- Separations and purifications questions
- Simple and fractional distillations
- Principles of chromatography
- Basics of chromatography
- Thin layer chromatography (TLC)
- Calculating retention factors for TLC
- Column chromatography
- Gas chromatography
- Gel electrophoresis
- Resolution of enantiomers
Simple and fractional distillations
Learn how chemicals can be separated and purified through distillation, a process which separates them based on their respective boiling points. By Angela Guerrero. . Created by Angela Guerrero.
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- If H2O is going in and out of the condenser, how does it not mix with the distilled substance?(15 votes)
- It is going into a separate part of the condenser. The condenser is a tube with two walls, so you have two chambers that are totally separate from each other. The water runs through the outside chamber, cooling the wall of the inside chamber so that your con condense your product.(36 votes)
- Could you help me understand the importance of the vacuum adaptor2:30(1 vote)
- The vacuum lowers the pressure, making it easier to reach higher boiling points. Boiling occurs when the liquid's vapor pressure is equal to the pressure of the gas above it, so lowering the gas pressure makes it possible to boil liquids at a lower temperature.(6 votes)
- At8:42, how do the "stars" condense the ethanol and water (in the fractionating column)? Do the "stars" have to be cold or something?(2 votes)
- Most of the time the stars that are shown are cold glass beads, and retain their temprature.(2 votes)
- At5:30we learn about the temperature plateau of the mixture due to the phase change of the acetone molecules as they reach their boiling point. How come the temperature of the entire mixture plateaus if the remaining molecules haven't reached their boiling point yet?(1 vote)
- This is because the energy normally associated with raising the temperature (increasing molecular kinetic energy) goes into breaking the attractive forces between the molecules (a phase change).
This energy is called latent heat energy. For evaporation and condensation, it is the latent heat of vaporisation.
Another way to think of this is to imagine the acetone molecules in the phase change process drawing energy from the other molecules.(4 votes)
- Would the setup for distillation be the exact same thing shown in the video or would it be on a larger scale?(2 votes)
- Could someone tell me if a liebig condensor is used in either of these examples?(2 votes)
- It is, Liebig condenser is very similar to simple distillation though, it has a water jacket around it and a thermometer, whereas simple distillation just has a pipe and two tubes connecting it(1 vote)
- At8:11,does the filling of the fractional column means that filling it with some substance in along its sides or just pouring it just like that so that it would get mixed with the components that has to be separated out?(1 vote)
- No, it doesn't have to be along the sides. You need to fill the column with the packaging materials with some air space, of course. This is done so that the more volatile material a.k.a the substance with lower boiling point gets to go out into the flask, while the less volatile matter just remains within the column. Because think about it, if the more volatile substance will pass through the tube while the less volatile material will keep hitting the packaging material, which here is the stars and thus it'll just keep condensing again. The more volatile material will keep hitting the stars too, but they will boil very quickly as opposed to the less volatile substance. In the end, if you want to separate the less volatile substance, which here is water, just let the column cool off for a while after you have completely separated the alcohol and the water will eventually drip down the column into the distilling flask.(2 votes)
- How can we separate Naphthalene and Ammonium Chloride?(1 vote)
- Naphthalene is highly insoluble in water while ammonium
chloride is not.
We can add distilled water to the mixture to dissolve the
ammonium chloride and then recover the ammonium
chloride by evaporation; the naphthalene will not
dissolve in water in any substantial quantity, therefore
you can separate naphthalene from ammonium chloride.(2 votes)
- In my text book, it says in fractional distillation, the vapour is run through glass beads, allowing the compound with the higher boiling point to repeatedly condense and fall back into the solution. however, in this video she is saying that the compound will go up and will be transferred to the other glass. Which one is right?(1 vote)
- If fractional distillation is more precise, why is simple distillation used at all? Why not only use fractional?(1 vote)
Have you ever wondered why vodka is such a strong alcoholic drink compared to other beverages? That's because they use a process known as distillation once or even multiple times to increase the concentration of ethanol in the drink. Today, we'll be talking about how distillation works. You can do this in your organic chemistry lab, and let's take a look at the setup I've drawn here. First, in green, you have what's called the distilling flask. This is where you put in your mixture of compounds that you want to separate out. Next, in orange, you have your oil bath. You want to use an oil bath, because oil won't evaporate when you heat it up, and it's good for maintaining a constant temperature throughout this process. Shown up there in red, you have the thermometer. You need to be able to measure what temperature your compounds are boiling out at. And shown in yellow is the condenser. With a condenser, water has to cycle in and then out. This keeps the condenser cool, and the reason the condenser needs to be cool is because distillation involves a series of vaporizations and condensations. So initially what happens is, you have some liquid in your distilling flask, and as it gets heated up, it turns into a gas. Then, because the condenser is so cool, it'll condense down the distilling flask, ultimately landing here in the pink receiving flask as a liquid. This also needs to be kept cold. So what I've shown here in blue is the ice bath. And again, it's kept cold for the exact same reasons. You want this whole right side of the setup to be cold, so that the liquid can readily condense back into its pure form. There's one more tiny thing we haven't labeled yet, and that's this. This is a vacuum adapter. Why would you need a vacuum in distillation, you might ask. Isn't it enough to just heat it up really hot to get it to evaporate to a gas? Well, no actually, because sometimes you have compounds that have very, very high boiling points. If you have such a high boiling point, it can be difficult to distill. But lowering the pressure of the entire system makes it easier to vaporize substances, because at lower pressure there isn't much of a force pushing back down on the liquid, which makes it so much easier for it to vaporize upwards into the gas phase. Let's take a two-component mixture. The first thing you have is hexane, and I'll show that here in the flask. The second thing you have is toluene. This is a pretty conjugated aromatic ring, which is why it has a higher boiling point, and I'll also show that here in the flask. How do we monitor what's going on during a distillation? Usually, you'd want to plot this out in the form of a graph. We're plotting temperature versus time, with temperature on the y-axis and time on the x-axis. And what happens first is, initially, you're just heating up the system. So the temperature's rising slowly but surely. When you approach the boiling point of hexane, around 68 degrees, you see a plateau. Why is it that you see a plateau? Let's quickly review what happens during a phase change. The temperature stays constant. What you'll see here as the hexane is going from liquid to gas is it gets vaporized up here. You'll see this temperature register in the thermometer, and then it'll condense back down into the liquid phase since this side is so cool, and there you'll be collecting these two drops of hexane. What happens after we've collected that flask? What you'll see again is an increase in temperature. And make sure to switch out your receiving flask. You'll see me magically change the color of the flask to show that this is a brand new flask for collecting pure toluene. You have this toluene now at 110 degrees, again hitting a plateau, because once more that represents a phase change going from liquid to gas, then condensing back into liquid again and dripping into this new receiving flask. So ultimately what we've collected are these two flasks, one with toluene and one with hexane. And there we were able to do a pretty successful distillation. What happens if instead you have a three-component mixture? Well, this works pretty much the same as a two-component mixture, except that you'll see more plateaus in your graph of temperature versus time, which I'll draw here on the side. The first compound that we have here is acetone, which looks like this. The next one is cyclohexane, which has a slightly higher boiling point. And lastly, you have acetic acid. This has a higher boiling point than the other compounds, because it's capable of hydrogen bonding, meaning there's more forces between the acetic acid molecules, making it harder to pull them apart into the gas phase. So again, let's look at our graph. First, what you might see again is a slight increase at the beginning when you're just heating up your flask. But as soon as you hit 56 degrees, you'll see that plateau as acetone vaporizes and condenses. Then, you'll see the temperature increase again until 81 degrees, where it'll hit a plateau, and that represents cyclohexane vaporizing and condensing. Lastly, you'll see another increase. And finally, you'll be able to get acetic acid. Let's take our final example and answer the question, how is it that they get vodka and other drinks to be so strong. To produce strong drinks, this is the kind of distillation they might need to do. As you can see, ethanol and water, their boiling points aren't too different from each other, only 22 degrees Celsius. Do you think that will affect what happens during the distillation process? Well ideally, what you'd want to see in your graph of temperature versus time is like what we've seen in the past. You'd hope that what would come out is something that looks like an increase in temperature, followed by a plateau at 78 degrees, followed by another sharp increase, and finally a plateau at 100 degrees. However, that's not really what happens. Instead what you get is something that looks kind of like this purple graph. You might get this increase at the beginning, but instead here you have this slope. Why is this is a problem? Well, before you might have been able to get the pure ethanol, meaning the pink line, and pure water separate. But here, they're kind of mixing into this purple. So anything you see between these two points isn't really pure ethanol or pure water, it's some mixture of the two. And if you're still getting a mixture, it means your alcohol still isn't very strong. So how can we fix this problem? You might think, what happens if I distill the compound again? If you were to distill this compound again, the next time you might get something that looks kind of like this orange line. This would be a little bit flatter, maybe it would get a little bit steeper than before, but it still wouldn't be very pure. And if you kept distilling it over and over again, you might eventually reach what you had hoped to get in the beginning, that ideal blue and pink separation. But just doing a simple distillation multiple times can be extremely time consuming, so is there another way we can do it? There's actually another setup that will allow us to effectively do multiple distillations at once. This is known as fractional distillation. If you look at this picture in the right, the only thing different between this picture in the picture on the left is that you have a fractionating column here. This column can be filled with a number of substances, such as beads or other things, but just for fun I'm going to fill it with some stars. So you see, you want to completely fill this column. And how does that affect what goes on during distillation? If you had your two compounds again-- let's just say that you have purple representing two compounds in here-- what happens is that instead of just going straight up, vaporizing once, and then condensing again, it will go up, vaporize, and then maybe condense onto one of these stars. And from there, it'll vaporize again then condense into another of these stars. So as it goes up and up past the packaging material, it's going through so many vaporizations and condensations so that when it finally does reach the receiving flask, it'll be much purer than what you would get through just one simple distillation. So let's summarize what we've talked about today. We talked about how you would set up a simple distillation and how that's great for separating out compounds with pretty big boiling point differences, say a difference bigger than 25 to 30 degrees Celsius, and fractional distillation, which is great for separating out compounds with smaller differences in boiling point.