Boiling point
Efficiency of fractional distillation Columns: Theoretical plates
(Y1/Y2)/(X1/X2)... The composition of the vapor at the top of the column, Y1/Y2, the composition in boiler, X1/X2
boiling point dimethyl ether
-25C
See next page A) distilling flask: the mixture is heated here and the more volatile component is vaporized first B) condenser: vapors in contact with the cool glass condense to form pure liquid distillate which then goes to the receiver flask
What is A? What is it used for? What is B? What is it used for?
See next page for question Dissilation
What is this apparatus used for?
See next page for question a vapor pressure-temperature nomograph
What is this graph an example of?
See back page for question The horizontal column is used to condense vapor;The vertical column is used to increase theoretical plates for better separation
Which arrow points to the column used to condense vapor? Which is used to increase theoretical plates for better separation?
See back page for question The horizontal one uses cooling water
Which of these columns uses cooling water
using a phase diagram how do we determine the composition of vapor phase?
Y is starting concentration. Go straight up from Y until you hit the first line. Then go straight across from that point until you hit the second line. At this point go straight down, this is new composition
An ____ is a mixture of two ore more liquids in such a ratio that its composition cannot be changed by simple distillation
azeotrope
If we combine high MW compounds with water, the mixture will ____
boil at some temperature slightly less than 100C
The _____ of a compound is that temperature at which the vapor pressure equals the total pressure exerted on the liquid surface
boiling point
_______= temperature at which the vapor pressure of the liquid exactly equals the pressure exerted on it by the atmosphere
boiling point of a pure liquid
the ____ of an organic compound reflects its molecular structure, specifically the types of intermolecular interactions that _____
boiling point; bind the molecules together in the liquid state
typically you can use simple distillation to separate compounds with _______
boiling points within 100C of one another
Fractional distillation is used to separate two compounds with ____
boiling points within 40C of one another
for compounds with approximately the same molecular weight- list the following in order of increasing boiling point: compounds with dipole-dipole, compounds with hydrogen bonding, compounds with van der waals
compounds with van der Waals < compounds with dipole-dipole interactions < compounds with hydrogen bonding
Simple distillation employs a ____ that will use a cooling jacket column to condense vapor that travels out of the distillation flask
condensing column
Simple distillation employs a condensing column that will use a _______ to ____
cooling jacketed column; condense vapor that travel out of the distillation flask
Distillation is a separation technique based on the ______ of components of a ____ mixture
differences in the vapor pressure (boiling points); liquid
What are the two types of intermolecular forces having to do with polarity
dipole-dipole; H-bonding
____ is widely used for separation and purification of liquids
distillation
A rotary evaporator is a device used in chemical laboratories for the _____ from samples by ____
efficient and gentle removal of solvents; evaporation
Crude oil is separated into fractions by _____
fractional distillation
The separation process of two liquids with similar boiling points uses ____
fractional distillation
____ is used to separate two compounds with boiling points within 40C of one another
fractional distillation
When ____ is added to a liquid, its temperature increases as well as the kinetic energy of the molecules
heat
after all the liquid vaporized (the _____ was added) temperature _____ when the vapor is heated more
heat of vaporization; begins to rise again
After all the liquid vaporized (the heat of vaporization was added) temperature begins to rise again when the vapor is ___
heated more
a compound with a low boiling point has a ____ vapor pressure
high
Through the use of steam distillation a ______ can be distilled and purified under ____
high boiling compound; mild conditions
a maximum boiling azeotrope is also called _____
high boiling or negative azeotrope
when a pure compound has a low vapor pressure its boiling point (temperature) is ___ and we say that it is ____
high; not very volatile (not easily converted to vapors)
at higher total pressure the boiling point is ___
higher
the stronger the intermolecular forces, the ____ the boiling point
higher
Two ______ do not follow Raoult's law
immiscible solvents
the stronger the ____, the higher the boiling point
intermolecular forces
where does the filtrate go after exiting the condenser
into the receiver flask
When a pure compound has a high vapor pressure its boiling point _____ and we say it is a ____ compound
is low; volatile
cyclohexane is miscible with ____ and immiscible with ____
isopropanol; acetonitrile
____ and ____ form a low boiling azeotrope
isopropanol; cyclohexane
acetonitrile is miscible with ____ and immiscible with ___
isopropanol; cyclohexane
For compounds with similar functional groups: the _______ and the ______ the higher the boiling point
larger the surface area; more polarizable the atoms
The boiling point of a compound is the temperature at which _____
liquid molecules are converted into gas
a compound with a high boiling point has a ____ vapor pressure
low
isopropanol and cyclohexane form a _____
low boiling azeotrope
at lower total pressure the boiling point is ____
lower
what does N_A_ mean
mole fraction of A
if a compound is not easily converted to vapors it is ___
not very volatile
efficiency of fractional distillation: theoretical plates are the ______
number of plates needed to achieve a standard separation
when boiling point is reached, the heat is used to ____ which keep molecules ____. This is the heat of ____
overcome intermolecular forces; in the liquid phase; vaporization
in boiling, energy is needed to _____ in the more _____
overcome the attractive forces; ordered liquid state
What does P_A_ mean
partial pressure of A
when the boiling point is reached, the heat is used to overcome intermolecular intermolecular forces which keep molecules in the liquid phase and the temperature _____ as molecules ____
remains constant; leave the liquid phase and move to the gas phase
In fractional distillation you must ____ many times in order to achieve ____
repeat the heating process and cooling process; a pure enough compound
A _____ is a device used in chemical laboratories for the efficient and gentle removal of solvents from samples by evaporation.
rotary evaporator
Distillation is a ____-_ based on the differences in the vapor pressure (boiling points) of components of a liquid mixture
separation technique
In our experiment we apply fractional distillation and use a ______.
short path distillation column
for compounds with _____ the larger the surface area, the higher the boiling point
similar functional groups
A horizontal column is used to condense vapor for collection in _____.
simple distillation
typically you can use ____ to separate two compounds with boiling points greater than 100C of one another
simple distillation
Through the use of ____ a high boiling compound can be distilled and purified under mild conditions
steam distillation
a _____ describes the liquid gas equilibria for a mixture of two compounds
temperature-composition phase diagram
when heat is added to a liquid, its ____ increases as well as the _____
temperature; kinetic energy of the molecules
the boiling point of a compound is the temperature at which ____
the vapor pressure equals the total pressure exerted on the liquid surface
The boiling point is the moment at which ____
the vapor pressure of the liquid is equal to the atmospheric pressure
Two immiscible solvents do not follow Raoult's law but instead ____
their vapor pressures are independent of mole fraction and depend on the sum of the vapor pressures of pure A and B
boiling point depends on ____
total pressure
normal boiling point is defined for ____
total pressure
Typically you can use simple distillation to separate ____
two compounds with boiling points that are 100C apart from of one another
An azeotrope is a mixture of _____ in such a ratio that its _____
two or more liquids; composition cannot be changed by simple distillation
the boiling point of an organic compound reflect the ____ that bind the ______
types of intermolecular interactions; molecules together in the liquid state
the total vapor pressure over a solution depends on the ____, ____ and ____
vapor pressure of each component; mole fraction of that component; temperature
what does P_A_^o^ mean
vapor pressure of pure A
a liquid at any temperature exerts pressure on its environment. This pressure called _____ results from molecules _____
vapor pressure;leaving the liquid phase to become vapor (gas phase)
In distillation the more volatile compound is ____
vaporized first
if a compound is easily converted to vapor it is ____
volatile
boiling point trimethylamine
3.5C
boiling point ethylmethylamine
37C
boiling point propylamine
49C
1 atm = ___ mm
760
boiling point of ethanol
78C
low boiling azeotropes boil ____ lower than each individual solvent
8-10 degrees celcius
water at 0.75 atm boiling point is ___
93 C
You use fractional distillation for compounds whose boiling points are ____
<50C difference
In simple distillation what type of column is used for cooling?
A horizontal column with cooling water, used to condense vapor for collection.
Why can an azeotrope not be distilled by simple distillation?
Because their composition is unchanged by distillation (the vapor has same composition as liquid)
_____ is separation technique based on the differences in the vapor pressure (boiling points) of components of a liquid mixture
Distillation
How many steps of fractional distillation are needed to obtain a pure compound A? (general process)
Go up from x to first line, then straight over to second line, then down to first then straight over to second over and over again until purified. Count the number of steps.
how to calculate mole fraction for a compound
N_A_= moles of A/ (moles of A+moles of B)
A solution of two volatile compounds A and B. How do we determine the vapor pressure of A and B components and what would be the boiling point. The two compounds differ in boiling points > 100 C
Since they are different by nearly 100, the vapor phase would be nearly pure A. Since the compounds differ in boiling points by 100C the liquid mixture can be separated by simple distillation. Almost all of A would vaporize before B. This means that you can catch all of A's vapor and then cool it separate from B to get pretty much pure A and B. In this case you only have to do it once
We have a mixture of compounds A and B. Compound A has a normal boiling point of 145 degrees Celcius. Compound B is a naturally occurring substance with a high molecular weight and is very nonvolatile (extremely high boiling point). It decomposes at 60C. If you want to separate the compound A from the compound B by evaporating A and leaving a pure compound B in the condensed phase, how would you accomplish this?
To solve this problem, the evaporation will have to be realized under "reduced pressure" using vacuum distillation. Using this technique, the boiling point of compound A can be attained at lower total pressure and thus a lower temperature.
__atm= 760mm
1
3 factors affecting boiling point
1) polarity 2) molecular weight 3) shape
water at 1 atm b.p. = ____
100 degrees Celcius
boiling point ethyl amine
17
In fractional distillation what type of column is used for cooling
2 types 1) a horizontal column with cooling water, used to condense vapor for collection 2) Vertical column w/o cooling water which is used to increase theoretical plates for better separation
boiling point ethyl amine
CH3-CH2-NH2
chemical formula ethanol
CH3-CH2-OH
chemical formula dimethyl ether
CH3-O-CH3
chemical equation Acetonitrile
CH3CN
isopropanol is miscible with ____ and immiscible with ___
Cyclohexane and Acetonitrile; nothing
See back page for question D) 83%A and 17%B
If the composition of the liquid mixturee is A+B is 55%A What will be the composition of distillate obtained by a simple distillation (one step) A) 50%A+50%B. B)95%A+5%B. C) 17%A+83%B. D)83%A+17%B. E)100% pure A.
We have a mixture of compounds A and B. Compound A has a normal boiling point of 145 degrees Celcius. Compound B is a naturally occurring substance with a high molecular weight and is very nonvolatile (extremely high boiling point). It decomposes at 60C. How do we estimate the pressure (level of vacuum) which would have to be established in order to reduce the boiling point of compound A under 60C?q
Such an estimate can be obtained from use of a vapor pressure-temperature nomograph. For a compound that boils at 145C we can lower its bp by applying a vaccum to the system. Therefore at 55mm pressure (system) compound A will boil at 60C. If the pressure is lowered to 5mm compound A will boil at 10C and therefore compound B could be isolated after the evaporation of A without decomposition.
What can be said about azeotropes distillation?
The distillation can be purified only along the lines to the right or to the left of the azeotropic point. No amount of distillation can make the distillate or the residue arrive on the opposite side of the azeotrope from the original mixture. For maximum boiling points you can at least purify the compounds by traveling to right or eft of the azeotrope, for minimum boiling every step that you take in the distillation process brings you closer and closer to the azeotrope