Analytical Chemistry

Learn the toughest concepts covered in your Analytical Chemistry class with step-by-step video tutorials and practice problems.

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Filtration & Evaporation

Filtration and evaporation are methods that separate solids from liquid mixtures. 

Filtration and Evaporation




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in this video, we take a look at the methods of filtration versus evaporation. So when it comes to filtration, we're gonna say that this technique involves the separation of an insoluble solid. So that means the solid hasn't dissolved from a liquid by its movement through a filter. Now we're gonna see that this insoluble solid is left behind on the filter paper and is termed the residue. So you're solid that's left on your filter paper will be called the residue. And then we're gonna say the solvent passes through the filter paper and is termed the fill trait. Now this can be accomplished by two different methods. So in this first method we have a regular beaker here and here we have a regular funnel. Now this funnel has a rounded filter paper. Your filter paper here is circular. What you do here first is you fold it in half and then you fold it in half again. And then what you do is you open it up and put your hand through it and it'll form kind of like think of those plastic cups that you have like at a water cooler in an office, right? So they kind of look like this three dimensionally. Okay, so that's how your filter paper will look if you do these folds, you place them here within the funnel, so it forms a semi permeable membrane. So here you're gonna take your solution that has dissolved solid in it, you're gonna pour it in. So the liquid portion will pass through the filter paper and here you have your fill trait. And then what you have left at the end on this filter paper will be a residue. The solid left behind. Another method to do this with is with a Buckner. Funny. So this one is different. This one here, we don't give it as much time for the liquid to drain out. Instead we use a Buckner funnel with a Buckner flask. We attach a hose here which is connected to a vacuum. So we turn that vacuum on and it's gonna basically force the liquid to come out of here much quicker. So that at the end we're gonna have uh we're gonna have a filter paper here inside of this with little holes in it for the water to pass through on this filter paper will have again solid being left behind. Okay, so that's what would happen here in this Butner funnel method, usually the solid isn't completely seen, it may have partially dissolved within the solvent. So you're gonna take that solution and just pour it in. And because we're using this vacuum, it'll get cold enough within the Buckner funnel so that some of that solid reforms on the filter paper. Okay, so this first version is best if we have clear insoluble solids that haven't dissolved in this second method, the solid has dissolved some but we can get more of it to re crystallize and become a solid again by using this buck, no funnel with a vacuum attached. Now here, a common example for filters is a coffee filter. It separates the the grit and the grind that's left behind. Once you've grounded up those those beans and it leaves behind just the coffee, right? So within its liquid form. So that's a common everyday use appliance, which covers this concept of filtration. Now, besides filtration, we have evaporation. This technique is similar but slightly different in evaporation. The technique involves the separation of a soluble solid so the solid here is completely soluble, it's dissolved within my solvent. So here we're separating the soluble solid from the liquid based on the boiling point of the solvent, the liquid portion. So we basically heat up the solution, the solvent portion. The liquid portion will evaporate off, leaving behind your solid. So you're gonna form chunks of solid material at the bottom of this heating heating bowl here or evaporation bowl. We can also sometimes refer to this process as crystallization. Okay, so we're just heating up the solution to drive off the liquid portion and re crystallize our solids at the bottom of this container here. Both similar processes for separating a solid from a liquid