Chapter 11: Alcohols, Phenols & Ethers Mock Test
Time: 1 Hour | Maximum Marks: 25
- All questions are compulsory.
- Section A contains Q1 (Multiple Choice) and Q2 (Very Short Answer).
- Section B contains Short Answer Type I questions (2 marks each). Attempt any 4.
- Section C contains Short Answer Type II questions (3 marks each). Attempt any 2.
- Section D contains Long Answer questions (4 marks each). Attempt any 1.
SECTION A
Q1. Select and write the most appropriate answer from the given alternatives: [4 Marks]
-
The IUPAC name of Anisole is:
(A) Methoxybenzene(B) Phenoxymethane(C) Methylphenyl ether(D) Ethoxybenzene
-
Which catalyst is used in the commercial preparation of phenol from cumene?
(A) Conc. $H_2SO_4$(B) Cobalt naphthenate(C) $AlCl_3$(D) $V_2O_5$
-
Phenol reacts rapidly with bromine water to give a white precipitate of:
(A) o-bromophenol(B) p-bromophenol(C) 2,4,6-tribromophenol(D) m-bromophenol
-
To prepare an unsymmetrical ether via Williamson synthesis with good yield, the alkyl halide must be:
(A) Primary ($1^\circ$)(B) Secondary ($2^\circ$)(C) Tertiary ($3^\circ$)(D) Vinylic
Q2. Answer the following questions in one sentence: [3 Marks]
- Name the product formed when a primary alcohol is oxidized using Pyridinium chlorochromate (PCC).
- What is denatured alcohol?
- Arrange the following in increasing order of their acidic strength: Phenol, p-nitrophenol, p-cresol.
SECTION B
Attempt any FOUR of the following: [8 Marks]
- Explain Williamson synthesis for the preparation of ethers with a suitable example.
- Why is phenol more acidic than ethanol? Explain.
- What is the action of concentrated $HNO_3$ on phenol? Write the chemical equation.
- Write a short note on Kolbe's reaction.
- How is ethanol prepared from ethene by the hydration process? Write the equation.
SECTION C
Attempt any TWO of the following: [6 Marks]
- Describe the preparation of phenol from cumene with necessary chemical equations. Why is this considered an excellent commercial method?
- Write a short note on the Reimer-Tiemann reaction.
- Explain the hydroboration-oxidation of propene. Name the major product formed.
SECTION D
Attempt any ONE of the following: [4 Marks]
- (a) Distinguish between primary, secondary, and tertiary alcohols using the Lucas test. [3 Marks]
(b) What are simple (symmetrical) ethers? Give one example. [1 Mark] - (a) Explain Dow's process for the preparation of phenol from chlorobenzene. [2 Marks]
(b) Explain why the boiling point of ethanol is higher than that of dimethyl ether, even though they have the same molecular formula. [2 Marks]
Solutions & Marking Scheme
SECTION A [7 Marks]
Q1. Multiple Choice Answers:
1. (A) Methoxybenzene [1 Mark for correct option]
2. (B) Cobalt naphthenate [1 Mark for correct option]
3. (C) 2,4,6-tribromophenol [1 Mark for correct option]
4. (A) Primary ($1^\circ$) [1 Mark. $2^\circ$ or $3^\circ$ leads to elimination instead of substitution]
Q2. Very Short Answers:
1. PCC Oxidation:
An Aldehyde. (PCC is a mild oxidizing agent that stops oxidation at the aldehyde stage). [1 Mark]
2. Denatured Alcohol:
Ethanol made unfit for drinking by adding toxic, foul-smelling substances like methanol, pyridine, or copper sulfate is called denatured alcohol. [1 Mark]
3. Acidic Strength Order:
p-cresol < Phenol < p-nitrophenol. [1 Mark]
SECTION B [8 Marks]
Q3. Williamson Synthesis:
It involves the reaction of an alkyl halide with sodium alkoxide (or phenoxide) via an $S_N2$ mechanism to prepare symmetrical or unsymmetrical ethers. [1 Mark]
$CH_3-CH_2-Br + CH_3-O^-Na^+ \rightarrow CH_3-CH_2-O-CH_3 + NaBr$
(Ethyl bromide) (Sod. methoxide) (Ethyl methyl ether)
Q4. Acidic nature of Phenol vs Ethanol:
Phenol is more acidic because after losing a proton ($H^+$), the resulting phenoxide ion is highly stabilized by resonance (the negative charge is delocalized over the benzene ring). [1 Mark]
In ethanol, the ethoxide ion formed has no resonance stabilization. Moreover, the $+I$ effect of the ethyl group intensifies the negative charge on oxygen, destabilizing it. [1 Mark]
Q5. Action of conc. $HNO_3$ on Phenol:
Phenol reacts with a nitrating mixture (conc. $HNO_3$ + conc. $H_2SO_4$) to yield 2,4,6-trinitrophenol, commonly known as Picric acid. [1 Mark]
$C_6H_5OH + 3HNO_3(\text{conc}) \xrightarrow{\text{conc. } H_2SO_4, \Delta} C_6H_2(NO_2)_3OH \text{ (Picric acid)} + 3H_2O$
[1 Mark for reaction]Q6. Kolbe's Reaction:
When sodium phenoxide is heated with carbon dioxide ($CO_2$) under pressure (4-7 atm) at 400 K, it undergoes electrophilic substitution to form sodium salicylate. Subsequent acidification yields Salicylic acid (2-hydroxybenzoic acid). [1 Mark]
$C_6H_5ONa + CO_2 \xrightarrow{400 \text{ K}, 4-7 \text{ atm}} \text{Sodium salicylate} \xrightarrow{H_3O^+} \text{Salicylic acid}$
[1 Mark for reaction]Q7. Hydration of Ethene:
Ethene reacts with concentrated sulfuric acid to form ethyl hydrogen sulfate, which upon boiling with water undergoes hydrolysis to form ethanol. [1 Mark]
$CH_2=CH_2 + H_2SO_4 \rightarrow CH_3-CH_2-OSO_3H \xrightarrow{H_2O, \Delta} CH_3-CH_2-OH + H_2SO_4$
[1 Mark for reaction]SECTION C [6 Marks]
Q8. Phenol from Cumene:
Step 1 (Oxidation): Cumene (isopropylbenzene) is oxidized in the presence of air at 423 K using a cobalt naphthenate catalyst to form cumene hydroperoxide.
$C_6H_5-CH(CH_3)_2 + O_2 \xrightarrow{\text{Co-naphthenate}} C_6H_5-C(OOH)(CH_3)_2$ [1 Mark]
Step 2 (Hydrolysis): Cumene hydroperoxide is decomposed by dilute acid ($H_2SO_4$) to yield Phenol and Acetone.
$C_6H_5-C(OOH)(CH_3)_2 \xrightarrow{H^+} C_6H_5OH \text{ (Phenol)} + CH_3COCH_3 \text{ (Acetone)}$ [1 Mark]
Commercial viability: It is highly preferred industrially because a valuable by-product, Acetone, is formed in large quantities, offsetting the production costs. [1 Mark]
Q9. Reimer-Tiemann Reaction:
When phenol is treated with chloroform ($CHCl_3$) in the presence of aqueous sodium hydroxide ($NaOH$) at 340 K, an intermediate benzal chloride is formed. [1 Mark]
This intermediate undergoes alkaline hydrolysis, followed by acidification, to yield Salicylaldehyde (2-hydroxybenzaldehyde) as the major product. [1 Mark]
$\text{Phenol} + CHCl_3 + 3NaOH(aq) \xrightarrow{340 \text{ K}} \text{Intermediate} \xrightarrow{H_3O^+} \text{Salicylaldehyde} + 3NaCl$
[1 Mark for reaction]Q10. Hydroboration-Oxidation of Propene:
Propene reacts with diborane ($B_2H_6$) to form tripropylborane as an intermediate. [1 Mark]
This intermediate is then oxidized using alkaline hydrogen peroxide ($H_2O_2/OH^-$) to yield a primary alcohol. The overall reaction amounts to the Anti-Markovnikov addition of water to the double bond. [1 Mark]
Major Product: Propan-1-ol. [1 Mark]
SECTION D [4 Marks]
Q11. (a) Lucas Test [3 Marks] (b) Simple Ethers [1 Mark]
(a) Lucas Test: The Lucas reagent is a mixture of concentrated $HCl$ and anhydrous $ZnCl_2$. It distinguishes alcohols based on the formation of insoluble alkyl chlorides, which create turbidity (cloudiness). [1 Mark]
- Tertiary ($3^\circ$) alcohols: React immediately and form turbidity instantly. [1/2 Mark]
- Secondary ($2^\circ$) alcohols: React slower; turbidity appears after 5 to 10 minutes. [1/2 Mark]
- Primary ($1^\circ$) alcohols: Do not react at room temperature; the solution remains clear. (Turbidity appears only upon heating). [1 Mark]
(b) Simple Ethers: Ethers in which both the alkyl or aryl groups attached to the oxygen atom are identical. Example: Diethyl ether ($C_2H_5-O-C_2H_5$). [1 Mark]
Q12. (a) Dow's Process [2 Marks] (b) Boiling Point Reasoning [2 Marks]
(a) Dow's Process:
Chlorobenzene is fused with aqueous NaOH at a high temperature (623 K) and high pressure (300 atm) to form sodium phenoxide. Acidification of this salt with dilute HCl yields phenol. [1 Mark]
$C_6H_5Cl \xrightarrow{NaOH, 623 \text{ K, 300 atm}} C_6H_5ONa \xrightarrow{H^+} C_6H_5OH \text{ (Phenol)}$ [1 Mark]
(b) Boiling Point of Ethanol vs Dimethyl Ether:
Ethanol ($C_2H_5OH$) contains an $-OH$ group, which allows its molecules to form strong intermolecular hydrogen bonds. This requires a large amount of thermal energy to separate the molecules, resulting in a higher boiling point. [1 Mark]
Dimethyl ether ($CH_3-O-CH_3$) lacks a hydrogen atom attached directly to an electronegative oxygen, so it cannot form hydrogen bonds. Its molecules are held together only by weak dipole-dipole interactions, resulting in a lower boiling point. [1 Mark]
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