An Introduction to Simple Distillation

Summary

This script delves into the principles of simple distillation, explaining how it purifies liquids from mixtures. It covers key chemistry laws like Raoult's and Dalton's, and the Ideal Gas Law, which are crucial for understanding vapor pressures and mole fractions. Using a hypothetical mixture of toluene and benzene, the script demonstrates how distillation can concentrate one component over another. It introduces a simple distillation apparatus and explains its components, showing how it can be used to enrich a sample. The script concludes with a discussion on liquid vapor composition plots, which predict distillation efficiency, setting the stage for further exploration of achieving pure samples.

Takeaways

• 🔬 **Fundamental Laws**: The script discusses the importance of Raoult's Law, Dalton's Law, and the Ideal Gas Law in understanding simple distillation.
• 🌡️ **Vapor Pressure**: Raoult's Law predicts that the vapor pressure of a component in a mixture is the product of its mole fraction and its vapor pressure when pure.
• 🌐 **Total Pressure**: Dalton's Law states that the total pressure in a system is the sum of the partial pressures of each component.
• 🔄 **Ideal Gas Law Rearrangement**: The Ideal Gas Law is rearranged to show that the mole fraction of a gas is equal to its partial pressure divided by the total pressure.
• 🧪 **Distillation Process**: Simple distillation is used to purify a liquid from a mixture by exploiting differences in vapor pressures.
• 🌡️ **Boiling Point and Composition**: The script explains how the boiling point of a mixture and the composition of the vapor phase can be predicted using the mentioned laws.
• 🔬 **Mole Fraction in Vapor**: The vapor phase of a mixture can have a different composition than the liquid phase, which is crucial for distillation.
• 🏭 **Distillation Apparatus**: A simple distillation setup includes a boiling flask, a condenser, and a receiving flask to collect the purified substance.
• 🔍 **Liquid Vapor Composition Plot**: This plot helps predict the efficiency of simple distillation by showing the relationship between temperature and mole percent of a component in the vapor phase.
• 🚀 **Purification Goal**: The script concludes by hinting at the next discussion on achieving a 100% pure sample through distillation techniques.

Q & A

What is the significance of Raoult's Law in simple distillation?

Raoult's Law is crucial in simple distillation as it predicts that the vapor pressure exerted by a liquid in a mixture is equal to the vapor pressure of that liquid when it is pure, multiplied by its mole fraction within the mixture.

How does Dalton's Law relate to the total pressure in a distillation system?

Dalton's Law states that the total pressure in any system is equal to the sum of the vapor pressures of each component, regardless of the identity of that component. This is important in distillation as it helps to understand the overall pressure exerted by a mixture of liquids.

What rearrangement of the Ideal Gas Law is used to relate the mole fraction to the partial pressure?

The Ideal Gas Law is rearranged to PV/nT = R, which allows for the calculation of the mole fraction of a compound as the ratio of its partial pressure to the total pressure in the system.

Why does the vapor composition differ from the liquid composition in a distillation process?

The vapor composition differs from the liquid composition because different compounds in a mixture have different volatilities, leading to different mole fractions in the vapor phase compared to the liquid phase.

What role does the boiling flask play in a simple distillation setup?

The boiling flask in a simple distillation setup is used to contain the liquid mixture, which is heated to create vapor that can be separated based on differences in volatility.

What is the purpose of the three-way condenser in a simple distillation apparatus?

The three-way condenser, or still head, in a simple distillation apparatus is used to divert vapor from the boiling flask into a cooler environment where it can be condensed and collected.

How does a West condenser contribute to the cooling process in distillation?

A West condenser contributes to the cooling process in distillation by providing a long, narrow tube with a water jacket around the outside. Cold water is circulated through this jacket, creating a cold surface area for the vapor to condense on.

What is the function of the vacuum adapter in a simple distillation setup?

The vacuum adapter in a simple distillation setup serves two purposes: it diverts the flow of condensed liquid into the receiving flask, and it has a hose barb open to the atmosphere to prevent heating a closed system.

How does the composition of the vapor phase affect the efficiency of a simple distillation?

The composition of the vapor phase directly affects the efficiency of a simple distillation because it determines the separation of components based on their relative volatilities. A higher difference in volatility leads to a more efficient separation.

What is a liquid vapor composition plot, and how is it used in distillation?

A liquid vapor composition plot is a graphical representation of the relationship between temperature and the mole percent of one constituent in a binary mixture. It is used in distillation to predict the efficiency of separating two compounds and to determine the composition of the distillate at various temperatures.

Outlines

00:00

🔬 Fundamentals of Simple Distillation

This paragraph introduces the basic principles of simple distillation, focusing on the laws of chemistry that govern the process. It starts with Raoult's Law, which states that the vapor pressure of a component in a mixture is proportional to its mole fraction in the mixture. Dalton's Law is then discussed, explaining that the total pressure in a system is the sum of the partial pressures of each component. The Ideal Gas Law is also mentioned, rearranged to show that the mole fraction of a compound in a gas phase is equal to its partial pressure divided by the total pressure. The paragraph uses these laws to predict the behavior of a distillation process, demonstrating how a mixture of toluene and benzene can be separated based on their different vapor pressures.

05:00

🌡️ Simple Distillation Apparatus and Process

The second paragraph delves into the practical application of simple distillation using an apparatus known as a simple still. It describes the components of the still, including the boiling flask, the three-way condenser (still head), the West condenser for cooling, and the vacuum adapter for directing the flow of condensed liquid. The paragraph explains how the vapor from a boiling liquid mixture is diverted into the condenser, where it cools and condenses before being collected. It also discusses the prediction of distillation efficiency using a liquid vapor composition plot, which is a graphical representation of the mole percent of a component in the liquid and vapor phases at various temperatures. The paragraph concludes by suggesting that future discussions will cover achieving a 100% pure sample through distillation.

Keywords

💡Simple Distillation

Simple distillation is a fundamental separation technique used to purify a liquid from a mixture based on differences in boiling points. In the context of the video, it is used to separate a binary mixture of toluene and benzene. The process involves heating the mixture to create vapor, which is then condensed and collected separately. The script explains how simple distillation can be understood through the application of Raoult's Law, Dalton's Law, and the Ideal Gas Law.

💡Raoult's Law

Raoult's Law states that the vapor pressure exerted by a liquid in a mixture is equal to the product of the vapor pressure of the pure liquid and its mole fraction in the mixture. This law is crucial in distillation as it predicts the partial pressure of each component in the vapor phase, which is used to calculate the composition of the vapor. The script uses Raoult's Law to predict that the vapor above a 50 mole percent benzene-toluene mixture will have a different composition.

💡Dalton's Law

Dalton's Law posits that the total pressure in a system is the sum of the partial pressures of each component in the system. This law is applied in the script to understand how the total vapor pressure is calculated from the partial pressures of individual components like toluene and benzene, which is essential for predicting the behavior of the vapor during distillation.

💡Ideal Gas Law

The Ideal Gas Law is expressed as PV = nRT, where P is pressure, V is volume, n is the number of moles, R is the ideal gas constant, and T is temperature. The script rearranges this law to PV/nT = R, which allows for the calculation of mole fractions based on pressures. This rearranged form is used to relate the mole fraction of a compound to its partial pressure in the vapor phase, which is critical for predicting the outcome of a distillation process.

💡Mole Fraction

Mole fraction is the ratio of the number of moles of a particular component to the total number of moles of all components in a mixture. It is a key concept in the script as it relates to the composition of the vapor phase during distillation. The script explains that the mole fraction of a compound in the vapor phase can be determined by its partial pressure relative to the total pressure, which is essential for understanding the efficiency of the distillation process.

💡Vapor Pressure

Vapor pressure is the pressure exerted by a vapor in equilibrium with its condensed phases at a given temperature. In the context of the script, vapor pressure is used to predict the behavior of the components in a boiling mixture. For instance, the partial pressures of toluene and benzene at the boiling point of the mixture are calculated to predict the composition of the vapor phase, which is crucial for the distillation process.

💡Boiling Flask

A boiling flask is a piece of laboratory equipment used to heat and boil liquids. In the script, it is part of the simple distillation apparatus where the binary mixture of toluene and benzene is heated. The boiling flask is essential for generating vapor from the liquid mixture, which is then subjected to distillation.

💡Three-Way Condenser

A three-way condenser, also known as a still head, is a component of the distillation apparatus that directs vapor from the boiling flask to a cooling environment for condensation. The script describes its role in the distillation process, where it diverts vapor into a West condenser for condensation and subsequent collection.

💡West Condenser

A West condenser is a type of condenser used in distillation to cool and condense vapors. It is characterized by a long, narrow tube with a water jacket around it. In the script, it is used to cool the vapor from the boiling flask, allowing it to condense back into a liquid. The West condenser plays a critical role in the distillation process by providing a cold surface for vapor to condense on.

💡Vacuum Adapter

A vacuum adapter is a piece of equipment used to connect the condenser to a receiving flask and to the atmosphere. In the script, it serves two purposes: to direct the condensed liquid into the receiving flask and to maintain an open system, preventing pressure build-up during heating. The vacuum adapter is essential for the safe and controlled operation of the distillation apparatus.

💡Receiving Flask

A receiving flask is a container used to collect the condensed liquid in a distillation setup. In the script, it is placed over an ice bath to keep the condensed liquid cool. The receiving flask is where the purified or enriched component is collected after distillation, which in the case of the script's example, would be the enriched benzene.

💡Liquid Vapor Composition Plot

A liquid vapor composition plot is a graphical representation used to predict the efficiency of a simple distillation. It plots temperature against the mole percent of one constituent in a binary mixture. The script describes how such a plot is constructed and used to determine the composition of the distillate. This plot is a visual tool that helps in understanding the separation of components during distillation.

Highlights

Raoul's law states that the vapor pressure of a liquid in a mixture is equal to the vapor pressure of the pure liquid times its mole fraction.

Dalton's law predicts the total pressure in a system is the sum of the vapor pressures of each component.

The Ideal Gas Law, rearranged as PV/nT = R, allows relating the pressure and mole fraction of a gas.

Mole fraction is equal to the partial pressure of a compound divided by the total pressure in the system.

Distillation can purify a liquid by exploiting differences in vapor pressures of components in a mixture.

A binary mixture of toluene and benzene is used to illustrate the distillation process.

At the boiling point, the partial pressures of toluene and benzene are 300 Torr and 1200 Torr, respectively.

The vapor phase of a 50 mole percent benzene mixture is predicted to be 80 mole percent benzene.

A simple distillation apparatus, or still, is composed of a boiling flask, a condenser, and a receiving flask.

The West condenser cools vapor, allowing it to recondense before collection.

The vacuum adapter diverts condensed liquid and prevents heating a closed system.

The receiving flask collects the condensed vapor, which is enriched in the more volatile component.

Distillation enriches benzene in the vapor phase to 80 mole percent from an original 50 mole percent mixture.

A liquid vapor composition plot predicts the efficiency of simple distillation for separating compounds.

The plot is generated by plotting temperature against mole percent of one constituent at various compositions.

The curve on the liquid vapor composition plot represents the behavior of the system during distillation.

The plot can be used to determine the composition of the distillate without complex calculations.

Future discussions will cover achieving 100 percent purity in distillation processes.

Transcripts

welcome to a brief discussion of the

fundamental concepts behind simple

distillation in order to properly

understand how it is that simple

distillation can allow us to purify one

liquid from a mixture we need to go back

to general chemistry and think about

several of the important laws that we

use during that course the first of

these is routs law which predicts that

the vapor pressure exerted by a liquid

in a mixture is equal to the vapor

pressure of that liquid when it is pure

times its mole fraction within the

mixture

the second is dalton's law which

predicts that the total pressure in any

system is equal to the sum of the vapor

pressures of each component regardless

of the identity of that component and

finally we need to think about ideal gas

law for a moment PV equals NRT is the

most commonly shown arrangement of this

particular equation but we need to

rearrange this to PV over NT equals R

giving us an equation which has a

constant result for all gases at all

times because of this we could say the

pressure of compound a and the number of

moles of compound a can be related to

the pressure in the system overall and

the total amount within there notice

that in this case when we arrange the

equations this way for two different

sets of gases if they're contained

within the same space volumes will

cancel and of course if they're within

the same space they must be at the same

temperature meaning the temperatures

will also cancel from this equation

leaving us with a more simple equality

we can rearrange this equality to arrive

at an expression where the number of

moles of a over the total number of

moles is equal to the partial pressure

of a over the total pressure in other

words the mole fraction of any compound

is simply equal to is partial pressure

in the system divided by the total

pressure within the system now let's

take a look at how we can use these

three observations to predict how a

distillation will behave

shown here is a beaker filled with a

liquid it's a binary mixture of two

different compounds in this case we're

going to say that the blue spheres

represent molecules of toluene and that

the red spheres represent molecules of

benzene so the depiction here would be

of a mixture which is about 50 mole

percent benzene and toluene

we go to the data tables we find that at

the boiling point of this mixture the

partial pressure of toluene or pure at

this temperature it was 300 Torr

well the partial pressure exerted by

benzene would be 1200 Torr if we apply

rounds law to this system what we find

is that the partial pressure exerted by

the toluene is actually 150 tor because

it's mole fraction is 0.5 and similarly

benzene is expected to exert a vapor

pressure equal to half that of pure

benzene at this temperature or 600 Torr

relying on ideal gas law to convert

these partial pressures to a mole

fraction we arrive at the conclusion

that the vapor above this liquid is in

fact not 50 mole percent benzene but

rather 80 mole percent benzene so by

boiling the mixture we have created a

vapor which is more concentrated in

benzene than the original liquid now we

need to come up with an apparatus which

will allow us to take advantage of the

fact that this vapor is of a different

composition depicted in this image is a

simple distillation apparatus or a

simple still the components of the

simple steel are as follows a boiling

flask which is placed on a heat source

next is a three-way condenser or it's

still head whose purpose is to divert

vapor from the headspace of the boiling

flask into a cooler environment where it

can be recondense and collected the

cooling is provided by a device known as

a West condenser which is a long narrow

tube with a water jacket around the

outside water is plumbed in the bottom

and out the top of the West condenser in

order to provide cold surface area on

which

vapor can rican dense next we had a

vacuum adapter at the end of the West

condenser the vacuum adapter serves two

purposes first diverting the flow of our

condensed liquid into our receiving

flask and second having a hose barb open

to the atmosphere which means that we're

not heating a closed system finally the

material flows through the vacuum

adapter into a receiving flask which is

placed over an ice bath or kept cool in

some other fashion so that the condensed

liquid remains in the liquid phase if we

place our liquid mixture back into the

boiling flask and we heat this mixture

will notice that the vapor will still

begin to form at a ratio of 80% benzene

to 20% toluene however in this case

because we have the steelhead attached

instead of simply escaping the vapor is

now diverted into the West condenser

where it can later be collected and

you'll notice if you watch carefully

that only about one in five molecules

which escapes this boiling liquid is

actually toluene or as one in two

molecules in the embroiling liquid is

toluene so to take a look at an overall

simple still as it operates we'll look

at the entire system now again we built

our simple still by attaching a boiling

flask to a steelhead which diverts the

flow of gas into a West condenser and

that liquid then drains through the

vacuum adapter ultimately landing in the

receiving flask where it is collected if

we begin with the mixture of 50 mole

percent benzene our calculations based

upon route

Dalton's and ideal gas laws leads us to

the prediction that what will accumulate

in the receiving flask is in fact 80

mole percent benzene

and over time we will collect a usable

amount of our enriched benzene sample

the liquid vapor composition plot is

typically used to try to predict how

efficient a simple distillation will be

when separating two compounds from one

another in order to construct a liquid

vapor composition plot a plot is

generated on which temperature is

plotted as a function of mole percent of

one constituent of the binary mixture in

our case we'll use benzene we can start

by tracing a line at the temperature at

which we know our mixture was boiling at

this particular temperature a mixture of

50 mole percent benzene and toluene is

expected to boil recall from our

calculations we determined that that 50

mole percent benzene mixture will

actually be 80 mole percent when it

reaches the vapor phase so we're going

to plot these two points along our

temperature line first the 50 percent

liquid composition and then the 80

percent vapor composition if we were to

perform similar calculations for a range

of temperatures in a range of

compositions what we would find is that

there is a curve associated with the

behavior of these systems and we can

then connect the dots to produce what is

known as a liquid vapor composition plot

now that we have this information we can

instead of using the routs law

calculation simply go to the plot and

select the composition with which we

know we'll be starting and then

determine the composition of the

distillate when a simple distillation is

performed in our next installment we'll

discuss what to do when we want to have

that 100 percent pure sample rather than

something that is in our example eighty

percent pure