 In a previous video we looked at pure substances and mixtures. Mixtures are made by combining pure substances in various ways, but sometimes you have a mixture and you want to do some kind of separation on it so that you can retrieve the pure substances from it. In this video we'll look at various ways that you can separate mixtures by making use of the physical properties of the things that are in the mixtures. Recall from the last few videos that we talked about different kinds of physical properties. Here's a list, including a couple of new ones, magnetism and electrostatic attraction, that can be particularly useful when you want to separate substances. The first one, and perhaps the one you'd have most experience with in everyday life, is particle size. If the components of a mixture are of different sizes, then some kind of filter can be used to separate them out. When you drain the water from pasta in a colander, you're filtering. The big pieces of pasta stay behind while the water flows through the holes of the colander. These archaeologists are using a wire mesh to sift dirt to find artefacts from a dig in India. It uses the same principle. In the lab the most common piece of equipment that uses this effect is the filter funnel and filter paper. You pour the mixture into the paper and the paper filters out the solids. A faster method of doing the same thing is the booker funnel, which uses a vacuum to suck the liquid through the filter paper faster. Magnetism is another useful property for separating things. If one of the components of your mixture is magnetic, a magnet can be used to attract it away from the other components. Recycling centres use this to remove magnetic material from mixed recycling streams. You can see in this diagram that the roller at the end of the conveyor belt is magnetic, meaning that the red particles, which must be magnetic themselves or respond to magnets, get pulled around underneath the roller and so are separated out from the blue ones. Tiny magnetic beads are also used by molecular biologists. The beads can be treated so that specific DNA molecules bind to them. That means that particular molecules can be easily removed from solution simply by collecting the beads with a magnet. Solubility can also be used to separate substances. At its most basic, if you had a soluble and an insoluble substance mixed together, you could put both of them in water or some other solvent and then filter out the insoluble one. This is used by students the world over in the classic salt and sand separation problem. But solubility can be used in more subtle ways. For instance, if you have two substances that have different solubilities, one is more soluble than the other, then it's possible to carefully control the evaporation of the solvent in which they're dissolved so that one substance crystallizes out before the other one does. If substances have different melting and boiling points, these can also be used to separate them out. When your ice cream melts and then refreezes, you'll often find that crunchy ice crystals are formed on the surface. This is an example of the solidifying pure water, which freezes at zero degrees Celsius, separating out by crystallization from the still liquid fats of the cream and other ingredients. Distillation is another technique that uses these properties. A mixture of two liquids can be separated by heating them until one of the liquids boils. The apparatus you use to do this in the lab looks like this. The liquids are heated in the flask here and one of them will vaporize before the other and travel up the column here, thermometer is for monitoring the temperature. The vapor of your separated substance will travel down into the condenser and this has a glass jacket around it through which you flow cool water. That cools the vapor down, it condenses back into a liquid and then you can collect it at the other end here. Ethanol, that's alcohol, is purified from alcohol water solutions by this method. Distillation is also frequently used in industry. For instance crude oil is separated into thick oils, petrol and light hydrocarbons by this method since all these components have different boiling points. But a much larger arrangement is obviously necessary to deal with the huge quantities required. Yet another useful property is density. If a material is denser than the solution that it's in, it will sink. So a mixture of different solids shaken up in a liquid can be allowed to settle and the densest material will settle down to the bottom first. In this picture a clay slurry is settling, the liquid on top will then be decanted off and the solid material can be retrieved. To speed up the settling or decanting process, centrifugation can be used. This is where the mixture is spun around at high speeds to effectively increase the force of gravity. This technique tends to be used more in biochemistry and biology than in chemistry because they have a need to separate out, for instance, different parts of cells or different sizes of DNA or proteins. Here's a slightly odder example that uses exactly the same principle. In the name of modern cuisines some peas have been whizzed and then centrifuged. And it turns out that they separate out into the starchy pea solids, a dense layer of fatty substance, who knew peas contain fat, and watery pea juice on the top. Finally we have electrostatic attraction. The most well-known example of this is called electrophoresis and it has applications in both chemistry and biology. The principle is that a particle with a charge if placed in an electric field will move towards the oppositely charged pole. So if you had positively and negatively charged molecules you could have them move in different directions by putting them in an electric field and that would separate them. More commonly though scientists end up having to separate molecules that have the same charge. So you put the mixtures into a gel, turn on the electric field and then the smallest molecules will move faster than the big ones. And so you get separation on the basis of size. This picture shows an electrophoresis gel under UV light. A number of mixtures were loaded onto the gel at the top end here. And after being exposed to the electric field the different molecules in each mixtures moved different distances through the gel. Each pink band shows a cluster of molecules of the same size and charge. Okay so that's all our separation procedures that we're going to look at for now. The task is to design a simple separation method that you could use to separate out the products of this reaction and write it up just very briefly but in the form that you would for a scientific report including a list of equipment that you would need.