Hello, my name's Mrs. Nevin, and today we'll be looking at mixtures in a little bit more detail by focusing in on solutions.

This is so that we can feel a little bit more confident as we address that big question of how can we explain how substances behave.

By the end of this lesson, you should be able to use key terms to describe a solution, but also be able to describe how making a solution will affect its overall mass.

The key terms that we'll be using throughout today's lesson are solution, soluble, solute, solvent, and conservation of mass.

Now some of those words sound very similar to each other, so you might find it very useful on this next slide, which shows the definitions being used in a sentence to pause the video, to read through those sentences, or perhaps even jot down those definitions before continuing.

In today's lesson, we'll be looking at two main things, firstly making solutions, and then secondly, that idea of conservation of mass.

So let's get started by looking at making solutions.

You'll be familiar with the idea of dissolving from some of your previous learning, but just to get the juices flowing thinking about solutions for today's lesson, I'd like you to consider some comments that students were making about what would happen when a teaspoon of sugar was dissolved in a glass of water.

Who do you agree with? There's no right or wrong answer here.

It's just what do you reckon? Now, Aisha said you cannot see sugar in solution, whereas Alex said the solution includes sugar in the liquid state.

Sam reckons you could taste the sugar in the solution if it were safe to try it, and Izzy suggested you can't see the sugar in the solution, so it's not there.

Now at first glance, many of the mixtures that you may come across in everyday life, things like orange juice or apple juice may not appear as a mixture in the first place because it's not obvious that it has two or more different substances in it.

And that's usually because they look clear, meaning there aren't any easily seen solid pieces in it.

So mixtures of that type are more appropriately called solutions.

So let's look more closely at what a solution is.

A solution is an example of a mixture that forms when a solid and a liquid mixed together so well that that solid dissolves meaning it's no longer visible.

So a substance that dissolves in a liquid would be described as soluble.

And a good example of this might be sugar.

And an substance that does not dissolve in your liquid would be described as insoluble.

And a good example of that would be sand.

So when a soluble substance dissolves into a liquid, what you've made then, the result, is a solution.

If that soluble substance is white, the solution will appear clear, meaning there are no bits, and colourless so it doesn't have any colour.

An example of that is shown here.

If however the solute is coloured, the solution will appear clear and coloured.

And you can see that here, adding that soluble substance, mixing it together, and we can see here a clear, that means there's no bits in it, and coloured, looking slightly blue solution.

So it's about the same colour as that soluble substance.

Now regardless if the solution that's formed is colourless or not, each part of that solution is more accurately referred to as either the solute or the solvent.

So let's take a closer look at those two terms. So that soluble substance that dissolves in a liquid will be known as the solute, and here it looks that white powder that we start with.

The liquid then into which that soluble substance dissolves is known as the solvent.

And those then combine to make our solution.

Now technically a solvent could be any fluid, so that's a liquid or a gas, but the most common solvent tends to be water and that makes sense 'cause we have quite a lot of it on the planet.

A very good example of water being used as a solvent is in saline solution.

That's a salt and water solution that's used in hospitals, but if you've ever made yourself a squash or cordial drink, you will have been using water as a solvent there as well.

Now the thing is most substances can actually be dissolved, it's just we need to find the most appropriate solvent in which that material would dissolve.

For instance, there are some other common solvents that you may have come across and not realised it.

Ethanol for example, helps to dissolve iodine, which is used as then a disinfectant.

Hexane for instance, helps to dissolve oils that are used in things like essential oils or reed diffusers, things like that.

And then propanone is used to dissolve or actually remove nail varnish.

So you've come across other solvents besides water before.

So what we need to understand about a solute is that if it doesn't easily dissolve in one solvent, it might dissolve in another.

For instance, we have an example here of iodine on its own.

Then when it's put in water, and then when it's put in cyclohexane.

And we can clearly see that it has dissolved in the cyclohexane because that substance looks clear but now coloured slightly purple similar to what it looks like normally.

The sugar, if we put that in water, it's clear and colourless suggesting that it's dissolved in water but not in the cyclohexane.

So in this instance we can see that iodine is soluble in cyclohexane but not water, but sugar is soluble in water and not cyclohexane.

Time for a quick check.

Some pupils are discussing this polystyrene cup that they found floating in the river.

Who do you agree with the most? Laura suggested that the polystyrene might be soluble, we just need to find an appropriate solvent.

Lucas says the cup is soluble.

You can see bits have broken off it in places.

And Jacob has suggested he doesn't think that the polystyrene is soluble in anything and that's why we use reusable cups now.

So who do you agree with the most? Well done if you chose Laura.

The polystyrene might be soluble.

It just doesn't look like it here in the water of the river, but we could perhaps find a more soluble solvent.

So up to this point we've been looking at solutes that are mostly in the solid state, things like the salt and the sugar, but it's important to note that a solute could also be a liquid or gas.

So if you look at these two pictures, we've got fizzy drink and a cordial drink, and in both of these we have a liquid solvent and the solute is different as well.

The cordial in our cordial drink is the solute and in the fizzy drink it's those gas bubbles that have been dissolved within the solvent.

We don't talk about gas solutes in a solution very frequently because they tend to be in sealed containers.

So even though we don't talk about 'em, that doesn't mean you haven't come across them before.

You will have seen these in our fizzy drinks.

These are sealed containers, but as soon as you open those sealed containers, there is now an opening for those gases that were dissolved in the solvent to escape, to un-dissolve, and leave the container.

And you can see that every time you pour out a fizzy drink with those bubbles that form as the drink is being poured.

If you leave that container unsealed as much of that gas as possible will be able to un-dissolve and your fizzy drink becomes flat.

Time for a quick check.

I'm gonna show you an example and then I'd like you to have a go.

So the first thing we need to do is we are going to identify the solute and solvent in this image.

Looking at these sugar cubes going into a mug of coffee, the sugar cubes are the solute because that is the substance that is going to be dissolved and then the water in the coffee is going to be the solvent because that is the substance that is dissolving the sugar.

Now I'd like you to have a go.

What do you think is the solute and solvent in this image? So the solute is the bath bomb or what is being put into the bath and the solvent is the actual bath water.

So well done if you manage to get either or both of those, very well done.

Time for your first task.

We've come across lots of key terms that sound very similar to each other so far in this lesson.

So the first thing I'd like you to do is to match the keyword to the correct statement.

So pause the video here and return when you're ready to check through your answers.

Okay, let's see how you got on.

So soluble is meaning that it will dissolve, a substance will dissolve.

That means then insoluble does not dissolve.

A solution is what is formed when a solvent and solute combine, the solute tends to be what is dissolved and the solvent tends to be a liquid.

Well done if you've got all those correct.

Okay, second part of our task now is to see if we can use some of our keywords correctly.

What I'd like you to do is to read these sentences and complete them using either the word solute or solvent.

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

Okay, let's see how you got on.

So for a, gravy granules dissolve in oil.

So oil is the solvent, it's the liquid here.

B, petrol will dissolve in oil.

So petrol is the solute because it's what's being dissolved.

C, sugar dissolves in water.

So water is the solvent, it's what's doing the dissolving.

D, sugar dissolves in tea.

So sugar is the solute, it's what's being dissolved.

And e, salt will dissolve in water.

So salt is the solute.

Again, like in d, it is being dissolved, so it's the solute.

Well done if you managed to get those correct.

Okay, the last part of this task then is looking at solvents.

We said earlier that water is a very common solvent, but it's not used in nail varnish remover.

Propanone is used instead.

So why do you think water is not used to remove nail varnish? What I'd like you to do is write your answer to that question, but challenge yourself to use these keywords in your answer, soluble, insoluble, solute, insolvent.

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

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

There were lots of different ways that you could have answered this question.

So your answers may have included some sentences along these lines.

You could have said something about water is not used to remove nail varnish remover because it's not a suitable solvent.

The nail varnish is insoluble in water.

You could have instead focused on propanone is being used as a nail varnish remover because it's a suitable solvent.

The nail varnish is soluble in propanone.

and you could have said that in this example, the nail varnish is the solute and the propanone is the solvent.

It's a tricky task, well done for having a go.

What I might recommend as well is in your work, sometimes it's helpful when you're using lots of very similar key terms to highlight them in your answers and it makes them easier to identify when you need to correct them or also to identify them when you reread your material for later to see how it's used in a sentence and in a longer answer.

But very well done for having a go at a tricky task.

Okay, let's head on to the second and final part of today's lesson.

Looking at conservation of mass, you will recall from previous learning that all substances contain particles and we have them represented here showing us a solid using the particle diagram on the top and those representing a liquid, the particle diagram on the bottom with the substance that's in the beaker.

What we also need to remember is that particles have mass and that mass is measured in grammes, and it's measured using a balance.

So we have here then the mass for our solid and the mass for our liquid.

So when a solute and a solvent combine to create a solution, the mass of each of those also combine to give us the mass of the solution.

So if we start with the solid solute mass of 0.

10 grammes being added to and mixed with the liquid solvent mass of 130 grammes, it creates then a solution with the mass of 130.

10 grammes.

This idea is known as the conservation of mass.

That is everything that's been combined, so shown here on the left of the arrow, the masses of everything that has been put together to start with will equal then the mass of everything that is produced.

That's shown here on the right side of the arrow.

Now if we use a container that has a sealed lid on it, we could introduce a gas solute and again, mass would be conserved.

So in this example we have a gas solute that has a mass of 0.

02 grammes being added to a solvent with mass 163 grammes, which means the solution that forms will have a mass of 163.

02 grammes, mass is still conserved.

Okay, time for a quick check.

True or false, the mass of a solution depends solely on the mass of the solvent.

What do you reckon? Well done if you said false, but which of these statements best justifies that answer? Is it that all matter has mass so when matter is mixed together, their masses are added together or is it that only solutes have mass, so solutions mass will depend on how much solute is added.

Which best justifies that answer? Well done if you chose a, all matter has mass, so when matter is mixed together, the masses are added together, good job.

Time for another check.

A beaker of water and a dish of sugar are placed at each end of a balance.

Then the sugar and the water on the A side, so on the left hand side are mixed until the sugar can no longer be seen.

What do you reckon will happen to the balance when the sugar is added to the water on side A and mixed to dissolve? Will it be that side A is lighter, side B is lighter, or will both sides have the same mass? Well done if you chose C because of conservation mass, it doesn't matter that that solute or the sugar has dissolved into the water.

The mass is exactly the same on both sides, well done.

Now that we have a good understanding of what we mean by conservation of mass, we can use that relationship to calculate an unknown mass whenever we're making a solution.

So we have an example here where an unknown mass of solute was added to 130 grammes of solvent to make a solution of mass 142.

63 grammes.

Using that conservation of mass relationship, we can come up with a mathematical equation that the unknown solute mass added to the solvent mass will give us the solution mass.

What we need to do then is take those values from the balances and put them into our equation.

When we do that, we will then be able to take the mass of the solvent away from the mass of our solution and that will give us the mass of our unknown solute and that is 12.

63 grammes.

Let's take that a little bit further to calculate some unknowns.

I'm going to do some examples first and then you can have a go.

So to remind us about that conservation of mass mathematical relationship, I've put the equation at the top that solute mass plus solvent mass will give us the solution mass.

So for beaker number one with a solute mass of 2.

10 grammes and a solvent of 4.

92 grammes, I'm going to add those two together to get the solution mass of 7.

02, which I'll put into my table now.

For the second beaker, I can see that I've used solute of 0.

25 grammes, but the solution that was formed had a mass of 4.

56.

So to find the mass of the solvent, I'm going to take 4.

56 and take away 0.

25, and that will give me the mass of the solvent, which is 4.

31, which I put into my table here.

Now it's your turn.

What I'd like you to do is to have a go at calculating the unknown masses for beakers three and four.

You may use a calculator if you'd like, and it may take you a little bit longer than normal.

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

Okay, for beaker number three, you should have added the 0.

03 and 20.

14 for your solute and solvent to give you the mass of a solution, which is 20.

17 grammes, and I'll put that in the table.

For number four, you would've taken the mass of the solution and subtracted the mass of the solvent.

So 157.

09, take away 142.

98, and that gives us a mass of solute that was added as 14.

11 grammes of solute that was used.

Well done if you got this correct.

Now you'll notice in both of these examples, my example and the answer key that I gave you, that I've shown the working out, some of you may be able to do this maths in your head and that's absolutely fine, but I would always recommend that you are writing out your work so that if for some reason you do go wrong, you can refer back to your work, identify where your error occurred, and then you'll be able to identify how you can improve going forward.

But well done for a tricky task with some maths.

Time for the last task in today's lesson.

We're going to focus it around a soda stream for the first part of this task.

A soda stream is essentially a machine that's used to carbonate or add fizz to everyday drinks, and it does that by adding carbon dioxide or dissolving carbon dioxide gas into your drink.

And in this instance, we're going to use tap water to turn it into sparkling water.

So for the first part, I'd like you to identify the solute and solvent in the resulting solution and to justify your choices.

For the second part, I'd like you to consider how adding carbon dioxide gas to the water affects the mass of the sparkling water that's produced.

And I'd like you to explain your answer using a because clause.

So have a think, pause the video to jot down your answer and come back when you're ready to check it.

Okay, let's see how you got on.

In the first part, you were asked to identify the solute and solvent in this resulting solution and to justify your answers.

So the solute is the carbon dioxide gas and it's the solute because it's what's being dissolved into the water.

The solvent then is the tap water because that's the liquid that the gas is being dissolved into.

In the second part, you were asked to explain the effect of adding carbon dioxide gas will have on that resultant sparkling water, and I was really looking for that because clause to link up your thinking to your answer.

Hopefully what you've said is that the mass of the sparkling water will increase compared to the mass of the tap water you started with, and that's because carbon dioxide gas has mass and that mass will add to the mass of the tap water.

Well done if you managed to get that, very, very well done.

For the final part of this task, I'd like you to use that idea of conservation of mass to calculate the unknown masses for each of these beakers.

As a reminder, the conservation of mass says the mass of the solute added to the mass of the solvent should equal the mass of the solution.

You may use a calculator in this and remember, it's always useful to show you working out.

What I'd like you to do now then is to pause the video, have a go, come back when you're ready to check your answers.

Okay, let's see how you got on.

So for beaker one, the solution mass should be 10.

77 grammes.

For beaker two, the solute mass that was used was 0.

02 grammes.

For beaker three, the solvent mass should be 5.

76 grammes.

For beaker four, the solvent mass was 94.

63 grammes.

And for beaker five, the solvent mass was 239.

59 grammes.

Well done if you managed to get those correct.

Fantastic job, guys.

Let's review what we've learned in today's lesson.

We've learned that solutions are an example of a mixture, and they're formed when a solute dissolves in a suitable solvent.

Also, when the solutions form, the number of solute and solvent particles doesn't change, and because of that mass is conserved.

That means that the mass of the solute adds to the mass of the solvent and that gives us the mass of the solution.

We can use that mathematical relationship to calculate an unknown mass when making a solution.

I hope you've had a good time learning with me today, and I look forward to seeing you again soon.