higher boiling point.

Let's stop again for another quick check.

For which of these mixtures would boiling be the most appropriate method to separate the liquids in the mixture? Well done if you chose C, the ink and water.

We can see very clearly in A, that we have layers that are forming between the cranberry juice and water.

So we could decant or use a separating funnel, and it's a little tricky to see in that first bottle of the salad dressing, but the second one definitely shows layers as well.

And therefore, I would say that B probably is not a great choice for using boiling.

You could decant or use a separating funnel.

So well done if you managed to choose C.

Let's now move to our last task.

What I'd like you to do is to use the data that is listed on the left here on the thermometer, to help you to decide which liquid might boil first if we applied heat to each of these mixtures.

So you'll want to pause the video here, maybe have a discussion with the people next to you, and then come back when you are ready to check your answers.

Let's see how you got on.

Now the main thing to decide which of these substances would boil first, is you needed to look at which of the pairings had the lower boiling point.

So when we compare each of these pairs, we're always looking at the one that is lower on that thermometer.

So in A, the answer with water would boil first.

For B, acetone is lower on the thermometer, so it would boil first.

C, ether would boil first.

D, ethanol would boil first if it's mixed with water.

But if we boil ethanol with acetone, it's the acetone that would boil first.

So well done if you managed to get all of those correct.

Good job.

Let's now summarise what we've learned in today's lesson.

Well, we've learned that scientists rely on the physical properties of the substances in a mixture to help us to separate them.

And the properties that we'd look at for liquids that are in a mixture are probably their densities and their boiling points.

We've also learned that immiscible liquids don't mix together, and because of that, they eventually settle into layers that are based on each liquid's unique density.

And that's really useful, because once they're in the layers, they could be separated by either decanting or by using a separating funnel.

We've also learned that liquids that do mix together are known as miscible liquids.

And because they don't form those layers, we rely on their different boiling points as a way to separate them, and we do that by applying heat to the mixture of those miscible liquids.

I had a really lovely time learning with you today, and I hope to see you again soon.