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General Chemistry

Learn the toughest concepts covered in Chemistry with step-by-step video tutorials and practice problems by world-class tutors

4. BONUS: Lab Techniques and Procedures

Distillation & Floatation

Distillation and Floatation represent procedures that can be used to separate components of a mixture. 

Mixture Separation

Distillation can be used to separate liquids or gases based on their different boiling points, while floatation can be used to separate solids based on their different densities. 


Distillation and Floatation

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Now in order to separate the different components of a mixture, it first must be heterogeneous. So we need them to be in different phases from one another. Now in this form, each component maintains its individual physical properties. Now chemical reactions rarely produce a single pure product. So these types of mixtures are common now with distillation, we're going to have two different apparatuses that we can use for distillation. We're going to say This technique involves the separation of liquids and gasses based on a difference in their boiling points. There are many types of distillation methods, but the two most common forms are simple and fractional distillation. So from these two images, the one on the left represents a simple installation and the one on the right represents a fractional distillation. Now they have some things in common with one another, but they also have some differences. We're gonna say they both have thermometers here which helped to monitor the temperature because we're trying to figure out differences in boiling point. And let's say that both of them have a mixture of few compounds, one compound and one compound beat and both of them have a heating source here. This one's using a Bunsen burner. This one here is using a hot plate. They both serve the same function to heat up our mixture. And what we're going to say here is that for the simple distillation and and for the fraction, let's say that compound A is methanol. Methanol is an alcohol With a boiling point equal to 67°C compound B let's make it water which we know its boiling point is 100 degrees Celsius. So both of these sources are going to heat up my mixture. What's gonna start happening is they're gonna vaporize and become a gas. And we're gonna travel up here and up here in the fractional distillation we have here, what's called a fractional column. We don't have that with simple distillation in this fractional column. We have little beats. These little beads are supposed to help us to have more surface area for the gas particles to travel to. This also serves another purpose because it helps to lengthen the amount of time it takes for the gas molecules to get through the column. In doing that. Some of them are going to re condense back into a liquid. This helps us to increase the cycles of vaporization and condensation, fractional distillation is a longer process. What happens now is some of the gas particles will travel here and travel here and they're gonna get to these two tubes. Both of them are called leibig condensers, basically they're both connected to hoses. This host here is cold water that's going into the tube and filling it up here and this one helps the cold water to exit. You have warm gas traveling through this tube traveling through this tube and on either side we have cold water. This is gonna help it to condense and so it's gonna drip down as liquid here with simple distillation. It's faster and you make a bigger yield of this fill. Trade here. Unfortunately it is not as pure you're gonna get, let's say you wanted to isolate ethanol, ethanol vapors rise sooner because it has a lower boiling point. You're trying to isolate ethanol but you're gonna have a mixture of ethanol and water here with fractional distillation. The process is longer because it has to travel through the fractional column which has those beads. But you're going to get a much better pure product at the end here, it's gonna be a majority of a, most of the water is gonna re condense back down drip into here. Get vaporized again, you're gonna have more cycles of condensation and vaporization. Now, simple distillation is great. If you're two substances have boiling point difference is greater than 25°C. So in this example I use methanol and water. Their difference in temperature is 33°C. So simple distillation here will be good. But let's say that we changed compound a from methanol to ethanol if I change it to that Its boiling point is now 97°C. Those temperatures are too close. So simple distillation will not work. You will need to use fractional distillation fractional distillation works better if the boiling point difference between your two liquids is less than 25 degrees Celsius here, the process is longer, you don't make as much of this Phil trait liquid. But it's going to be very pure, it's gonna be more of ethanol or methanol. Now here, if we take a look at this graph, let's say here that we have temperature and we can have it into Greece, Celsius or kelvin up to you and it's increasing as we go up. And let's say, we're going back to our original methanol, uh methanol water mix. So here we have mole fraction of methanol and here we have mole fraction of water. So here, let's say we start out with zero amount of methanol and here we have just all water Over time, our amount of methanol would increase a 0. 0.40 0.60 0.80. And then here 100% methanol and here zero 0.20 0.40 0.60 And then .80. So we're starting out here and let's say we're starting out with a sample that is um a lot of methanol or I mean a lot of water initially, as we start to vaporize our mixture, We're trying to get to the point where we have 100% of the filter, right? We want, which in this case is not at all. Each one of these levels represents a vaporization that occurred vaporization one, two and three. Because I told you through the, through the glass beads are in the fractional column, the gasses travel, it takes so long that some of it re condenses back into water at the bottom. Words vaporized again and go through the whole process, We're gonna have more instances of vaporization and condensation which causes more cycles of vaporization to happen With the hope of when you get to your fill trade at the end, it's gonna be 100 methanol And 0% of water. And what you have back in the original container that's still on the hot plate is just water. So this is what this is showing us is showing us a vaporization condensation cycle that's occurring within fractional distillation. So just remember if you're trying to make it quick and try to get the two samples separated and their temperatures are greater than 25°C in terms of boiling point, you can go with simple distillation. But if you want a pure fill trade at the end, fractional distillation is the better option.