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