Acid Base Extraction
Acid Base Extraction
The purpose of this laboratory assignment was two-fold, first, we were to
demonstrate the extraction of acids and bases, finally, determining what
unknowns were present. Second, we were to extract caffeine from tea. These two
assignment will be documented in two separate entities.
Introduction: Acid/base extraction involves carrying out simple acid/base
reactions in order to separate strong organic acids, weak organic acids neutral
organic compounds and basic organic substances. The procedure for this
laboratory assignment are on the following pages.
3) Separation of Carboxylic Acid, a Phenol and a Neutral Substance
The purpose of this acid/base extraction is to separate a mixture of
equal parts of benzoic acid(strong acid) and 2-naphthanol(weak base) and 1,4dimethoxybenzene(neutral) by extracting from tert-butylmethyl ether(very
volatile).The goal of this experiment was to identify the three components in
the mixture and to determine the percent recovery of each from the mixture.
4) Separation of a Neutral and Basic Substance
A mixture of equal parts of a neutral substance containing either
naphthalene or benzoin and a basic substance containing either 4-chloroaniline
or ethyl 4-aminobenzoate were to be separated by extraction from an ether
solution. Once the separation took place, and crystallization was carried out,
it became possible to determine what components were in the unknown mixture, by
means of a melting point determination.
Results
Procedure
Observations
Inference
Dissolve 3.05g Phenol
Mixture was a golden-Neutral acid
in 30ml
brown/yellow color t-butyl methyl ether in
Erlenmeyer flask and transfer mixture to 125ml separatory funnel using little
ether to complete the transfer
Add 10 ml of water
Organic layer=mixture
aqueous layer=water(clear)
Add 10 ml saturated aqueous
Sodium bicarbonate
dissolves in solution sodium bicarbonate
water. to funnel and mix cautiously with stopper on
NaHCO3
Vent liberated carbon
Carbon dioxide gas dioxide and shake the
mixture
was released three times thoroughly with frequent venting of the
funnel
Allow layers to separate
Layer = H2O +NaHCO3 completely and draw
off lower layer into 50ml Erlenmeyer flask 1
Add 10ml of 1.5 aqueous NaOH
Flask 2 = H2O + NaHCO3 (5ml of 3M and 5ml
H2O)
to separatory funnel, shake mixture, allow layers to separate and draw off lower
layer into a 25ml Erlenmeyer flask 2. Add additional 5ml of water to funnel,
shake as before
Add 15 ml NaCl to funnel. Shake Bottom layer is white and
added to the mixture and allow layers to separate
gooey.
wash the ether and draw off lower layer, which is
layer and to remove discarded
organic
substances
NaCl was
NaOH and
NaHCO3 Pour ether layer into 50ml Erlenmeyer flask from the top of the
separatory funnel (not allowing any water droplets to be transferred) Flask 3
Add anhydrous NaSO4 to ether extract until it no longer clumps
together and set it aside
Acidify contents of flask 2
Litmus went from
Acidification was now by dropwise addition of
blue to pink. Flask
complete concentrated HCl while
2 = creamy color testing
with litmus paper and cool in ice
Acidify contents of flask 1
Litmus went from
Acidification was now by adding HCl dropwise
blue to pink. Flask
complete while testing with litmus
2 = white solution paper
and cool in ice
Decant ether from flask 3 into a tared flask
Boil ether with boiling chips
Do a vacuum filtration and
Solution turns to a
Crystallization is now recrystallize ether by dissolving it solid.
complete in 5ml, taking out boiling chips, adding drops
of Ligroin until the solution was cloudy and cool it in ice
Isolate crystals from flask 2 by
Crystals = creamy-white
Dried
crystals are now vacuum filtration and wash with powder
ready for melting point a small amount of ice water
determination and recrystallize it from boiling water
Repeat the above for flask 1
Crystals = white powder
Flasks number 4 and 5 were done by the following diagram.
Results:
As a result of this acid/base experiment, the following results were obtained:
Flask 1:
31.113g
-30.223g
.890g
Flask 2:
36.812g
-36.002g
.810g
Flask 3:
90.789g
-90.114g
.065g
% yield = experimental weight x 100%
theoretical weight
Flask 1:
.890g x 100% = 89%
1.00g
Flask 2:
.810g x 100% = 81%
1.00g
Flask 3:
.675g x 100% = 67.5%
1.00g
When taking the melting points of the unknowns, flasks 4 and 5, I came
to the conclusion that the samples contained, benzoin, melting point of 136137Degrees(C) and 4-chloroaniline, melting point of 67-80 degrees(C),
respectively.
Flask 4:
90.912g
-89.174g
1.738g
% yield = 1.738g x 100% = 90.4%
1.922g
Flask 5:
87.833g
-86.064g
1.769g
% yield = 1.769g x 100% = 87.3%
2.027g
Conclusion:
After each procedure was complete, it became apparent that flask number
4 and flask number 5 contained benzoin and 4-chloroaniline, respectively. The
melting point range that was experimentally determined for each was 136-137 for
benzoin and 67-70 for 4-chloroaniline. As you can see, this experiment was not
error-free, as my percentage yield was not 100%. This is expected for any
experiment; for there is no way that, under the conditions, this experiment can
be free of error. This error could have occurred for many reasons. The most
prevalent reason, I feel that maybe not all of the substance was transferred
from the flask to the vacuum, giving a slight error. Also, some residue could
have also been left in the vacuum funnel when transferring the crystal
substances.
Questions
2) It is necessary because nothing would come out of the stopcock- the reason
for this is because of pressure. Leaving the stopper on, would decrease the
pressure pushing down on the liquid and the pressure pushing upward would
prevail, allowing nothing to escape.
3) I would not expect p-nitrophenol (pka = 7.15) to dissolve NaHCO3(pka = 6.4)
because having a weak acid and a weak base, the reaction would favor the
products, not the reactants, hence, the reaction would not proceed forward. I
would expect 2,5-dinitrophenol(pka = 5.15) to dissolve in NaHCO3 the reaction
would proceed forward.
5) a) 1g benzoic acid x 1mol = .00699 mol benzoic acid
143g benzoic acid
b) 1ml 10% solution NaHCO3 x 1g_ x 1mol = .00116 mol NaHCO3
4ml 96g NaHCO3 .00699 moles
of benzoic acid
Introduction:
The purpose of the second part of this laboratory assignment was to
extract caffeine from tea using dichloromethane and then to confirm the identity
of it by preparing a derivative of the extracted caffeine which has a sharp
melting point, unlike caffeine itself. Once the extraction was complete, we
were to test for melting point and get a HPLC reading for our derivative.
Discussion:
Tea leaves contain acidic, colored compounds as well as a small amount
of undecomposed chlorophyll, which is soluble in dichloromethane. Caffeine can
be easily extracted from tea. This procedure can be done using conventional
methods. Simply pouring hot water on the tea bags and steeping the bags for
about 5-7 minutes would extract most of the caffeine that the tea contains.
Pure caffeine itself is a white, bitter, odorless crystalline solid, therefore,
it is obvious that more than just caffeine is in the liquid tea solution since
tea is a brown color. Because of this, dichloromethane is used to dissolve the
caffeine that is in the tea, which leaves the other constituents in the aqueous
layer. Using a separatory funnel, it becomes possible to extract the dissolved
caffeine from the aqueous layer and the extraction is now ready for further
procedure.
Results
Procedure
Observation
Inference
To a 250ml beaker containing 7 tea bags, add 100ml of boiling water.
Allow the mixture to stand
Brown aqueous solution for 5-7 minutes
while steeping
containing caffeine and the tea from the bags
other impurities.
Decant the mixture into another flask
Cool solution to near
Dichloromethane = room temperature and
water soluble, clear, extract twice with 15ml
heavier
that water. portions of dichloromethane using a gentle rocking motion and
venting.
Drain off dichloromethane
Dichloromethane
Evaporation of the layer on first extraction;
organic layer found
solvent leaves crude include emulsion layer on
on the
bottom of the
caffeine, which on the second extraction.
funnel where the
sublimation, yields
caffeine is dissolved.
a
relatively pure
Chlorine = top, aqueous
product.
solution.
Drain extraction 1 and 2 back into the funnel
Dry combined dichloromethane
The solvent layer is solutions and any
emulsion
yellow. layer with sodium sulfate
Wash the drying agent
Residue of greenish with further
portions of
white crystalline weighs solvent and steam bath
50mg(solid) the solvent
To 5mg of the
Salicylic acid is water sublimed caffeine in
water soluble. beaker, add 7.5mg of salicylic acid and .5 ml of
dichloromethane.
Heat mixture to a boil
Petroleum ether is a poor and add a few drops
solvent for the product. petroleum ether until the mixture turns
cloudy.
Insulate beaker and allow it to cool slowly to room temperature and then cool in
an ice bath
Remove the solvent with
Needle-like crystals are
Caffeine
salicylate is a Pasteur pipette while the
isolated(white color)
formed. beaker is in the ice bath then vacuum filter.
Caffeine beaker:
51.61g
-51.56g
.05g = 50mg
% yield = .05g x 100% = 20%
.25g
Caffeine salicylate:
17.198g
-17.036g
.062g
% yield = .062g x 100% = 25%
.25g
Conclusion
According to the HPLC graph that follows, my product was very pure. The
actual melting point of caffeine salicylate is 137 degree(C), my product was
found to have a melting point of 138 degrees (C). As before, of course this
experiment was not done completely error-free, the error is due almost entirely
on human error.
Keywords:
acid base extraction acid base extraction purpose this laboratory assignment fold first
were demonstrate extraction acids bases finally determining what unknowns were present
second were extract caffeine from these assignment will documented separate entities
introduction acid base involves carrying simple reactions order separate strong organic
acids weak organic acids neutral organic compounds basic substances procedure this
laboratory assignment following pages separation carboxylic phenol neutral substance
purpose this separate mixture equal parts benzoic strong naphthanol weak
dimethoxybenzene neutral extracting from tert butylmethyl ether very volatile goal
experiment identify three components mixture determine percent recovery each from
mixture separation basic substance equal parts substance containing either naphthalene
benzoin basic containing either chloroaniline ethyl aminobenzoate separated ether
solution once separation took place crystallization carried became possible determine
what components unknown means melting point determination results procedure
observations inference dissolve phenol golden brown yellow color butyl methyl ether
erlenmeyer flask transfer separatory funnel using little complete transfer water layer
aqueous layer water clear saturated aqueous sodium bicarbonate nahco dissolves solution
sodium bicarbonate water funnel cautiously with stopper vent liberated carbon carbon
dioxide dioxide shake released three times thoroughly with frequent venting funnel allow
layers layer nahco completely draw lower into erlenmeyer flask aqueous naoh flask
nahco separatory shake allow layers draw lower into erlenmeyer additional shake before
nacl bottom white nacl added allow layers gooey wash draw lower which remove
discarded substances naoh pour into separatory allowing droplets transferred anhydrous
naso extract until longer clumps together aside acidify contents litmus went acidification
dropwise addition blue pink complete concentrated while creamy color testing with
litmus paper cool acidify contents litmus went acidification adding dropwise blue pink
complete while testing white solution paper cool decant tared boil boiling chips vacuum
filtration turns crystallization recrystallize dissolving solid taking boiling chips adding
drops ligroin until cloudy cool isolate crystals crystals creamy white dried crystals
vacuum filtration wash powder ready melting point small amount determination
recrystallize boiling repeat above powder flasks number done following diagram results
result experiment following results obtained yield experimental weight theoretical weight
when taking melting points unknowns flasks came conclusion that samples contained
benzoin point degrees chloroaniline degrees respectively yield yield conclusion after each
procedure became apparent that number number contained benzoin chloroaniline
respectively range that experimentally determined each experiment error free percentage
expected there under conditions free error error could have occurred many reasons most
prevalent reason feel maybe transferred vacuum giving slight also some residue could
have also been left when transferring crystal substances questions necessary because
nothing would come stopcock reason because pressure leaving stopper would decrease
pressure pushing down liquid pressure pushing upward would prevail allowing nothing
escape expect nitrophenol dissolve because having weak reaction favor products reactants
hence reaction proceed forward expect dinitrophenol dissolve reaction proceed forward
benzoic benzoic moles introduction purpose second part laboratory extract caffeine using
dichloromethane then confirm identity preparing derivative extracted caffeine which
sharp unlike itself once test hplc reading derivative discussion leaves contain acidic
colored compounds well small amount undecomposed chlorophyll which soluble
dichloromethane easily extracted done using conventional methods simply pouring bags
steeping bags about minutes most contains pure itself bitter odorless crystalline solid
therefore obvious more than just liquid since brown color dichloromethane used leaves
other constituents becomes possible dissolved ready further observation inference beaker
containing bags stand brown minutes while steeping other impurities decant another near
room temperature soluble clear twice heavier portions gentle rocking motion venting
drain evaporation first found solvent leaves crude include emulsion bottom second where
sublimation yields dissolved relatively pure chlorine product drain back combined
solvent solutions emulsion yellow sodium sulfate wash drying agent residue greenish
further portions crystalline weighs solvent steam bath solid salicylic sublimed soluble
beaker salicylic heat boil petroleum poor drops product petroleum until turns cloudy
insulate beaker slowly room temperature then bath remove needle like salicylate pasteur
pipette isolated formed bath then filter salicylate conclusion according hplc graph follows
product very pure actual salicylate degree found have degrees before course done
completely free almost entirely human
Keywords General:
Essay, essays, termpaper, term paper, termpapers, term papers, book reports, study,
college, thesis, dessertation, test answers, free research, book research, study help,
download essay, download term papers