Lesson video

Hello, my name's Mrs. Nivin.

And today we're going to be looking at how we can separate mixtures as part of our larger topic on separating substances in general.

Now, you might have some experience of this already, either from your previous learning or from experiences outside the classroom.

For instance, if you do any car mechanics, cooking or work with paints and artistry.

But what we do in today's lesson will help us to better understand how we as chemists, can separate any mixtures that we might encounter as part of our investigations or other studies, and also help us to answer those big questions of how can we explain how substances behave and also how we can say what things are made of.

So let's get started.

By the end of today's lesson, you should be able to describe what a mixture is and suggest some methods that might be used to separate them.

Throughout the lesson, we'll be using a few keywords and they include mixture, property and separate.

Now the definitions for these keywords are found in sentence form on the next slide, and you may wish to pause the video here, so you can read through them or perhaps jot them down so you can refer back to them later on in the lesson.

So today's lesson we'll be looking at two main things, firstly, we're looking at what mixtures are, and then we'll be looking at how we can separate those mixtures.

So let's get started by reminding ourselves what a mixture is.

Now many of the starting materials that chemists work with on a regular basis are actually found in nature, and those materials tend to exist as mixtures in nature.

So a lot of the materials that chemists might use could come from rocks, it might start as part of the seawater or it could even be found in air.

Now the thing to remember though, is that a mixture is a material that contains two or more different substances, and those substances could be elements and/or compounds.

But crucially, those substances are not chemically bonded together.

So when we take a closer look at rocks, they tend to be a mixture of many minerals, and some of those minerals may actually include some useful metals.

So the materials we might want to separate from this mixture could include some of the materials you might find in electronics, like your mobile phones, things like that.

In sea water, it's actually a mixture of the salt and the water.

Anybody who's ever gone in the sea and accidentally got some in their mouth, will be able to taste the salt, but be able to separate this particular mixture out.

We'll be able to use water that we can help to hydrate ourselves, and also salt that might be able to use to preserve or flavour food.

So it's useful to separate this mixture.

And air for instance, is actually a mixture of lots of gases and they include things like argon, water vapour, nitrogen, carbon dioxide, and oxygen.

There's many other gases that are still in the air, but these tend to be the ones that are there in the largest proportions.

Let's pause here for a quick check to see how you're getting on.

Which of the diagrams below shows a mixture? Well done, if you said B, C, and D.

All three of those show a mixture.

And the reason they show a mixture firstly, is because they have two different substances within those diagrams. And we can see that by the different colours.

Secondly, we can see that they're not joined together.

They may look like they're joined together, but they're not overlapping, and therefore, they're not chemically bonded together and could potentially be separated from each other.

Well done, if you managed to get those three correct.

So a quick and easy way to distinguish if the substance you're looking at is pure or a mixture, is to consider the temperature that it changes state of matter.

For instance, a pure substance would change state at a very definite temperature.

Like water boils if it's pure at exactly 100 degrees Celsius and it would melt at zero degrees Celsius.

So if we are looking at these two samples over the bunsen burners in the picture here, pure water on our thermometer then, would boil at zero degrees Celsius.

Whereas sea water, which is a mixture of salt and water, would probably boil closer to 102 to 123 degrees Celsius.

Mixtures, on the other hand, tend to change state over a range of temperatures.

For instance, whilst pure gold, that's 24 karat gold, would melt at 1,064 degrees Celsius, a mixture of metals, so probably an alloy.

For instance, here we've got rose gold, which is a mixture of gold and copper, that would melt anywhere between 1,000 and 1,100 degrees Celsius.

Let's stop here for another quick check.

Which of the following would help a chemist decide if a sample is a pure substance or a mixture? You may wish to pause the video here so you can read through and discuss your options and then come back when you're ready to check it.

Well done, if you said D.

The temperature at which a substance melts would help a chemist decide if a substance is pure or a mixture.

We could also look at whether or not the temperature at which it boils.

A doesn't really work because if substances are mixed to make it, it might have actually resulted in a chemical reaction.

Likewise, for C.

What happens when it's added to water? It could tell us whether or not it reacts or not, and that's not really gonna give us a good indication of whether or not it's pure or a mixture.

Neither will it tell us if it's natural or manmade will help us.

Really, we need to look at its physical properties and that is its melting or boiling points.

So well done, if you answered D.

Time for our first Task.

What I'd like you to do for this part is for each of the diagrams that are shown, I want you to decide if the substance is pure or a mixture.

Once you've decided that, tell me do you think it will have a definite melting point or if you think it will melt over a temperature range? And then finally, can you tell me, is this displaying an element, a compound, or a combination of both? Pause the video here and come back when you're ready to check your answers.

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

So for diagram A, you should have said that it was a mixture.

And that's because we can see two or more substances that are not bonded together.

And because it's a mixture, it's going to melt over a temperature range.

And what we see here is an element shown by the single pink circles and then a compound, which is the white and blue circles that have been overlapped and therefore, are bonded together.

For diagram B, we can see that it's a pure substance, because all of the circles in there are the same colour and because it's pure, it's going to melt at a very definite temperature.

And because all of the circles are the same, we can say that it is an element.

For diagram C, we can say that it is a pure substance.

And because it's pure, it is going to have a definite melting temperature, melting point.

And we can say that it is a compound.

If we look at these, we have always, one red element with two of the white elements bonded to it, because they're overlapping.

So each of these units are composed of just one red and two white circles.

And so our diagram here is showing that pure compound substance.

Now for diagram D, it gets a little bit more complicated.

I personally would draw circles around the different components that I have, so I can try and keep track of 'em.

But when I do that, I can see that it is a mixture.

And because it's a mixture, it's going to melt over a range of temperatures.

And when I look at them, I can see that I have two different compounds.

One compound is composed of one black and two red circles, whereas the other compound is composed of one red and two white circles and they are overlapping, so it's compounds.

So that was a really, really tricky task.

I would say give yourself a massive pat on the back if you managed to decide if they're pure or a mixture.

Fantastic work, if you managed to also tell me if it was going to melt at a specific temperature over a range of temperatures.

And very large kudos, if you were able to tell me if it was an element, a compound, or a combination of both, because that would've relied on you remembering some of your previous learning.

So incredibly well done on this first part of Task A.

Great job, guys.

Now that we're feeling more comfortable being able to decide whether or not a substance is pure or a mixture, let's move on to look at how we might be able to separate mixtures.

Sometimes we come across substances that are mixed together but can't be easily separated.

And a good example of that might be cake batter.

You would put together maybe some flour, eggs, milk, vanilla, flavourings, things like that, mix 'em all together, and once that's done, it's very difficult to get the eggs back the way they were or the milk back.

And the same could be said of something like cement, where you have the cement powder maybe mixed with water, some aggregate pebbles, things like that.

They've all been mixed together, but it's very difficult to then separate them completely from each other, once they've been mixed together.

Now in everyday life, you might refer to cake mix that you could find.

You can actually get a cake mix box down the bakery aisle.

And we refer to these large trucks that are carrying cement from place to place as a cement mixer.

But when we're talking about a mixture in a chemistry lab, a key feature of the definition of a mixture is that the different substances that make up that mixture, the different components can be physically separated from each other rather easily.

So the way that we talk about a mixture is very different from real life.

In chemistry terms, cake batter is not a mixture, and neither is cement.

So chemistry refer to a mixture as a material made of two or more substances that can be easily separated.

Now those can be easily separated, because the individual substances, the individual components of that mixture, retain or keep their chemical and physical properties even when they're in that mixture.

So when we're looking at sea seawater, the water would keep its chemical and physical properties and the salt would keep its chemical and physical properties.

What chemists do is they exploit those properties in order to separate the mixture into its individual components.

Now, in order to do that, the chemist needs to consider the mixture itself, the properties of the individual components within that mixture, and then decide what technique is going to be best used to separate one component from the others in that particular mixture.

So let's look at an example.

The metals, iron, nickel, cobalt, and steel are all magnetic materials, okay? That means that if I need to remove any of those four metals from a mixture, I could simply use a magnet.

So I've considered the mixture, it containing one of those four metals.

I know that those metals are magnetic, so therefore, I'm going to use a magnet to remove them from the mixture.

Another property I might be able to exploit in separating a mixture is the fact that a pure substance has a very specific density.

Likewise, substances that are more dense than other materials in a mixture, might sink to a bottom of my container, whereas others that are less dense than other substances in the mixture, could actually float, and I'd be able to easily scoop them up off the top of that mixture.

Meanwhile, some components in a mixture might dissolve in water or another solvent, and others might not, and that would impact on the technique that I'm using in order to separate out a component.

For instance, if I have an insoluble substance, I might use this technique, and if I have a soluble substance, I might use another technique.

Now, another thing a chemist might be able to do is consider a change of state in order to fully isolate a component.

Now, if that's a consideration, we might need to think a little bit more carefully about the component's properties, in order to separate it in the first place or to ensure that it's completely isolated from the other components of that mixture.

For instance, if I just had one liquid that I wanted to remove from a mixture and isolate in another container, I might use this setup.

But if I had a mixture that contained two liquids and I wanted to fully isolate them into separate containers, I might need to adjust the setup slightly in order to make sure that it's separated fully.

Let's pause here for a quick check to see how you're getting on.

Which of the following is a property that chemists could use to separate components in a mixture? Well done, if you said all of them.

There is an arsenal of properties that chemists can consider and exploit in order to separate out the mixture, which is fantastic.

It means you have a lot of options open to you in order to pick the best technique for the mixture or component that you're considering.

Let's move on to the last Task of today's lesson.

Aisha and Izzy are deciding which properties of iron filings, pebbles and seeds, are important when separating them from a mixture.

What I'd like you to do is to suggest a method for fully separating a mixture that contains these substances.

You'll probably want to pause the video here to consider and discuss your options with the people nearest to you and jot those down, and then come back when you're ready to check your answer.

Okay, let's see how you got on.

So one of the first things you could have thought about doing is maybe adding water to the mixture, so actually adding another component to this mixture.

But there is a reason why.

If you do that, then the seeds would float to the top and you could simply pull them out the top of it.

You could just scrape them off the top of your mixture.

The next thing you might be able to do is to use a magnet then, to remove those iron filings from the mixture.

Now, iron filings tend to be quite fine and very difficult to pick up.

So using a magnet would be the best option here.

And the other thing we could think about is the fact that pebbles tend to be quite dense, so they would've sunk to the bottom of our container.

And if that happens, the next thing you could do is simply pour the water off the top, or you could maybe pour the entire mixture of the pebbles and water through a sieve, and that might leave the pebbles behind and let the water through, completely isolating all of the components of that mixture.

So lots of options open up to you.

Well done, if you managed to suggest even one or two and fantastic work, if you've managed to suggest a method that would've isolated all of those different components.

Great job guys, and an excellent start to this topic of separating substances.

Let's take a moment now to summarise what we've learned in today's lesson.

Well, we've learned that a mixture consists of two or more elements and/or compounds, that are not chemically bonded together, and because of that, they can be easily separated.

We've figured out as well, that one way to distinguish between a pure substance and a mixture is looking at the temperature at which they change state.

So a pure substance will boil or melt at a specific temperature, whereas a mixture will do so over a range of temperatures.

We've also learned that the chemical and physical properties of each substance in a mixture remain unchanged, they're retained.

And chemists then can exploit the properties of these individual components in order to separate them out from the mixture in which they are.

And finally, we've reminded ourselves that there are many different processes that we can use in order to separate out the components of a mixture.

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

Great job today, guys.