CHEM 219 | CHEM219 Module 6: Principles of
Organic Chemistry with Lab - Portage Learning
Updated and Latest Questions and Correct
Answers with Rationale
1. What is the IUPAC name for the compound CH3CH2CH2CHO?
A. Propanal
B. Butanone
C. Butanal
D. Pentanal
Correct Answer: C
Expert Explanation: The compound contains a four-carbon chain including the carbon in
the aldehyde group. In IUPAC nomenclature, the suffix for aldehydes is ‘-al’ which replaces
the ‘-e’ of the parent alkane. Since the parent alkane for four carbons is butane, the name
becomes butanal. The aldehyde group is always located at the end of the chain, so a locant
number is not required. This naming convention distinguishes it from the ketone version
which would be butanone.
2. Which reagent is specifically used to distinguish aldehydes from ketones by forming a silver
mirror?
A. Tollens’ Reagent
B. 2,4-Dinitrophenylhydrazine
C. Sodium Borohydride
D. Jones Reagent
Correct Answer: A
Expert Explanation: Tollens’ reagent consists of a solution of silver nitrate in aqueous
ammonia. It acts as a mild oxidizing agent that reacts with aldehydes but not with ketones.
During the reaction, the aldehyde is oxidized to a carboxylate ion while the silver ions are
reduced to metallic silver. This metallic silver deposits on the inner surface of the test tube,
creating a characteristic silver mirror. Consequently, this test is a standard laboratory
procedure for identifying the presence of an aldehyde functional group.
3. What is the result of a positive 2,4-DNP (Brady’s reagent) test?
A. Formation of a silver mirror
B. A blue to red color change
,C. Formation of a yellow, orange, or red precipitate
D. Evolution of carbon dioxide gas
Correct Answer: C
Expert Explanation: The 2,4-DNP test is used to detect the presence of the carbonyl
functional group in aldehydes and ketones. When the reagent reacts with a carbonyl
compound, it forms a 2,4-dinitrophenylhydrazone derivative. This derivative typically
appears as a distinct yellow, orange, or red crystalline precipitate. The color of the
precipitate can often indicate the extent of conjugation in the original carbonyl compound.
Since both aldehydes and ketones react with this reagent, it serves as a general test for
carbonyls rather than a distinguishing test between them.
4. Which of the following describes the polarity of the carbonyl (C=O) group?
A. Nonpolar because carbon and oxygen have similar electronegativity
B. Polar with a partial positive charge on oxygen
C. Polar with a partial positive charge on carbon
D. Ionic because oxygen completely removes electrons from carbon
Correct Answer: C
Expert Explanation: The carbonyl group consists of a carbon atom double-bonded to an
oxygen atom. Oxygen is significantly more electronegative than carbon, leading to an
unequal sharing of electrons in the pi bond. This creates a dipole where the oxygen carries
a partial negative charge and the carbon carries a partial positive charge. This polarity
makes the carbonyl carbon electrophilic and susceptible to attack by nucleophiles.
Understanding this electronic distribution is fundamental to predicting the chemical
reactivity of aldehydes and ketones.
5. In nucleophilic addition reactions, what part of the carbonyl group is attacked by the
nucleophile?
A. The oxygen atom
B. The alpha hydrogen
C. The carbonyl carbon atom
D. The pi bond electrons
Correct Answer: C
Expert Explanation: Nucleophilic addition is the most common reaction type for
aldehydes and ketones. The nucleophile is an electron-rich species that seeks out electron-
deficient centers. Because the carbonyl carbon has a partial positive charge due to the
electronegative oxygen, it acts as an electrophile. The nucleophile attacks this carbon,
, causing the pi bond to break and moving electrons onto the oxygen. This step results in a
tetrahedral intermediate where the carbon is now bonded to the nucleophile.
6. What is the IUPAC name for the simplest ketone, commonly known as acetone?
A. Propanone
B. Ethanal
C. Butanone
D. Ethanone
Correct Answer: A
Expert Explanation: Acetone is the common name for the smallest possible ketone
structure. It consists of three carbon atoms, with the carbonyl group located on the middle
carbon. Following IUPAC rules, a three-carbon chain is named propane, and the ketone
suffix ‘-one’ is added. By dropping the ‘-e’ from propane, we get the systematic name
propanone. Because the carbonyl must be on the second carbon to be a ketone, the number
‘2’ is usually omitted as there are no other isomers.
7. Why do aldehydes and ketones have higher boiling points than alkanes of similar molar
mass?
A. They can form hydrogen bonds with each other
B. They experience dipole-dipole interactions
C. They are completely nonpolar
D. They have stronger London dispersion forces
Correct Answer: B
Expert Explanation: Aldehydes and ketones possess a polar carbonyl group that creates a
molecular dipole. These permanent dipoles allow for dipole-dipole intermolecular forces
between adjacent molecules. Alkanes are nonpolar and only experience weak London
dispersion forces. Dipole-dipole interactions are stronger than dispersion forces, requiring
more energy to overcome during the boiling process. However, aldehydes and ketones lack
a hydrogen atom bonded directly to oxygen, so they cannot form hydrogen bonds with
themselves like alcohols do.
8. Which compound will yield a positive iodoform test (yellow precipitate of CHI3)?
A. 3-Pentanone
B. Benzaldehyde
C. Acetophenone (Methyl phenyl ketone)
D. Pentanal
Organic Chemistry with Lab - Portage Learning
Updated and Latest Questions and Correct
Answers with Rationale
1. What is the IUPAC name for the compound CH3CH2CH2CHO?
A. Propanal
B. Butanone
C. Butanal
D. Pentanal
Correct Answer: C
Expert Explanation: The compound contains a four-carbon chain including the carbon in
the aldehyde group. In IUPAC nomenclature, the suffix for aldehydes is ‘-al’ which replaces
the ‘-e’ of the parent alkane. Since the parent alkane for four carbons is butane, the name
becomes butanal. The aldehyde group is always located at the end of the chain, so a locant
number is not required. This naming convention distinguishes it from the ketone version
which would be butanone.
2. Which reagent is specifically used to distinguish aldehydes from ketones by forming a silver
mirror?
A. Tollens’ Reagent
B. 2,4-Dinitrophenylhydrazine
C. Sodium Borohydride
D. Jones Reagent
Correct Answer: A
Expert Explanation: Tollens’ reagent consists of a solution of silver nitrate in aqueous
ammonia. It acts as a mild oxidizing agent that reacts with aldehydes but not with ketones.
During the reaction, the aldehyde is oxidized to a carboxylate ion while the silver ions are
reduced to metallic silver. This metallic silver deposits on the inner surface of the test tube,
creating a characteristic silver mirror. Consequently, this test is a standard laboratory
procedure for identifying the presence of an aldehyde functional group.
3. What is the result of a positive 2,4-DNP (Brady’s reagent) test?
A. Formation of a silver mirror
B. A blue to red color change
,C. Formation of a yellow, orange, or red precipitate
D. Evolution of carbon dioxide gas
Correct Answer: C
Expert Explanation: The 2,4-DNP test is used to detect the presence of the carbonyl
functional group in aldehydes and ketones. When the reagent reacts with a carbonyl
compound, it forms a 2,4-dinitrophenylhydrazone derivative. This derivative typically
appears as a distinct yellow, orange, or red crystalline precipitate. The color of the
precipitate can often indicate the extent of conjugation in the original carbonyl compound.
Since both aldehydes and ketones react with this reagent, it serves as a general test for
carbonyls rather than a distinguishing test between them.
4. Which of the following describes the polarity of the carbonyl (C=O) group?
A. Nonpolar because carbon and oxygen have similar electronegativity
B. Polar with a partial positive charge on oxygen
C. Polar with a partial positive charge on carbon
D. Ionic because oxygen completely removes electrons from carbon
Correct Answer: C
Expert Explanation: The carbonyl group consists of a carbon atom double-bonded to an
oxygen atom. Oxygen is significantly more electronegative than carbon, leading to an
unequal sharing of electrons in the pi bond. This creates a dipole where the oxygen carries
a partial negative charge and the carbon carries a partial positive charge. This polarity
makes the carbonyl carbon electrophilic and susceptible to attack by nucleophiles.
Understanding this electronic distribution is fundamental to predicting the chemical
reactivity of aldehydes and ketones.
5. In nucleophilic addition reactions, what part of the carbonyl group is attacked by the
nucleophile?
A. The oxygen atom
B. The alpha hydrogen
C. The carbonyl carbon atom
D. The pi bond electrons
Correct Answer: C
Expert Explanation: Nucleophilic addition is the most common reaction type for
aldehydes and ketones. The nucleophile is an electron-rich species that seeks out electron-
deficient centers. Because the carbonyl carbon has a partial positive charge due to the
electronegative oxygen, it acts as an electrophile. The nucleophile attacks this carbon,
, causing the pi bond to break and moving electrons onto the oxygen. This step results in a
tetrahedral intermediate where the carbon is now bonded to the nucleophile.
6. What is the IUPAC name for the simplest ketone, commonly known as acetone?
A. Propanone
B. Ethanal
C. Butanone
D. Ethanone
Correct Answer: A
Expert Explanation: Acetone is the common name for the smallest possible ketone
structure. It consists of three carbon atoms, with the carbonyl group located on the middle
carbon. Following IUPAC rules, a three-carbon chain is named propane, and the ketone
suffix ‘-one’ is added. By dropping the ‘-e’ from propane, we get the systematic name
propanone. Because the carbonyl must be on the second carbon to be a ketone, the number
‘2’ is usually omitted as there are no other isomers.
7. Why do aldehydes and ketones have higher boiling points than alkanes of similar molar
mass?
A. They can form hydrogen bonds with each other
B. They experience dipole-dipole interactions
C. They are completely nonpolar
D. They have stronger London dispersion forces
Correct Answer: B
Expert Explanation: Aldehydes and ketones possess a polar carbonyl group that creates a
molecular dipole. These permanent dipoles allow for dipole-dipole intermolecular forces
between adjacent molecules. Alkanes are nonpolar and only experience weak London
dispersion forces. Dipole-dipole interactions are stronger than dispersion forces, requiring
more energy to overcome during the boiling process. However, aldehydes and ketones lack
a hydrogen atom bonded directly to oxygen, so they cannot form hydrogen bonds with
themselves like alcohols do.
8. Which compound will yield a positive iodoform test (yellow precipitate of CHI3)?
A. 3-Pentanone
B. Benzaldehyde
C. Acetophenone (Methyl phenyl ketone)
D. Pentanal
