One of the standard techniques in synthetic chemistry is filtration, which is separating solid materials from liquid materials. You can do this several ways. This video is going to talk about how to filter using gravity. Filtration is a separation process. Frequently you will have solids mixed with liquids as we do here, and you want only one of the two. Pouring the mixture through a filter paper, as we have here, allows you to separate the liquids and the solids, keeping the solid behind and the filtrate the liquid coming through. One of the most common examples of this is making coffee. Hot water and ground up coffee are mixed, and the liquid forms a hot drink that many of us consume daily. The solid coffee grounds are not too wonderful though, and so they are retained in a filter while the drinkable fluid comes through the filter and is available for consumption. There are several methods of filtering. Gravity filtration, which we are talking about today, allows separation with only gravity pushing the liquid through the filter paper. The paper is put into a funnel, supported, the slurry poured into the funnel, and the separation takes place as the liquid passes through the paper itself. Filter papers are circular, fold it in half, and then in half again. Take this quarter circle and open it with three on one side and one on the other, and you have a small cone, and that fits into the funnel. You'll need to have your funnel sitting above a receiving vessel. I'm using a flask here. You can use a beaker. Sometimes you may need to support this with a clamp, but usually it will just sit in the neck of the vessel. Take your mixture of solid and liquid, and swirl it to suspend the solid in the liquid and pour. Be careful when you're pouring that you don't over-top the liquid as it goes through, otherwise it will just run down the outside of the filter paper, and it won't be much use. Maybe that you need to take a break and pour some more if you're too much capacity. Now you may notice I didn't get all of the solid in the first time, and so what I need to do is do a second round on this and transfer it with liquid. The best liquid to use is in fact this one right here. The filtrate is already a saturated solution of my solid, and so if I transfer it here, I'm not going to lose any of the solid into solution as I would if I was using fresh water or fresh solvent. That's pretty much stopped filtering now, so I'll lift this up and just transfer the filtrate back into the beaker and swirl again and pour again. I've got almost all of the solid out that time. You can do this recycling of the filtrate as many times as you need to to get a decent separation of the solid and the liquid. In this case I'm actually interested in the solid. Sometimes you're only interested in the liquid, in which case just passing it through once as long as there's no solid left is all you need to do. Once you have finished transferring the solid into the filter paper, you may want to wash it. This won't happen all the time, but sometimes you do wish to wash it, sometimes with water, sometimes with a second solvent. In that case once it has finished dripping off, add a little bit of the second solvent and let that drip through as well. Once the wash has drained through, you're ready to remove it. Now do be careful not to overwash with either the actual solvent or a new solvent because overwashing nearly always leads to diminished product, but the washing is necessary to remove other materials. Then take the filter paper out of the funnel and spread it open. If you put this on a watch glass, it will dry more quickly. Sometimes if you can spread the solid out, you will also get a better drying time by increasing the surface area. In conclusion, filtration is a separation process designed to separate solids from liquids and sometimes to wash the solids while you're on the filter. You should now understand how to filter solids on the back row scale equipment.