Untitled Essay Research Paper The purpose of

Untitled Essay, Research Paper

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

1,4-dimethoxybenzene(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 InferenceDissolve 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 transferAdd 10 ml of water

Organic layer=mixture

aqueous layer=water(clear)Add 10 ml saturated aqueous Sodium

bicarbonate NaHCO3 dissolves in

solution sodium bicarbonate

water.

to funnel and mix cautiously

with stopper onVent liberated carbon

Carbon dioxide gas

dioxide and shake the mixture was released three times

thoroughly with frequent venting

of the funnelAllow layers to separate Layer = H2O +NaHCO3

completely and draw off

lower layer into 50ml Erlenmeyer

flask 1Add 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 beforeAdd 15 ml NaCl to funnel. Shake Bottom layer is white and

NaCl was 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

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 3Add anhydrous NaSO4

to ether extract until it no

longer clumps together

and set it asideAcidify 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 iceAcidify 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 iceDecant ether from flask

3 into a tared flaskBoil ether with boiling chipsDo 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 iceIsolate 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

waterRepeat the above for flask 1 Crystals = white

powderFlasks 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 136-137Degrees(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.

Questions2) 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 acidb) 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 InferenceTo 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 flaskCool 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 funnelDry combined dichloromethane The solvent layer is

solutions and any emulsion yellow.

layer with sodium sulfateWash the drying agent

Residue of greenish

with further portions of white crystalline

weighs

solvent and steam bath 50mg(solid)

the solventTo 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 bathRemove 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.