Hello, my name's Mrs. Nevin, and today we'll be looking at chromatography as part of our topic on "Separation Techniques." And what we talk about in today's lesson will also help us as we try to answer that big question of how can we explain how substances behave? Now, some of you may have experience of chromatography in possibly another science lesson, or potentially in an art class, where you may have used chromatography to create a new design.

But what we're gonna look at today, is how we can use chromatography going forward.

It's an incredibly useful technique, and exactly why it's so useful, we'll find out in today's lesson, so let's get started.

So by the end of today's lesson, you should be able to describe how to set up chromatography in order for the technique to be used, but also be able to interpret the results of chromatography to answer questions about a substance that has undergone that process.

Now we'll be using some keywords throughout today's lesson, and those include chromatography, solvent, soluble, chromatogram, and compare.

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 could read through them, or perhaps take a quick note of what they mean so that you can refer back to them later on in the lesson.

So there's a lot to think about when we're talking about chromatography, and to help us on the lesson, we're gonna break it up into three main parts.

We'll look first at the basics of chromatography, then we'll look at how you can actually carry it out, and then finally, we'll finish up the lesson by being able to interpret different chromatograms. So let's get started by talking about those basics of chromatography.

Now in the grand scheme of things, chromatography is actually a fairly recent separation technique that's only really taken off in the last hundred years or so.

But if we look at this word chromatography, we can break it apart and it helps give us a clue as to what we might experience when chromatography takes place.

Now both parts of this word actually come from the Greek.

The first one, chromato, means colour, and the second one, graphy, comes from the Greek graphene, which means to write.

Now, the reason this word was used to describe this particular technique is because it has originally used to help separate out the different parts of the coloured substances in plants.

And an example of the chromatography that was developed in those early stages of using it is shown in the picture on the right here, and we can see that it looks like somebody trying to write using different colours.

Now the great thing about chromatography and what makes it particularly useful is that you can actually conduct this particular separation technique and test using really small samples of a substance.

So you could use it to analyse different inks in pens, you could use it to detect maybe perhaps different drugs, or you could even use it in identifying different debris, things like that.

So in terms of different types of techniques, this would also be called perhaps forensic separation, 'cause we're gonna be using incredibly small samples to separate.

Now there are lots of different types of chromatography that a scientist could use.

There's paper, thin layer, column, gas chromatography, and most of those, you wouldn't look at until after you've left school, but all of these different kind of chromatopgraphies use a very similar method.

The first step is that you take a sample and you place it in or on a particular medium, and that medium tends to be absorbent.

The second step then, is that a solvent is applied, and what that will do is help to dissolve the sample, and so you're creating a solution on that medium of the solvent and the sample you put on it.

And then finally, as that solution is absorbed along that medium, the different parts of the sample could become separated and then more visible.

So an example here, we can see that there's the sample of the sweet and then the adding of the solvent dripping water onto it, we can see that it's creating that solution, being pulled apart, and you can see that some of that sweet candy layer on the outside has been left behind.

Now the pattern then, that forms as a result of chromatography is called a chromatogram.

It's the bit that's left over.

So if we take that dripping water onto a sweet that's on the left, and then you leave that solvent to spread across the medium of that absorbent paper, and then leave that to dry a little bit, what you're left with is a picture on the right of that chromatogram.

Now the thing with chromatography is that in a substance, in that sample, the more soluble a substance is within that particular sample and in that solvent that was used, the further away from the sample source it's going to travel.

So if we look at this example of a chromatogram that was shown earlier, the sample source is the exact centre, the darkest part of that particular chromatogram, and we can see that the less soluble substances then stay close to the centre, and then the more soluble substances have managed to travel further away from that sample source.

Moreover, if a substance in a sample, or even the sample itself, is not soluble or is insoluble in the solvent that was used, it's not going to move from that sample source.

So if we look at these examples on the bottom here, we can see that the sample source has been marked with an X, so we can see that kind of shows us where that sample was placed originally.

And at the picture on the left, we can see that some colour has moved away from it, and so we can see that that contains soluble substances in that solvent.

Whereas on the right, there's no movement, there's no colours that have been separated, and so we could say that that particular sample was insoluble in that solvent.

Let's pause here for a quick check.

For which of the following do you think chromatography is a useful technique? You may wish to pause the video here and come back when you're ready to check your answer.

Well done if you said C, chromatography would be very useful to identify debris found on a shoe.

Separating sand from water, I would say probably filtration is better as a separation technique, because the sand is insoluble.

And then crystallising sugar from a solution, better to apply heat and crystallise it rather than using chromatography.

But well done if you managed to choose C.

Let's try another quick check.

Which chromatogram contains an insoluble sample? So which of the letters at the bottom do you think represents an insoluble sample? And crucially, I want you to try to explain your answer.

So I'm looking for a "because" clause in your answer.

So you might want to have a little chat with the people nearest you, jot down your answer.

So pause the video here, and then come back when you're ready to check your work.

Right, let's see how you got on.

So I would've said chromatogram A is the insoluble sample, and the reason is because sample A's spot has not moved from that sample source from the X or that start line, there's nothing above it, there's no colours vertically above it, and therefore chromatogram A is insoluble.

Well done if you managed to get that.

Let's move on to our first task.

Now, Izzy has created a chromatogram by dripping some solvent onto her absorbent paper, and this is the pattern that has formed.

What she'd like you to do is help her to label the different parts of that chromatogram using the terms that are in the bullet points on the left.

What I'd like you to also do is explain why you've placed the labels where you have, so I'm looking for a "because" clause in your answer.

So you'll want 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, whenever I'm looking at a chromatogram, I always like to start at the sample source, so that's the first thing that I'm going to try to label.

And the sample source is essentially where that X is, or where the spot has been placed, so the very centre of our chromatogram here, is going to be the sample source.

The insoluble part of our sample then, is going to be the spot that is left on that X.

It has not managed to move away from where that X is and therefore, is indicating that it's insoluble.

Okay? Now, the less soluble bits could be either the yellow or thinner green circles that form around that sample source, and that's because it's simply moved away from the sample source, but it's still close to it, so either of those would work.

The most soluble then, part of our chromatogram is that thicker purple circle that is formed the furthest from that sample, and that's why it's the most soluble, because it has moved the furthest away from the sample source.

Now that was a tricky one to do.

What I would say is definitely give yourself a great pat on the back if you managed to label them correctly, and give yourself a massive round of applause if you've managed to get the "because" clauses, the explanations for why you've labelled them as you have, correct.

Tricky task, very well done for a first one.

Great job.

Now that we're feeling a little more confident talking about the basics of chromatography, let's look at the specifics of how it's carried out.

Now, chromatography is one of those practicals that you can do very easily at home as well as in the laboratory, but you're going to need some very specific pieces of equipment in order to do so.

So the first thing you need is a container with a very small volume of solvent in it.

So here we've got a glass and the solvent could be water, but in a school, you might use a beaker of some sort.

You'll obviously need the sample that you're using.

I have here some food colouring, but you could use some coloured markers, or pens, or something like that.

You'd need some form of absorbent paper.

Now kitchen roll might work, or loo roll, a little bit.

I've found actually, coffee filter paper is particularly useful here if you're doing this at home, as an absorbent paper, it's just been cut down to a thin strip there.

Then you're going to need some kind of implement to add the sample to your absorbent paper.

Now that's particularly important if you're using a sample in another container, like say a bottle of ink or this food colouring for instance.

Now here we've got a toothpick, but you could use a very thin paintbrush or something like that would work.

Then you're gonna need a ruler, and then you'll also need a pencil.

So the first thing you need to do then, is you're going to use your pencil and your ruler, and you're going to draw a straight line about one to two centimetres from one end of your absorbent strip of paper.

And then in the centre of that line, you want to draw an X, and that then is your sample source, it's where you're going to be placing your sample.

Now the key here is that it does need to be done in pencil, and that's because pencil tends to be insoluble in most solvents.

And so by using pencil there, any kind of separation that takes place on this absorbent medium is not going to affect the overall chromatogram or pattern that develops as chromatography takes place.

The next thing you're going to do then, is you're going to add a very, very small amount of your sample to the centre of that X.

So here you can see that I have my food colouring and my toothpick at the ready, and by dipping that toothpick into the sample and very gently tapping it against the middle of the X, you can see that a spot starts to develop.

If you're using a marker or a pen, you could simply blot it with the tip of your marker or pen.

But there is a key here, you want to make sure that you are keeping the spot of your sample to less than one centimetre wide.

And a good way of doing this is by simply tapping it once and letting the sample that's been put onto that X dry, and then come back and add another drop onto it.

So what you're doing is concentrating the sample that you're putting onto that X.

Now it's really important that X is kept.

Not the X, sorry, that the spot that you are making stays small, because if it does get too large, it could make your chromatogram that develops really muddled, and that would make it quite difficult to interpret.

So the key here is less is more.

Keep that sample nice and small so you get better results afterwards.

So this next step then, is a little fiddly.

What you're going to need to do is to fasten this paper that you've created to a support of some sort.

Now here I've used a splint that you might have in the lab, and then simply a paperclip to hold it in place.

The key here, is the support needs to be wide enough and secure enough to be able to support the paper in hanging vertically in the container that you're using, a beaker, or a glass, or whatever.

So I've in the past, used something as simple as a spoon or a fork.

I've even used a paintbrush to hold it across.

So as long as it holds it nice and still, that will work.

The next thing you're gonna do then, is you're gonna add a small volume of solvent to that container, the beaker or the glass that you're using.

And again, the key here is less is more, we want a very, very small amount, because the next thing you're going to do is you're going to gently lower the paper into the solvent.

And you can see here, that the support now is resting along the top of that container.

Now you need to be very careful as you put the paper into the solvent, because what we want to do is make sure that that solvent stays below the pencil line, and more than that, that it's staying below the sample spot.

And the reason is if the sample spot goes into the solvent, that sample could go and dissolve into the solvent rather than the solvent coming up the paper, creating the solution as it gets absorbed the paper, and then pulling that sample apart as it goes up it.

So it's really important, the placement of the paper in the solvent, so go slowly.

And then what you need to do is just really, really patiently wait for that chromatogram to develop.

So what we've got here then, is an image of a chromatogram actually developing.

And you'll notice that the spot was put on an X, and that it is being pulled apart.

You can just about make out that solvent being pulled up the absorbent paper, and those colours of the sample being pulled apart.

But again, remember, it's really, really important that that sample spot is kept above the solvent that's in that container.

And this, as I said, is gonna need to be a lot of patience.

This image that you're seeing was sped up 10 times the time it took to actually show it to you.

So it's quite fun to watch it, but you do need to have quite a lot of patience.

Let's take a moment now for a quick check.

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

Absolutely not.

We're not gonna be using pen because it tends to be made of ink, and that could potentially separate out with our solvent, and it might dissolve into it, so it can muddle our chromatogram.

We should always be using pencil, not pen.

And to be fair, one of those rub out pens will not do, just stick with the pencil.

Borrow one if you need to.

Let's try another one now.

True or false, the larger the sample spot, the clearer the chromatogram produced? Well done if you said false, but which of these statements best supports your answer? Well done if you said A, a sample spot should be limited to one centimetre wide, not a minimum of one centimetre wide.

If it gets bigger than one centimetre wide, it's gonna be difficult and they might start to mix together if you have more than one sample on your absorbent paper.

So well done if you managed to get that correct.

Okay, let's move on to our next task.

You can see here, that we have a chromatography set up that's been labelled, but there are a few errors in it.

I'm wondering, can you find what the errors are? And how might you fix those errors? So pause the video here and then come back when you're ready to check your answers.

Okay, let's see how you got on.

So one of the areas that I noticed is that the sample spot is actually resting below the solvent line.

It is resting in the solvent.

So one of the things we could do to fix that is to just move that paper up a little bit on our support so that it doesn't dip into the solvent.

Just raise it up a little bit.

And for something like this where it's actually resting on a splint, you could probably just fold it over and reattach that paperclip.

The other error that I found was that the line has been drawn in pen.

So what we need to do to fix that then, is simply to swap out the pen and use pencil instead.

Well done if you managed to identify the errors, and very well done if you've managed to suggest how to fix them.

Great job, guys.

Now for the second part of this task, I'd like you to help Laura.

She's curious about the different food colorings and whether or not they might be pure or a mixture.

So what I'd like you to do is to work in small groups to use what we've learnt in this last learning cycle, to create a chromatogram for each of the following food colours, so blue, red, green, and yellow.

You may find it useful to work in a big group and then each pair does one colour, or you could work in a group of four and each person does one colour, and then you can share your results at the end.

So pause the video here, and come back, and we can see if your chromatograms match mine.

Let's see how you got on.

Now these are the chromatograms that I managed to create using the food colorings that I had in my cupboard.

Now, the brand that I used and this amount that I've put on as my samples may have a result of a different chromatogram than what you see.

But what we can see here is that I've used my pencil, I've drawn my straight line about a centimetre to two centimetres above the bottom of my absorbent paper.

I've obviously put a sample spot on.

The yellow sample was really hard to keep that sample spot small.

It was just a very drippy liquid.

So some of them were.

Maybe turned out a little bit better than others.

So the quality of your chromatogram will come down to the care that you take when you are putting together that absorbent paper.

So very well done though, if you've managed to create a chromatogram for any of these dyes.

Well done, guys.

So we know how chromatography works, and we know how to set it up to actually create a chromatogram, let's move on to now looking at how we can interpret what the chromatogram tells us about those samples.

Now, the most basic analysis of a chromatogram can tell us whether or not our sample is simply pure or a mixture.

A pure sample tends to show us only one spot or one colour, where a mixture will tell us multiple spots or show us multiple colours.

So let's have a look and see how you can interpret these chromatograms. Which one or ones do you think indicate that a mixture was present in this sample? Well done if you said A, we can clearly see two colours, green and yellow, so we definitely have a mixture here.

You may have also said B, because we can see an incredibly dark blue towards the centre, and a far lighter blue on the outside.

Now you might think that that makes it a pure substance, but the blues are separating where the dark is staying quite central in that circle towards the centre, which makes me think that we have two different blue colours, and therefore a mixture of two different blue dyes.

C just shows us the one yellow, and therefore it is a pure chromatogram sample.

Well done.

So besides telling us whether or not one of our samples is pure or a mixture, chromatograms can also help us to identify an unknown substance in our sample.

Now what you need to do for that is you need to compare a chromatogram of your unknown sample against chromatograms of known samples.

And we can see here, on the right in our example, that the unknown sample is labelled with a question mark.

So when you're comparing these chromatograms, you're looking for similarities.

And if those chromatograms match, then the substances in those samples are the same.

So again, looking at our example on the right, because the chromatogram for the question mark and the one for A look almost identical, we could say that they are the same substance.

Now more often than not, multiple chromatograms are being formed on the same absorbent medium.

So you're gonna have quite a few different things to compare and it can get a little muddled.

So there are two main ways that we might want to interpret a chromatogram, vertically or horizontally.

If we interpret a chromatogram vertically, we're deciding whether or not that sample is pure or a mixture.

And what I would recommend then, is to get that pencil and ruler out again, and start to draw lines vertically from that X.

And what you're doing then, is it's just helping you to make that analysis a little bit easier, a little bit faster for you.

So you're not having to try and think of things, you can just follow the line.

Now, if you have one spot on that vertical line, then your sample is pure.

So in this example here on the right, we could say that samples B and D are pure because they only have one spot on those lines.

If you have multiple spots on your line, then your sample is a mixture.

And again, looking at our sample on the right, we could say then that samples A, C, and our unknown as a question mark, are mixtures because they all contain multiple spots on those vertical pencil lines that we've drawn.

If you then move to interpret your chromatogram horizontally, that's when you start to compare one against the other.

So one way to do this is to actually identify substances that might be found within a mixture.

So if we compare just samples A, B, and C on my example here on the right, I'm going to draw my pencil lines again, to help with analysis, horizontally, and then what I'm going to do is compare those spots that might be on those particular horizontal lines.

And by doing that, I can say that sample A is a mixture of samples B and C, and that's because the spots match almost exactly for the spots that I see in samples B and C.

Now, interpreting a chromatogram horizontally can also help us to find an unknown sample.

So again, drawing my pencil lines all the way across and comparing all of these samples, I could say that because my question mark unknown sample does not contain a red dot, then samples A and B are not found in my unknown.

But when I compare the lines for samples C and D, they do match up with those spots that are found in my unknown, and therefore those substances are most likely going to be in my unknown sample.

Now the thing I want to highlight here, is you'll notice that these lines I've drawn to aid my analysis have been drawn in pencil.

So once I've drawn them vertically and I've answered the questions about whether or not a substance is pure or a mixture, I can easily rub them out and then draw my horizontal lines to help with my comparison.

The beauty of pencil.

Let's pause here for a quick check about chromatograms. What information about a sample can actually be found on a chromatogram? Why don't you pause the video here, have a quick chat, and come back to check your work? Well done if you said all of them, you'd be exactly right, as a chromatogram can tell us a lot of information, and that's one of the reasons why chromatography is such a useful separation technique.

It's just not the fact that it can tell us if it's pure or a mixture, but the analysis and the amount of information we can get from the product of chromatography makes it incredibly useful technique to use.

Okay, let's move on to our last task of the day.

What I'd like you to do for this first part is to use the chromatogram to answer these questions, but don't forget to justify your answers.

So the first one I'd like you to tell me, which sample contains an insoluble substance and why you think that.

And then I'd like you to tell me which sample contains the most soluble substance, and again, tell me why you think that.

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 part A, the substance that contains an insoluble substance is going to be sample B, and that's because the spot has not moved from the start line or its sample spot source.

It is stayed where it is, it's not moved from that line.

For B, which sample contains the most soluble substance? We're looking for a spot that is the highest up, so that's sample A.

And then my justification is because it's the highest spot or the spot that has moved the most from that start line or the spot source.

So well done if you are able to choose the correct samples for each of those answers, and even better well done and huge congratulations if you managed to justify your answers correctly.

Good job, guys.

Great start.

Now for this next part of the task, it's gonna be a little bit trickier 'cause we don't have any coloured spots.

You're gonna have to use your analysis techniques that we talked about before.

So for this particular one, I'd like you to tell me which substances are pure, which are mixtures, and to explain your choices.

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

Okay, let's see how you got on.

So what I would do, first of all, is to draw my pencil lines and they need to be vertically drawn 'cause we're deciding which are pure and which are mixtures, so we need to know how many different substances are in each sample.

And by doing that, I can decide that the pure samples is simply sample A, and that's the only one because it's the only sample that has just one spot.

The other two then, samples B and C, will be mixtures, and that's because they both contain more than one spot, so multiple spots.

Well done if you've managed to correctly identify the pure and mixture samples, and even better if you've managed to explain your choices correctly.

You're on a roll, guys.

Let's see what you can do with the next one.

So for this next part of the task, I'd like you to now compare the chromatograms to the colours found in samples A, B, and C.

So we're increasing the difficulty of our chromatogram interpretation, but I know you guys can do this.

Just pause the video, take it nice and slow, chat with your neighbour, and then come back when you are ready to check your answers.

Okay, let's see how you got on with this more complicated comparison.

So just like last time, I'm going to draw my pencil lines to make it a little bit easier to compare, because we're comparing one sample against another, they have to be horizontally drawn.

And when I do that, looking at samples A, B, and C, I can see that sample A, because it only has one spot, contains just blue.

Sample B has two spots, and those spots match up with the blue and the red coloured ones.

And then sample C then, looking at those two spots, I should have two colours, and therefore it is red and yellow that is found in that particular sample.

So very, very well done if you've managed to correctly identify at least one of the colours in each of the samples, and even better if you've managed to identify the second colour in both B and C.

Okay, final part of our last task of today, what I'd like you to do is go back to the chromatograms that you produced in Task B, part 2, of those different food colorings, and I'd like you to identify any similarities that you can between them.

So if you don't have your own chromatograms, you can use the ones that I have shown here.

But ideally, you want to go back to the chromatograms that you have actually compared.

Now what I would suggest you do with those different chromatograms is what I've shown you in the picture below, and that even though the paper strips are different sizes, what I've tried to do is line up those pencil lines, the start lines, so that the comparison is a little bit easier to do.

So my recommendation is to line up the pencil lines and then do your comparisons.

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

Okay, let's see how you got on.

So what you might be able to see when you compare the red and the blue is that they don't seem to have any similarities with the other samples when you look across.

You might be able to start to see a comparison between the red and the yellow at the top, but it's not clear there.

So I would argue that there aren't any similarities between the red and the blue, the green and the yellow.

The green looks like it may contain some yellow dye in it because we've got some matching up towards the bottom of the spot there, between the green and the yellow.

And then the yellow, we're not quite sure if it, we could say it matches part of the green, but you could also say here, that it's potentially a pure substance.

Now that's looking at just the chromatogram of the image that I'm showing you, your chromatograms might be slightly different, so always go by the chromatograms that you are using in front of you on this.

Now that was a really, really tricky task.

I hope you guys had a good time creating the chromatograms and are feeling very accomplished having interpreted them in the first place, because that's not an easy task and you've been working supremely well.

Very well done.

Now, we've gone through a lot of things in today's lesson, so let's summarise what we've managed to learn.

So we've learned that chromatography is a technique that can be used for the separation of very small samples, but also the analysis of the results that form from it.

We've also found that there are many inks that are soluble in water, and because of that, pencil is used because it's insoluble in water.

So when we're preparing our chromatogram, we use pencil.

We also learned that the more soluble a substance is in the solvent that we are using, the further it will travel from that sample source.

The resulting pattern then, that forms when we've added that solvent to our prepared chromatogram medium is called a chromatogram, okay? So the pattern that forms is that chromatogram.

And on a chromatogram, a pure substance will show one spot, while a mixture might show many spots or many colours.

And when you compare those chromatograms from one to the other, you might be able to identify an unknown in a sample, or be able to identify different parts of a mixture.

I've had a fantastic time learning with me today, I hope you did too, and I hope to see you again here soon.