Alcohols, Phenols, and Ethers – A Comprehensive Guide for Class 12 Chemistry

Introduction

Alcohols, Phenols, and Ethers are important organic compounds with diverse applications in medicine, industry, and daily life. This guide covers their structures, properties, and key reactions to help Class 12 students prepare effectively for the West Bengal Higher Secondary Examination.

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Alcohols

Structure and Classification

Alcohols are organic compounds containing one or more hydroxyl (-OH) groups attached to a carbon atom. They are classified as:

• Primary (1°) Alcohols: -OH group attached to a primary carbon (e.g., Methanol, Ethanol).
• Secondary (2°) Alcohols: -OH group attached to a secondary carbon (e.g., Isopropanol).
• Tertiary (3°) Alcohols: -OH group attached to a tertiary carbon (e.g., Tert-Butanol).

Preparation of Alcohols

• Hydration of Alkenes: $$C_2H_4 + H_2O → C_2H_5OH$$
• Reduction of Aldehydes and Ketones: $$CH_3CHO + H_2 → CH_3CH_2OH$$

Chemical Properties

1. Oxidation: Primary alcohols oxidize to aldehydes and then carboxylic acids.
2. Reaction with Sodium Metal: Produces hydrogen gas.
3. Esterification: Reacts with carboxylic acids to form esters.

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Phenols

Structure and Properties

Phenols contain a hydroxyl (-OH) group attached to an aromatic benzene ring. Example: Phenol (C₆H₅OH).

• Acidic Nature: Phenols are more acidic than alcohols due to resonance stabilization.
• Solubility: Partially soluble in water due to hydrogen bonding.

Preparation of Phenols

• From Benzene Sulphonic Acid: $$C_6H_6SO_3H + NaOH → C_6H_5OH + Na_2SO_3$$

Chemical Reactions

1. Electrophilic Substitution: Phenols undergo bromination, nitration, and sulfonation.
2. Reaction with FeCl₃: Produces a violet color (qualitative test for phenols).

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Ethers

Structure and Classification

Ethers have an oxygen atom bonded to two alkyl or aryl groups (R–O–R).

• Simple Ethers: Both R groups are the same (e.g., Diethyl ether).
• Mixed Ethers: Different R groups (e.g., Methyl Phenyl Ether).

Preparation of Ethers

• Williamson’s Synthesis: $$RONa + R'X → ROR' + NaX$$

Chemical Properties

1. Reaction with Halogens: Forms haloalkanes.
2. Cleavage by HI/HBr: Produces alcohol and alkyl halide.

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Important MCQs for West Bengal HS Exam

Alcohols

1. What is the general formula of alcohols?

   • (A) CₙH₂ₙO
   • (B) CₙH₂ₙ₊₁OH
   • (C) CₙH₂ₙ₋₂O
   • (D) CₙH₂ₙ₊₂OH
     (Ans: B)

2. Which of the following alcohols is most reactive towards Lucas test?

   • (A) Methanol
   • (B) Ethanol
   • (C) Isopropanol
   • (D) Tert-Butanol
     (Ans: D)

3. The oxidation of primary alcohol produces:

   • (A) Ketone
   • (B) Carboxylic acid
   • (C) Aldehyde
   • (D) Ether
     (Ans: C)

Phenols

4. Phenol is more acidic than alcohol because of:

   • (A) +I Effect
   • (B) -I Effect
   • (C) Resonance stabilization
   • (D) Hyperconjugation
     (Ans: C)

5. What happens when phenol reacts with bromine water?

   • (A) No reaction
   • (B) White precipitate forms
   • (C) Yellow precipitate forms
   • (D) Brown precipitate forms
     (Ans: B)

6. Which reagent gives a violet color with phenol?

   • (A) FeCl₃
   • (B) NaOH
   • (C) NH₄OH
   • (D) AgNO₃
     (Ans: A)

Ethers

7. The functional group of ethers is:

   • (A) –OH
   • (B) –CHO
   • (C) –O–
   • (D) –COOH
     (Ans: C)

8. Williamson’s synthesis is used for preparing:

   • (A) Alcohols
   • (B) Phenols
   • (C) Ethers
   • (D) Ketones
     (Ans: C)

9. Diethyl ether reacts with HI to form:

   • (A) Ethanol
   • (B) Ethyl iodide
   • (C) Both (A) and (B)
   • (D) Acetic acid
     (Ans: C)

General Questions

10. Which among the following is the strongest acid?

    • (A) Ethanol
    • (B) Methanol
    • (C) Phenol
    • (D) Ether
      (Ans: C)

11. The reaction of an alcohol with a carboxylic acid forms:

    • (A) Ether
    • (B) Aldehyde
    • (C) Ester
    • (D) Ketone
      (Ans: C)

12. Which of the following is used as an anesthetic?

• (A) Ethanol
• (B) Methanol
• (C) Diethyl ether
• (D) Phenol
  (Ans: C)

Alcohols

13. What is the product of the dehydration of ethanol in the presence of concentrated H₂SO₄?

    • (A) Methane
    • (B) Ethene
    • (C) Ethane
    • (D) Acetaldehyde
      (Ans: B)

14. Which alcohol is commonly used as an antiseptic?

    • (A) Methanol
    • (B) Ethanol
    • (C) Isopropanol
    • (D) Tert-butanol
      (Ans: C)

15. The process of converting sugar into ethanol using yeast is called:

    • (A) Fermentation
    • (B) Esterification
    • (C) Hydrolysis
    • (D) Hydrogenation
      (Ans: A)

16. Which of the following reagents is used to test for the presence of alcohol?

    • (A) Lucas Reagent
    • (B) Tollens’ Reagent
    • (C) Fehling’s Solution
    • (D) Benedict’s Solution
      (Ans: A)

17. Which alcohol is also known as "wood alcohol"?

    • (A) Ethanol
    • (B) Methanol
    • (C) Propanol
    • (D) Butanol
      (Ans: B)

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Phenols

18. What is the IUPAC name of phenol?

    • (A) Hydroxybenzene
    • (B) Carbolic Acid
    • (C) Benzenol
    • (D) Benzyl Alcohol
      (Ans: A)

19. Phenol can be converted to benzene by reacting with:

    • (A) Zn Dust
    • (B) H₂O
    • (C) O₂
    • (D) Br₂
      (Ans: A)

20. Phenol reacts with chloroform in the presence of NaOH to give:

    • (A) Benzyl alcohol
    • (B) Salicylaldehyde
    • (C) Anisole
    • (D) Benzophenone
      (Ans: B)

21. Which of the following is NOT a property of phenol?

    • (A) Acidic nature
    • (B) Soluble in water
    • (C) Less reactive than benzene
    • (D) Undergoes electrophilic substitution
      (Ans: C)

22. What is the major product when phenol reacts with concentrated nitric acid?

    • (A) Ortho-nitrophenol
    • (B) Para-nitrophenol
    • (C) Picric acid
    • (D) Benzophenone
      (Ans: C)

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Ethers

23. Ethers are generally prepared using:

    • (A) Aldol Condensation
    • (B) Williamson’s Synthesis
    • (C) Grignard Reaction
    • (D) Friedel-Crafts Reaction
      (Ans: B)

24. Which of the following ethers is used as a solvent?

    • (A) Dimethyl Ether
    • (B) Diethyl Ether
    • (C) Methyl Phenyl Ether
    • (D) Benzyl Ether
      (Ans: B)

25. Ethers have a boiling point lower than alcohols of similar molecular mass due to:

    • (A) Dipole-Dipole Interaction
    • (B) Van der Waals Forces
    • (C) Hydrogen Bonding
    • (D) Ionic Bonding
      (Ans: C)

26. What is the common name of methoxybenzene?

    • (A) Anisole
    • (B) Toluene
    • (C) Benzaldehyde
    • (D) Benzyl Alcohol
      (Ans: A)

27. When diethyl ether is exposed to air for a long time, it forms:

    • (A) Aldehydes
    • (B) Ketones
    • (C) Peroxides
    • (D) Alcohols
      (Ans: C)

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General MCQs on Alcohols, Phenols, and Ethers

28. Which of the following is used as a disinfectant?

    • (A) Phenol
    • (B) Ethanol
    • (C) Ether
    • (D) Methanol
      (Ans: A)

29. Which reagent is used for distinguishing between primary, secondary, and tertiary alcohols?

    • (A) Fehling’s Solution
    • (B) Tollen’s Reagent
    • (C) Lucas Reagent
    • (D) Iodoform Test
      (Ans: C)

30. The reaction between alcohols and hydrogen halides produces:

    • (A) Ethers
    • (B) Alkyl Halides
    • (C) Aldehydes
    • (D) Ketones
      (Ans: B)

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These 30+ MCQs cover the most important concepts for Alcohols, Phenols, and Ethers in Class 12 Chemistry. They are essential for scoring well in the West Bengal Higher Secondary Exam.

For more such study materials and MCQs, visit MightyKnowledge! 🚀

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Conclusion

Alcohols, Phenols, and Ethers are crucial organic compounds with significant industrial and biological importance. Understanding their properties and reactions is essential for Class 12 students preparing for the West Bengal Higher Secondary Examination.

~ For more such in-depth study materials and MCQs, visit MightyKnowledge!