CHEM 211
Experiment 2 – Solubility
Minyan Wang
5292561
ChEM 211 D Lab
Locker #2
Experimental
Materials used
- test tubes
- stir bar
- steam bath
- test tube clamp (used with steam bath)
- 50mL beaker
- gloves
- 2mL pipettes
- Benzoic acid
- Distilled water
- Ethanol
- Acetone
- Hexanes
- Potassium permanganate
- 18-crown-6
- Triethylene glycol
Experimental procedure
In the first part of this lab 20mg of benzoic acid was added to four test tubes. Four
solvents – distilled water, ethanol, acetone, and hexanes were added to each of the test
tubes. Observations were made in a solubility chart, and then the test tubes were heated in
a steam bath. Observations after the steam bath were recorded.
In the second part of the experiment 2mL of KMnO4 was placed into two test tubes along
with 2mL toluene in each. Tetrabutylammonium was then added to one of the test tubes
and observations were made. The organic layer of the tetrabutylammonium containing
test tube was isolated and added to cyclohexene.
In the last part of the experiment KMnO4 was added into 3 test tubes containing 2 mL of
dry toluene. 5-6mg of 18-crown-6 was added into the first tube, triethylene glycol into the
second, and nothing into the third. Observations were made before a drop of cyclohexene
was added into the first test tube.
The experiment was carried out according to the steps outlined in the lab manual, and no
changes were made.
Results
Solute\Solvent
Benzoic Acid
Distilled water
Insoluble
Ethanol
Insoluble
Acetone
Soluble
Hexanes
Insoluble
Benzoic Acid
and elevated
temperatures
Insoluble
Soluble
Soluble
insoluble
KMnO4 + Toluene
Tetrabutyl
ammonium bromide
The organic layer is
clear and is at the
bottom. The top
layer is purple and
the organic layer is
translucent with a
purple tint.
Soluble.
Nothing
No changes
occurred after the
shake.
Insoluble.
Organic layer
Solute\Ligand
KMnO4
Cyclohexene
The color turned
from having a
purple tint to having
a slightly yellow tint
18-Crown-6
Cloudy solution.
After the addition of
cyclohexene it
becomes a yellow
translucent solution
with no solid.
Soluble
Triethylene Glycol
A red solution is
formed.
soluble
None
No apparent
reaction.
Insoluble.
Discussions
Part 1
Acetone is a ketone, meaning it has a carbon chain with oxygen attached to it. Ethanol is
an alcohol; it is an ethyl group with a hydroxyl group attached to it. Water is a very polar
molecule, and hexane has no dipole moments. The solute benzoic acid dissolved in
ethanol and in acetone. Both ethanol and acetone contain none polar carbon chains with
polar branches. This allows the carboxyl region of benzoic acid to interact with the polar
regions of these two molecules while the benzyl group interacts with the non-polar
carbon chains. Ethanol would be the best for recrystallizing benzoic acid since it can be
dissolved in it at slightly higher temperatures. However it is also insoluble enough in
ethanol that it doesn’t dissolve at room temperature, unlike acetone. That way, benzoic
acid can be dissolved and recrystallized very easily.
Part 2A
The tetrabutylammonium ion contains a positive nitrogen ion in the middle, which allows
the negative permanganate ion to attract to it. The carbon chains that extend out from the
positive ion are non-polar. This allows the ions in the middle to dissolve in non-polar
solvents. With the permanganate ion attracted to the central positive ion, and the nonpolar arms, it was able to dissolve in the toluene. It was successful because there was a
noticeable reaction. It was also shown to be successful because after adding cyclohexene
into the non-polar organic layer there was another noticeable reaction. That could only
have happened if the permanganate ion was present in the non-polar organic solvent. The
second reaction is that of cyclohexene being oxidized.
3C4H8-CH=CH + 2MnO4- + 2H3O+  3C4H8-CH(OH)-CH(OH) + 2MnO2
Part 2B
The macrocyclic ligands seemed to be more effective at dissolving the ion because the
solutions appeared to have one phase after shaking. While the solution still had two
distinctive layers when using tetrabutylammonium bromide. The entire content of the test
tube with 18-crown-6 turned into a translucent yellow solution after adding cyclohexene,
meaning that the ion has dissolved. On the two macrocyclic ligands there were non-polar
regions on the edge and polar regions in the center where oxygen was present. The ion is
attracted to the central polar region, and the outer non-polar region allows it to dissolve in
the non-polar solvents. This is different from the ammonium salt because the
permanganate ion switches places with Br- and attracts to the central positive ion due to
the opposite ionic charges.
Findings vs Theory
The findings were consistent with the theory. Benzoic acid dissolved in ethanol at slightly
elevated temperatures, and once it’s been cooled crystals were reformed. In part two the
salt KMnO4 was not soluble in the non-polar toluene. However using the phase transfer
agents, MnO4- was dissolved in toluene.
Experimental Errors
The 0.5mL of solvent added to the four test tubes containing benzoic acid was an
estimate using a 2mL pipette. The fact that the solvent was 0.5mL in all the beakers can
have an affect on how well the solute dissolved. Some of the KMnO4 stuck to the test
tubes not allowing a very clear observation to be seen.