 The last technique that I'll show you today is perhaps the most commonly utilized technique that we have in synthetic chemistry and that is what we call column chromatography. Now you guys might think that chromatography is only really useful for separating different colors of pen ink but in synthetic chemistry we can use it for so much more than that. Firstly we have to run a thin layer chromatography plate which lets us know exactly how much our compound is going to stick to the stationary phase. Column chromatography makes use of differences in polarity between two different compounds. Now polarity is found in a molecule depending on how the electrons are distributed around the molecule. If there's one half of the molecule that has most of the electrons and another half that doesn't have many at all then that is a very polar molecule. However if the electrons are evenly distributed around the entirety of the molecule then we say that this molecule is particularly non-polar. The way that we utilize these differences is by having a stationary phase that is very very polar. So in this example here the stationary phase is a very polar substance called silica dust and the mobile phase is a combination of a variety of organic solvents such as petroleum spirits, ethyl acetate or dichloromethane. Different compounds with different polarities have different affinities to the very polar stationary phase or the less polar mobile phase. If a compound is more polar it's more likely to stick to the stationary phase and so moves slower through the silica. However if it's less polar it doesn't stick as well to the polar stationary phase and so it moves faster. Here you can see that where the yellow is moving slowly through the column and the yellow is the compounds that I desire and once this compound reaches the bottom of the column it drips out the bottom and I'm able to collect it and remove the solvent to afford my nice clean compound. So the takeaway from this video is for you guys to understand that the main way that we separate mixtures of compounds is by exploiting differences in their physical or their chemical properties which allow us to separate complicated mixtures. All of these techniques are made possible by understanding how different compounds interact and react with each other and so I hope that this video has given you a bit of a brief insight into how real world chemists use these different techniques in their real life research.