ALDEHYDES AND KEYTONES
Experiment # 5
Group # 2
Jamina Fay Sanoy
Jasper Marion Ancheta
Kevin Gattoc
Hans Ruar
Joanna Pangilinan
Joy Santos
Department of Chemistry College of Art and Science, Central Luzon State University
October 13, 2021
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ABSTRACT- This study focused on aldehydes and ketones. Aldehydes contain the carbonyl group
bonded to at least one hydrogen atom. Ketones contain the carbonyl group bonded to two carbon atoms.
Aldehydes and ketones are organic compounds which incorporate a carbonyl functional group, C=O. The
result showed that the tests performed were capable of detecting the presence or absence of specific
functional groups such as aldehydes and ketones.
Keywords: Chromic Acid Test, Tollen’s Test, Iodoform Test, 2,4-Dinitrophenylhydrazine (DNPH) Test
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INTRODUCTION
Aldehydes and ketones contain the carbonyl group. Aldehydes are considered the most important
functional group. They are often called the formyl or methanoyl group. Aldehydes derive their name from
the dehydration of alcohols. Aldehydes contain the carbonyl group bonded to at least one hydrogen atom.
Ketones contain the carbonyl group bonded to two carbon atoms. Aldehydes and ketones are organic
compounds which incorporate a carbonyl functional group, C=O. The carbon atom of this group has two
remaining bonds that may be occupied by hydrogen, alkyl or aryl substituents. If at least one of these
substituents is hydrogen, the compound is an aldehyde. If neither is hydrogen, the compound is a ketone
(Farmer et.al, 2020).
METHODOLOGY
A. Chromic Acid Test
A few drops of formaldehyde, benzaldehyde, cyclohexanone and acetone were placed on four
different test tubes. Chromic acid was added to each test tubes and was observed to form a green solution
with formaldehyde and benzaldehyde as both were oxidized. No reaction was observed in cyclohexanone
and acetone due to the lack of oxidizable hydrogen atom in it.
B. Tollen’s Test
About 5 drops of formaldehyde, benzaldehyde, cyclohexanone and acetone were placed on four
different test tubes. All samples were dissolved using 20 drops diethyl ether. Another 10 drops of tollen’s
reagent were added on each test tubes. All test tubes were shaken and placed on a water for a few minutes.
After heating the test tubes, a silver mirror precipitate was observed in formaldehyde and benzaldehyde
while no silver mirror precipitate was observed in both cyclohexanone and acetone.
C. Iodoform Test
About 15 drops and more of 6M NaOH was added in formaldehyde, benzaldehyde, cyclohexanone
and acetone. All sample were placed on a water bath for 3 minutes. The I2-KI reagent was added in each
test tubes for about 20 drops until the color become light brown. Stop adding more of the reagent if there is
no changes happen after the addition of 20 drops. No reaction was observed on formaldehyde,
benzaldehyde, cyclohexanone. The acetone produced a light-yellow solution with a yellow precipitate.
D. 2,4-Dinitrophenylhydrazine (DNPH) Test
About 15 drops of 2,4-DNPH was added in test tubes with formaldehyde, benzaldehyde,
cyclohexanone and acetone. After which, all samples produce a yellow solution with yellow precipitate in
test tube with benzaldehyde. The samples with yellow precipitate were subject to water bath for about 5
minutes and cooled at room temperature.
RESULT AND DISCUSSIONS
1. Chemical Tests
A. Chromic Acid Test
Table 1: Chromic Acid Test
Compounds
A. Formaldehyde
B. Benzaldehyde
C. Cyclohexanone
D. Acetone
Test results
Forms green color solution (Aldehydes)
Forms green color solution (Aldehydes)
No reaction (Ketones)
No reaction (Ketones)
The table above shows the test result of Chromic acid test for Aldehydes and Ketones. The
Formaldehyde forms green solution as it added with Chromic acid it tends to form formic acid and
gain 2H atom added with Cr+3 responsible for green solution. The Benzaldehyde also forms green
solution as it added with Chromic acid because it oxidized to carboxylic acids while the Cr+6 ion in
the chromic acid is reduced to Cr+3. The Cyclohexanone and Acetone forms no reaction because
they have no oxidizable Hydrogen atom.
B. Tollen’s Test
Table 2: Tollen’s Test
Compounds
A. Formaldehyde
B. Benzaldehyde
C. Cyclohexanone
D. Acetone
Test results
Forms white precipitate (supposed to form
silver mirror)
Forms white precipitate (supposed to form
silver mirror)
No reaction
No reaction
The table above shows the test result of Tollen’s test for Aldehydes and Ketones. The
Formaldehyde and Benzaldehyde precipitates (supposed to form silver mirror). The
Cyclohexanone and Acetone gives no reaction because they are not oxidized by Tollens’ reagent.
The aldehyde is oxidized by the Tollens reagent and forms a carboxylic acid. The silver ions present
in the Tollens reagent are reduced into metallic silver.
C. Iodoform Test
Table 3: Iodoform Test
Compounds
A. Formaldehyde
B. Benzaldehyde
C. Cyclohexanone
D. Acetone
Test results
No changes in color
It changes to light brown color
It changes to light brown color
It changes from clear to translucent
appearance
Iodoform test helps identify the presence of methyl ketone on the compounds – aldehydes and
ketones (Isac-García, Dobado, Calvo-Flores & Martínez-García, 2016). The table above shows the
different reaction of the compounds on the iodoform (triiodomethane). Test tube A (which contains
Formaldehyde) did not changed to light brown color which indicate that it has no presence of
methyl group that is directly attached to a carbonyl. On the other hand, both test tube B (which
contains benzaldehyde) and C (cyclohexanone) changed colors to light brown which means that
the two compounds are positive to iodoform test. Acetone from the test tube D also changed its
appearance but not to light brown, instead it changed from clear to translucent appearance.
The test tubes B and C were then combined with sodium hydroxide (NaOH) to turn them back from
colorless compounds. Both test tubes did not turn back to colorless compound and stayed in light
brown color.
D. 2,4-Dinitrophenylhydrazine (DNPH) Test
Table 4: 2,4-Dinitrophenylhydrazine (DNPH) Test
Compounds
A. Formaldehyde
B. Benzaldehyde
C. Cyclohexanone
D. Acetone
Test results
Forms orange precipitate
Forms orange precipitate
Forms orange precipitate
Forms orange precipitate
The table above shows the same results on 2,4-Dinitrophenylhydrazine (DNPH) Test. The four
compounds – formaldehyde, benzaldehyde, cyclohexanone, and acetone – formed orange
precipitate which indicate the positive test for DNPH test. The melting point of these precipitates
is extremely high which support the presence of carbonyl compounds. This is a condensation
reaction, which occurs when two molecules join together and lose water (Hill & Holman, 2000).
CONCLUSION
Four different tests (Chromic acid test, Tollen’s test, Iodoform test, and 2,4Dinitrophenylhydrazine (DNPH) test) were carried out in this laboratory experiment to learn about the
chemical properties of Aldehydes and Ketones, as well as to distinguish between the two. The Chromic acid
test revealed that Formaldehyde and Benzaldehyde are both Aldehydes, whereas the remaining two samples
that were not oxidized were found to be Ketones. In the Tollen’s test, both Formaldehyde and Benzaldehyde
formed white precipitate, supposedly silver mirror precipitate, once again indicating that they are
Aldehydes. As for the Iodoform test, Benzaldehyde and Cyclohexanone both tested positive, indicating the
existence of methyl ketone on the substances. Acetone, on the other hand, switched color from clear to
translucent, but not to light brown. Finally, the existence of carbonyl compounds in all of the samples tested
was confirmed by the positive results of all of the compounds utilized in the 2,4-Dinitrophenylhydrazine
(DNPH) test.
However, these tests were not carried out flawlessly, and certain flaws occurred that resulted in
unexpected outcomes. During the lab, one issue that was faced was the lack of freshly prepared tollens
reagent, or the use of contaminated tollens reagents, which resulted in the creation of white Aldehyde
precipitates instead of silver mirror precipitates. Another error was encountered in the Iodoform test,
wherein Acetone should have tested positive. As a result of these issues, correct preparation for each tool
and sample should be strictly adhered to in order to achieve the intended outcomes.
Despite the issues encountered, the results obtained showed that the tests performed were capable
of detecting the presence or absence of specific functional groups such as aldehydes and ketones.
REFERENCES
Benzaldehyde
Tests.
(1999).
Www.Chem.Uiuc.Edu.
Retreieved
http://www.chem.uiuc.edu/weborganic/orglab/qualknown/Benzaldehyde.htm
from:
Byjus, (n.d.). General Data Protection Regulation (GDPR) Guidelines BYJU’S. BYJUS. Retrieved
October 8, 2021, from https://byjus.com/chemistry/tollens-test/
Farmer (2020). Nomenclature of Aldehydes & Ketones. Chemestry LibreTexts
https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modules_(Or
ganic_Chemistry)/Aldehydes_and_Ketones
Graham Hill and John Holman, 2000, adapted from Chemistry in Context, 4th Edition.
Joaquín Isac-García, José A. Dobado, Francisco G. Calvo-Flores, Henar Martínez-García (2016),
Experimental Organic Chemistry, Academic Press, ISBN 9780128038932,
(https://www.sciencedirect.com/science/article/pii/B9780128038932500061)
Larsen, D. (2018, June 13). Exceptionally rapid oxime and hydrazone formation promoted by
catalytic amine buffers with low toxicity. Chemical Science (RSC Publishing).
https://pubs.rsc.org/en/content/articlelanding/2018/sc/c8sc01082j
Wellesley Academics (n.d.). Academics.Wellesley. Edu. Chem 211 - Tests for Aldehydes and
Ketones.
Retrieved
October
8,
2021,
from
http://academics.wellesley.edu/Chemistry/chem211lab/Orgo_Lab_Manual/Appendix/Cla
ssificationTests/aldehyde_ketone.html