Alcohols Phenols and Ethers — Class 12 Chemistry NCERT Solutions (Free)

Free step-by-step NCERT solutions for Class 12 Chemistry chapter "Alcohols Phenols and Ethers" — 8 important questions with detailed answers for CBSE board exam preparation.

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TL;DR: Free step-by-step NCERT solutions for Class 12 Chemistry chapter "Alcohols Phenols and Ethers" — 8 important questions with detailed answers for CBSE…

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Key Questions Covered:

What is the difference between an alcohol and a phenol? Give structural formu…
Explain why phenols are more acidic than alcohols. Write the equation for the…
Write the equation for the reaction of phenol with bromine water. What is the…
What are ethers? Give the general structural formula and two examples with th…
Explain the relative solubility of alcohols and ethers in water. Why is dieth…
Describe the reaction of ethers with dilute mineral acids. Write an equation …
+ 2 more questions in the full chapter

Solutions Summary:

Question	Status
What is the difference between an alcohol and a phenol? G…	✓ Solved
Explain why phenols are more acidic than alcohols. Write …	✓ Solved
Write the equation for the reaction of phenol with bromin…	✓ Solved
What are ethers? Give the general structural formula and …	✓ Solved
Explain the relative solubility of alcohols and ethers in…	✓ Solved
Describe the reaction of ethers with dilute mineral acids…	✓ Solved

Showing 6 of 8 questions

Q1: What is the difference between an alcohol and a phenol? Give structural formulas and one example of each.

Alcohol: A compound with an -OH group bonded to an sp3 hybridized carbon atom (aliphatic carbon). Example: CH3CH2OH (ethanol, alcohol) Structural formula: R-OH where R is an alkyl group Phenol: A compound with an -OH group bonded directly to an aromatic benzene ring (sp2 hybridized carbon). Example: C6H5OH (phenol) Structural formula: Ar-OH where Ar is an aromatic group Key differences: 1. Bonding: In alcohols, OH is on sp3 carbon; in phenols, OH is on sp2 (aromatic) carbon 2. Acidity: Phenols...

Q2: Explain why phenols are more acidic than alcohols. Write the equation for the ionization of phenol in water.

Ionization equation: C6H5OH ⇌ C6H5O- + H+ Ka = 1.3 × 10^-10 (pKa ≈ 10) Why phenols are more acidic than alcohols: 1. Resonance stabilization of phenoxide ion (C6H5O-): The negative charge on the oxygen is delocalized into the aromatic ring through resonance. The electron-rich aromatic ring can accommodate the negative charge through resonance structures: - O- can form π bonds with the ring carbons - This distributes the negative charge across the aromatic ring - Resonance stabilization lowers ...

Q3: Write the equation for the reaction of phenol with bromine water. What is the product, and why is this reaction so vigorous?

Reaction equation: C6H5OH + 3 Br2 → C(Br)3 C(Br)3... (Actually forms 2,4,6-tribromophenol) Correct equation: C6H5OH + 3 Br2 (in H2O) → 2,4,6-C6H2(OH)(Br)3 + 3 HBr Product: 2,4,6-tribromophenol (white precipitate) Why is this reaction so vigorous? 1. High reactivity of the benzene ring: The -OH group is an ortho-para directing activating group. It strongly activates the benzene ring toward electrophilic aromatic substitution. 2. Resonance activation: The lone pair on oxygen resonates into the...

Q4: What are ethers? Give the general structural formula and two examples with their IUPAC names.

Ethers: Compounds with two alkyl or aryl groups bonded to the same oxygen atom through single bonds. General formula: R-O-R' where R and R' are alkyl or aryl groups. Structural features: - The oxygen is sp3 hybridized - C-O-C bond angle ~ 104° - Two C-O single bonds - No H on oxygen (differs from alcohols) Examples with IUPAC names: 1. CH3-O-CH3 (dimethyl ether) IUPAC name: methoxyethane (incorrect) → actually called dimethyl ether IUPAC nomenclature: When naming ethers, use the group wi...

Q5: Explain the relative solubility of alcohols and ethers in water. Why is diethyl ether slightly soluble in water while diethyl disulfide is insoluble?

Solubility in water: Alcohols (e.g., ethanol CH3CH2OH): - Highly soluble in water due to strong hydrogen bonding - The -OH group can form hydrogen bonds with water molecules - Can act as both hydrogen bond donor (through H of OH) and acceptor (through O) - Example: Ethanol is miscible with water in all proportions Ethers (e.g., diethyl ether C2H5-O-C2H5): - Slightly soluble in water (5.6 g/100 mL at 20°C) - The ether oxygen can act as a hydrogen bond acceptor only (has no H on oxygen) - Cannot...

Q6: Describe the reaction of ethers with dilute mineral acids. Write an equation for the reaction of diethyl ether with HBr.

Reaction with dilute HBr: Equation: C2H5-O-C2H5 + HBr → C2H5Br + C2H5OH Full reaction: (C2H5)2O + HBr → C2H5Br + C2H5OH (diethyl ether + hydrobromic acid → ethyl bromide + ethanol) Mechanism (SN1): 1. Protonation of ether oxygen by HBr: C2H5-O-C2H5 + H+ → [C2H5-O+-C2H5] The lone pair on oxygen is protonated 2. Formation of carbocation: [C2H5-O+-C2H5] → C2H5+ + O-C2H5 The O-C bond breaks, forming a carbocation intermediate (In practice, this is concerted with the next step) 3....

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