Hello, my name's Mrs. Niven.

and today we're going to be talking about saturated solutions as part of our topic on solutions.

You may have come across this idea of saturation in some of your previous learning or even some of your experiences outside of the classroom, but what we learn in today's lesson will help us not only answer that big question of how can we explain how substances behave, but also help us as we journey through science further and think about how we can separate substances from within a solution.

So by the end of today's lesson, I hope you'll be able to feel more comfortable comparing data involving the solubility of different solutes and also be able to use that data to describe this idea of saturation.

Throughout the lesson, we'll be using a variety of keywords including solubility, saturated solution, and line of best fit.

Now, the definitions for these keywords are given in sentence form on the next slide, and you may wish to pause the video here to read through them, and perhaps jot a quick note about what each means so you can refer back to it later in the lesson.

Today's lesson will be looking at two main things.

Firstly, what a saturated solution is, and secondly, how we can compare solubility.

So let's get started by looking at what we mean when we say we have a saturated solution.

Now, the word saturated is used to describe a lot of different things, and probably a lot of experiences that you've had as well.

For instance, we might say that a sponge is saturated or that the ground is saturated.

In fact, those of you who play any field sports will probably be very familiar with the saturated ground because a lot of fixtures tend to be cancelled because the ground is so wet and saturated.

You may have also experienced a saturated atmosphere.

When that happens, we tend to get a lot of precipitation, things like rain and snow, and you can see in here the rain in the distance from this saturated atmosphere.

What saturated actually means in all of these instances is that something is full, it's holding as much as it can.

So our sponge is holding as much of the soapy water that it can.

The ground is holding as much of the water that it possibly can, and the atmosphere as well.

And because it can't hold anymore, some of that precipitation in the atmosphere tends to fall out.

It's just full.

Now, before we move on to describe what we mean by a saturated solution, we need to just remind ourselves what's actually happening when a solution is formed in the first place.

If we recall, there needs to be an attraction between the solute and solvent particles that is strong enough to overcome that force of attraction between the solute particles themselves.

So when we are putting this salt into our solvent of water, the attraction between the water particles and the salt particles is so strong that it's able to rip apart and overcome those forces of of attraction between the particles in the salt itself.

And when that happens, we say that it's dissolved and our solution is formed.

Now, in order for that to happen, there needs to actually be enough solvent particles available to create those forces of attraction between the solute and solvent particles.

If we wanted to increase the solubility of the solute, so, really make sure that more solute particles could dissolve, we could do a few things.

We could increase the volume of the solvent that's used as shown here, and what that does is it increases the number of solvent particles available to surround those solute particles as they enter the solvent, and also that will result in more forces of attraction that can then develop between the solvent and solute particles, allowing for that dissolving to take place.

Now, if we don't have any more solvent to hand, another way that we could increase the solubility is to increase the temperature of the solvent that we're using.

If we imagine that the previous solvent that we used in the example was at room temperature, so around 20 to 25 degrees centigrade, we could warm that up to A higher temperature and potentially be able to dissolve a little bit more solute than we would've previously.

Because when we warm up the solvent, what we're doing is we're providing more energy to those solvent particles, and that allows them to overcome those forces of attraction between the solute that allows it to break apart a little bit more easily and dissolve better.

Now, that is true for most substances.

But for complex reasons, there are some substances that the higher the temperature is, the solubility actually decreases.

But we're not gonna go into that just here.

In general, we might say that as the temperature increases, solubility will increase as well, but not always.

So if we bring all of these ideas together, we could say that a saturated solution is one in which no more solute can dissolve in a solvent at a particular temperature.

And there's a few reasons for this.

One might be that there's simply not enough solvent particles available to create that force of attraction that's necessary between the solvent and solute particles to help it dissolve.

Another reason might be that there's simply not enough energy available to overcome those forces of attraction between the solute particles to help it dissolve.

So in effect, a saturated solution is simply full.

The solvent is full and can hold no more solute in it.

Believe it or not, you've probably come across saturated solutions in nature, either in person or by watching films or TV programmes.

For instance, honeycomb contains the saturated solution of honey.

Another example would be some rather shallow lakes or salt pans.

This salt lake found in Chile, you can just about see on the edges of that picture, actually contains salt crystals.

Other saturated solutions could even just be made either in the lab or at home.

If you were to dissolve some sugar and water, it could be processed in one way to make what was an early sweet called rock candy or could be processed in another way to create some sponge sugar decorations for baked goods.

Let's take a moment for a quick check to see how you're getting on.

Which two of the following will usually increase the solubility of a solute in a solvent? Pause the video here and come back when you're ready to check your answers.

Well done if you said B and D.

So either increasing the volume of the solvent or creating a higher temperature of that solution or solvent will both help to increase more of our solute, and therefore increase the solubility of it.

Well done if you managed to get that.

Now, we said earlier that if we were to change the temperature of our solvent, we'd be able to create a solution a little bit faster because it's allowing for faster dissolving, but actually increasing the temperature might also allow for more solute to dissolve.

For instance, if you wanted to make a chocolate milk drink, you could add some cocoa powder to some milk, stir it together, and you'd be able to have your nice drink.

But if you were able to warm up that milk, you might actually be able to get more of that cocoa powder to dissolve, creating a more chocolatey drink.

So in essence, a saturated solution can be made in one of two ways.

It can either heat the solution to allow for more of the solute to dissolve, or you might remove some of that solvent possibly by heating it as well.

A really good example of this would be collecting maple syrup sap.

Maple syrup sap is a roundabout 98% water, so this can actually be processed.

So this is creating a saturated solution by removing that solvent by boiling, and we end up with this lovely syrup that we can use in our pancakes that tastes a little bit of maple.

Another example of this would be found in very shallow lakes or in salt pans where they're able to collect the solution of salt water, and then, again, this is processed usually by removing the solvent, and this time through evaporation.

And then you're ended up with this sea salt that can then be collected and possibly sold on or used.

So when a saturated solution starts to cool down, we can actually see evidence of that saturation because those solute particles that we're able to dissolve because of that increase in temperature, because that extra energy available to overcome those forces of attraction, it's no longer there.

The solution is cooled.

So those particles that could have dissolve can no longer stay dissolved, and we can see evidence of that.

One of the things you might see is the solute collecting at the bottom of a container.

So if you've ever made a hot drink using that cocoa powder and you've left it to cool, you might actually see this chocolatey sludge collect at the bottom of your cup.

The same thing could be said if you've made a cup of tea.

Sometimes you might see little bits at the bottom there.

Another thing you might find is crystals forming.

So if you take a sugar solution and leave it to cool for a little bit, and this is a saturated solution, then you start to see crystals forming.

A really good example of this is if you have a jar of maple syrup and perhaps you save it and keep it in the refrigerator.

You might find crystals forming on the neck of that container.

Another example would be a jar of honey.

If you leave it in your cupboard in the winter months when the house might be a little bit colder, you might find crystals forming in the bottom of the jar.

Time for a quick check.

True or false, a saturated solution can only hold a certain mass of solute.

Well done if you said false.

But what's the reason why? Pause the video here and come back when you're ready to check your answer.

Well done if you said A, how much solute can dissolve in a solvent depends on the temperature and the volume of the solvent.

It will also depend on the solvent used, but that's not the only condition.

We also need to consider how much of the solvent we're using and the temperature that it's at.

Well done.

Time for our first task in today's lesson.

"Jacob is in a timed baking competition and he wants to make some sponge sugar decorations for his cupcakes.

He knows he needs to make a saturated sugar solution and he is going to use 250 grammes of sugar and 225 centimetres cube of water." Now, Jacob has dissolved a little of the sugar at a time, but he observes something that suggests his solution has become saturated after adding only 200 of his 250 grammes of sugar.

What has he observed and why has he observed that? And then what I'd like you to do is suggest one way in which Jacob could make more sugar dissolve in his solution and describe why that might help.

Pause the video here and come back when you're ready to check your work.

Okay, let's see how you got on.

So in the first instance, Jacob was dissolving some sugar and he noticed that he couldn't get all of it to dissolve and had stopped.

And we asked you what you think he might've observed and why he saw that.

And a really good answer would be suggesting that some of those sugar crystals were maybe collecting at the bottom of the pan, and that's because they're no longer dissolving.

At that particular temperature, nothing more can dissolve.

So we asked you to suggest a way in which Jacob might be able to increase the amount of sugar he can dissolve in that solution and describe why that suggestion might help him.

And one of the easiest ways to do this would probably be to change the temperature solution by heating it.

Cooling it down won't make much of a difference.

We do really need to heat it at this point, and that's because when you heat that solvent, you're providing more energy to the solvent particles, and that means that they are going to more easily overcome those forces of attraction that exist between the solute or sugar particles to create that solution.

Well done on a tricky task.

Now that we're feeling a little more comfortable defining what a saturated solution actually is, let's look at how we can compare saturation.

Now, we said earlier that a saturated solution is a solution in which you can't get any more solute to dissolve in a solvent at a particular temperature.

And the key to comparing saturation is in this definition: at a particular temperature.

That means that at any given temperature, there is a limit to how much solute you can actually dissolve in a solvent.

You could get that milk to the highest temperature possible before it starts to burn and still not be able to dissolve any more hot cocoa powder into it because there is a limit to that saturation.

So to find out at what mass of solute a solution becomes saturated at a particular temperature, scientists use what's known as a solubility curve, and it looks a little bit like this.

And it has two of the most important pieces of information we need when we're talking about solubility.

It talks about the temperature and it also looks at the mass of solute that will dissolve in a particular volume of a particular solvent.

Now, a solubility curve is simply a line of best fit that's been drawn on a scatter graph of collected solubility data.

And if you remember, a line of best fit shows the relationship between two variables.

And in this case, the variables are temperature and the mass of the solute.

Now because of that, we can use this line of best fit to suggest a value for an unknown.

Let's look at an example.

So if I use this particular graph and this particular solubility data, I could try and answer this question of what maximum mass of sugar will dissolve at 100 centimetres cubed at 75 degrees centigrade? And if I look at the plots on my graph, I can see that at 75 degrees centigrade, there is no plotted data, so this is what I need to use my line of best fit.

What I'll do is look at 75 degrees centigrade.

I'll draw a line from that 75 point up until it hits that line of best fit.

At this point, I'm going to draw backwards to my y-axis which tells me the mass of sugar, and this is going to be the maximum mass of sugar that will dissolve.

And from there, I can read off the y-axis that at this point, looking at the resolution or the scales on my y-axis that this line here is hit at 350 grammes.

Let's look at another example.

Now, I'm using the exact same solubility data that is presented here, but this time I want to know at what temperature no more than 275 grammes of sugar will dissolve in 100 centimetres cubed of water.

So I'm gonna do a slightly similar but different way of using my line of best fit.

Okay, at this time, I'm gonna start on the y-axis at 275 grammes and draw a line out to my line of best fit.

At this point, where it hits that line of best fit, I'll draw a line downwards to my x-axis to find the temperature at which that mass of sugar will be able to dissolve.

And when I read the scale and the resolution on my x-axis, I can say that at 55 degrees centigrade is when I'll be able to dissolve 275 grammes of sugar, but no more.

Time for a quick check to see how you're getting on interpreting solubility curves.

What I'd like you to do is to use the information here to tell me what is the maximum mass of sugar that will dissolve in 100 centimetres cubed of water at 25 degrees centigrade.

Pause the video here and come back when you're ready to check your answer.

So if we go through the answer and how to find it then, I'll see that I need to find the mass at 25 degrees centigrade.

So I'll look at my graph and draw a line up to where it hits the line of best fit, then I'll draw a line to the y-axis to find the maximum mass of sugar.

And I can see the line hits just slightly above that 200 gramme mark.

And because of that, I'm going to suggest that around 205 grammes of sugar is the maximum that might dissolve, and there's usually a plus or minus.

So there is some wiggle room as it were in terms of suggesting the answer to this particular question.

Well done if you got a little over 200 grammes.

Good job.

Let's try another check.

This time, what I'd like you to do is tell me at what temperature will no more than 400 grammes of sugar dissolve in 100 centimetres cubed of water.

Again, pause the video and come back when you're ready to check your answer.

We're going to use the solubility curve in a similar way, but this time, because we're are given the information of 400 grammes, we're gonna start from the y-axis and draw our line out to the line of best fit.

And then from where it hits that line, we're going to draw a vertical line down to my x-axis to find the temperature.

And I can see that it hits ever so slightly above that 85 mark, and therefore I'm gonna suggest a temperature of about 86 degrees, plus or minus a few degrees.

Again, you can see that there's a little bit of wiggle room, so don't think that just because you don't get an exact answer, that you're not close to it.

So always, always, always have a go and see what you can come up with.

If it's close, you're on the right track.

So well done.

It's not easy interpreting these curves in the first instance.

Now, once solubility data has been collected for several different solutes, what we tend to do is to plot that data on the same graph.

And that's because by putting it all in the same graph, we're able to allow for a little bit better comparison of these saturated solutions.

A lot of really useful information can be found on solubility curves that are plotted on the same graph, but you need to take a lot of care to make sure that you're interpreting it correctly.

And the key here is using that key of data or the legend.

So for this particular solubility curve, I'm going to look at the colour and the shape of the plotting.

So the colour of that line of best fit and also the shape of the plotting points.

So using that information, I might want to decide what solute has been most soluble over that temperature range of zero to 100 degrees centigrade.

And looking at this, I can compare from the start to the finish, from zero to 100 degrees, and see that the blue line with the blue circles has been the most soluble, that means it's dissolved the most solute, and therefore my answer is going to be lead nitrate.

Another question might be, which solute is least soluble at five degrees centigrade? So I'm going to look at my graph and find the five degrees section.

And when I compare those lines, I can see that the least soluble is going to be the lowest line because that has dissolved the smallest mass of my solute.

And that is the pink line, and those have the pink plots.

So again, using my key of data or the legend, I can see that the least soluble solute here is the aluminium sulphate.

Time for you to have a go at trying to compare saturation on the same solubility graph.

For this, I'd like you to tell me which solute requires less than 50 grammes to create a saturated solution at 100 degrees centigrade.

Pause the video here and come back when you're ready to check your answer.

So the first thing you might want to do here is to, again, decide we're looking at 100 degrees centigrade.

So I'm going to look at this area of my graph.

The other thing I need to remember is that I've been asked to find less than 50 grammes.

So I would read across from my y-axis where the 50 gramme mark is, and I can see that there's only one of my solutes that will dissolve less than 50 grammes to become saturated, and that is the green line or the diamond plotted points, and therefore my answer is gonna be sodium chloride.

Well done if you manage to get that answer.

Time for the last task in today's lesson.

For this first part, I'd like you to use this solubility graph to answer the questions about the saturated solutions plotted on it.

In the first part, I'd like you to put these solutes in order from the least to the most soluble at 20 degrees centigrade.

Pause the video and come back when you're ready to check your answer.

Let's see how you got on.

So the question was for you to put the solute in order from the least to most soluble at 20 degrees centigrade.

So looking at the graph, you need to focus in your or get some tunnel vision on that 20 degree centigrade lines of best fit.

And when we look at that, we need to remember we're going from the least soluble to the most.

And the least soluble is able to dissolve the smallest mass, and therefore we're going to be reading our graph from the bottom upwards.

So starting with the blue line with the circle plots, we've got potassium bromate, then a hydrogen chloride, then a magnesium bromide, and potassium hydroxide.

So well done if you got those in the correct order.

You may have accidentally put these orders in reverse 'cause you read your graph from top to bottom.

So it's really important that we remembered that the least soluble has the smallest mass.

I sometimes find when I have a lot of information, I just kind of annotate the question.

So I might have highlighted the word least in the question and just put a little line next to it that said "smallest mass," just to give me a little bit of guidance in terms of how I'm reading this graph.

When we try and keep all that information in our head, it can get a little bit muddled.

So if you put it down on a piece of paper, it's a little bit easier to keep track of and gives you a reference point later on.

So well done if you managed to get that correct.

Moving on, I'd like you to use, again, the same solubility graph, but this time I'd like you to tell me what mass of hydrogen chloride is needed to make a saturated solution at 45 degrees centigrade.

Pause the video here and come back when you're ready to check your answer.

Let's see how you got on.

So the question was asking you about hydrogen chloride.

So the first thing I need to do is double check my key of data or my legend to make sure that I'm looking at the correct line of best fit to answer that question of what mass is needed to make a saturated solution at 45 degrees centigrade.

So for this one, I'm gonna be looking at the purple line with the crosses as my plotting points and drawing a lineup to that purple line from the 45 degree centigrade, I can see where it hits that line of best fit.

Then I'll draw a line back to that y-axis and see where it hits the y-axis there.

And I could say that roundabout 60 grammes of mass will be needed of my hydrogen chloride to create a saturated solution.

It's really important here that you're double checking the scales have been used on your graph so that you don't get complacent and just assume that you know what those smaller boxes mean.

So take a moment and just double check those whenever you're writing down your answers.

Some of you may have said 55 rather than 60 because you were used to reading previous graphs in a particular way.

So just take a little bit of care.

But very well done if you manage to get that right.

For this last task, we're gonna bring everything together that we've learned about solutions, saturations, and the skills along the way to finish this task.

What I'd like you to do is use the table of results to draw a graph of solubility.

Now, you'll notice here that we have two different substances that have dissolved here, so you might want to use two different coloured pencils going forward as you do this.

What I might recommend as well, just to help you keep things straight, is if you lie a strip of paper over the data that you're not plotting, so you're only looking at one thing at a time, that might help you to keep things a little bit clear as you draw your graph.

But remember, always use pencil, so if you do go wrong, you can easily fix those mistakes.

Once you've created your graph of solubility or your solubility curves, I want you to use your graph to answer the following questions.

What mass of lithium chloride will dissolve at 30 degrees centigrade and at what temperature will 85 grammes of iron II chloride dissolve? This might take a little bit of time, so definitely pause the video here and come back when you're ready to check your answers.

Okay, let's see how you got on.

Now, that graph was a little tricky to draw, but what we'd be looking for first of all is that we have the axis labelled correctly.

So we should have the temperature and degrees centigrade on the x-axis at the bottom, and then the mass that will dissolve in 100 centimetres cubed of water, and that's in grammes as our label for the y-axis along the side.

The next thing I'd be looking for is that the scales for each of these axes are going up in regular numbers.

So along the x-axis, they're going up by 25 on those larger numbers.

And then we can see on the y-axis that they're going up by twenties.

So, 40, 60, 80, 100.

The next thing I'm looking for then is for your plots to be correct so that you've put your symbols representing each set of data correctly on there.

So you can see that the iron II chloride has been given the green line and the Xs for the plotting points.

And then the lithium chloride.

I've used a pink pencil and we've got triangles for our plotting points here, and then a line of best fit that follows there.

It's really important when you're doing this that you include a key.

Don't just randomly use two different colours and not tell me which is which.

Alternatively, you could actually label the lines of best fit as well if you didn't have different colours.

So well done if you managed to draw the graph correctly.

That was not an easy thing to do.

But the key for these was not just the plotting points, it was drawing in those lines of best fit because that's what you need in order to answer the follow-up questions.

And the first of those follow-up questions was, "What mass of lithium chloride will dissolve at 30 degrees centigrade?" So first of all, I can see that my lithium chloride is the pink line with the triangle plots.

So I'll find 30 degrees there and draw a line back to the mass.

And when I do that, I should have about 85 grammes is the answer there, give or take a few grammes.

And the second follow-up question then was, at what temperature will 85 grammes of iron II chloride dissolve? At this point then, iron II chloride is the green line with the Xs for the plotting points.

So I would draw a line out from the y-axis at 85 grammes until it hits that green line of best fit, then draw a line down to the temperature.

And when I do so, it should be about 75 degrees centigrade, give or take a few degrees, depending on the quality of your graph.

Now this is a very complicated question and task that you were asked to do.

So if you were able to simply get started on that graph, you are making some great strides, particularly if you are feeling comfortable answering the questions about interpreting a graph.

To be able to take a table of results, turn it into an appropriate representation of that data, and then using that line of best fit to answer questions about it is some very high level difficult things to be doing, particularly at this stage.

And I am so proud of you for having a go.

Really, really well done.

So let's summarise what we've learned in today's lesson.

Well, we've learned that there is a limit to how much solute can actually dissolve in any solvent.

And a solution that contains the maximum amount of solute is referred to as a saturated solution because the solvent is full.

We've also learned that as the solution cools, its dissolved solute may become insoluble and either fall out of solution and collect at the bottom of the container or even form crystals.

We've also learned that a line of best fit indicates a trend in the data on a scatter graph and can actually be used to predict an unknown value.

And that's really useful when we're talking about solubility and saturated solutions.

We've also learned that data collected from multiple experiments can be plotted on the same graph, and that helps us to make comparisons between these different solutes and solubilities when they're all on the same graph.

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