CHM457 FUNDAMENTAL ORGANIC CHEMISTRY
EXPERIMENT 1 : ACID – BASE SEPARATION
NAME : NUR HISMANIZA BINTI MORSIDI
MATRIC NO : 2019653874
GROUP : AS245S2
PARTNER’S NAME : ASRIN AWANG SELAN
LECTURER’S NAME : DR MOHD TAJUDIN MOHD ALI
DATE OF EXPERIMENT : 3 OCTOBER 2019
DATE OF SUBMISSION OF REPORT : 11 OCTOBER 2019
OBJECTIVES
1. To separate mixture of an acid, base and a neutral compound into its individual
components
2. Purify the unknown by re-crystallization
3. Analyse and identify the compound by melting point determination
INTRODUCTION
Extraction is a process of transferring a solute from one solvent to another. Extraction is often
used to separate one or more components from a mixture. However, extraction, unlike
recrystallization and distillation, it rarely gives pure product. Recrystallization may be needed
to purify a crude product extracted from a mixture. another use of extraction is to wash the
solution the solution of an organic solute in an organic solvent free of inorganic impurities.
Extraction is accomplished by shaking a solution in a separatory funnel with a solvent that is
immiscible with the one in which the desired substance is dissolved and in which the desired
substance is more soluble. Two liquid layers are formed which can be separated form each
other by draining the bottom layer through the stopcock of the separatory funnel. Immiscible
is used to describe two phases of state that do not dissolve each other.
For example, a reaction is carried out in aqueous solution and the desired product is an
organic compound. The reaction mixture is shaken then with a small amount of an organic
solvent such as ether where upon the organic solute, being more soluble in the organic solvent
than in water transfer primarily to the organic layer. Then, the undesired aqueous layers is
drawn off resulting organic solution is shaken with a small amount of distilled water to wash
the organic solution to remove inorganic impurities. The new aqueous layer containing
inorganic impurities is then discarded. The organic solution that remains is now ready for
further treatment to isolate the desired product.
If two solutes are both soluble in an organic solvents but insoluble in water, they can
be separated by extraction if one of the solutes can be converted to a water-soluble salt. For
example, a mixture of benzoic acid and naphthalene (neutral hydrocarbon) can be separated as
follows. The mixture is dissolved in a small amount of ether. Then, the mixture is poured into
a separatory funnel. A small amount of diluted NaHCO3 solutions is added. The naphthalene
being a neutral which is remains in the ether. After that, the aqueous layer can be separated
from the ether layer by opening the separatory funnel’s stop cock and draining the aqueous
solution into a separate container.
PROCEDURE
1. Extraction
i. 0.24 g of unknown sample and 0.12g of benzoic acid were weighed and added into a
test tube.
ii. 10 mL ether was added to the mixture and the test tube was shaken to dissolve the
mixture.
iii. The solution was then transferred to the separatory funnel and 5 mL of 1M NaOH was
added, tightly capped and the layers were mixed by gently swirling and shaking for
thirty seconds. Pressure was vent by tilting the funnel and opening the stop cork.
iv. The mixture was shaken, vent and closed with stop cock again. The mixture was let
stand to allow the layers to separate. The bottom layer which was the aqueous layer was
drained into an Erlenmeyer flask and labelled as first extraction NaOH.
v. Another 5 mL of ether was added to the ether layer in the funnel and the steps from (i)
– (iv) were repeated and the product was labelled as second extraction NaOH
2. Filtration
i. The flask was taken to the hood and by using a glass rod slowly stirring when 6M HCl
was added into each Erlenmeyer flask until the solution was acidic by using blue litmus
paper.
ii. Afterwards, the flask was taken to cool in an ice bath for about fifteen minutes or until
thoroughly chilled.
iii. The solid benzoic acid was collected using Buchner funnel and filter flask
iv. 2 – 3 mL water was used to wash, and the suction was allowed to continue for five
minutes to get the solid as dry as possible.
v. The solid was gently scraped into a watch glass was put into an oven for complete
dryness.
3. Removing sodium hydroxide, NaOH
i. 5 mL of saturated solution of sodium chloride was added to the ether layer in the
separatory funnel to remove any trace of NaOH solution.
ii. The layer was separated like before, capped, mixed and vent.
iii. The aqueous layer was discarded. The ether layer was then transferred into an
Erlenmeyer flask and 1 g of anhydrous magnesium sulfate was added to remove
moisture inside.
iv. The stop cork was closed and swirled and left to stand for ten minutes.
v. A small dry beaker or Erlenmeyer flask was weighed while the ether layer was drying.
vi. The dried ether layer was transferred to the beaker with a clean Pasteur filter pipet. The
beaker was then brought carefully into a steam bath in the fume hood to evaporate the
ether.
vii. After evaporation, the beaker was cooled down at room temperature, dried and
reweighed to determine the yield of two unknown sample.
viii. The melting point was obtained and compared to the two chemicals given.
RESULT/DATA
Actual weight of benzoic acid = 0.1201g
Weight of benzoic acid recovered = 0.1059g
Percent recovery of benzoic acid = 88.2%
Actual weight of unknown sample = 0.2406g
Weight of unknown sample recovered = 0.0799g
Percent recovery of unknown sample = 33.2%
Observed melting point of unknown sample = 178C
Observed melting point of benzoic acid = 165C
Literature melting point of triphenylmethanol = 164C
Literature melting point of 1,2,4,5-tetrachlorobenzene = 140C
Calculation :
Benzoic acid :
Filter paper: 1+2 = 0.3372g + 0.3251g = 0.6623g
Watch glass: 18.3829g + 19.2723g = 37.6552
Extraction NaOH (after drying) = 38.4235g – 38.3176g = 0.1059g
𝑅𝑒𝑐𝑜𝑣𝑒𝑟𝑒𝑑 𝑤𝑒𝑖𝑔ℎ𝑡
Percent benzoic acid recovered = × 100
𝐴𝑐𝑡𝑢𝑎𝑙 𝑤𝑒𝑖𝑔ℎ𝑡
0.1059𝑔
= × 100
0.1201𝑔
= 88.2%
Unknown sample :
Beaker = 60.9297g
Beaker + Unknown sample = 61.0096g
Unknown sample = 61.0096g – 60.9297g
= 0.0799g
𝑅𝑒𝑐𝑜𝑣𝑒𝑟𝑒𝑑 𝑤𝑒𝑖𝑔ℎ𝑡
Percent of Unknown recovered = × 100
𝐴𝑐𝑡𝑖𝑎𝑙 𝑤𝑒𝑖𝑔ℎ𝑡
0.0799𝑔
= × 100
0.2406𝑔
= 33.2%
White precipitate of benzoic acid and white precipitate of unknown sample was formed
DISCUSSION
In this experiment, the understanding of the results from the acid-base compound is really
needed. One had to know which compounds can dissolve into different solutions. The
compounds in the mixture are all dissolved in the ether solution but insoluble in the aqueous
layer until further conditions allowed for solubility. Water is a poor solvent of covalent
molecules but rapidly dissolves ionic molecules such as acid and base.
The extraction order was done chronologically starting from benzoic acid substance.
Re-crystallized benzoic acid recovered was quite high in purity. The observed melting point of
unknown sample is quite high passing the known melting point of both triphenylmethanol and
1,2,4,5-tetrachlorobenzene. The results obtained made it hard to discern the identity of the
unknown sample. Since triphenylmethanol and 1,2,4,5-tetrachlorobenzne substance were
extracted after benzoic acid, it is possible that the layers could have mixed, and contamination
occurred in the extracted layer from the pipette.
Backwashing step was used as an effort to remove any possible contaminates from both
the solutions and substance. An contaminates present will transfer to the ether layer and then
can be removed via pipette. Though the experiment only called for a single backwash, multiple
attempts would have resulted in a purer solution. This could have gained closer accuracy in
melting point ranges and reflected a purer substance.
CONCLUSION
The experiment was done and had successfully studied the separation of an acid, base and a
neutral compound into its individual components, purifying the unknown by re-crystallization
and identifying the unknown compound by melting point determination. The objectives were
achieved. The percent recovery of unknown sample was 33.2%.
QUESTIONS
1. List four water-immiscible liquids other than ether that could be used to extract
organic compounds for aqueous solution
Cyclohexane
Dichloromethane
Chloroform (trichloromethane)
Carbon tetrachloride
2. Why is it wrong to leave a bottle of anhydrous sodium sulfate or calcium chloride
open?
When the bottle of anhydrous is opened and exposed to air, the air which contains moisture
or water, it will cause the anhydrous to absorb the water particles in the air. Hence, it will
affect the effectiveness of anhydrous during the experiment.
3. Draw the structure of the product when benzoic acid reacts with sodium hydroxide.
Why is the product of this reaction easily extracted into H2O, while the original
benzoic acid is not so easily extracted into H2O?
It is because the more OH- that remove a hydrogen H+ to form a salt, the polar salt is
soluble in aqueous solution, where both OH- and benzoate are bases, the stronger base
takes the H+ to form the weaker base.
4. Why does benzoic acid precipitate out when the aqueous layer is acidified with HCl?
Benzoic acid is a stronger base that Cl-, so each one take H+ from the HCl. The acid forms
are insoluble in water; therefore, they precipitate out from the solution.
5. Develop a procedure for isolating a neutral compound from a mixture containing a
basic impurity by drawing a flow chart as on page 20
Ether
Naphthalene trace of
NaHCO3
Water Ether
Small amount of
Naphthalene
NaHCO3
Dry (magnesium
(discarded) sulfate) evaporate
ether
Naphthalene
REFERENCES
1. 1,2,4,5-Tetrachlorobenzene. (n.d.). Retrieved October 11, 2019, from
https://pubchem.ncbi.nlm.nih.gov/compound/1_2_4_5-
Tetrachlorobenzene#section=Boiling-Point.
2. Triphenylmethanol. (n.d.). Retrieved October 11, 2019, from
https://pubchem.ncbi.nlm.nih.gov/compound/6457#section=Depositor-Supplied-
Synonyms.
3. Extraction. (n.d.). Retrieved October 11, 2019, from
http://www.pitt.edu/~ceder/lab2/extraction.html.
4. Pavia, D. L., Lampman, G. M., Kriz, G. S., & Engel, R. G. (2016). A small scale approach
to organic laboratory techniques. Australia: Cengage Learning.
