Hello, my name's Mrs. Niven, and today we're going to talk about how we can separate pure salt from some dirty rock salt.

And you might have some ideas on how to do this already, from some of your previous learning.

But what we're going to do today is look at how we might be able to combine some different techniques to really get what we want out of a mixture.

And this will help us moving forward, as a lot of the mixtures that we can create in science, or some of the materials we might need in science, exist in mixtures and this will help us to figure out the best way forward on how we can extract what we need.

It also helps us in trying to answer that big question of how can we explain how substances behave? So by the end of today, you should be able to suggest some combination of techniques that we could use in order to extract pure salt from dirty rock salt.

The keywords that we'll be using in today's lesson include "separation technique," "property," "soluble" and "insoluble." Now, the definitions for these keywords are on the next slide and you may wish to pause the video here so you could read through them or perhaps jot down some notes so you can refer to them later on in the lesson.

Today's lesson will be composed of two parts.

We'll look first at how we might combine separation techniques and then we'll move on to using that understanding to separate the pure salt from that dirty rock salt.

So let's get started and look at how we might combine different separation techniques.

Now, as I mentioned earlier, many of the materials that we might need for science would actually be found in nature, probably mixed with other materials.

And in order for us to get that useful material, we'll have to use some kind of appropriate separation technique in order to isolate that really useful substance from the mixture in which it's found.

So when we're talking about a separation technique, we're talking about some kind of method for us to be able to extract and pull out one part of our mixture that we want.

So if we look at this example.

In nature, and you might have actually seen some TV shows that are about this, we might be looking for something like gold.

Now, depending on where that gold is found, we might need to use a different method or different separation technique in order to extract the gold from where it's found.

For instance, it might be mixed with dirt, in which case all we need to do is dig it out, possibly dust it off.

But if the gold is actually mixed with water, we'd probably have to pan for it.

We'd probably need to use some kind of sieve in order to get the different pieces of gold, we will be washing it off.

So there's two different techniques in order to extract the material that we want.

Now, ultimately, the technique or method that you use in order to separate a useful material from the mixture in which it's found depends on the properties of all those different substances in the mixture.

So if we were were to look up the definition of "property" in a dictionary, several different definitions might come up 'cause we can use that word in multiple different ways in everyday life.

But in science, when we're talking about a property, what we're talking about is a feature or a characteristic of that substance that we can use to help us classify it or help us describe how it might behave.

So if we look at this example of sea water as a mixture, it is essentially a solution that's mostly of salt and water.

And we know that water as a property can actually flow in the liquid state.

And if we look at salt by itself, some of those properties might include that it's white, that it's made of crystals, that it's in the solid state and that salt is actually soluble.

So to pick that separation technique, we need to look closer what we mean by properties and the types of properties that we might be able to use to describe a different substance.

Now, properties tend to come in two different classifications, two different groups.

One group is physical properties, and that really describes how a substance looks or how it behaves.

And some examples might include the colour.

Here you might describe yellow feathers or blue feathers.

It could be if it's shiny or if it's dull in appearance.

We might be looking at how soluble a material is, or even what it's boiling point or melting points are.

Now, that's its physical properties.

The other type of properties that you might be able to describe are its chemical properties, and that's how the material actually reacts with other materials.

So you might describe how flammable it is, or you might describe how reactive it is.

But when we're talking about a separation technique, the only properties we really care about to decide the most appropriate technique is the physical properties.

And that's what we wanna look at going forward.

So let's do a little check together.

If I want to describe the physical properties of this material here, this picture, even if I didn't know what it was, I could say some of the physical properties about it.

From looking at it, it looks very round.

It looks like it has quite a rough surface.

It has different colours in it.

I can see some white, some greys, some darker colours, but it looks mostly red.

It looks quite large, so it might have a very high mass.

So there's lots of different things.

I could even describe it, probably because it looks as a solid state material, it might have a very high melting point because I know that other solid state materials tend to have high melting points.

So these are just an example of some of the different ways that I might describe the physical properties of this material.

So what I'd like you to do now is to take a moment and to describe some of the physical properties of the materials you can see in this picture.

You might wanna pause the video here and come back when you're ready to check your answers.

Right.

There are lots of different things that you could have said here, but some of them might have included things like it looks like this material includes some insoluble substances.

I can see some things that have settled to the bottom, some little black bits at the top.

It doesn't look clear, so I can't see through it.

There are bits and pieces in that material.

It does look like there's a settled substance there at the bottom, and that means that there might be more dense materials in there.

It also looks like there's some floating substances in there that might be a little less dense.

So, well done if you were able to describe any of those.

You might have also mentioned things like the colour of the material.

Those are some other physical properties as well.

So, well done even if you've got one or two different physical properties listed for that substance.

So once we're able to identify some of the properties in the substance, we need to start to link that up to the different types of techniques we might be able to use to separate out that particular material.

For instance, here we can see that we have a floating substance, a liquid state substance, and a settled substance in this container.

So, before I even get started, I might think about what's the best way to separate these? For instance, the floating substance, it looks insoluble and it looks less dense.

That's why it's floating.

I know that a liquid state substance could actually be poured or it might even be boiled or evaporated.

And a settled substance, by definition, is more dense and, therefore, it's sunk in that liquid state substance and it also looks to be insoluble.

So I'm gonna use these to think about what's the best way forward to separate them out? Now, the thing to remember is that if your mixture contains multiple substances, so I'm thinking a mixture that contains three or more materials, you might need to use more than one separation technique in order to isolate all the different parts of it.

So if we stick with this particular example of these materials in my container, I could possibly just scoop out those floating bits, those floating pieces, that are less dense, and put them on a separate watch glass to the side.

That leaves me then with my liquid state material and my insoluble more dense material.

And my suggestion is because it's an insoluble substance and a liquid, I could filter them out.

And what that would leave me with then is that more dense or insoluble substance as the residue collected in the filter paper.

And then my liquid state material would go through and form my filtrate.

And so I've taken the three different substances of my mixture and separated them out into three different parts through a combination of different techniques.

One thing to be aware of as well when we're trying to decide the most appropriate separation technique, is that some of them, such as decanting, filtering, evaporating and crystallising, is gonna require the mixture to be a solution first.

So if you have a mixture like this that is just sand and sugar, we need to think of ways that we can separate them out.

The problem that we have with these is when you look at the properties is that they're both small particles, and we know that the sand particles are very dense, but the sugar particles being so small, they've mixed in with them.

But crucially, the sand is insoluble and the sugar is soluble.

So to separate them, I can focus in on that different property between them.

Simply add water to this mixture to dissolve that soluble substance.

So I'm adding another substance of water to my mixture, making it a little bit more complicated, but by doing so, I'm giving myself more possibilities of different separation techniques I can use in the future.

So whilst I've made my mixture a little bit more complicated by adding water, what it has done is given me more opportunities of choosing an appropriate separation technique, because my soluble substance now has been separated from the insoluble substance because it's now mixed in with the water or the liquid that I've chosen as my solvent.

When that's happened then, I want to now decide what's the best way to remove that insoluble substance? Now, because in this particular example, my sand is actually quite small particles, I have two options.

I could decant or I could filter out that insoluble sand.

Now, I'm going to choose filtration, because the particles are quite small and I know that decanting doesn't always give me full separation.

So I'm gonna stick with filtering to separate out the sand.

So once I get my filtration set up here with the filter paper, the funnel and the conical flask, I'll pour my mixture in through it, and when that happens, I'll be able to collect that insoluble sand, the residue, in my filter paper.

And then my filtrate will be a combination of the water that I added earlier and the sugar that was dissolved in it.

So what I'm left with then, is that insoluble sand on the filter paper.

And I'm gonna use a different technique to separate out that sugar that was originally mixed with it.

So that dissolved sugar then is now in the filtrate and I need to separate out that water.

So the easiest way to do that is usually by heating, by somehow removing then the solvent that I added earlier that had allowed me to dissolve that soluble substance, in this case the sugar.

So I'll pour it into an evaporation basin, I'll heat it up and I can heat it slowly or I can heat it quickly.

I'm gonna choose to heat it slowly because I really like the big crystals that form as a result of that slow heating.

And what I have now then is the sand that's left in my filter paper and the crystals of the sugar that have formed as a result of heating.

Time for a quick check.

True or false? Adding water to a mixture will dissolve insoluble substances? Well done if you said false.

But which of these substances best justifies that answer? Well done if you said B.

Adding water to any soluble substances makes a solution.

Magnetic substances will not dissolve, they won't make a solution, they'll simply settle to the bottom, usually.

Well done if you got that correct.

Time for our first task.

So we have Sophie here and she wants to separate a mixture that contains salt, iron filings and flour.

And what you need to do is to help Sophie consider the different physical properties of the substances in her mixture, the best separation technique that she can maybe use to isolate each of those into a different place.

And then consider then what order she might want to conduct those different techniques.

So which one will she separate first, second, and then third? You may wish to pause the video here so that you can have a think about it, talk it over with your neighbours, and then come back when you are ready to check your work.

Okay, let's see how you got on.

So the first thing we wanna think about when we are deciding how to separate out our different substances is what are those physical properties that we could exploit? What could we use to decide the best technique? So when I look at the salt, I can see that it's small particles, but I remember that salt is soluble.

The iron filings are also really small, but I remember that iron is one of my four magnetic metals and, therefore, the magnetic is a good property to include.

And then the flour is also small particles, but these are insoluble.

And when I look down this column, I can see that all three of the substances are small particles.

So I'm gonna have to focus in on those other properties that salt is soluble, iron filings is magnetic, and flour is insoluble, to decide those separation techniques.

So if I start with salt.

Because it's soluble, I'm probably gonna need to add water at some point and, therefore, I'm going to need to add heat to then remove the water afterwards.

So evaporation or crystallising is the best way.

The magnetic iron filings could be removed using a magnet.

And the insoluble flour then, because it's insoluble, filtration is probably gonna be the best.

You could have said decanting at this point, but remember decanting doesn't completely separate out some materials.

So if you want full separation, filtering is probably the best.

The last thing I asked you to do then was to consider what order would you conduct these different techniques in? Which would you separate out first, second, and then last? Now, what I would recommend is actually separating out the iron filings first, using that magnet.

It might take a little bit of time, but just holding that magnet over the different substances and the mixture would be able to get the vast majority of them out.

Then I would probably do filtration to separate my insoluble substance, but I'd have to do that after adding water to it, so that I have something to pour, the flour by itself wouldn't be able to separate out the salt.

And then once I've done that, I could then use crystallisation and evaporation to remove the water that I added before step two and then get my salt separated as crystals.

So there was a lot of different things to think about there.

Excellent work if you got the physical properties, even better if you managed to suggest an appropriate technique and incredibly well done if you were able to suggest an order that made sense.

This is not an easy task and you guys have worked supremely well.

Very well done.

So now that we're feeling more comfortable about how we might be able to combine some separation techniques to separate out a particular part of a mixture, let's move on to look at how we can separate out pure salt from some dirty rock salt.

Now, people have been using salt throughout history.

They've been using it not only to preserve their food, but also to flavour their food.

And in fact, the root of the word "salary" actually comes from the Latin meaning salt.

And this led some people to try to make some links to it.

So it's been suggested that some Roman soldiers used to be paid a certain amount of money, called a solarium, that they could use to purchase salt because it was such an expensive but essential part of their daily life.

But this is probably due to a mistranslation, but you can see just how far back this use of salt has gone.

Now, salt continues to be used even today for flavouring and preserving of our food, but there are also some new uses and other uses that we use salt for.

For instance, we can use it for gritting roads, we can use it for making soaps, and we can also use it for dealing with hard water, which tends to leave those really kind of gritty bits around some of our taps.

Now, one of the reasons that salt has been used so frequently throughout the ages, is that it's found in so many different locations in nature.

For instance, it could be found in a salt flat.

If you live near the seaside, it's obviously found in the seawater, and it could also be found in rocks.

But the issue with each of these sources, is that it only provides dirty rock salt, so it's mixed with the other substances.

And in order for us to use it, it needs to be extracted from that mixture with the other substances.

Time for a quick check.

Which of these is not a use of salt? Is it flavouring, preserving, lubrication, or road grit? Well done if you said lubrication.

Lubrication usually uses something like an oil that you'd use on your chain on your bike or something like that.

But well done if you managed to get that correct.

Let's try another one.

Which of the following is a source of salt? Is it soap, rock salt, or lakes? Well done if you said rock salt.

Now, soap is what is made from salt, and lakes tend to be referred to as a lake because it's a fresh water lake.

But well done if you managed to get rock salt.

Now, in order for us to be able to use these salt for things like the soap or flavouring our food, preserving our food, things like that, the pure salt needs to be separated from the mixture that it's found in.

So we're going to need to use some form of separation technique or techniques in order to separate out that pure salt from our dirty rock salt.

Now, the thing to remember is that rock salt contains the soluble salt and the insoluble rock particles.

So the very first thing we're gonna need to do is to exploit those different physical properties and add some water.

We're gonna need to dissolve that salt within the rock salt before we are able to separate it.

So, in order to dissolve as much salt as possible, what we want to do is we want to break up these large pieces of rock salt into smaller pieces.

And we're gonna do that using a piece of equipment known as a pestle and mortar.

And it looks a little bit like this.

So this is the scientific diagram labelled for you.

And it may look familiar if you've ever used something similar in your food technology classes, because sometimes you can use these to grind up different spices or to mix smaller pieces like garlic or chilies or something like that together.

Very, very handy for making spices for curries, things like that, but the main thing that we need to remember when we're using a pestle and mortar is that we never pound.

You're not going up and down.

You're going to be doing a circular motion, pushing that pestle around into the mortar.

We're not pounding or pushing, we're just twisting that pestle as it's pushed down into the mortar, and that action, the friction and the pressure that you're producing on there, is enough to be able to break up those larger rock salt pieces into the smaller rock salt pieces.

And what that does, it will help that salt to dissolve away from the rock and into the water that you add.

So at this point, once you've got your smaller rock pieces, you can add your solvent and stir to mix them and dissolve the salt as much as you can.

So now that our salt has been dissolved in the water, we need to remove the rock that we have to get out of there, to make it cleaner and ready for use.

So we're gonna filter it at this point, and when you pour then that mixture with the dissolved salt and the rock into your filter paper, the insoluble rock pieces will be caught and trapped in the filter paper.

And then the filtrate will contain the salt and water that's able to flow through that filter paper.

The filtrate then is going to be evaporated in order to remove the water that we added earlier.

And then that should hopefully leave us with our salt crystals that are now pure and ready for use.

Let's try a little trickier check to see how you're getting on.

Which of these diagrams is correctly labelled for filtering a rock salt solution? There's a lot of information to look at here, so you may wish to pause the video and come back when you're ready to check your answers.

Well done if you said B.

Part A is not an appropriate label, because it's showing soluble rock and rock is not soluble, it's insoluble, so it should be in the filter paper, not in the filter as it's shown there.

And diagram C is not the correct diagram, because it's showing a rock salt and vinegar mixture and we don't dissolve the salt in the vinegar, we dissolve it in the water.

So, very well done if you managed to choose diagram B.

Time for our next task.

What I would like you to do is looking at the diagrams at the bottom and reading through those descriptions, you want to match them up.

Which description would you match to the correct diagram? 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 first one says, "Crush the sample of dirty rock salt." And I remember I need to use my pestle and mortar in order to do that.

Then filtering the solution, I'm gonna need a funnel with my filter paper.

So that's gonna be the first diagram.

The next one says to gently heat to create a saturated solution.

Now, I'm heating something, I'm going to use something like a Bunsen burner, so that's my fourth diagram with the red arrow.

Then the next description says, "Leave in a warm place so the salt can crystallise." So I'm gonna need to leave it somewhere.

So it's the solution as it is.

So that's gonna be the second diagram of just that evaporation dish with the solution in it.

The second to last description says, "Add water to dissolve the salt from the sample." So I'm going to need to simply see my beaker with the added water in it.

That's the last diagram.

And finally pouring the filtrate into an evaporation dish.

I'm gonna be looking for a pouring action and that evaporation dish.

So that's the second to last diagram.

Very well done if you managed to get those correctly matched up.

Okay, so now that we've correctly matched our descriptions and the diagrams, what I'd like you to do now is to put them into a logical order that we could use as a method to then produce a pure salt sample.

So you may wish to pause the video here to read through them and then move them around into the order that you'd like to use.

And then we'll come back when you're ready to check your answers.

Okay, let's see how you got on.

So the very first step to producing this pure rock sample is to crush that rock.

So the first step would be crush the sample of the dirty rock salt using our pestle and mortar.

The next step then would be letter E, adding water to dissolve the salt from the sample.

We'll do that in a beaker, and probably stir it to help it dissolve a little bit better.

A, then, would be the next step.

I'm going to filter out that solution to remove the rock.

Then, F, means I'm gonna take that filtrate that came through from the step before and I'm going to pour it into an evaporation dish.

Now, in order for this to crystallise, I need to gently create a saturated solution.

So I'm going to have my Bunsen burner set on a very gentle light blue flame and just let it heat until I see some crystals, very small crystals, forming just on the edge of the solution on my evaporation dish.

And once that happens, I'm going to turn the Bunsen burner off and finally let it cool a little bit and then move my evaporation dish to a warm place somewhere in the room.

And just leave that solute to form crystals as the solvent slowly evaporates.

So it will take a little bit of time to crystallise.

You might need to leave it for a little bit, but these are the steps in the order in which you would use it to create pure salt from dirty rock salt.

So, well done if you managed to get those in the correct order.

Very well done.

Okay, now for the last task.

What I'd like you to do is follow the method that you just created in Task B, part 1b, and I want you to produce your own sample of salt from dirty rock salt.

So you'll need to go back and use your method from the previous task.

Now, if you're unable to do this, you can click on the watch button below to watch a video of this demonstration showing those different steps in order.

And then once you've done that, I want you to think about and try to answer this question for part B, which is why might the separated salt still not be suitable for us to use immediately? Okay, so you're gonna wanna pause the video here and come back when you're ready to check your answer.

So the first thing we're gonna do when we are going to create our salt from rock salt, is I need to crush up that rock salt sample in my pestle and mortar, and notice we're using that twisting and pressure movement to try and break up those big pieces.

Then I put it in my beaker, add some water and stir to dissolve as much salt as possible.

Then, I'm going to prepare my equipment for the filtration, ensuring that my filter paper is prepared properly.

And then add a few drops to keep the filter paper in place before I pour my mixture into that filter paper.

And we can see then, the filtrate start to drip out the bottom.

And we're pouring this in just a little bit at a time so that it doesn't overfill the top of the filter paper.

And over time then we can see that the rock has been collected as the residue and the filtrate then is poured into an evaporation dish so that we can start to create that saturated solution.

Now there are two ways to do this.

You can heat it directly or you can heat water in a beaker and the evaporation dish on top, which is a little bit safer, it keeps the solution from spitting out.

But either way you're gonna do that until it starts to boil a little bit, and you can see that with the bubbles that are forming.

And then you're gonna do that until the little crystals form along the edges.

And at this point turn the Bunsen burner off and place somewhere for it to gently evaporate.

I hope you had a really good time using all that different equipment to try and create your own sample of salt.

And hopefully you've managed to get some really big crystals forming.

And if you did heat it a little bit faster that you were very careful of the spitting that might have happened as you were heating up that solution.

But, really I wanted you to think about this last question here.

Why might this particular salt still not be suitable for using? It's a bit of a tricky question, but what we need to remember is the separation techniques that we used may not have managed to get rid of all the other substances that might be harmful in that original rock salt sample.

So all we've done is remove the rock and then separated out of the salt.

We've not checked the melting point.

Remember, checking the melting point is one of the easiest ways for us to decide whether or not something is a pure substance.

So we've made the salt as pure as it possibly could be using the separation techniques at our disposal, but there is the possibility there are still some impurities within our salt sample that we've not managed to separate using the techniques that we've used just here.

So, it's not quite suitable for using just yet.

But very, very well done on a task where you really needed to stay organised with your equipment and your method.

So, hopefully you had some really good communication going on in your partners or if you worked alone, very well done for organising.

I love this practical and I hope you did too.

So let's summarise what we've managed to learn in today's lesson.

Well, we've learned that the properties of a substance in a mixture help us to determine the technique that is best used to separate them.

And the properties we're thinking about here are really the physical properties, describing how a substance looks or how it might behave.

Then, when a mixture contains more than two components or more than two parts to it, you might need to use more than one technique in order to separate all the different parts of them into its individual pieces.

The other thing we need to remember is that in order to separate out a mixture and the different parts of it, you might need to actually create a solution first by adding water or another suitable solvent in order to make a soluble substance dissolve, and then use other techniques to separate the rest out.

And finally, we brought all of these ideas together to separate out salt from rock salt.

And the way we did that was first by making a solution of our rock salt, filtering off that insoluble rock, and then crystallising the salt from the filtrate.

I had a fantastic time today.

I hope you did too, and that you'll come back to learn with me again soon.

Bye for now.