Distillation & Floatation: Study with Video Lessons, Practice Problems & Examples

To separate components of a heterogeneous mixture, distillation techniques exploit differences in boiling points. Simple distillation is effective when the boiling point difference exceeds 25°C, yielding a larger but less pure product. In contrast, fractional distillation, which includes a fractional column for enhanced vaporization and condensation cycles, is ideal for mixtures with smaller boiling point differences, producing a purer filtrate. Understanding these methods is crucial for applications in chemistry, particularly in isolating compounds like alcohols, where boiling points dictate the choice of technique.

Distillation and Floatation

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 2 different apparatuses that we can use for distillation. We're going to say this technique involves the separation of liquids and gases 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 distillation, 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 going to say they both have thermometers here, which help 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 2 compounds, 1 compound A and 1 compound B. And both of them have a heating source. Here this one's using a Bunsen burner, and 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 in the fractional distillation, let's say that compound A is methanol. Methanol is an alcohol with a boiling point equal to 67 degrees Celsius. 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 going to start happening is they're going to vaporize and become a gas, and they're going to 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 beads. 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 recondense 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 going to get to these 2 tubes. Both of them are called Liebig condensers. Basically, they're both connected to hoses. This hose 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 going to help it to condense, and so it's going to drip down as liquid here. With simple distillation, it's faster, and you make a bigger yield of this filtrate here. Unfortunately, it is not as pure. You're going to get, let's say you wanted to isolate ethanol. Ethanol will vaporize sooner because it has a lower boiling point. You're trying to isolate ethanol, but you're going to 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 going to be a majority of A. Most of the water is going to recondense back down. Drip into here, get vaporized again, you're going to have more cycles of condensation and vaporization. Now, simple distillation is great if your 2 substances have boiling point differences greater than 25 degrees Celsius. So, in this example where I use methanol and water, their difference in temperature is 33 degrees Celsius. 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 degrees Celsius. 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 filtrate liquid but it's going to be very pure it's going to 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 in degrees 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, 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 0 amount of methanol, and here we have just all water. Over time our amount of methanol would increase so 0.20, 0.40, 0.60, 0.80, and then here 100% methanol. And here is 0, 0.20, 0.40, 0.60, and then 0.80. So we're starting out here, and let's say we're starting out with a sample that is, 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 filtrate we want, which in this case is ethanol. Each one of these levels represents a vaporization that occurred, Vaporization 123. Because I told you through the glass beads that are in the fractional column, the gases travel, it takes so long that some of it reconnects back into water at the bottom, where it's vaporized again and go through the whole process. We're going to have more instances of vaporization and condensation which causes more cycles of vaporization to happen, with the hope of when you get to your filtrate at the end it's going to be a 100% methanol and 0% of water. And what you have back in the original container that's still on the hotplate is just water. So this is what this is showing us, it's 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 2 samples separated and the temperatures are greater than 25 degrees Celsius in terms of boiling point, you can go with simple distillation. But if you want a pure filtrate at the end, fractional distillation is the better option.

Here’s what students ask on this topic:

What is the difference between simple and fractional distillation?

Simple distillation and fractional distillation are both techniques used to separate components of a mixture based on differences in boiling points. Simple distillation is effective when the boiling point difference between the components is greater than 25°C. It involves heating the mixture to vaporize the component with the lower boiling point, which is then condensed and collected. Fractional distillation, on the other hand, is used when the boiling point difference is less than 25°C. It includes a fractional column filled with beads that provide a larger surface area for repeated vaporization and condensation cycles, resulting in a purer product. While simple distillation is faster and yields a larger amount of product, fractional distillation produces a more refined and pure filtrate.

How does fractional distillation work?

Fractional distillation works by exploiting the differences in boiling points of the components in a mixture. The process involves heating the mixture to vaporize the component with the lower boiling point. The vapor then travels up a fractional column filled with beads, which provide a large surface area for repeated cycles of vaporization and condensation. As the vapor ascends the column, it undergoes multiple condensation and re-vaporization steps, which help to separate the components more effectively. The vapor eventually reaches a Liebig condenser, where it is cooled and condensed back into a liquid, resulting in a purer product. This method is particularly useful for separating components with boiling point differences of less than 25°C.

When should you use simple distillation over fractional distillation?

Simple distillation should be used when the boiling point difference between the components of the mixture is greater than 25°C. This method is faster and yields a larger amount of product, although it may not be as pure as the product obtained from fractional distillation. Simple distillation is ideal for separating mixtures where the components have significantly different boiling points, such as methanol (67°C) and water (100°C). If the boiling point difference is less than 25°C, fractional distillation is recommended, as it provides a purer product through repeated cycles of vaporization and condensation.

What are the main components of a distillation apparatus?

The main components of a distillation apparatus include a heat source (such as a Bunsen burner or hot plate), a distillation flask containing the mixture, a thermometer to monitor the temperature, a condenser (such as a Liebig condenser) to cool and condense the vapor, and a receiving flask to collect the distilled liquid. In fractional distillation, an additional component called a fractional column is used. This column is filled with beads that provide a large surface area for repeated vaporization and condensation cycles, enhancing the separation of components with close boiling points.

Why is fractional distillation more effective for separating components with close boiling points?

Fractional distillation is more effective for separating components with close boiling points because it includes a fractional column filled with beads. These beads provide a large surface area for repeated cycles of vaporization and condensation. As the vapor ascends the column, it undergoes multiple condensation and re-vaporization steps, which help to separate the components more effectively. This process increases the number of theoretical plates, enhancing the separation efficiency and resulting in a purer product. Simple distillation, lacking this column, cannot achieve the same level of separation for components with close boiling points.