 Hi guys, my name is Josh and I am currently studying my second year of my PhD at the Australian National University and my research is in organic synthetic chemistry and what this means is that on a regular basis I have to be able to synthesize new compounds that no one's ever made before and figure out how to purify them to get nice clean compounds out the other end. So let's take a look at how these work and some real examples that I do in the lab. The way that we go about doing these separations in the lab is to exploit differences in physical and chemical properties between compounds. Now these properties can range from things like size or the electrostatics of the compounds to the density or the solubility. I'll run you through a few of these techniques and see how they utilize these differences to purify complicated mixtures of products. So the first difference that I'll talk to you about is the difference in size between molecules and in the same way that in a kitchen you would use a sieve to separate small particles from large particles we can use something called a molecular sieve to separate small molecules from large molecules. In addition we can also use a technique called gel electrophoresis particularly with proteins to separate different fragments of proteins that have been chopped up by their size. So next we have differences in solubility and density and these two properties often go hand in hand when we're trying to separate a mixture. As you can see here I've got two separate layers of material in my separating funnel. One of them is organic and one of them is aqueous. Now we can use differences in solubility of molecules to get them to dissolve in either the organic layer or the aqueous layer and then we can separate out these layers of solution to remove either aqueous or organic impurities from a given solution. Another really important part of this separation technique is utilizing differences in density. As you can see the organic layer and the aqueous layer are both not miscible with each other and also in this example the organic layer is less dense than the aqueous layer and so we can get them to separate without forming a painful emulsion to deal with. Next in this experiment I can utilize differences in boiling points to separate mixtures. So now my mixture is a mixture of the solvent that I've used to dissolve my solution and my solid mixture of products and I want to remove the solvent. So I can use the boiling point, the low boiling point of this solution to evaporate it off leaving just the solid product that I want. In the same way we can also use differences in the melting point between compounds. So instead of looking at the boiling point where we're evaporating off our solvent or our product we look at the freezing point where our product will crash out of solution as crystals or a powder and then we can use filtration to remove the non-crystalline parts of the mixture and leave us with nice clean crystals. We can also use differences in electronic properties of molecules to separate components of these compounds. For example if a compound is made up of one or more ions like a salt for example sodium chloride we can use an electric current to force one ion maybe the positive ion to one electrode and the negative ion gets pushed to the other electrode and in this way we can separate ions in a solution from each other.