Hello, my name's Mrs. Nevin, and today we're going to be talking about paper chromatography as part of our unit on separating substances.

Now, you may have some experience of chromatography from your previous learning, but what we do in today's lesson will help us to better understand how we can use separation techniques, not just to separate out a substance into its different components, but how we might also be able to use it to classify the components as being pure or impure, as well as being able to identify the different components within a mixture.

Not only that, what we learned today will also help us to answer those big questions of what are substances made out of, and how can we explain how substances behave.

So, by the end of today's lesson, you should be able to describe how to carry out paper chromatography, and also start to analyse chromatograms to be able to classify substances, as being either pure or a mixture.

Throughout the lesson, I'll be referring to some key terminology, and these include chromatography, stationary phase, mobile phase, and chromatogram.

Now, the definitions for these key terms are in sentence form on the next slide, and you may wish to pause the video here, so you can read through them and maybe make a note of them so that you can refer to them later in the lesson, or later on in your learning.

Today's lesson will consist of three main sections.

We'll look at the basics of chromatography, how we might describe chromatography.

Then we'll look at how you can carry out, specifically paper chromatography, and we'll finish off the lesson by looking at some initial analysis of the chromatograms that are formed.

So, let's get started by looking at the basics of chromatography.

Now, in the grand scheme of things, chromatography is a fairly recent separation technique that's been developed, and it's become more and more popular throughout the 20th century.

But, what is chromatography? Well, if we break the word up, we can see that "chromato" actually comes from the Greek, for colour, and "graphy" comes from the Greek, graphene, which means to write.

So, to bring it all together, chromatography might mean to write in colour, and that was the term to use to describe this particular separation technique, because it was a process that was used to separate the different coloured components in plants, initially.

But, over the years, chromatography has become more useful for a variety of things, and one of the reasons that makes it so useful is that the technique uses only really small samples.

You don't need a lot of your sample in order to perform chromatography on it.

And, because of that it's incredibly useful for things like forensics, for identifying things like ink and analysing it, for being able to detect drugs in different blood samples, for instance, for athletes and doping, and things like that, and also for identifying different debris that might be collected at different sites.

Now, there are several different varieties of chromatography available to chemists, but regardless of which one you're using, they all contain two essential parts.

Now, the first one is the stationary phase.

It remains stationary, meaning it doesn't move.

So, this is a substance as part of their chromatography setup that doesn't move with the components of our mixture.

The other part is the mobile phase.

It's mobile, it's moving.

So, this is the part of our chromatography setup that actually moves along with our substances.

So, it involves the solvent, and any dissolved components from our sample.

Now, the separation that takes place through chromatography depends on how the components of a sample interact with both of these phases, both the stationary phase and the mobile phase throughout chromatography.

And so, it's worth looking at these in a little bit more detail.

Now, our lesson is about paper chromatography, so the rest of what we're talking about is going to focus on that specific type of chromatography.

Now, in paper chromatography, then the stationary phase tends to be something that is an absorbent paper, usually filter paper.

The mobile phase, then, is simply any suitable solvent that will work.

Now, water is commonly used.

It's easily accessible, and it tends to be an incredibly good solvent.

However, you can use other ones.

Some other solvents that might work are things like ethanol, hexane, and propanol.

And, dependent on what you are trying to separate, you might need to use a different solvent to help that separation be a little bit more efficient.

Let's stop here for a quick check.

True or false, the stationary phase travels with the components of a sample? well done if you said false.

However, which of these statements best supports your choice? Well done if you chose B, "The mobile phase moves with the sample," not the stationary phase.

The stationary phase stays still, the mobile phase moves.

That's the way I remember it, anyway.

Well done if you got that correct.

Let's try another one.

"Which of the following could be used as a solvent?" Well done if you said all of them.

Depending on what mixture you are trying to separate, you might need to use a different solvent.

So, nail varnish remover, ethanol and water can all be used as a solvent in your mobile phase.

So, well done if you manage to choose all of them.

Great start, guys.

Now, as I said earlier, there are several different types of chromatography and all of them will have a stationary phase, and a mobile phase.

As well, all of them follow a rather similar method in terms of how it's carried out.

So, the first step is that a sample is placed either on or in a stationary phase.

Then a solvent is added, and this is used to dissolve the components of the sample, and in effect, creating a solution.

What happens then is the mobile phase, which is the solvent and any dissolved components, will move along or travel along that stationary phase, and then the components of the sample will get separated out from each other, so that you are separating that particular mixture.

So, as these components, then, are pulled along the stationary phase, it starts to develop a pattern on that stationary phase, and the result, then, is known as a chromatogram.

So, we have an example here of a sample.

Our sample is a purple sweet, and we are dropping water, which is the solvent onto it, as our mobile phase.

And then, you can see that morphile phase move along the paper towel, acting as our stationary phase.

And, when we are finished with it and we let it dry, we have this chromatogram that has developed on it, this pattern.

Now, I said earlier that in paper chromatography, we'll normally use an absorbent paper, like filter paper, but you can use different mobile phases, different solvents to develop your chromatograms of the same sample.

So for instance, here, I could do the chromatography of four different purple ink samples, and when I put that into water as a solvent, I might develop a chromatogram that looks a little bit like this, on the right, but if I put that same samples onto a new piece of absorbent paper, a new stationary phase, and put it into a different solvent, this time I'm gonna use propanone, which is the ingredients that we find in nail varnish remover.

I get a very different chromatogram that develops as a result of it.

So, this is a good example of how the interaction between the mobile phase and the stationary phase can cause us to have a different distribution of the components along that stationary phase, giving us different patterns and different chromatograms. So, once a chromatogram has been developed, it gives us some really quick and easy information about the solubility of the components of our original mixture, because the more soluble a component is, the further it will travel from the sample source.

So, if we look at this chromatogram that was developed from our sweet earlier, we can see that the sample source is at the very centre.

So, that's where our sample started, and the colours that are closest to that sample source will be less soluble than the others, because they stayed quite close by.

They haven't moved very far.

However, these blue colours, or the colours further away from the centre of our sample source, would be more soluble because they've managed to travel further.

Let's try another quick check.

"True or false, changing solvents has no effect on the chromatogram that's produced?" Well done if you said false, but which of these statements justifies your answer? Well done if you chose a B, "Different solvents may dissolve the components differently." Components solubility definitely changes with the solvent, so you might be able to change it, and get a different chromatogram produced.

So, well done if you manage to get that correct.

Good job, guys.

One other thing that we can see from the chromatography related to the solvent used is that if the substance in the sample, or even the sample itself, is insoluble in the solvent, it's not going to move from the sample source.

So, if we look at these two chromatograms that are shown here, we can see that the sample source is marked with an X.

So, we can see where the sample was placed on the chromatogram to start with, and then we can see that there are definitely some soluble substances on this chromatogram on the left, because we can see a separation.

There's different spots, different colours that have developed here.

But, when we look on the right, we can see that the sample has not moved from that sample source, which tells us that it is insoluble in the solvent that has been used.

Time for the first task of today's lesson, Izzy has been carrying out some chromatography.

So, you can see she has her absorbent paper here.

She's got an X labelled, and she's placed a dot on it.

And, when she has added her mobile phase, she has developed a chromatogram that looks a little bit like this.

What I'd like you to do now, is to help her label the chromatogram using the terms that are in the bullet points to the left.

But, after you've done that, I'd also like you to explain why you've chosen to put the labels where you have.

So, you may wish to pause the video so that you could have a chat with the people nearest you, have a little think, jot down your ideas, and then come back when you're ready, to check your answers.

Okay, let's see how you got on.

Well, we had quite a few things that we needed to try and label, and we also needed to explain why they were labelled the way they were.

So, the first thing I decided to label was my sample source, and that's the X on Izzy's absorbent paper, and this is where the sample is going to be placed, okay, on those Xs.

In the same location, that black spot in the centre shows me that this particular component of my mixture is insoluble.

And, it's insoluble because it hasn't moved from that sample source of where it's been placed, okay? Then I can label, the less soluble components will be the two inner rings.

So, that yellow one and the thinner green one just around it, those are going to be less soluble because they've moved from the sample source in the centre, but they're still close to it.

And, finally then, the larger purple ring towards the outside of my absorbent paper is going to represent the most soluble component of my mixture, and that's because it managed to move the furthest from the sample source.

So, firstly, very well done if you've managed to label the different parts of the chromatogram correctly, and incredibly well done if you were to explain the reasoning behind your choices, it's not an easy thing to do, to add that because clause of why did you do this? So, very well done, and I would challenge you to continue justifying your choices as you go through the tasks in these lessons.

Really, well done guys.

Now that we're feeling a little bit more comfortable looking at the basics of chromatography, let's look more specifically at how we can carry out paper chromatography.

To carry out paper chromatography, you're going to need some specific equipment.

This includes a container that you can hold a small volume of solvent in.

You'll obviously need your sample that you're going to see if you can separate via chromatography, you'll need a stationary phase, remembering that's an absorbent paper.

So, if you're at school, it'll probably be filter paper.

If you're at home, cut up coffee filter paper will work.

You'll need some small implement to add your sample to the stationary phase.

So, I've got a toothpick here, but if you have a pen, or even a very fine paintbrush would work as well.

You're also going to need then a ruler and a pencil to get started.

So, the first thing you're going to do then, is you're going to use the pencil and the ruler, and you're going to draw a straight line around about one to two centimetres from the bottom of your stationary phase, and draw that straight line.

Then in the centre of that line, you want to draw a small X.

Remember, this is your sample source in the centre of your line.

So, it will remind us where that sample was originally placed, if it is soluble in your solvent, and it is moved away from it into the different components that make up that mixture.

Now, it's really, really important that you are using a pencil for this job, and we're doing that because pencil tends to be insoluble in most of the solvents that you use.

And, because of that, as the mobile phase moves along the stationary phase, that pencil will not affect the chromatogram then that develops.

So, make sure you've got a pencil.

If you haven't got one, borrow one, it makes all the difference.

Next, what you're going to do is to use your small implement to add a very small amount of your sample to the centre of your X, okay? <v ->Now, it's actually really important</v> that we consider the size of the sample that you are putting on your sample source.

We want to try and keep that sample spot to be less than one centimetre wide.

And, there's a very good reason for this, because if that dot becomes too large, the separation that we're aiming for with chromatography starts to become very unclear, and the chromatogram then will be difficult to interpret later on.

So, less is more when it comes to putting the sample onto your stationary phase.

Next, you're going to fold and fasten that paper to some form of support.

And, fastening it is as simple as using a paperclip.

I would not recommend tape because that could interfere with the chromatogram that is developing.

So, definitely something that you can easily remove and isn't going to interfere with it.

Then you're going to have a small beaker, with a very, very small volume of solvent in it.

So, what I would actually recommend is just enough to cover the base of the container, your beaker, and just a few extra drops after that, we don't need a lot.

Then, at this point, what you're going to do is you're going to gently lower the paper into the solvent, and this next bit is absolutely essential.

As, you're lowering it, you need to make sure that this solvent stays below the pencil line, and below the sample spot that you have put on that pencil line, okay? And, that's to make sure that the sample does not dissolve into your solvent reservoir, and instead, is going to be carried along that stationary phase, as the solvent is absorbed into it.

Now, what you need to do is simply patiently wait for the chromatogram to develop.

So, here we show a chromatogram that's actually developing, and remember we need to take care that that sample spot stays above the level of the solvent in the container.

But, it is, it very much is an exercise in patience.

This little video that you're seeing here was sped up tenfold to show you just how quickly it can be done, but it, yeah, it really does need to just have a little bit of patience as you go through.

It's quite fun to watch, actually.

Let's stop here for a quick check.

"Which of the following is not needed to conduct chromatography?" Well done if you said C.

You do not need a pen in order to conduct chromatography, you if you're using pen rather than that pencil to draw that start line and your X, then the ink may dissolve in the solvent, and that could interfere with the chromatogram that is developing.

So, well done if you've managed to choose the pen as being not needed for chromatography.

Let's try another one.

"True or false, the larger the sample spot, the clearer the chromatogram that's produced?" Well done if you said false, but which of these statements best justifies your choice? Well done if you said A, we really need to make sure that a sample spot is limited to one centimetre wide.

A minimum of one centimetre wide, suggests that it could be larger than that, and we really don't want it to be larger than one centimetre.

So, well done if you manage to get this correct.

Good job! Time for the next task in today's lesson.

We have here a setup for chromatography, but there are two errors in it.

I'd like you to identify what the errors are, and suggest how those errors could be fixed.

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, one of the errors that I noticed in this setup is that the sample spot is resting in the solvent, which is a big no-no.

So, what we could do to fix that is we could actually suspend that stationary phase, the paper, a little bit higher so that the spot does not dip into the solvent.

We might need to just fold that paper over the support a little bit more, and just fashion it, fasten it, sorry, a little bit higher.

The other error that was found in this setup, is that the line has been drawn in pen.

So, to fix that, very simple.

We just need to start over again, but this time draw that line in pencil.

So, well done, if you first of all, managed to identify the errors, and very well done, if you managed to suggest how we could fix those errors, you're doing really well, guys.

Keep it up! For the next part of this task, I'd like you to help Lucas.

He's curious to see if different food colorings are pure or a mixture, and he is asked for your help to prepare some chromatograms, that we could then look at to answer that question.

So, working in a small group, I'd like you to create a chromatogram for each of the following food colours.

I'd like you to create one for blue, red, green, and yellow.

Now, you may wish to work in a group of four, where you each make your own chromatogram, or you may wish to work in pairs, and each of you do two.

It's completely up to you, but have a go now, and then come back to me when you are ready to check to see how you got on.

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

Now, depending on the brand that you used for each of your food colorings, you might have a slightly different chromatogram that has developed, but these are the ones that I managed to develop for my blue, red, green, and yellow food colouring that I have here at home.

And, your results may look slightly similar, but what we're looking for in this particular task is have you drawn your lines and pencils? Do you have your Xs to represent that sample source? And, have you managed to keep the dots of your samples small enough so that you've got some good clear separation as that chromatography has taken place? So, really well done if you've managed to create a few useful chromatograms. Well done, guys.

Okay, so we've now spent the lesson learning a little bit about the basics of chromatography.

You've had a go at learning more specifically about carrying out paper chromatography, and made your own chromatograms. Now, what we're gonna look at is how we can initially analyse those chromatograms. Now, an initial analysis of a chromatogram tends to be what we call qualitative, which means we're just looking at it and making comparisons, and decisions.

We're not taking any measurements, we're not doing anything with numbers.

So, quality, qualitative analysis.

And, what this can show us with a chromatogram is really quickly, whether or not a sample that we've separated using chromatography, is either pure or a mixture.

So, if a sample is pure, it will show just one colour or one spot on its chromatogram.

If a substance is a mixture, it should show multiple colours, or multiple spots on it.

So, what I'd like you to do here is tell me which of these chromatograms do you think, Ben, indicates that the sample was originally a mixture.

Well done if you chose A.

Now, A definitely looks like it was a mixture.

I can see two very distinct colours here, green and yellow, two different shadings as well.

Now, if you might have said B, could be a mixture as well, so we take a closer look at that.

There's a darker colour towards the centre, and a lighter colour towards the, yeah, it's almost brighter on that outside edge of the chromatogram.

So, that could be a mixture as well.

And C definitely is not a mixture, because we can only see the one colour in the one spot.

So, well done, if you chose A, and I think you can make an argument for B, as well.

Good job.

Now, sometimes chemists will develop chromatograms that contain several samples on the same stationary phase.

So, we can see here in our diagram we have five different samples, labelled A through E, that have undergone chromatography.

Now, we can do the same kind of qualitative analysis looking at them vertically to see if a sample is pure, or a mixture.

The issue when we look at a chromatogram like this, though, is that it can get very muddled, very quickly.

So, to help me in my analysis, I'm gonna take my pencil and ruler, and I'm gonna draw lines from the sample source X, vertically upwards.

Now, drawing those lines in pencil one, using pencil means it doesn't interact with the chromatogram that's been developed, so it's not gonna muddle it up.

And it also helps to keep my analysis a little bit more organised.

So, if I wanted to try and decide which of these samples was pure, I'd be looking for something that had only one spot.

So, when I look along these vertical lines that I've drawn, I can see that samples B and D contain only one spot, and therefore, the samples were pure.

If I'm trying to identify the samples that were mixtures, I'm going to be looking for samples that have multiple spots along those vertical lines, and looking at this analysis, then I can see that A, C, and E are all mixtures because they contain more than one spot along that vertical line.

Let's stop for another quick check.

"What information can be determined from analysing a chromatogram?" You may wish to pause the video here so you can have a discussion, and then come back to check your answer.

Well done if you said all of them, you'd be exactly right.

Our qualitative assessment helps us to decide if a sample is pure or not, 'cause I could look at how many spots there are developing from or different colours are developing on the chromatogram.

I could see how many components make up a sample, based on the number of colours or spots that I can see.

And, I could also decide on the solubility of the samples based on where those spots are in relation to where the sample spot started, remembering the further it travels, the more soluble it was.

So, very well done if you manage to choose all of them.

You get a lot of information from a chromatogram, it's an incredibly useful technique.

Okay, time for the last task for today's lesson, what I'd like you to do is to use this chromatogram to answer the questions, and don't forget to justify your answers.

So, tell me why you've made that decision in your answer.

So, for A, tell me which sample contains an insoluble substance, and why.

And, for B, which sample contains the most soluble substance and why did you choose that one? So, pause the video here, and come back when you're ready to check your answer.

Okay, let's see how you got on.

So, for question A, you were asked which sample contains an insoluble substance, and hopefully you chose sample B, because the spot has not moved from the start line or that spot source, it's still on that pencil line.

B asks you to say which sample contains the most soluble substance, and hopefully you chose sample A, and that's because it has the highest spot on our chromatogram, or the spot has moved the furthest from its start line in that sample source.

So, very well done if you managed to choose the correct samples, and incredibly well done, if you're able to justify your choices, with that because clause.

Great start, guys.

Very well done for this task.

For the next part of this task, I'd like you to use this different chromatogram, and I'd like you to decide which of these samples, A, B, and C, are pure and which are mixtures.

And, like before, I'd like you to explain your choices using a because clause.

So, you might 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 now, because I'm trying to decide whether or not these substances are pure or mixtures, and I have three different samples on the same chromatogram, I'm going to get my pencil and ruler out, and draw those vertical lines.

Now, remember that a pure substance should only have one spot, and therefore, sample A is pure because it's the only one that has one spot.

That means, then, that samples B and C are mixtures, and that's because they contain more than one spot.

They have multiple spots on that vertical line.

So, well done if you are able to correctly identify sample A as pure and samples B and C as mixtures, and even better if you've managed to explain your choices using that because clause.

Really well done, guys.

Okay, for the final part of our final task in today's lesson, I'd like you to go back to the chromatograms that were produced in Task B, part two to answer this question.

"Which of the food colorings that you created chromatograms for are pure, and which are mixtures?" Now, if you didn't manage to create all four of the chromatograms, do what you can with the ones that you did manage to produce.

If you use different colorings, that's fine, and if you didn't get a chance to do any, you may use the image of the chromatograms I produced here below.

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

Okay, let's see how you got on.

Now, trying to answer this question of deciding which of the food colorings are pure, or are mixtures, is going to depend wholly on the chromatograms that you have produced.

But, if I go by analysing the craft grammes in the image here, maybe this will help guide you in checking your own answers.

So, looking at these chromatograms, I've decided that the yellow sample is a pure colouring, 'cause when I look at that yellow food colouring sample, I can see just the one spot.

It's all exactly the same colour, and therefore, I would assume that it is a pure food colouring.

I think that the impure or mixture food colorings, are going to be the blue, red and green ones.

Now, the blue chromatogram, I can see that we've got a long streak of blue towards the top, and then there seems to be another blue colour, that's kind of almost a purpley colour if you look at it closely, that is very close to that X at the bottom.

So, I think there might be two different colours there.

I can clearly see two different colours on the red sample, there's the red right on the X, and then there's kind of a yellowy orange streak that's towards the top of that chromatogram.

The green one's a little bit trickier to interpret.

I would say that this is possibly a mixture, because it looks like we have a little bit of a yellow streak above, but then that green sample looks like it's insoluble, potentially, and has just stayed on that X.

So, it looks like I have, potentially, two different components of that green food colouring mixture sample.

So, how you look at this is going to be dependent on the chromatograms that you've made, but very, very well done, trying to do a tricky task of interpreting the chromatograms that you have produced yourself.

So, good job guys, not an easy task.

Now, we've gone through quite a lot of information, and did quite a lot of work in today's lesson.

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

Well, we've learned that chromatography consists of two main phases, that's the stationary phase and the mobile phase.

And, effective and useful separation of any of the samples that undergo chromatography, depends on how the sample interacts between both of those phases, the mobile and stationary phase.

So, you can change the stationary phase, change the mobile phase, and you will produce a different result.

Now, we can use both aqueous, that's water, and non-aqueous solvents in chromatography.

So, we could use things like propanone, which is nail varnish remover, or hexane, or ethanol as alternative solvents in our chromatography.

We've also learned that an initial analysis of chromatograms can help us to identify if the sample we're looking at is pure or impure.

Impure, possibly it's a mixture.

Now, pure substances will show one spot or one colour, whilst an impure mixture will show multiple spots on that chromatogram.

And, we've also realised that chromatograms can provide some information about the solubility of the components for the phases that were used.

So, there's a lot of information that we can get from producing a chromatogram, and this initial analysis is all qualitative.

It's simply based on what you can observe with your eyes, not through any measurements or number taking here.

So, a lot of work that we've done today, guys, you have been outstanding throughout this particular lesson.

I am so impressed.

I hope you've had a good time learning with me.

I certainly did, and I hope to see you again soon.

Bye for now.