Classifying an Unknown Compound by Functional Groups Lab Report
Emily Muller
4/23/13
Introduction:
The purpose of this lab was to identify the functional groups in three unknown
compounds. In order to accomplish this, a variety of different tests were done. First, solubility
tests were run on each compound. The results of the solubility tests can indicate the size and
polarity of unknown compound. The solubility tests helped to narrow down the possible
functional groups in the unknown. Once the options were narrowed, further classification tests
were run. These tests were used to identify specific functional groups in each unknown sample.
Experimentation:
Solubility Tests
1. Water Test
The first solubility test was done in water. Each compound was place in the water to
determine whether it was soluble in water.
2. 5% Sodium Hydroxide Test
If unknown compounds were insoluble in water the next test was to determine whether
they were soluble in 5% sodium hydroxide (NaOH). The sodium hydroxide test
demonstrated whether the unknown was a carboxylic acid or a phenol because the
compound would be soluble. The reactions were as follows:
5% Sodium Hydroxide Test - Carboxylic Acid
NaOH
H2O
5% Sodium Hydroxide Test - Substituted Phenol
NaOH
H2O
3. 5% Sodium Hydrogen Carbonate (NaHCO3) Test
Afterwards, the unknowns that were soluble in NaOH, were tested in 5% sodium
hydrogen carbonate (NaHCO3). This solubility test can distinguish between a carboxylic
acid and a phenol. The strong acidity in the carboxylic acid will cause the unknown to be
soluble. However, the phenol is not as acidic; therefore, it is not soluble.
5% Sodium Hydrogen Carbonate Test
NaHCO3
H2CO3
H2O + CO2
4. 5% Hydrochloric Acid (HCl) Test
Next, 5% hydrochloric acid was used to determine if an unknown, insoluble in 5%
NaOH, was an amine. An amine would be soluble in HCl. If the unknown was insoluble
in HCl, a wide variety of functional groups were possible such as an alkene, an alcohol,
an aldehyde, or a ketone.
5% Hydrochloric Acid Test
HCl
5. Sulfuric Acid (H2SO4) Test
The solubility of the unknown compounds was finally assessed using sulfuric acid
(H2SO4). Sulfuric acid dissolves molecules containing alkenes, oxygen, or nitrogen.
Therefore, if the unknown was insoluble in H2SO4, the functional group was indicated to
be an alkane, alkyl halide, or an aromatic compound.
Classification Tests
1. Potassium Permanganate Test
The potassium permanganate (KMnO4) test was used to determine whether the unknown
was an alkene. Potassium permanganate reacts with the C=C bond, oxidizing it into a
diol. If an alkene was present, it would change from the original purple color of
potassium permanganate to a dark brown precipitate. This result would indicate the C=C
bond was broken and the two alcohol groups were formed.
Potassium Permanganate Test
KMnO4
MnO2
2. Beilstein Test
Next, the Beilstein Test was used to determine whether an unknown was an alkyl halide.
The unknown compound is placed on a copper wire and then directly into a flame. The
flame turns bright green if the unknown is an alkyl halide.
3. TCICA Test
The TCICA test was used to determine whether an unknown was an alcohol. The TCICA
is an oxidizing agent, therefore, reacts, reducing the compound. Primary and secondary
alcohols will reduce in the presence of TCICA. The duration of time it takes for a
precipitate to form indicates whether the compound is a primary or secondary alcohol.
Primary alcohols take longer to react, whereas, secondary alcohols react almost instantly.
TCICA Test
3
3
3 HCl
4. Iron (III) Chloride Test
Iron (III) chloride was used to identify unknowns containing a phenol group. Compounds
that contain a phenol will react with the iron (III) chloride to produce a bright color.
However, the color change can happen very quickly and some phenols may not react.
5. Bromine in Water Test
The next test used bromine in water to classify a phenol. If the unknown was a phenol,
the dark bromine color would disappear.
Bromine in Water-Test for Phenol
n HBr
n Br2
n
6. 2,4-Dinitrophenylhydrazine (DNP) Test
2,4-Dinitrophenylhydrazine (DNP) can be used to classify aldehydes or ketone functional
groups. When the 2,4-Dinitrophenylhydrazine is added to the unknown, in the presence
of an aldehyde or ketone, the DNP would react forming a bright yellow, orange, or red
precipitate.
2,4-Dinitrophenylhydrazine Test
H+
H2O
Results:
Unknown 7
Unknown 7 Functional Group - Phenol
Unknown 7
Unknown 7
Solubility Tests
Classification Tests
Water
Insoluble
5% NaOH
5%NaHCO3
Soluble
Insoluble
Table 1 – Unknown 7 Solubility Tests
FeCl3
Test
Positive
(Eugenol)
Dark Blue
Positive (2Bromine
isopropylphenol)
(Br2)
Test
Yellow
Negative
(Benzyl alcohol)
Yellowish
Brown
Negative (2propanol)
Dark
Gold/Orange
Unknown 7
Yellow
Unknown 7
Light
Orange
Table 2 – Unknown 7 – Classification Tests
The results of the solubility tests, as seen in Table 1, indicate that Unknown 7 was a
phenol. Two classification tests were used to support this conclusion. First, the FeCl3 test was
performed. The results displayed in Table 2 indicate the unknown was not clearly a positive or
negative for a phenol. Therefore, this test was inconclusive. Also, the bromine test was
performed to determine if the unknown was a phenol. The results, also in Table 2, of this test
were also inconclusive. The color change of the unknown did not match either the positive or the
negative. The classification tests failed to indicate that Unknown 7 was a phenol. However, by
using the solubility tests, it was suggested Unknown 7 was a phenol. One possible reason for the
error in the classification tests is presence of the unknown phenol has decreased over time. Also,
the dark color of the unknown made it difficult to detect the color changes in the classification
tests.
Unknown 17
Unknown 17 Functional Group – Secondary Alcohol
Unknown 17
Unknown 17
Solubility Tests
Water
Insoluble
5% NaOH
Insoluble
5%HCl
Insoluble
H2SO4
Soluble
Table 3 – Unknown 17
Solubility
Classification Tests
2,4DNP
Test
KMnO4
Test
TCICA
Test
Positive (4methyoxyacetophenone)
Negative
(benzoic acid)
Unknown 17
Orange
Precipitate
YellowishOrange; No
precipitate
YellowishOrange; No
precipitate
Positive
Negative
Unknown 17
None
Positive
(2,2dimethyl
1,3
propanediol)
None
Purple
Negative
(benzoic acid)
Unknown 17
No precipitate
Precipitate in
60 seconds
Precipitate in
30 minutes
Table 4 – Unknown 17 Classification
According to Table 3, the results of the solubility tests indicated Unknown 17 could
possibly be an alkene, alcohol, aldehyde, or a ketone. Further classification tests were used in
order to narrow down the possibilities in order to reach a conclusion. First, the 2,4-DNP Test was
used in order to determine whether Unknown 17 was an aldehyde or a ketone. As Table 4 shows,
the lack of precipitate formed suggests that Unknown 17 was not an aldehyde or ketone.
Therefore, Unknown 17 could be an alkene or an alcohol. To determine which functional group
was present in Unknown 17, the potassium permanganate test was performed. The results, in
Table 4, indicate Unknown 17 was not an alkene because the unknown remained purple and did
not form a brown precipitate. Therefore, the results thus far suggest Unknown 17 was an alcohol.
To confirm, the TCICA Test was performed. According to Table 4, Unknown 17 precipitated
almost immediately during the TCICA Test. These results indicate Unknown 17 was a secondary
alcohol.
Unknown D
Unknown D Functional Group – Alkyl Halide
Unknown D
Unknown D
Solubility Tests
Water
5% NaOH
Insoluble
Insoluble
5%HCl
Insoluble
H2SO4
Insoluble
Table 5 – Unknown D – Solubility
Flame
Test
Classification Tests
Positive Negative Unknown D
Green
Nothing Green Flame
Flame
Table 6 – Unknown D - Classification
Using the results from Table 5, the solubility tests suggested that Unknown D could be an
alkane or an alkyl halide. In order to determine which it was, the Beilstein Test was used.
According to Table 6, Unknown D produced a bright green flame suggesting it was an alkyl
halide. The result from the Beilstein Test was very clear; therefore, no further testing was done.
Conclusion:
The purpose of the experiment was to identify the functional groups of three unknown
compounds using solubility tests and chemical classification tests. The solubility tests narrowed
down the potential possibilities for each unknown and then further testing was done to make a
conclusion about each. Based on the solubility test results, Unknown 7 was a phenol, despite the
inconclusive results from the classification tests. One possible reason for this is the low amount
of the phenol present in the solution. Unknown 17 was concluded to be a secondary alcohol
based on a variety of tests. The TCICA test conformed this. Lastly, based on the results of the
solubility tests and the Beilstein test, Unknown D was an alkyl halide. In conclusion, identifying
functional groups of an unknown compound can be done using solubility tests and classification
tests.