Distillation Videos

Question 1

define boiling point

Answer 1

the temperature where vapor pressure of liquid phase becomes equal to atmospheric pressure. if you change external pressure you change boiling point

Question 2

define distillation

Answer 2

relies on fact that different components of a mixture will boil and vaporize at different temperatures

Question 3

compare simple to fractional

Answer 3

simple: purification which contains non-volatile impurities. Difference of two BPs is LARGE, >= 100C

fractional: separation where difference of two BPs is closer, BP >= 30C

Question 4

Which distillation would be better to separate methanol and water

Answer 4

fractional

Question 5

define azeotrope

Answer 5

a mixture w a fixed composition that cannot be separated by distillation. behaves as a pure cmpd and distills from beginning to end at a constant temperature, giving a distillate of constant composition

Question 6

methanol and water do not form an azeotrope

Answer 6

true

Question 7

ethanol and water are an azetorope have a BP of 78 composition is 95.5% ETHANOL BY WEIGHT (MEANS pure ethanol cannot be isolated by dsitillation)

Answer 7

true

Question 8

which of these is a good use for fractional distillation
a. to separate two liquids with a 100 degree difference in BP
2. separate a liquid from non-volatile impurities
3. to separate two liquids with a 30 degree difference in BP

Answer 8

3.

Question 9

define vapor pressure

Answer 9

the pressure exerted by the gas above the liquid in a closed container

Question 10

a high vapor pressure means a ___ boiling point

Answer 10

low

Question 11

a low BP means volatility

Answer 11

true

Question 12

how do intermolecular forces come into play with BP and VP

Answer 12

diethyl ether has dipole dipole
ethanol has weaker hydrogen bonds
watr has weaker hydrogen bonds

h bonding is a stronger intermolecular force than ethanol

Question 13

what is raoult’s law

Answer 13

when two miscible (can dissolve in each other, mixable) liquids (A and B) form an ideal solution, the law states

Pt=Pa + Pb
Pt=sum of partial vapor pressures. temp at which total pressure equals applies pressure, the solution boils

Pa=Na(liquid) x Pa
Pb= Nb liquid x Pb

where Pa/b is vapor pressure of pure A or B
Na/b liquid is mole fraction of A/B (moles A/moles A+B)

Question 14

what is vapor enrichment

Answer 14

when a mixture of two miscible liquids with different BPs is heated, the vapor will have a different composition than the liquid.
vapor is enriched in the more volatile (lower boiling) component

Na vapor= Pa/Pt

is A is more volatile than B BPa < BPb Pa> Pb

Question 15

define Boiling point

Answer 15

internal vapor pressure of liquid is equal to pressure exerted by its surroundings

internal VP of a pure liquid rises steadily as temperature increases until BP is reached

temperature remains constant throughout boiling process of a pure liquid. At the boiling point. liquid and vapor are at equilibrium

Question 16

can you change the boiling point of a liquid?

Answer 16

you can decrease BP of water at high altitude because you’re changing the pressure.

you can increase BP of water at a higher pressure using a pressure cooker

Question 17

as the temperature of a liquid increases before reaching its BP, its vapor pressure
a. stays constant
b. decreases
c. increases

Answer 17

c increases

Question 18

when will simple distillation work?

Answer 18

difference in BP greater than 100
when one component will not distill because of a lack of volatile
impurity present in small amount

Question 19

imagine an ideal solution of 50% benzene and 50% toulene is distilled

it boils at 91C and composition of vapor is 74% benzene

as distillation continues, the composition of the undistilled lqiuid would move in direction of A

temperature of distillation would continue to increase

Answer 19

see notebook for diagram

Question 20

if we collect some of first distillate that contains 74% benzene and redistill it using same figure, liquid starts to boil at 84C
initial distillate contains 90% benzene. if we continue to redistill, eventually would reach a liquid with a composition of nearly 100% pure benzene

Answer 20

this is what happens in fractional distillation

Question 21

true or false: the number of theoretical plates is used to measure the efficiency of a column

Answer 21

true number of theoretical plates in a column is related to the number of vaporization/condensation cycles that occur as a liquid mixture travels through it
count the horizontal lines (see ntbk) there are 5, thus 5 theoretical plates