An Introduction to Simple Distillation
Summary
TLDRThis 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
🔬 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.
🌡️ 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.
Mindmap
Keywords
💡Simple Distillation
💡Raoult's Law
💡Dalton's Law
💡Ideal Gas Law
💡Mole Fraction
💡Vapor Pressure
💡Boiling Flask
💡Three-Way Condenser
💡West Condenser
💡Vacuum Adapter
💡Receiving Flask
💡Liquid Vapor Composition Plot
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
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