Critical Thinking

In purification. In order to follow through with

In
this experiment, an acid base extraction was done in order to separate a
mixture of benzoic acid, 4- chloroaniline and naphthalene. Find the melting
points of each of the compounds and compare with the actual melting points. To
separate these organic compounds, it is a must to use solvent- solvent extraction
that will help attain product purification. In order to follow through with the
extraction, the solvents must be immiscible (Korry). Korry also mentions that
in this experiment, the mixture will react with HCl in order to react with
amine (which has a nitrogen in it) which at the end will give solid salts that
can be weighed. The extraction includes a separatory funnel, it plays the most
important role in this experiment, which helps separate two compounds by
shaking it. Acid- base extraction is used for separating different organic
compounds that have same functional group (Libretexts). This extraction helps
separate acid, base and a neutral compound. In this extraction, organic acid
and organic base can be separated from organic solvent through the process of
adding aqueous solution to it (from WayBack Machine).

Experimental Section (Weldegirma, 12-13) :

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1)    Solid mixture (acid, base, and neutral)
of 3 grams was collected. 30 mL diethyl ether was added to dissolve.

2)    Both, the mixture and the ether were
added into the separatory funnel with 20 mL of fresh ether. 30 mL of 5% HCl was
added. Capped the funnel.

3)    Shook vigorously, uncap the vent, repeat
a few times until separate layers of the mixture was seen.

4)    Top layer was benzoic acid. Drew the
bottom layer into a 125 mL Erlenmeyer flask which contained protonated amine.

5)    This was in Flask #1.

6)    Then 3 M NaOH was added, dropwise, until
the solution turned basic.

7)    The solid amine, 4- chloroaniline
appeared at the base. Used pH strip to determine if it was basic yet. Placed in
ice for 15 minutes.

8)    Used vacuum filter, rinsed with cold
water to get the remaining solution out.

9)    Obtained dry crystal out, allowed to air
dry, then measured its weight.

10) Back to separatory funnel, added 50 mL 5%
NaOH. Capped it. Shook vigorously, uncap the vent, repeated few times until two
layers were observed.

11) Naphthalene, organic layer, appeared on
the top. Acid, aqueous layer, appeared on the bottom. The bottom layer was
drawn out.

12) This was in Flask #2. Added 6 M HCl. Put
in ice bath for 10- 15 minutes, used the pH strip to check the acidity of it.

Repeated steps 8 and 9.

13) Naphthalene, left in the separatory
funnel, added 20 mL NaCl which removed the traces of water. Repeated step 3.

14) Drew the bottom layer out, and discarded
it in aqueous waste. Drew the organic layer, the top layer, into flask #3.

15) Added , then waited 15 minutes. Transferred
flask #3 into a tared 125 mL vacuum flask.

16) Rinse the drying agent with 10-15 mL
fresh diethyl ether. Using vacuum pump, all the liquid was evaporated until
only solid remained, which was weighed.

Table of Chemicals:

Benzoic
Acid:

4-
Chloroaniline:

Naphthalene:

Physical
properties: Carboxylic acid, white crystal

Physical
properties: an amine, white or pale yellow solid

Physical
properties: aromatic hydrocarbon, white crystal with mothball odor

Molar
Mass: 122.12 g/mol

Molar
Mass: 127.57 g/mol

Molar
Mass: 128.17 g/mol

Melting
point: 122°C
Boiling
point: 480.6 °F

Melting
point: 68-71°C
Boiling
point: 449.6 °F

Melting
point: 80°C
Boiling
point: 424.4 °F

 

Results:

#

Benzoic
Acid

4-
Chloroaniline

Naphthalene

Mass:

1
g

1
g

1
g

Mass
recovered:

1.002
g

0.882
g

0.519
g

Percent
Recovery*:

100.2%

88.2%

51.9%

Melting
Point:

122°C

68-71°C

80°C

Melting
Point found:

123°C

72°C

80°C

 

*Percent
Recovery for Benzoic Acid:  * 100%

 =  * 100% = 100.2%

Percent
Recovery for 4- Chloroaniline:

=
 * 100% = 88.2%

Percent
Recovery for Naphthalene:

=
* 100% = 51.9%

Discussion:

The
experimental results obtained for benzoic acid, 1.002 g (100.2%) was more than
1 g (100%) due to error such as not letting it air dry for enough time which
causes the solid to still contain a little bit of liquid in it. It could have
also had a little bit of base in it, from the first flask. The results for 4-
Chloroaniline obtained was 0.882 g (88.2%) which was less than 1 g (100%). This
could have been due to not letting it sit in the ice bath for enough time, or
moving too quickly through the vacuum flask. The value obtained for naphthalene
was 0.519 g (51.9%) which was almost half of 1 g (100%). The error that may
have caused this vast difference in the percent recovery is due to the waiting
for all of the liquid to evaporate from the flask which may have caused the
solution to evaporate more than it was acquired. Due to experimental error of
turning on and turning off the vacuum flask during the process, it may have
caused more solution to evaporate rather than be obtained. The melting point
for benzoic acid is 122°C and was found to be 123°C. There is
a difference of 1°C and it may have been due an error while
finding the melting point. 4- Chloroaniline has a range of melting point
between 68-71°C and the melting point found was 72°C. The
obtained melting point was 1°C higher than the range, which can be due
to experimental error while finding the melting point. The melting point of
naphthalene is 80°C and was found to be 80°C, which
means that there was no difference in the literature value and the experimental
value of naphthalene.

Conclusion:

The
theory of this experiment was an easy way to separate acid, base and a neutral
compound from the mixture of them. The compounds in the mixture were immiscible
which means that they can be separated much easily. In the lab, HCl and NaOH
were added to the mixture in order to separate the base from the mixture first,
then the acid was separated. The procedure used in this lab can be used in
daily life, for example: in order to separate oil from water, this method can
be used. There are many other separations that can be performed using this
technique, because the less dense liquid will form its layer on the top of the
denser liquid. The lab successfully accomplished the aim of the experiment which
was to separate acid, base and a neutral compound using acid- base extraction
method.

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