Simple and fractional distillations | Chemical processes | MCAT | Khan Academy

Summary

This script explains the process of distillation, used to increase the concentration of ethanol in beverages like vodka. It covers the setup, including a distilling flask, oil bath, thermometer, condenser, and ice bath, and the use of a vacuum to lower boiling points. The script discusses how to monitor distillation through temperature-time graphs for two- and three-component mixtures. It also addresses the challenges of distilling ethanol and water due to their close boiling points and introduces fractional distillation as a solution for purifying substances with similar boiling points.

Takeaways

• 🔬 Vodka's strength comes from the distillation process, which increases the concentration of ethanol.
• 🧪 Distillation involves heating a mixture to vaporize components and then condensing them back into a liquid.
• 🌡️ A thermometer is used to monitor the temperature at which compounds boil and condense.
• 🧊 An ice bath and condenser are used to keep the setup cold, facilitating the condensation of vapors back into liquid form.
• 🔗 The distillation setup includes a distilling flask, oil bath, thermometer, condenser, and receiving flask.
• 💧 A vacuum adapter can be used to lower the pressure, making it easier to vaporize substances with high boiling points.
• 📈 The process is monitored by plotting temperature versus time, showing plateaus at the boiling points of different compounds.
• 🌀 Fractional distillation, using a fractionating column, allows for multiple vaporizations and condensations, resulting in purer substances.
• 🥃 In the production of strong alcoholic drinks, multiple distillations or fractional distillation can be necessary due to the close boiling points of ethanol and water.
• 🔄 Repeated distillation can lead to purer substances, but it is time-consuming, making fractional distillation a more efficient method.

Q & A

What is the primary reason vodka is a strong alcoholic drink?

Vodka is a strong alcoholic drink because it undergoes a process known as distillation, which increases the concentration of ethanol in the beverage.

How does distillation work in separating compounds?

Distillation works by heating a mixture to vaporize its components based on their boiling points, then condensing the vapors in a cool environment to collect them as a liquid, effectively separating them.

What is the purpose of an oil bath in a distillation setup?

An oil bath is used in distillation because oil does not evaporate when heated, allowing it to maintain a constant temperature throughout the process.

Why is a thermometer necessary in the distillation process?

A thermometer is necessary to measure the temperature at which the compounds are boiling and vaporizing, which is crucial for monitoring the distillation process.

What is the role of a condenser in distillation?

A condenser in distillation cools the vaporized compounds, causing them to condense back into a liquid form, which can then be collected in a receiving flask.

Why is it important to keep the receiving flask cold during distillation?

Keeping the receiving flask cold ensures that the vaporized compounds condense back into their liquid form efficiently and can be collected without re-evaporating.

What is the function of a vacuum adapter in distillation?

A vacuum adapter lowers the pressure of the system, making it easier to vaporize substances with high boiling points by reducing the force pushing back down on the liquid.

How does monitoring the temperature versus time graph help in distillation?

Monitoring the temperature versus time graph helps in identifying the boiling points of different compounds and indicates when they are vaporizing and condensing, allowing for their collection at the right time.

What is the significance of a plateau in the temperature versus time graph during distillation?

A plateau in the temperature versus time graph signifies that a compound is undergoing a phase change from liquid to gas and is being vaporized and condensed at a constant temperature.

How does fractional distillation differ from simple distillation?

Fractional distillation involves a fractionating column filled with packing material, which allows for multiple vaporizations and condensations of the compounds, resulting in a purer separation compared to simple distillation.

Why might distilling a mixture with compounds that have close boiling points be challenging?

Distilling a mixture with compounds that have close boiling points can be challenging because they may not separate cleanly, resulting in a mixture rather than pure compounds, which affects the strength and purity of the final product.

Outlines

00:00

🧪 Understanding Distillation: The Science Behind Vodka's Strength

This paragraph delves into the process of distillation, a method used to increase the concentration of ethanol in beverages like vodka. The setup for a basic distillation experiment includes a distilling flask for the mixture, an oil bath for consistent heating, a thermometer to monitor temperatures, and a condenser to cool and condense vapors back into liquid form. A vacuum adapter is also mentioned for substances with high boiling points, as it facilitates vaporization under lower pressure. The paragraph explains how distillation works by heating a liquid to turn it into a gas, which then condenses back into a liquid when cooled. The process is illustrated with a two-component mixture example, showing how hexane and toluene with different boiling points can be separated through distillation. The monitoring of the distillation process is discussed, suggesting the use of a graph plotting temperature against time to track the phase changes and collect pure substances in separate flasks.

05:00

📈 Enhancing Distillation Efficiency: From Simple to Fractional Distillation

The second paragraph expands on the distillation process, focusing on the challenges and solutions when dealing with mixtures of compounds with closer boiling points, such as ethanol and water in vodka production. It describes how a simple distillation might not suffice to separate such compounds effectively, leading to a mixture rather than pure substances. The concept of fractional distillation is introduced as a more efficient method, which involves a fractionating column filled with a packing material (illustrated with stars). This setup allows for multiple vaporization and condensation cycles, significantly increasing the purity of the separated compounds. The paragraph concludes with a summary of the differences between simple and fractional distillation, with the former being suitable for compounds with large boiling point differences and the latter for those with smaller differences.

Keywords

💡Distillation

Distillation is a process used to separate mixtures based on differences in their volatilities at different temperatures. In the context of the video, distillation is used to increase the concentration of ethanol in alcoholic beverages like vodka. The script describes how distillation involves heating a liquid to turn it into a gas, which then condenses back into a liquid when cooled, allowing for the separation of components with different boiling points.

💡Ethanol

Ethanol is an organic compound with the molecular formula C2H5OH, commonly known as the type of alcohol found in alcoholic beverages. The video discusses how distillation is used to increase the concentration of ethanol in drinks, making them stronger. Ethanol has a lower boiling point than water, which is significant for the distillation process described.

💡Boiling Point

The boiling point of a substance is the temperature at which it changes from a liquid to a gas. In the video, boiling points are crucial for distillation as they determine when a substance will vaporize and can be collected. The script mentions that substances with high boiling points can be difficult to distill, which is why a vacuum adapter is used to lower the pressure and facilitate vaporization.

💡Condenser

A condenser in the context of distillation is a device that cools the vaporized substance so it can condense back into a liquid. The video explains the need for a condenser to be cool, which is achieved by circulating water through it. This is essential for the distillation process as it allows the vapor to condense and be collected in the receiving flask.

💡Vacuum Adapter

A vacuum adapter is used in distillation to lower the pressure of the system, which facilitates the vaporization of substances with high boiling points. The video script explains that without a vacuum, it would be difficult to distill compounds that require very high temperatures to vaporize, as the pressure would prevent them from easily turning into a gas.

💡Fractional Distillation

Fractional distillation is a more advanced form of distillation used to separate substances with similar boiling points. The video describes how it involves a fractionating column filled with a packing material, which causes the vapor to condense and re-vaporize multiple times, resulting in a purer separation. This is particularly useful for substances like ethanol and water, which have close boiling points.

💡Phase Change

A phase change refers to the transition of a substance from one state of matter to another, such as from liquid to gas or vice versa. The video script explains that during distillation, substances undergo a phase change as they are heated and vaporized, then cooled and condensed. This is illustrated by the plateaus in the temperature versus time graph, indicating when a substance is vaporizing and condensing.

💡Temperature versus Time Graph

In the context of the video, a temperature versus time graph is used to monitor the progress of a distillation. The graph plots the temperature of the mixture against time, showing plateaus that correspond to the boiling points of different substances. This visual representation helps in understanding when each substance is being vaporized and collected, which is crucial for the distillation process.

💡Hexane and Toluene

Hexane and toluene are two organic compounds used in the video as examples of substances that can be separated through distillation. The script explains that hexane has a lower boiling point than toluene, which is why it vaporizes and condenses first during the distillation process. These compounds are used to illustrate the basic principles of distillation.

💡Ice Bath

An ice bath is used in the distillation setup to keep the receiving flask cold. The video script mentions that the right side of the setup, including the receiving flask, needs to be cold to facilitate the condensation of the vapor back into a liquid. The ice bath helps maintain this low temperature, which is essential for the successful collection of the distilled substances.

Highlights

Vodka's strength comes from the distillation process, which increases ethanol concentration.

Distillation involves vaporization and condensation to separate compounds based on boiling points.

A distillation setup includes a distilling flask, oil bath, thermometer, condenser, and receiving flask.

An oil bath is used for maintaining a constant temperature during distillation.

A condenser is essential for cooling the vaporized compounds before they condense back into a liquid.

A vacuum adapter can be used to lower the pressure and make it easier to vaporize substances with high boiling points.

Hexane and toluene are used as an example of a two-component mixture in distillation.

Monitoring distillation is done by plotting temperature versus time, showing distinct plateaus for each compound.

Acetone, cyclohexane, and acetic acid are used as an example of a three-component mixture.

Ethanol and water have close boiling points, making their separation challenging in distillation.

Multiple distillations can be performed to achieve a purer ethanol concentration for stronger drinks.

Fractional distillation is introduced as a method to effectively perform multiple distillations at once.

A fractionating column filled with packing material, like beads or stars, aids in the separation of compounds.

Fractional distillation results in a purer substance due to multiple vaporizations and condensations.

Simple distillation is suitable for compounds with large boiling point differences, while fractional distillation is for smaller differences.

Transcripts

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.