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

Now, you may have experiences of solutions before, from some of your previous learning, or from some of your experiences outside of the classroom.

For instance, if you've ever made a squash or a cordial drink, you have experience of solutions, but what we learn in today's lesson will help us not only identify a solution simply by looking at the chemical equations, but if we're better able to understand how a solution forms, then we're also better prepared to think about the best way to separate a solution, and not only that, what we learn today will help us to better answer those big questions of, "What are things made of?" And, "How do different substances behave?" So, let's get started.

By the end of today's lesson, you should be able to explain how solutions form, and, also, how we can use state symbols and equations.

Throughout the lesson, I'll be referring to some keywords, and these include: state symbol, soluble, insoluble, solute, and solvent.

Now, some of these keywords may be familiar to you already, but just in case, the definitions for these words are available on the next slide in sentence form, and you may wish to pause the video here, so you can read through them or perhaps make a note of them, so you can refer back to them later in the lesson.

So, today's lesson is broken up into two main sections.

Firstly, state symbols, and then we'll look at solutions in a little bit more detail.

So, let's get started by looking at some state symbols.

The thing to remember is that substances exist in one of three main states of matter, and that is a solid state, the liquid state, or the gas state.

Now, which state of matter a particular substance is found in depends on two things.

The first one is that substance's melting point and boiling point.

So, if we had a thermometer, we could actually point out the boiling point and the melting point for that particular substance on it.

The next thing we need to consider is the temperature we are currently at.

So, again, if we refer to our thermometer, we could extend the lines for the boiling point and melting point.

Now, if we are currently at a temperature that is above the boiling point of that substance, then that substance will be in the gas state.

If the temperature is between the boiling point and melting point for that substance, it's in the liquid state, and if the temperature is below the melting point for that particular substance, it will exist in the solid state.

Now, that's quite a lot of information to get your head wrapped around, so let's look at an example.

If we had pure water, we could mark its boiling point and melting point on the thermometer.

So, pure water will boil at 100 degrees Celsius and it melts at zero degrees Celsius.

So, if the current temperature is above 100 degrees Celsius, then the water exists as a gas, and we refer to gaseous water as steam.

If the temperature is between the melting point and boiling point, then the water, pure water, will exist as a liquid, and we just refer to that as water.

If the temperature is below the melting point, so, for pure water, below zero degrees Celsius, then it exists in the solid state, and we refer to water that is in its solid state as ice.

Now, chemists prefer to refer to different substances by their chemical formula, and if we use just chemical formula to distinguish between steam, water, and ice, it's actually quite tricky to do so.

So, if you think about starting with pure water, the temperature is above 100 degrees, steam would look like this, H2O.

If the temperature is between the melting point and boiling point for water, again, the liquid state water would simply show the formula of H2O, and if the temperature is below zero degrees Celsius, so below the melting point, the ice would simply have the formula H2O.

So, when you compare all the formula for the steam, water, and the ice, they are exactly the same.

Enter state symbols.

Now, state symbols indicate the physical state of a substance.

They are always written in the lowercase and subscript, so that means sub, below, script, where you write, so below the line that you're writing on, and they're also shown in brackets.

Now, if we're going to refer to the state symbols, then, for a gas, it would be a lowercase (g) in brackets, a liquid is a lowercase (l) in brackets, and a solid, then, is a lowercase (s) in brackets.

So, when we look at our steam, which is above 100 degrees Celsius, I could change H2O to H2O with a (g) in brackets to show it's in the gas state.

For the liquid state, between the melting point and boiling point, I'd have an (l), and for the ice I could simply add that subscript in brackets, lowercase (s), to show that my water is in the solid state at that particular temperature.

Let's take a moment for a quick check.

State symbols indicate the chemical state of a substance.

Is that true or false? Well done, if you said false, but which of these statements correctly support your answer? Well done, if you chose B.

the state symbols indicate the substances physical state at a particular temperature.

The reactivity is the chemical state, so because it's a false statement, reactivity is also false.

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

Great start, guys.

Now, we said that the state symbols are used to indicate the physical state of a substance at a particular temperature, but a lot of substances actually exist as a mixture, and as part of a mixture in which one of those components is water.

Now, if we look at this particular example, now I've got here a mixture of a body soap, and I look at the ingredients list, the very first ingredient is aqua.

Now, what that indicates to me here, it just automatically makes me think of this word, "aqueous," and when I pull it apart, I get "aqua," which comes from the Latin for water, and, "eous," which means, "characterised." So, something that has aqua or aqueous in it means that we're talking about a substance that includes water.

So, many substances can dissolve in water, and water is represented by aqua a lot of times, from the Latin, and dissolving is a physical change, which affects a substances physical state.

So, we can actually indicate that using a state symbol that helps us to think about water being involved, and that state symbol of (aq) indicates a substance that's been dissolved in water.

So, if we have something that looks like this, so the formula is NaCl, with lowercase brackets (aq), that would tell me I have NaCl, which is the formula for sodium chloride, but because it has that state symbol of (aq), I can say that, actually, that sodium chloride has been dissolved in water.

Let's have another go at a quick check.

Which of the following does not represent a state symbol? Well done, if you chose both B and D.

B is not a state symbol, because the letter is in the capitalised or uppercase, and it should be lowercase, as it's shown in letter A, and D is not a state symbol.

Not only does it not have brackets, but it should only be one or two letters, not the full word.

So, well done if you've got at least one of those correct, and very well done if you managed to get both of the incorrect state symbols.

Great job, guys.

Time for our first task.

What I'd like you to do here, please, is to match up the state symbol to the correct meaning.

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

Okay, let's see how you got on.

So, the, (s) in brackets means a solid, the (aq), if you remember, aq is for water, aqua, aqueous, so that's dissolved in water, the (g) is for gas, and the (l) is for liquid.

So, most of these are actually quite easy.

The hardest one to remember, I think, is the (aq) for water, and I just constantly remind myself, "aq, aqua, aqua, aqua, aqua is water." So, well done, if you've got all of those correct.

Okay, this second part might be a little bit trickier, but what I'd like you to do is to think about what we've just learned, and I want you to decide what state each of these substances would be at minus 10 degrees celsius, 25 degrees Celsius, and 150 degrees Celsius.

You might find it useful to draw a number line or a thermometer, and then mark on the melting point and boiling point for each of these substances first, before deciding what state each of them will be at those three temperatures.

I've always used the mantra, "When in doubt, draw it out," because it makes it so much easier for you to try to see things visually, on a piece of paper, or on some scrap paper than it does to try and visualise it in your head.

So, make it easier for you, draw it out, and then, for B, you're gonna be doing something very similar.

What I'd like you to do now, then, is to pause the video, so you can talk it over and get some ideas down, and then come back when you're ready to check your answers.

Okay, let's see how you got on.

So, for vinegar at minus 10 degrees celsius, that is below vinegar's melting point, and because of that, the temperature being below its melting point, vinegar would be a solid at minus 10 Celsius.

25 degrees Celsius would fall between the melting point and boiling point for vinegar, and therefore, it would be a liquid at that temperature.

At 150 degrees Celsius, that is above its boiling point, and therefore, vinegar would exist as a gas, at a temperature of 150 degrees Celsius.

For olive oil, then, at minus 10, it would be a solid, at 25 degrees, it would be a liquid, and because it's boiling point is over 150 degrees Celsius, it would be a liquid at that temperature, as well.

For hydrazine, which is a type of rocket fuel, it would be a solid at minus 10 Celsius, a liquid at 25 degrees Celsius, and a gas at 150 degrees Celsius, because 150 is above its boiling point of 114.

If we go then to question B, you were asked to do the same thing, find the state symbol, though, this time, rather than what state it would be at, for the bromine at a 20 degrees Celsius, and that would be a liquid, therefore, it should be the lowercase (l), within the brackets.

For iron, then, at 20 degrees Celsius, that temperature is below its melting point, and therefore, it will be a solid, but I'd indicate the solid using the state symbol of a lowercase (s) in the brackets.

Well done, if you managed to get all of those correct.

Fantastic work, guys.

Okay, now that we're feeling a little bit better about state symbols, let's move on to talk about solutions.

So, a solution forms when one substance dissolves into another, and any substance that can dissolve is described as soluble in that other substance, whilst substances that do not dissolve would be described as insoluble in this substance, and you can see that it's insoluble, because there are bits that are floating on top, and there is stuff that has collected at the bottom of that container, they have not dissolved.

Whereas, on the left-hand side, we can see that it is a clear, that means it doesn't have any bits in it, kind of solution.

It's simply coloured.

So, that means that any solid that was in there has dissolved into it.

What this means is that, at the minimum, a solution contains two different substances.

The substance that dissolves is known as the solute, and the substance that it dissolves into tends to be a fluid, usually a liquid, and that would be called a solvent.

So, when you take a solute and dissolve it into the solvent, you end up with a solution.

What you'll notice here, as well, is that when we have a white solute going into our solvent, the solution appears colourless.

We can tell that it's completely dissolved, because there are no bits of that white solute in it anymore.

They have completely dissolved, the colour is dispersed, and it looks completely colourless, but clear means there are no bits in it.

If the solute is coloured, then the solution formed will be also coloured, but it will also be clear.

So, when we take this solute and put it into that solvent, you can see the solution forming here.

There are no bits, but that our solvent has now looked blue.

It's changed colour, and that's because our solute has dissolved.

Now, how well a solute dissolves in a particular solvent to create that solution is described by its solubility.

Now, solubility can be a little bit of a tricky thing to get your head wrapped around, so it's helpful to have an example in the back of your head to think about, and I always like to use a cup of coffee or a cup of tea to help me think about solubility.

So, there's a lot of different things that can affect how well a solute dissolves, and one of the first things to consider is whether or not that solute is being mixed in, is it actually being stirred to mix in and to help it to dissolve? And you might have noticed a difference if you try to dissolve a sugar cube in a hot drink, if you leave it to dissolve of its own accord, or if you stir it to make, sometimes, it will dissolve faster when stirred.

The size of those solute particles, so, again, sticking with that sugar cube, how easy is it for the sugar cube to dissolve versus sugar granules that you've actually, so, broken up pieces of sugar? You might think about how much or the mass of the solute that you are dissolving.

Are you trying to dissolve just one sugar cube or three sugar cubes? How well are those dissolving? You might think about the temperature of your solvent.

How easy is it for that sugar cube to dissolve with freshly brewed coffee or tea versus coffee or tea that's sat there for half an hour and has cooled down a bit? The other thing you could think about is the choice of your solvent.

Is it dissolving in water or is it dissolving in something else? That might affect how well that solute dissolves.

So, a lot of things to consider that might affect the production of a solution.

Now, I said that one of the factors of the solubility of a solute is the choice of your solvent, and water is actually an incredibly common solvent, and we can find it being used in many products.

We've already seen, earlier in this lesson, about it being used in beauty products, but it's also used in drinks, food, paints, adhesives, things like glue, medicines, health and beauty products, besides just the body soap, fertilisers, and even some protectants that you might use for different equipment.

But the thing is, whilst water is very versatile as a solvent, it's not able to dissolve every solute.

So, we have an example here of iodine pellets, and when we put it in water, they don't dissolve, the iodine just stays there, so we're going to need to use a different solvent, but if you use cyclohexane as your solvent, then the iodine will dissolve.

So, some of the other solvents that you might be able to use are things like ethanol, which will also dissolve the iodine besides the cyclohexane, you could use hexane, which helps to dissolve essential oils, things like that, so they're used quite frequently in things like reed diffusers.

And then you could also use things like propanone.

This is probably something you definitely have at home, if you have any nail varnish around, because that helps to dissolve that nail varnish.

Let's stop here for a quick check.

Which is the correct term for describing how well a substance dissolves? Well done, if you chose C, it's solubility.

Soluble is a word that we use to describe a substance that dissolves in a particular solvent.

A solvent is the liquid that tends to have a solute dissolved into it to make the solution, and a suspension is something that develops when an a really fine, insoluble substance becomes dispersed throughout the solvent.

It doesn't dissolve, but it also doesn't float at the top or sink to the bottom, it kind of just disperses amongst it.

So, well done if you managed to choose solubility.

Good job, guys.

Now, what we can do is we can take together everything we've learned so far about state symbols and the formation of a solution to actually write an equation to represent that solution forming, and I have an example here of sugar that's being dissolved in water to create a sugar solution, and we've provided the chemical formula for the solute and solvent.

The first thing I need to do is decide which state symbols to use.

So, when I look at the sugar, I can see that that's a solid, the water, then, is a liquid, and when we're talking about a solution, we're talking about something that's been dissolved.

So, to change this into an equation showing the formation of the solution and including those state symbols, I'm gonna start with my sugar.

Now, the formula, I've simply copied the formula I've been provided, but I've now included that state symbol of a lowercase (s) in brackets to show that it's in the solid state.

I'm going to bring that plus sign down, and now include the formula for water, which is my solvent, the H2O, and I'm showing that it's in the liquid form with that lowercase (l) in brackets, and, again, I'm using that arrow to say forms. That sugar solution, now, I know I don't have the formula for sugar solution, but I do have the formula for sugar, and that's C12H22O11, but, now that it's dissolved, the state symbol here is going to be a lower case (aq), in the brackets.

So, I can double check that I have the state symbols correct by going back and saying the solid as the lowercase (s), the liquid has a lowercase (l), and dissolved is shown with a lowercase (aq).

What I'd like you to do now is to have a go at writing your own equation for the formation of a copper sulphate solution, again, including state symbols.

You may wish to pause the video here so you can have a go, maybe talk it over with your neighbours to double check you agree, and then come back when you're ready to check your answers.

Okay, let's see how you got on.

So, the first thing I would do is the same thing I did on my example, which was to decide the states of each of your substances.

So, the copper sulphate I can see is in the solid state, the water is in the liquid state, and because I have a solution, something's been dissolved.

To write my equation, then, I'm simply going to copy the formula for the copper sulphate, which is CuSO4, but in include that state symbol of a lowercase (s), in brackets, written subscript to the formula.

I'll bring down that plus sign, because I'm putting my solute into the solvent of water, and, again, I'm using the same formula, H2O, and I'm showing that it's in the liquid state, using the lowercase (l) in brackets, and I've got my solution then, so I'm going to use my arrow saying forming that solution of copper sulphate, so CuSO4, but this time, to show that it's a solution, I have the (aq), in brackets, written subscript, and I'm going back to double check that the states that I chose to represent those particular substances, my solute, my solvent, and my solution of substance being dissolved and something is shown correctly using my state symbols.

That was a lot of work to try and do, but very well done if you managed to put the formulas in correctly.

Incredibly well done if you managed to get the state symbols in correctly, as well.

A lot of stuff brought together here, guys, very well done.

Time for the next task in today's lesson.

What I'd like you to do here is to match each key word to the correct statement.

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, "soluble," is a word we use to describe when a substance will dissolve, which means, "insoluble," is a word that means, "does not dissolve." A solution, then, is what is formed when a solute and solvent combine.

A solute, then, is what is dissolved, and the solvent is what a solute is dissolved into, and it's usually a liquid.

Now, these words are really easy to mix up and incorrectly match up to the definition, so I would always say, "Slow and steady." It doesn't matter if you finish the task, as long as what you've done is correct.

So, don't rush through things like this.

Take the time to really consider the differences between those statements to make sure that you're matching up to the correct keyword.

Very well done, though, if you managed to get all of those correct.

For the next part of this task, I'd like you to consider this statement.

Now, water is, well, as we said, an incredibly common solvent.

However, propanone is what is used in the solvent in nail varnish remover.

So, why do you think water is not used to remove the nail varnish? And what I'd like you to try and do within your answer is use some of those key words we were just looking at.

So, "soluble," "insoluble," "solute," and, "solvent," in your answer, and if you're struggling to remember the differences, maybe go back to the answers that we just went through, for Part One of Task B.

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

Okay, let's see how you got on.

Now, what I would always recommend is, when you are being asked to use specific words in an answer, I would underline, highlight, circle them somewhere in your answer for two reasons.

One, it helps you to keep track of the keywords that you're actually using, so you can quickly identify if you've forgotten to include one.

The second thing is is that it helps to highlight where that keyword is being used, so that you can double check that it's being used correctly within your sentences.

So, what I've done here is I've bolded the use of the keywords as we go through.

Now, there are a lot of different ways you could have answered this question, but it may have included something along these lines.

I've said, "Water is not used to remove nail varnish "because it is not a suitable solvent.

"The nail varnish is insoluble in water.

"Propanone is used because the nail varnish "is soluble in propanone." In this example, the nail varnish is the solute, and the propanone is the solvent.

So, very well done if you've managed to use your keywords in there, if you've managed to include even one or two of them, that's fantastic work, great job if you managed to include all four of them.

So, really, really well done.

It's quite a tricky thing sometimes to include so many keywords in an explanation, which is why I would suggest you highlight them as you go through, but it's also something I would recommend you go back and try and practise using.

At the very least, you don't have to use all the words at the same time, you can just simply write one sentence using one of those keywords, and build up to combining those sentences or combining the use of keywords within a sentence.

It's not an easy skill, but one that's definitely worth practising , 'cause the more you practise, the easier it gets.

So, well done on this, guys, great job.

Okay, last task of the lesson, guys, you can do this.

So, what we have is Sam, who has written some equations for the creation of two solutions, and what he's asked you to do is to peer evaluate it.

So, what you want to do is identify and correct any errors you think you can find in their work.

So, the first thing I would do is go through to double check everything, maybe circle any errors that you find first, and then go back to fix them.

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

Okay, let's see how you did.

Now, what you'll see here are a lot of blank spaces, and those indicate where the errors are in Sam's work.

So, well done, first of all, if you've managed to identify those errors, they will match up with the spaces.

The second thing you are asked to do is to correct any of the errors that you found, and I'm going to go through and show those corrections now.

I'm gonna start by focusing in on solution A, which is the iron (II) sulphate, and the first thing that Sam did is they incorrectly identified it as being dissolved, when really, it was in the solid state.

Likewise, the iron (II) sulphate solution, they originally said was a liquid, but, actually, it's dissolved.

Now, if we take those corrections to rewrite, now, the equation for the production of that solution, the solid iron (II) sulphate should be FeSO4, with a small (s) in brackets, added to the H2O, as a liquid, and that would form, then, iron (II) sulphate solution, which is represented as FeSO4 (aq), lowercase, brackets.

Now, I want to be very clear here, it's absolutely essential that you are writing these formulas correctly, copying them down exactly.

So, where the capital and lowercase letters are are really important, because they represent the specific elements that form those substances, and the numbers really do need to be subscript, same as those state symbols, so that you're writing these formulas correctly.

It's something that's very easy to become complacent or lazy about, but is absolutely essential if you want to be communicating in the language of chemistry correctly, that you are taking care in the way that you're writing these formulas.

So, do try and make an effort with these.

It's easy, I know I do it sometimes, so just learn from my mistakes, people, you can do this.

Okay, enough ranting.

Let me move on to solution B.

So, we have our ethanol, and Sam incorrectly identified the ethanol as a solid, 'cause they were so used to talking about solutions, starting with a solid solute.

The ethanol is actually in liquid form.

The water still is a liquid, but the solution of ethanol, now, again, Sam fell into the trap of thinking anything that's a solution is a liquid.

Actually, anything that's a solution is dissolved substances in a solvent, so that's dissolved.

Taking those corrections in order, then, the correct formula for the ethanol as a liquid would be C2H5OH, with the lowercase (l) in brackets, the water, H2O, with the lowercase (l) is unchanged, but the dissolved solution, then, should look like this now, with a C2H5OH, and the (l) that Sam originally put should be replaced with the (aq), showing that aqueous solution or dissolved substance.

Phew, that was a huge task with a lot of work required in there.

Not only did you have to find one, two, three, four, five, six, seven, eight different errors, but correct all of those errors, as well, so a fantastic job, if you managed to do all of that.

It was not an easy thing to do, and if you can do that, and you've done it well, my goodness, you are a flying start to chemistry.

Great job, keep it up.

Now, we have done a lot in today's lesson, so let's summarise what we've managed to learn today.

Well, firstly, we've learned that a solution is a type of mixture, and it forms when a solute dissolves in an appropriate solvent, and we say that many substances can act as a solvent, but water is probably the most common solvent that's used.

We've also learned that solubility is a measure of how well a chemical can actually dissolve, and if it does dissolve, it's referred to as soluble, and if that chemical does not dissolve, it's referred to as being insoluble in that solvent.

We've also learned that state symbols can be used to identify the physical state of a substance at a particular temperature, and that's the solid, liquid, gas, or aqueous state, and that those state symbols are particularly useful in distinguishing between the physical states of the same substance when they're being used in chemical equations.

You get a lot of information from a chemical equation, and state symbols help us significantly going forward.

So, incredibly well done today, guys.

I've had a great time learning with you today, and I hope you did, as well, and I hope to see you again soon.

Bye, for now.