Chapter Exam

Chapter-7 Alcohols — Online MCQ Test

Q: What is the general formula for alcohols?

Answer: A. CnH2n+2O — Alcohols have the general formula CnH2n+2O, where one hydrogen atom is replaced by an -OH group in alkanes.

Q: Which functional group is characteristic of alcohols?

Answer: B. -OH — The hydroxyl group (-OH) is the characteristic functional group of alcohols, bonded to a carbon atom.

Q: What is the IUPAC suffix used for alcohols?

Answer: A. -ol — IUPAC nomenclature uses the suffix '-ol' for alcohols, such as ethanol, propanol, and butanol.

Q: Phenol is a compound where the -OH group is attached to which type of carbon?

Answer: B. Aromatic carbon (benzene ring) — Phenol consists of an -OH group directly attached to a benzene ring (aromatic carbon), making it structurally distinct from alcohols.

Q: Which statement about phenols is correct?

Answer: A. Phenols are more acidic than alcohols — Phenols are significantly more acidic than alcohols due to the resonance stabilization of the phenoxide ion formed after deprotonation.

Q: What is the IUPAC name of the ether with structure CH3-O-CH2CH3?

Answer: C. Methoxyethane — The IUPAC name treats the smaller alkyl group as a prefix (methoxy) attached to the larger alkyl group (ethane), giving methoxyethane.

Q: Which alcohol shows the highest boiling point for a given molecular weight?

Answer: A. Primary alcohol — Primary alcohols have the most hydrogen bonding capacity due to less steric hindrance, resulting in higher boiling points compared to secondary and tertiary alcohols.

Q: When phenol is treated with Br2 in CCl4 (without water), the product is:

Answer: C. 2,4,6-tribromophenol — In CCl4 (aprotic solvent), bromine is more electrophilic and phenol undergoes rapid multiple brominations at all three reactive positions (2, 4, and 6), forming 2,4,6-tribromophenol.

CHEMISTRY · CLASS 12 SECOND PUC · Karnataka State Board

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Chapter-7 Alcohols — Important Questions & Answers (FAQ)

Frequently asked questions from Karnataka State Board CLASS 12 SECOND PUC CHEMISTRY — Chapter-7 Alcohols, with answers and explanations. These are sample questions; the exam has its own separate question set.

What is the general formula for alcohols?

A. CnH2n+2O ✓
B. CnH2nO
C. CnH2n-2O
D. CnH2n+4O

Answer: A. CnH2n+2O
Alcohols have the general formula CnH2n+2O, where one hydrogen atom is replaced by an -OH group in alkanes.

Which functional group is characteristic of alcohols?

A. -CHO
B. -OH ✓
C. -COOH
D. -C=O

Answer: B. -OH
The hydroxyl group (-OH) is the characteristic functional group of alcohols, bonded to a carbon atom.

What is the IUPAC suffix used for alcohols?

A. -ol ✓
B. -ale
C. -ane
D. -ene

Answer: A. -ol
IUPAC nomenclature uses the suffix '-ol' for alcohols, such as ethanol, propanol, and butanol.

Phenol is a compound where the -OH group is attached to which type of carbon?

A. Aliphatic carbon
B. Aromatic carbon (benzene ring) ✓
C. Alicyclic carbon
D. Saturated carbon

Answer: B. Aromatic carbon (benzene ring)
Phenol consists of an -OH group directly attached to a benzene ring (aromatic carbon), making it structurally distinct from alcohols.

Which statement about phenols is correct?

A. Phenols are more acidic than alcohols ✓
B. Phenols are less acidic than alcohols
C. Phenols and alcohols have the same acidity
D. Phenols show no acidic properties

Answer: A. Phenols are more acidic than alcohols
Phenols are significantly more acidic than alcohols due to the resonance stabilization of the phenoxide ion formed after deprotonation.

What is the IUPAC name of the ether with structure CH3-O-CH2CH3?

A. Methyl ethyl ether
B. Ethyl methyl ether
C. Methoxyethane ✓
D. Ethoxyethane

Answer: C. Methoxyethane
The IUPAC name treats the smaller alkyl group as a prefix (methoxy) attached to the larger alkyl group (ethane), giving methoxyethane.

Which alcohol shows the highest boiling point for a given molecular weight?

A. Primary alcohol ✓
B. Secondary alcohol
C. Tertiary alcohol
D. All show the same boiling point

Answer: A. Primary alcohol
Primary alcohols have the most hydrogen bonding capacity due to less steric hindrance, resulting in higher boiling points compared to secondary and tertiary alcohols.

Phenol is more acidic than ethanol because:

A. Phenol has more hydrogen atoms
B. The phenoxide ion is stabilized by resonance with the aromatic ring ✓
C. Phenol is a liquid at room temperature
D. Phenol has a higher molecular weight

Answer: B. The phenoxide ion is stabilized by resonance with the aromatic ring
The phenoxide ion (C6H5O-) is stabilized by resonance delocalization of negative charge onto the aromatic ring carbons, making phenol much more acidic than aliphatic alcohols.

When phenol is treated with Br2 in CCl4 (without water), the product is:

A. 2-bromophenol only
B. 2,4-dibromophenol only
C. 2,4,6-tribromophenol ✓
D. 4-bromophenol only

Answer: C. 2,4,6-tribromophenol
In CCl4 (aprotic solvent), bromine is more electrophilic and phenol undergoes rapid multiple brominations at all three reactive positions (2, 4, and 6), forming 2,4,6-tribromophenol.

Which of the following statements about the Williamson synthesis is correct?

A. It works equally well with primary and tertiary alkyl halides
B. It requires an SN2 mechanism, so tertiary alkyl halides give poor yields or elimination products ✓
C. The alkoxide must be more basic than the alcohol being displaced
D. Both A and C are correct

Answer: B. It requires an SN2 mechanism, so tertiary alkyl halides give poor yields or elimination products
Williamson synthesis proceeds via SN2 mechanism; bulky tertiary alkyl halides undergo elimination rather than substitution, making primary and secondary halides optimal for this reaction.

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