CH 220C Quiz 1

Distillation

A process that separates the substances in a solution based on their boiling points

when is fractional distillation used? (as opposed to simple distillation)

when the two liquids have boiling points that differ by less than 40℃

when is simple distillation used? (2 times)

(1) to separate a liquid from a solid

(2) to separate 2 liquids with a dif in BP of > 40-50℃

what is the difference between simple distillation and fractional distillation in the assembly?

Fractional distillation has an additional vertical column between the distillation flask and the condenser

What is the function of the additional vertical column in fractional distillation?

it promotes multiple iterations of condensation and vaporization as the vapor rises through the column, leading to better separation and the formation of a gradual temperature gradient due to the increase in the # of theoretical plates (longer distance)

What does the first temperature plateau correspond to?

the boiling point of the more volatile compound (lower BP, evaporates more easily)

What does the 2nd temp plateau correspond to?

the BP of the less volatile compound (higher BP, evaporates less easily)

How does the promotion of multiple iterations of condensation and vaporization allow the less volatile compound to be separated effectively?

when the soln heats up to the BP of the more volatile compound, the composition of the vapor has more of the volatile compound than it started with.

This vapor then condenses and falls down a little but revaporizes at an even lower BP. The vapor contains an even greater % of the more volatile compound.

This will condense and fall a little, but then revaporize at an even lower BP, producing a new vapor that is almost entirely the more volatile compound.

what is the basis of fractional distillation?

the vapor phase is richer in the more volatile component than is the boiling liquid with which the vapor is in equilibrium

during fractional distillation, a greater proportion of the __________ -_________ component travels up the column, is condensed back into a liquid in the condenser, then falls into a collection vessel (graduated falcon tube)

lower-boiling (more volatile)

what is gas chromotography?

separating compounds in a mixture by vaporizing a sample and passing it through a column of a mobile phase, typically called the carrier gas, and a stationary phase

what is the principle behind gas chromotography?

the components will distribute unevenly between the mobile and stationary phases due to polarity (have dif. affinities for the mobile/stationary phases)

the component that interacts more with the stationary phase will move more slowly in the direction of the flow of the mobile phase (will form a band closer to the start)

how does polarity relate to gas chromotography?

if the polarity of the stationary phase and compound are similar, the retention time increases and the component will not move as quickly as others

what does comparing GC retention times tell us?

the identity of each compound in the mixture

Describe how to set up the vertical column and thermometer: 5 steps

(1) place vertical column over the largest indentation of the aluminum block (centered on hotplate) & clamp it to the scaffolding

(2) connect the 3-way adapter and add a keck clamp

(3) get the straight adapter and put the rubber adapter over the rounded end. Slide the thermometer gently into the rubber adapter

(4) place the straight adapter in the top of the 3-way adapter and add a keck clamp

(5) adjust the thermometer so that the bottom is in line with the bottom of the arm of the 3-way adapter

what are the 5 steps to assemble the horizontal portion of the apparatus?

(1) get the condenser and attach water tubes to the side arms (water in lower than water out) with 2 metal clips

(2) attach condenser to the arm of the 3-way adapter and add a keck clamp

(3) clamp the condenser to the apparatus using a metal clamp

(4) connect the vacuum adapter at the end of the condenser and add a keck clamp

(5) position and use a metal clamp to add the first 15 mL centrifuge tube (Fraction A), below the vacuum adapter so it will collect outflowing liquid

What are the final 5 steps of assembly (collection flask and insulation)?

(1) place 30mL of the unknown mixture in a graduated cylinder and pour into a 100mL flask; AND A STIR BAR!

(2) pour a very small amount of grease on the condenser (vertical column) and slide on the round-bottom flask. Add keck clamp

(3) raise the hot plate by turning the knob on the riser until the round-bottom flask rests snuggly in the aluminum block

(4) loosely wrap with cotton (not touching hot plate)

(4) loosely wrap the whole apparatus with aluminum foil (including the round-bottom flask)

What is the purpose of including a stir bar in the distillation flask?

To ensure even distribution of heat throughout the solution

what are we trying to determine in lab?

the identity of the two solvents in the unknown liquid and their ratio

describe the process of collecting fraction A and recording temperature (5 steps):

(1) turn on magnetic stirring and hot plate to 200℃

(2) record the temperature once the first drop of distillate drops into falcon tube

(3) as each additional mL of soln comes into the falcon tube, record the temp.

(4) when the temperature plateaus, record the temp.

(5) when one condition is met (overflow or temp deviation), swap fraction A tube for fraction B

what should you do if the rate of droplets into the falcon tube exceeds ___ drops per second?

2

you should turn the hotplate down to 125℃

what are the 2 conditions that, if either is met, necessitate swapping out fraction A for a new centrifuge tube?

(1) the liquid is close to overflowing (or exceeding the graduated portion of the tube)

OR

(2) the temp. deviates from the plateau by > 3 ℃ (higher or lower)

describe how to collect fractions B and C, record temp, and cleanup.: (9 things)

(1) once fraction B is in place, turn up the hotplate temp. to 250℃.

(2) record the temp. as each mL of liquid comes over

(3) once the temperature has plateaued, swap out fraction B for fraction C.

(4) keep collecting liquid until the rate of drops slows. Do not distill to dryness.

(5) once most, but not all of the liquid has been distilled, cap fraction C and place upright in a beaker with the others.

(6) turn off and lower hot plate to let round-bottom flask cool.

(7) turn off the water in the condenser.

(8) perform GC analysis with the TA to get GC plots.

(9) disassemble distillation apparatus.

How do you know when the temperature has plateaued?

when 2-3 mL of liquid come into collection tube at the same temp.

How many metal clamps do you use in the distillation apparatus and where are they?

3

> one clamps the vertical column

> one clamps the horizontal condenser

> one holds the collection tubes in place

How should you store your fractions once they have been collected?

you are to store your fractions, securely sealed with caps and placed standing upright, in a beaker until you are ready to obtain GC data

What type of clips/clamps hold the water in/ water out tubes in place?

metal clips

how many keck clamps are you using in the fractional distillation apparatus and where?

5

> one securing the round-bottom flask to the vertical column

> one securing the vertical column to the 3-way adapter

> one securing the condenser to the 3-way adapter

> one securing the straight adapter/thermometer to the 3-way adapter

> one securing the condenser to the vacuum adapter

How does the composition of the liquid at the top of the fractional distillation column compare with the composition of the liquid at the bottom of the column?

it mostly consists of the low-boiling component (less volatile)

how do you avoid losing vapor from the apparatus?

Make sure all of the glass joints are tight

how should you turn on the water to the condenser?

turn it on very slowly until a slow steady flow is observed

how should you save your samples if you don't have time to do the GC analysis this lab?

parafilming over the lid of the centrifuge tubes. DO NOT put parafilm under the tubes cap because the parafilm will be dissolved by the solvent and ruin the GC column

should you turn on/off the GC, adjust the glass cylinders, or mess with the computer?

NO!!!

what should you double check is turned off before you leave?

your water lines

how many minutes before the end of lab time should you stop chemistry and start cleaning up?

30 minutes before

Would preparing drinking water from sea water require simple or fractional distillation? If neither method would be effective, select "neither".

simple

Would seperating diethyl ether (b.p. 35 °C) from p-dichlorobenzene (b.p. 174 °C) require simple or fractional distillation? If neither method would be effective, select "neither".

simple

Would separating benzene (b.p. 80 °C) from toluene (b.p. 111 °C) require simple or fractional distillation? If neither method would be effective, select "neither".

fractional

what should you do before pressing the start button on the GC analysis?

Above the start button is a line of text and a colored dot. Make sure that the dot is green and that the text says "Ready".

describe the steps to inject your sample into the GC:

(1) get 1 uL of sample into the microliter syringe (@ top of GC)

(2) if "ready" and "start" show on screen, hold the syringe into the center hole on top of the GC but don't insert it into the injector port

(3) press start, when timer reaches 0, insert the needle into injector port and push down the plunger to inject your sample and remove the syringe.

(4) wait 1 min for the spectrum to print out and 30 sec for the machine to prepare for the next run before starting again

what should you do while waiting to shoot your GC sample?

disassemble the distillation aparatus and clean up the bench and fume hood

what should you never touch on the GC/computer?

the power button

and don't log out of the computer!!

what fractions do you shoot in the GC?

A, B, and C

how do you prevent a pressure build-up in the fractional distillation apparatus? Where is it located?

you must have a vent in the system

it is located on the vacuum adapter

How does vapor that gets condensed in the column re-vaporized?

it is greeted with rising hot vapor which causes it to re-boil/ vaporize

every time the vapor moving up the column re-condenses and re-vaporizes, it will be richer in the _______- volatile component

more (lower BP)

the round-bottom flask becomes richer in the _____-volatile component over the course of the fractional distillation

less (higher BP)

what is the point of the packing in the column?

to maximize SA so that you have the maximum possible contact between the liquid trickling down and the hot rising vapor (so you can re-vaporize/ condense over and over!)

W/out this, the liquid would trickle down the sides of the column and not come into contact with the vapor rising up the middle

what is the head temp. in fractional distillation?

measured by the thermometer, it corresponds to the temperature of the vapor

how should the thermometer be positioned?

so that the top of the mercury bulb is even with the bottom of the sidearm outlet and a drop of conentrate must adhere to the bottom of the mercury bulb

if a pure liquid is being distilled, the head temp. will be equal to the temp. of the __________

boiling water

don't fill the round-bottom flask more than ______ of the way full

1/2

what is the total pressure = to?

P of sample + P of air

as temperature increases, the equilibrium vapor pressure of the _________ will increase and make up a larger proportion of the total pressure than the pressure of the ______

sample, air

what is boiling point?

when the equilibrium vapor pressure of the sample is = to the total pressure

why do you need to include the total pressure when reporting boiling point?

because BP is dependent on total pressure

lower total pressure = _______ BP

lower

lower vapor pressure of the sample = ____________ boiling point

higher

Dalton's law:

at constant volume and temperature, the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the component gases

Ptot = Px + Py + ...

Raoult's law:

describes the relationship between the partial pressure/vapor pressure of an individual liquid and the composition of homogenous mixtures

Px = NxPx°

(the partial pressure of component X is equal to the vapor pressure of pure X times the mole fraction (Nx) of X in the mixture.)

for a homogenous mixture, the BP is when...

the sum of the partial vapor pressures of the components are = to the external/total P

what is the equation for the mole fraction, Nx?

Nx = nX/ nX + nY + ...

what is a theoretical plate?

Each separate "mini distillation" is called a theoretical plate.

so each condensation/re-vaporization event

the more theoretical plates = a _____ successful distillation

more

the smaller the difference in BP, the ________ theoretical plates are needed

more

what 2 factors affect the # of theoretical plates?

(1) increased SA = more plates (accomplished by increasing column length, dif. column design, or dif. packing materials)

(2) temperature gradient (ideal # of plates is when the temp. in the dist. flask is = to the BP of the mixture, and the distillation head is = to the BP of the lower BP liquid)

how is proper heating/ creation of a temperature gradient accomplished during fractional distillation?

(1) insulation can maintian sufficient heat in the column so enough vapor is produced

(2) prevention of a flooded column (heating is too much = too much vaporizes and condenses = no separation/fractionation)

(3) maintaining a proper reflux ratio (10 drops of condensate returned for every 1 drop of distillate), higher = better, if too low, decrease heat

can two liquids w/ BP's less than 20-30℃ apart from each other be separated with fractional distillation?

no

what are the hazards of all of the chemicals?

" the fire is "fissie" (fussy)"

F: fire

I: inhalation

S: skin

I: ingestion

E: eyes

what is the hazard, prevention, and first aid for FIRE

(1) severe fire hazard, vapors may ignite at distant sources

(2) no flames, no sparks, no contact with hot surfaces

(3) regular dry chemical/powder, CO2, regular foam, water for cooling

what is the one chemical that doesn't ignite at distant sources?

heptane

"heptane" = "tame" = doesn't ignite @ distant sources

what chemical requires alcohol resistant foam instead of regular foam?

acetone

what two chemicals should you NOT use water to put out a fire?

(NO. W WITH H)

HEPTANE!!

and hexane

what is the prevention and first aid of inhalation of all of the chemicals?

P: ventilation and local exhaust

FA: remove from exposure immediately, get medical attention

which chemical requires you to give oxygen if breathing is difficult?

hexane

(Hex --> sex --> it's hard to breath during sex)

what are the symptoms of inhaling toulene?

fatigue, weakness, confusion, headache, nausea, and drowsiness

what are the symptoms of inhaling acetone?

irritation, dryness of mouth and throat, restlessness, anorexia, vomiting, slow/irregular respiration, slow/weak pulse, liver & kidney damage, CNS depression w/ weakness of the legs, headache, nausea

what are the symptoms of inhaling cyclohexane?

irritation, CNS depression w/ headache, dizziness, dullness, nausea, vomiting, degenerative changes in heart/lungs/liver/kidneys/brain

what are the symptoms of inhaling ethylbenzene?

severe irritation, cough, fatigue, depression, dizziness, headache

what are the symptoms of inhaling heptane?

dullness, headache

what are the symptoms of inhaling hexane?

irritation to upper respiratory tract, headache, dizziness, nausea

what is the prevention and first aid for most of the chemicals upon a chemical exposure of the skin?

P: protective gloves and clothing (ALL!)

FA: remove contaminated jewelry/clothes, thoroughly wash skin with water (toulene, acetone, cyclohexane, ethylbenzene)

what additional first aid should be done upon skin exposure of heptane?

rinse then wash skin with water and soap

get medical attention

wear protective clothes/gloves when administering first aid

what additional first aid should be done upon skin exposure of hexane?

Immediately flush skin with soap and copious amounts of water for at least 15 minutes.

what are the symptoms of skin contact with toulene?

irritation and drying

what are the symptoms of skin contact with acetone?

irritation, cellular damage to outside layer of skin, small amts absorbed through intact skin

what are the symptoms of skin contact with cyclohexane

irritation, redness, drying

what are the symptoms of skin contact with ethylbenzene

irritation, inflammation, 1st/2nd degree burns, absorption through skin --> systemic toxicity

what are the symptoms of skin contact with heptane

dry skin

what are the symptoms of skin contact with hexane?

skin irritation

what is the prevention and first aid for eye exposure of all of the chemicals?

P: safety goggles

FA: thoroughly wash eyes with water for several minutes, remove contacts if possible, seek medical attention immediately

what is a symptom of chemical exposure to eye for all chemicals?

irritation

what are the symptoms of chemical exposure to eye for toulene

irritation and corneal burns

what are the symptoms of chemical exposure to eye for acetone?

irritation and eye damage

what are the symptoms of chemical exposure to eye for cyclohexane?

irritation, tearing, redness, conjunctivitis

what are the symptoms of chemical exposure to eye for ethylbenzene?

irritation and tearing up

what are the symptoms of chemical exposure to eye for heptane?

redness, pain

what are the symptoms of chemical exposure to eye for hexane?

irritation

what is the general prevention and first aid for ingestion of a chemical?

P: do not eat or drink in the laboratory (ALL!)

FA: rinse mouth with water, contact physician, if vomiting occurs keep head lower than hips

when what chemical is ingested should you not rinse with water?

acetone

(alcohol and water don't go well together!)