 So what about mixtures? This video was supposed to be about the properties of mixtures after all. Okay, extensive properties of mixtures. Since they depend on the amount of material, there's not much of a distinction here. 10 cubic centimetres of pure water has the same volume as 10 cubic centimetres of salty water, which is a mixture. However, with intensive properties, it's a different story. Whereas for a pure substance, the intensive properties are unchanging as long as you keep those conditions constant. The intensive properties of a mixture can change, since they depend on what substances make up the mixture and the relative amount of each ingredient that is in the mixture. So let's take salty water as an example. I've got here some data that I pulled off the web which shows the concentration of different salty solutions. You can see grams of sodium chloride per 100 grams of solution, where the rest of the solution is made up of water. And then the density value for each of these solutions. So you can see the first line here. We've got 0.1 grams of sodium chloride per 100 grams, which means that 99.9 grams must be water. And the density of that solution is 0.9989 grams per centimetre cubed. Note that centimetre cubed is the same as a mill, so density is often quoted in units of grams per centimetre cubed, but that's exactly the same numerically as grams per mill. Okay, and what I'm going to do is graph this data and see if we can see any trends or changes. So we'll use a scatter graph. There we go. And I'm just going to spend a little bit of time tidying this up. There we go. Alright, so we've got our graph. And you can see that there's an obvious trend that as the concentration of salt in the salt solution increases, so does the density. This illustrates our point that the intensive property of density is not a fixed value for a mixture. It really depends on the proportions of the ingredients in the mixture. So here we've got, as you increase the proportion of salt, the density also increases. This makes sense because the atoms that sodium chloride is made up from, sodium and chlorine, each weigh more than the atoms that water is made up of, oxygen and hydrogen. So sodium and chlorine atoms weigh more and are denser than water molecules. So when you add them to water, if you increase the proportion of salt in the water, then you're making the whole solution denser. So the point here is that the concentration of our mixture determines the density. Now if you've got a nice predictable relationship like this, then if you know the density of a mixture, you can work out what its concentration is. And this is a technique that's quite frequently used for determining concentrations. If you know the ingredients of your mixture, you can determine its density and from that you can work out its concentration.