Hello, my name's Mrs. Niven.

And today we're going to be expanding on our understanding of those big questions, what are substances made of, and how do substances behave, to understand how different techniques might be adapted for better separation of the materials within a mixture.

Now, some of what we learned today, you might already be slightly familiar with, but what we do learn in today's lesson will help us to better understand and give us more techniques in terms of how we might separate a product of a reaction mixture.

It will also help us to better appreciate how some of the products that we might use in our everyday lives are actually isolated and prepared.

So by the end of today's lesson, you should be able to not only explain how fractional distillation works, but also how it is similar yet different to simple distillation in how it separates a mixture of fluids.

Now, throughout the lesson I'll be referring to some keywords, and these include boiling point, fractional distillation, miscible, fraction, and fractionating column.

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 maybe jot them down to refer back to you later on in the lesson or later on in your learning.

So today's lesson is broken into two parts.

The first looks at fractional distillation and the second looks at the uses of fractional distillation.

So let's get started by looking at what we mean by fractional distillation.

Now, distillation as a separation technique, regardless of whether or not it's a simple distillation or fractional distillation is very widely used.

And it's a process that exploits the different boiling points of the components within a mixture.

And some of the ways you might use it, you might be to take a synthesised or manmade mixture, usually in a lab, and be able to maybe isolate out an active ingredient that you might need for a product.

Another way you might use distillation is taking polluted water and turning it into clean water that can be used for various things like drinking, washing, or cooking.

Now depending on the type of mixture you start with, you might need a different distillation setup.

Now, this one you may be familiar with.

This is a simple distillation setup and it's used to separate shockingly, simple mixtures.

But what it does is collect just one liquid component.

So you're producing one distillate.

Simple mixtures tend to contain just two components, and those components tend to have a large difference in those boiling points that need to be exploited for distillation to occur.

Now, some examples of mixtures that you might use simple distillation on include things like sand and water, salt and water or ethanol and water.

Now that's not to say simple distillation couldn't be used to separate a mixture that is a little more complicated.

So something that contains more than two substances, it could be done, but there's a reason why chemists choose not to use simple distillation on those mixtures.

For one thing, it would be really inefficient.

When we're choosing a separation technique, we want to choose one that's going to save us both time and energy.

It would also be very impractical, especially if the boiling points of some of the components are close together.

So we're talking within about 25 degrees celsius of each other.

If that was the case, we would have to carry out distillation multiple times over closer and closer temperature differences.

And it's really difficult.

That would be very time consuming and energy consuming 'cause remember, you're gonna need to heat that mixture every single time.

So, it's just impractical.

There's gotta be a better way, and there is a better way.

Scientists have come up with this idea of fractional distillation and we use this to separate those more complex mixtures of miscible fluids.

So we're talking about fluids that mix together.

Now, a complex mixture then are those that contain many components, so that's over two substances and those that have very similar boiling points, so those are the components that are within about 25 degrees celsius of each other.

Now, when fractional distillation is carried out, you tend to form then multiple distillates.

Rather than the one you might get in simple distillation, this time you're gonna have multiple distillates.

And each distillate then, is actually referred to as a fraction of that mixture because it's part of that original mixture.

So each distillate from fractional distillation is known as a fraction, and fractions can actually be a pure substance or a mixture of substances.

So if I were to summarise the differences between simple and fractional distillation, this is what I would do.

Simple distillation tends to be used to separate a mixture that is contained of just two substances, and those substances tend to have a large difference in their boiling points.

And as a result of that, when you carry this out, you tend to have one distillate that is formed.

In fractional distillation, on the other hand, we'd use that to separate a mixture that's a little more complicated.

So it has more than two substances in the mixture.

And there might be a small difference then in the boiling points of those components.

So they're within about 25 degrees celsius of each other.

And as a result of that, you get multiple distillates and we call each distillate a fraction because it's a part of that starting mixture.

Let's stop here for a quick check.

True or false, simple distillation is best for separating a mixture of three or more liquids with very similar boiling points? Well done if you chose false.

But which of these statements best support that answer? Well done if you chose A.

Fractional distillation is best for separating a mixture of more than two substances.

Simple distillation would work if the boiling points had a large difference between them, but not if they are very similar in boiling points.

So well done if you manage to correctly identify that as a false statement and very well done if you chose the correct supporting statement.

Great start guys.

Good job.

Now, you may have noticed earlier in the diagrams when we had simple distillation next to fractional distillation.

That fractional distillation seemed to have an extra component, and what it contained was a fractionating column.

Now, fractionating column sounds a bit weird.

So if we pull that word apart, fraction we know means part of a whole.

And when you have ating at the end of a word, it tends to mean that you're talking about an action or a process.

And a column, we'll remember, is an upright pillar and it tends to be cylindrical in shape.

So a fractionating column, if we bring all these ideas together, is simply a column that helps to separate a whole mixture into its parts, into its fractions.

Now we use a fractionating column in these setups because it allows for far more efficient separation of these complex mixtures.

Remember, a complex mixture is one that contains more than two substances within it, but really a fractionating column comes into its own when you have components with very close boiling points.

Remember, these are ones where the boiling points are within about 25 degrees celsius of each other.

Now the reason that a fractionating column is so efficient at separating a mixture with similar boiling points is because as you move away from that heat source, a temperature gradient develops.

So the heat source here is circled in the bottom in red representing either a Bunsen burner or a heating mantle.

And as you move further and further away from that up towards the thermometer at the top, that is where the fractionating column will be the coolest separation that takes place in a fractionating column actually occurs over several stages.

And the first one obviously is gonna happen at the very bottom of the column.

The first thing that needs to happen is that mixture is heated, and when they heated, one of those components will start to change into a gas.

And when it does so, it rises into the column.

Now the key here to remember is that we've only just started distillation.

So the bottom of that column is gonna be initially quite cool.

So when those first gases hit that initially cool fractionating column, they're actually gonna condense and drip back down into the flask.

As this distillation process continues, the mixture continues to be heated, and this is when a temperature gradient starts to develop within that fractionating column.

That means then that the gases that initially hit that cool bottom part of the column turned into a liquid and dripped back into the flask continued to be heated, they turn into a gas a second time and are able to travel further up that fractionating column before they might hit a cooler pot, condense and drip back down into the flask.

Now remember, this mixture is being continually heated, so that means that the gases that have moved into that fractionating column hit the cooler parts of it and then condensed and we've backed down into the mixture are heated for longer.

And the longer that this heating goes on, the likelihood of that warmer section of our fractionating column is gonna move further and further up.

So the gradient becomes less distinct.

We the warmer section of our column gets higher and higher up that column.

Eventually, we get to a point where the component with the lowest boiling point reaches the top of the column as a gas, whilst the other components with a higher boiling point will condense within the column and drip back into the flask to be heated some more.

But that one that reached the top of the column, that's able to now enter our condenser.

So to summarise those main steps in how a fractionating column works, the first thing that happens is that, we heat the components in the flask, some of them change into gases, they hit that initially cool section of the fractionating column and drip back down into the flask.

The longer the mixture is heated then, we start to develop a temperature gradient within that fractionating column.

Again, the gases are able to travel a little bit further up that column before they condense and drip back down into the flask, until eventually the component with the lowest boiling point is gonna reach the top as a gas and enter the condenser.

Let's stop here for another quick check.

Which two of these statements are true about fractionating columns? Well done if you chose A and D.

So it's definitely a long cylindrical piece of apparatus.

It's a column, so it's cylindrical and it has a temperature gradient that is produced throughout it.

So it has a cooler section and a warmer section.

And because of that, B is definitely out.

It's not the same temperature throughout it.

And it has to be a long cylindrical piece of apparatus rather than a short one so that it can actually develop that temperature gradient.

So the taller it is, the larger the temperature gradient that can develop.

Well done if you chose A and D.

Time for our first task.

So for this first section, what I'd like you to do please, is to match each keyword to the correct description.

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

Okay.

Let's see how you got on.

So a boiling point is, the third description down, is the temperature at which a substance changes from a liquid to a gas.

And that's the key there, liquid to gas, as a change of state.

Now a fractional distillation then, is actually a technique that exploits components of different boiling points.

And again, those are kind of the red flags for me in that description that we're talking about exploiting boiling points.

So that's why fractional distillation matches best there.

Miscible describes fluids that can mix together.

So I remember mis and mix sound very close together, and that might be one way you can remember what miscible means in the future.

Fractionating column is a piece of apparatus that develops a temperature gradient.

And that's my, again, big red flag.

Fractionating column, temperature gradient.

So if you wanna try and match up those key ideas.

And a fraction then, is simply another name we give for a distillate formed specifically from fractional distillation.

Well done if you manage to get those correctly matched up.

What you may wish to do if you have a highlighter, a coloured pen or something, is to highlight those key phrases or words within each of the descriptions that might help you to match them to the correct keyword in the future.

Very well done if you manage to get those correct.

For the next part of this task, I'd like you to help Aisha who's asked you to help double check her homework.

In this homework, she was asked to label a fractional distillation setup.

So what I'd like you to do is to help identify any errors that she's made and I'd like you to correct them.

Now this might take a little bit of time to identify them and maybe you might want to discuss these with some of your neighbours.

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

Okay, let's see how you got on.

Hopefully you've identified that Aisha correctly labelled both the flask and the thermometer in her setup, but she did make a few errors that hopefully you've identified and we're now going to fix.

And the first one we have is that she originally labelled the fractionating column here, correctly labelled, as the condenser.

So we need to make sure that this is correctly labelled as the fractionating column.

She also had the temperature gradient the wrong way round.

Originally she had it coldest at the bottom.

It should actually be hotter at the bottom and then colder at the top.

Now if you said coldest, I would actually recommend colder is better.

So it's relative to other parts of that fractionating column.

I don't suspect that you would be penalised in any way for saying coldest or hottest, but a better answer is colder and hotter.

The next thing we did then is we need to fix that other label and correctly identify the condenser which Aisha had originally mentioned as the fractionating column.

One way I remember that the column and the condenser are the correct way around is the column is straight up and down and the condenser tends to be a little bit at an angle.

And then finally, we need to be labelling that last bit that comes out.

She originally labelled that as the filtrate, but a filtrate is what forms from filtration and this is distillation and therefore, it needs to be labelled as either the distillate or more correctly here as a fraction because this is what's formed from fractional distillation.

So well done if you've managed to first of all identify any of the errors that Aisha made and very well done if you've managed to correct them as well.

Very, very well done and a great start to this lesson, guys.

Keep it up.

Now that we're feeling a little more comfortable talking about fractional distillation and identifying some of its key features, let's look at the uses of fractional distillation.

Now, I said earlier that distillation as a process exploits the unique boiling points of the components in a mixture.

And that's true for both simple and fractional distillation.

And we know that you might choose fractional distillation rather than simple distillation, specifically if some of your components have boiling points that are really close together.

But sometimes you can actually have components whose boiling points are so close together that it would be too difficult to fully separate them from a mixture even by fractional distillation.

Now as a result of that, some of the fractions that are formed from fractional distillation can be either pure substances or remain a mixture just different to the starting mixture.

Now, an easy way to tell whether or not the fraction that has formed from fractional distillation is pure or a mixture, is to look at the temperature of which it boiled.

If it boiled at a specific temperature, then you have a pure fraction.

And if the fraction was formed by boiling over a temperature range, then it's most likely going to be a mixture.

So if we look at our examples here, on the bottom, we have a distillate that boiled between 150 and 100 degrees celsius.

Now because that temperature is a range, then we know that that distillate or fraction is actually a mixture.

This other distillate boiled at 100 degrees celsius, and that tells me because it's a distinct temperature that that fraction is a pure one.

Now, crude oil is an excellent example of how we can create useful materials by fractional distillation.

It is a bit of a complicated process though.

We can see simply here, the number of different fractions, and this is only a small selection of them that you can get from the fractional distillation of crude oil.

But you'll see some really common substances that formed from it.

For instance, petrol, diesel.

The refinery gases at the top tend to include things like propane or butane, so things you might use for camping gas stoves.

The bitumen that you find on the bottom there can be used for resurfacing roads.

But the key here, is that if you look at the boiling point ranges for each of these fractions is that actually is boiling over a range.

And because of that, each fraction of crude oil is actually a mixture itself of similar molecules with similar boiling points.

Believe it or not, air can actually be fractionally distilled.

And when that happens, we can get pure fractions.

So pure oxygen, so this would be having a boiling point of a distinct temperature can be distilled and used in healthcare.

The nitrogen from air could be fractionally distilled and then used to prevent food from spoiling as well, which is pretty cool when you think about it.

So let's stop for another quick check.

During fractional distillation, all distillates boil at a specific temperature.

Is that true or false? Well done if you said false.

But which of these statements justifies that answer? Well done if you chose B, distillates can be a mixture which boil over a temperature range, but they could also be a pure substance.

So because of that, we can have a variety of temperatures at which distillates boil.

So well done if you manage to choose false and very well done if you chose the correct justifying statement.

Great job, guys.

Now we've looked at how different fuels can be extracted from crude oil by fractional distillation and also how pure gases can be extracted from air by fractional distillation.

But those aren't the only products that can be formed by this separation technique.

For instance, some of the materials that we use in health and beauty products are obtained and then purified as fractions by fractional distillation.

So you might start with the flowers like lavenders or rose or the fruits, things like olives, and then eventually they can be distilled into some essential oils.

Another example is the ethanol that's used in alcoholic beverages.

That's a fraction that can be extracted by fractional distillation.

So you'd start with a fermentation process that's involved grains like wheat or barley, fruits like grapes or apples or vegetables like corn or potatoes.

And once that fermentation process has taken place, then the mixture would undergo fractional distillation.

And when that happens, you can create a mixture of ethanol in water of different proportions and create your different spirits.

Now, petrochemicals are mixtures of molecules in a fraction that's formed by fractional distillation of the crude oil.

And we looked at things like petrol and diesel and things like that.

So those are the fuels that can come from crude oil, but those aren't the only things.

We can also get lubricants from crude oil.

You can also get those road services that we talked about as well.

So all of these would be examples of petrochemicals that are extracted by fractional distillation of a mixture.

Let's start for another quick check.

Which of the following is a product of fractional distillation? Well done if you said all of them.

All of these products can be formed from fractional distillation.

The difference is the starting mixture that they come from.

Okay.

Let's move on to the last task of today's lesson.

The first thing I'd like you to do within this task is to write a summary about fractional distillation using at least six appropriate keywords from this box below.

So what I might recommend you do is put a little tick next to words you definitely want to use, maybe a cross next to ones that you definitely don't want to use, a question mark next the ones that you may want to use.

And those might be the ones that you want to discuss with the people nearest you to decide whether or not it's worth including, okay, This is gonna take a little bit of time, so I recommend you pause the video here and come back to check your answers when you're ready.

Okay, let's see how you got on.

Now, there was a wide variety of what you could have said about fractional distillation and you needed to use at least six appropriate keywords.

So what you might want to do now, if you haven't already done so, is to go through with a highlighter or a coloured pen and just circle or underline or highlight those keywords within your answer so that it's a little bit easier to keep track of how many keywords you've actually used within your box.

And then you can see whether or not you've used them appropriately within your summary.

But as I said, there were some words in here that maybe you shouldn't have used.

And the three that I would definitely hope you didn't include was filtrates because those are the products of filtration and we're talking about fractional distillation.

Immiscible, I would've recommended you not using because that would've been a component.

An immiscible component is what we might use for filtration and not distillation.

And melting points, again, I wouldn't have used that here either 'cause we're talking about a state change, that is a solid into a liquid.

And the state changes involved with fractional distillation have to do between liquids and gases.

So those are three keywords I hope maybe we didn't use in our summaries.

Now your answer may be somewhat similar to this, it may be slightly different.

But what we want to look at here is how these keywords have been used.

So I'm gonna read it out and you might wanna see if you have something similar within your own summary.

So distillation is a separation technique that relies upon components of different boiling points.

Fractional distillation is frequently used to separate miscible fluids such as crude oil.

This type of distillation uses a fractionating column which develops a temperature gradient.

The different distillates produced are known as fractions, which can be either pure or a mixture.

Now if you're unsure about whether or not your summary is correct or if you have used your keywords appropriately, you might want to get somebody else to take a look at it and you can have a discussion about it.

But what I'm looking for specifically is that you've used at least six of those appropriate keywords within your summary and that you've used them correctly within it.

So, well done 'cause this is not an easy thing to do.

Good job for persevering guys.

So for the next part of this task, what I'd like you to do is to do a little bit of data analysis.

Sophia is preparing to fractionally distil a mixture containing the components that are listed in the table.

What I'd like you to do is to use the information in it to predict the order in which she will be able to collect the fraction, so which will she collect first, second, and last.

And then I'd also like you to use this information to decide if the fraction is going to be a pure fraction or a mixture.

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

Okay.

Let's see how you got on.

So the first thing you needed to do was to use the information in the table to decide what order these fractions would be collected through fractional distillation.

And what we needed to remember is that the lowest boiling point will be collected first.

So that means then you will collect them in this order starting with rose oil, the next distillate then will be cyclohexane, and then finally we will be able to collect the kerosene.

Now using the information in those boiling point column as well, we'll be able to tell if these fractions will be pure or a mixture.

The rose oil will be a mixture because it boils over a range of temperatures.

The cyclohexane will be pure because it will boil at a specific temperature.

And like the rose oil, kerosene is also a mixture because it has boiled over a range of temperatures.

So very well done if you manage to put them in the correct order of collection.

And extremely well done if you've managed to remember how to identify whether or not a fraction will be pure or a mixture.

Really, really well done guys.

Good job.

We've gone through a lot of information in today's lesson.

So let's take a moment to summarise what we've learned.

Well, we've learned that fractional distillation is very similar to simple distillation except for one key component, it uses a fractionating column, and it's the addition of this fractionating column that makes fractional distillation so useful for specific mixtures, those that are a little bit more complex.

And when we talk about a complex mixture, we're talking about ones that contain three or more components or whose components have very similar boiling points.

So those are ones within about 25 degrees celsius.

When fractional distillation then takes place multiple distillates or fractions because they are part of that original whole mixture are formed.

And these fractions then can either be pure substances that boil at a specific temperature or a mixture of chemicals that boil over a temperature range and have very similar boiling points within them themselves.

We've also then looked at some real world applications of fractional distillation, including the distillation of air to produce pure gases and the distillation of crude oil to create a wide variety of petrochemicals like fluids, lubricants, and road surfaces.

Now that's a heck of a lot to go through, guys.

You've done an amazing job today.

I had a great time learning with you.

I hope you had a good time learning with me, and I hope to see you again soon.

Bye for now.