chem lab exam 2

when performing multiple extractions, the original solution containing the solute is extracted ________ by a _______ portion of solvent each time

repeatedly fresh

what are the requirements for simple distillation?

- compound is basically pure (>90% pure) - contains a trace of non-volatile impurities - boiling points separated by at least 100 degrees

what is the water drop test?

- determines where the aqueous layer is - water will mix with aq layer

what are the indicators for when the solution is dry

- drying agent is free flowing - no oily look - solution is clear - possible snow globe effect

what are the factors that affect retention time

- more volatile compounds (low BP) = move faster (they do not bond strongly with the stationary phase) - surface functional groups (some compounds bond easier to the stationary phase) - molecular weight of a compound

what are the options when a substance is a mixture with vapor pressure differences of T < 100 degrees?

- multiple simple distillations - fractional distillation

what glassware was used for fractional distillation

- round bottom flask - fractional column - distilling head - condenser - thermometer - catch beaker

in the extraction, the product is the ________ substance and the aqueous layer was the __________ substance

ORGANIC WASTE

how is an organic compound flowing out of the chromatography indicated?

as peaks on a chromatogram

what was the mobile phase in our distillations?

atmospheric air

compounds travel from start point to end point at a specific rate depending on their...

competing affinity for the mobile gas/liquid phase vs the stationary solid phase

what did we pack the fractional column with?

copper wire

how do you calculate mole fraction of a substance

corrected X/total corrected X+Y

how did we isolate the caffeine in the liquid-liquid extraction?

decant the solution from the drying agent into a pre-weighed flask

typically, in an extraction, you isolate the ___________ compounds into an _________ solvent

desired, organic

compounds adhere to the stationary phase through _________ interactions, _________ _________, and __________ __________

dipole dispersion forces ionic interactions

what is a theoretical plate

each cycle of condensation and evaporation

if an emulsion occurs, how do you get rid of it?

gently stirring with a glass stir rod adding a small amount of NaCl

what is fractional distillation a technique for?

separating mixtures of compounds into pure components

the more theoretical plates in the column, the better the...

separation between the compounds in a mixture will be

which apparatus is commonly used for a liquid-liquid extraction

separatory funnel

each cycle of re-evaluation and re-condensation in fractional distillation corresponds to one ________

plate

what are boiling chips or a stir bar meant to do?

prevent "bumping" of the liquid in the distilling flask

the area under the peak is _________ to the moles of compound eluted

proportional

which distillation process os slow and long?

simple

what is the formula for Kd?

solubility of X in organic / solubility of X in aqueous

liquid-liquid extraction is a technique used to separate or remove selected components from a mixture based on the difference in ______ or ______ _________

solubility, chemical reactivity

because organic salts are polar and charged, due to ionic bonding, they are ______ in water which is a ______ solvent

soluble polar

the area under a GC peak is proportional to the ______ of compound eluted

moles

The Venier Mini GC uses a metal capillary column coated with ______ stationary phase (____________)

nonpolar polydimethylsiloxane

How many times are response factors calculated

once

distilling the liquid to the point that the distilling flask runs dry can cause...

overheating and breaking of the flask or charring of the last few drops of liquid

extraction is a separation technique that relies on...

the partition of compounds between 2 liquid phases or between solid and liquid phase

why did the caffeine move to the organic layer in the liquid-liquid extraction layer?

the solubility is the highest in the organic layer

the mobile phase travels from...

the start point to the end point

what is retention time

the time it takes for a specific compound to exit the column after it is injected

why is it important to release pressure with the stopcock?

there is a buildup of carbon dioxide which is a by product of the acid base reaction or pressure due to low boiling point

what is a fractional column for?

to allow multiple simple distillations to occur over its length

what does the packing in the fractional column used for?

to allow the vapor to condense and vaporize multiple times as it travels up the column

why did we shake and vent the separatory funnel?

to maximize the amount of caffeine transferred from the aqueous layer to the organic layer

how many microliters were used of each distillation in the gas chromatography experiment?

0.2 microliters

how do you find K?

0.8 = (g of extract - X/X) * (mL of solution/ml of organic solvent)

one of the two components of a mixture will have a reaction rate of ____

1

how much distillate did we collect?

1 mL

in the distillation experiment, the heat was adjusted so that the collection rate of the distillate was about _________ drops per second

1-2

what were the general steps of the 1x30 liquid-liquid extraction

1. add 20 mL of caffeine and 30 mL of ethyl acetate 2. shake and vent 3. drain the aqueous layer 4. wash the organic layer with NaCl 5. pour into a flask 6. dry with anhydrous magnesium sulfate

what are the general steps of the 3x10 liquid-liquid extraction

1. add 20 ml of caffeine and 10 ml of ethyl acetate 2. shake and vent 3. drain the aqueous layer 4. add 10 ml of ethyl acetate 5. repeat 6. add 10 ml of ethyl acetate 7. wash with NaCl 8. dry

in the liquid-liquid extraction, how did we decant the caffeine solution?

1. rinse filter paper with ethyl acetate 2. suspend flask from a ring stand in a hot water bath 3. use air to evaporate the solvent from the caffeine solution

what is the BP of butyl acetate

126

basically, in fractional distillation, you are heating a mixture of ___ liquids slowly so the liquid with the ______ boiling point will evaporate first

2 lowest

how many fractions did we collect?

3

what is the BP of ethyl acetate

77.1

how do you calculate the corrected peak of a substance?

Area of X/Response factor of X

in the liquid-liquid extraction, the aqueous layer was ______

H2O

how do you calculate the equivalent initial mass of the caffeine?

L x molarity x g/mol

T/F Response factors are used to eliminate variances in response of the detectors to different compounds. Response factors are calculated only once using the peak areas from the equimolar standard solution

T

what is the vapor pressure difference required for fractional distillation

T < 100 degrees

what vapor pressure difference is required for simple distillation

T > 100 degrees

what is placed under the separatory funnel?

a catch container

what did we use to collect the distillates?

a graduated cylinder

what happens in a simple distillation?

a mixture is warmed slowly and the most volatile liquid vaporizes first, then condensed back to liquid and collected in a flask

what do you calculate the response factor with

a standard solution

the stationary phase is the _______ phase

absorbant

what are anhydrous compounds used for?

absorbing water from organic substances

in the gas chromatography, what did we clean the syringe with?

acetone

how do you find percent recovery?

actual total final mass/initial mass of caffeine placed in the funnel

what are the methods of distillation available to chemists for purifying liquid?

azeotropic fractional vacuum simple

what did we place in the RBF in the distillation experiment?

boiling chips

gas chromatography separates liquid according to...

boiling point and absorptivity (polarity)

in an extraction, the higher density area will be at the __________

bottom

the solvent with the highest density will be the _______ layer in an extraction

bottom

cooling water in the condenser must enter the condenser from the ______ and flow out from the _______ so it will continuously flow

bottom, top

which component of the ethyl acetate/butyl acetate mixture will be proportionally higher in the last volume of distillate collected during fractional distillation

butyl acetate

out of ethyl acetate and butyl acetate, which would have the largest retention time?

butyl acetate -- bigger molecule = higher BP

how do we identify compounds using distillation?

by looking at their retention times

once you got the distillate, what did you do?

capped the vial immediately to ensure no evaporation

in the liquid-liquid extraction experiment, after shaking, the caffeine is found in the ________ layer

ethyl acetate

in the liquid-liquid extraction, the organic layer was ____________

ethyl acetate

what is the solvent in the liquid-liquid extraction

ethyl acetate

which substance did we use as the reference for the response factor?

ethyl acetate

when were temperatures collected in the distillation experiment?

every 1 mL

T/F distillation of seawater to prepare potable water is an example of fractional distillation

false

when you have a lower BP in a fractional distillation, it get s pushed out (faster/slower)

faster

which distillation process involves separating multiple components?

fractional

the solubility of caffeine should ideally be (higher/lower)

higher

how many peaks there are corresponds with...

how many components there are in the mixture

when can mixtures be separated using simple distillation?

if there is a mixture with significantly different vapor pressures

in a liquid-liquid extraction, the solvent and solute must be ____________

immiscible/ polar + nonpolar

the stationary phase is _______ on the column or plate

immobile

in the distillation experiment, you want to demonstrate that the composition of higher BP component __________ as the distillation progresses

increases

what is the solubility of caffeine in ether

insoluble

in the liquid-liquid extraction, where did the organic layer go?

into a labeled flask

in the liquid-liquid extraction, where did the aqueous layer go?

into a waste beaker/flask

why must the cap of the drying agent always be on?

it can absorb moisture from the air

why did we rinse out the syringe with acetone after every use?

it can become clogged

what would happen if you overheated the caffeine in the decanting process?

it could maybe sublime

what happens if you let the RBF go dry while being heated?

it could shatter

what does adding NaCl do when added in a liquid-liquid extraction?

it increases the ionic strength of the aqueous layer

why did we wash with NaCl in the extraction experiment?

it is very polar

higher BP = ______ retention time

larger

larger compounds have _______ BP's

larger

simple distillation is going from a ______ to a _______

liquid, solid

heating a liquid provides a greater ______ ________ of the molecules with the kinetic energy to escape the gas phase

mole fraction

you calculate the response factor from the raw peak areas of the __________

standard

all types of chromatography use the same principles that include a ________ phase and a _________ phase

stationary mobile

the metal in the fractional column absorbs the heat of the vapor until...

the copper gets hot enough for the vapor to pass

what is a response factor

the correction factor

retention is how long...

the gas stays in the column

in the liquid liquid extraction, the organic layer was on the _____-

top

when washing, you are removing the ________ compounds in an _________ solution

undesired, aqueous

how did we separate the solid drying agent from the liquid in the extraction?

using hot gravity filtration

the aqueous phase contains _______-soluble components such as salt

water

what did we do after we washed the organic layer in the liquid-liquid extraction?

we added anhydrous magnesium sulfate drying agent to the organic layer

in the liquid-liquid extraction, what did we do after draining the aqueous layer?

we cleaned the organic layer with saturated sodium chloride solution with the same rocking and venting

what is the boiling temperature?

when the vapor pressure of a liquid equals the atmospheric pressure

once you find the response factor, what do you do?

you correct the raw peak area by dividing by the response factor