Mixtures

0:00- [Instructor] When we add some food color to water and stir it, you see that the food color mixes very nicely, spreads throughout the water. But now let's add some oil to the water. Stir it, stir it hard. And what we find is that, hey, that oil is not mixing throughout the water.

0:19It's not spreading throughout the water. So look, in both cases, we mix things, but the two mixtures look very different. And this difference is important in chemistry, so let's talk about them. Substances or matter in general can be classify into two kinds. We have pure substances and mixtures.

0:36What are pure substances? Well, think about gold. If you could zoom into it, you would find tiny particles of gold. Gold is made of gold particles and nothing else. Similarly, if you were to zoom into water, you would find water particles and nothing else. So you can think of pure substances as substances that are only made of one kind of substance.

0:59Gold is a pure substance because it's only made of gold particles. Water is a pure substance because it's only made of water particles. But what about the food color in water we saw earlier? Notice that it's not just made of one substance, it's made of water and it also contains food color.

1:15And the food color itself is made of many substances. Similarly, water and oil, it's made of more than one substance. There's water, there's oil, and oil itself is made of many substances. These are what we call mixtures. So mixtures are substances that are made of two or more kinds of substances.

1:35Another way to think about it is, pure substances cannot be physically separated into different substances. I mean, think about it. If you try to cut gold, you'll get just smaller pieces of gold. There's nothing you can do physically to get a different substance from it, right?

1:53Similarly, if you divide water or say boil water or do any other physical process, you will still end up with water. You cannot physically separate water into different substances. But mixtures, well, they can be physically separated into substances that make them up.

2:10You can separate water and food color. For example, you can let the water evaporate and the food color will be left behind. So you can separate them by physical processes. What about water and oil? You can separate them by physical processes. So mixtures can be physically separated.

2:28But, of course, you can see there is some difference between these two mixtures, right? What's the difference? Well, over here, notice that you cannot tell where the food color ends and where the water begins. Everything looks smoothly blended together. The mixture looks the same throughout.

2:50It's uniformly distributed, right? Such mixtures are what we call homogenous mixtures. In homogenous mixtures, the substances are uniformly mixed together, smoothly distributed. In contrast, in water and oil, you can clearly see where the oil is and where the water is.

3:11The different parts of the mixtures are clearly visible. The substances are not uniformly distributed. Such mixtures are called heterogeneous mixtures. So let's take some more examples to clarify the difference between them. So here are a bunch of mixtures that you can find in your everyday life, right?

3:30Why don't you pause the video and think about, which of these mixtures are homogenous and which are heterogeneous? Pause and try. All right, let's start with the salads. Well, you can clearly see the different parts that make up the salad, right? So it is a heterogeneous mixture.

3:48What about the caramel? Well, can you see the different parts over here that make it up? Nope, I can't. It looks all smoothly blended. It's uniformly distributed. Ooh, it's a homogenous mixture. What about seashells in cement? Well, we can clearly see the seashells and the cement separately.

4:08So this is a heterogeneous mixture. Okay, what about sand and water? Well, you can see the sand over here and the water over here, we can see the different parts. So, again, it's a heterogeneous mixture. What about ink? Hey, ink looks like a single substance. We cannot see the different parts that make it up.

4:29Ink is a homogenous mixture. Okay, what about a brass bowl? Well, can we see the different parts that make it up? Nope, we can't. So it looks the same throughout. It's a homogenous mixture. What about copper wire? Well, again, we cannot see the different parts that make it up.

4:48So we might think it's a homogenous mixture. But this was a trick question, because guess what? Copper is a pure substance, it's not a mixture at all. So this brings up an interesting point. Homogenous mixtures can look very similar to pure substances. So just by looking, it's not always possible to tell them apart.

5:10And that's why scientists use special tests to figure out whether something is a pure substance or a homogenous mixture. And this is not just important for scientists, it's important for us too. For example, if you're buying gold, you want to be sure that you're buying a pure gold, not a homogenous mixture of gold and something else, right?

5:36And that's why learning about this is really important. So to summarize, substances can be of two kinds. We have pure substances, which can only made of one kind of substance and they cannot be physically separated into more substances. Examples are gold water, copper, oxygen.

5:55They're all pure substances. And mixtures are made of two or more kinds of substances. Mixtures can be physically separated into substances that make them up. And these mixtures can be of two kinds. We have homogenous mixtures that look the same throughout because their substances are uniformly distributed.

6:15And we have heterogeneous mixtures, they do not look the same throughout. Different parts can be easily seen because their substances are not uniformly distributed.