CBSE Class 12 Chemistry Alcohols Phenols and Ethers MCQs Set G

Multiple Choice Questions (MCQs)

Question. The correct order of boiling point of primary (1°), secondary (2°) and tertiary (3°) alcohols is
(a) 1° > 2° > 3°
(b) 3° > 2° > 1°
(c) 2° > 1° > 3°
(d) 2° > 3° > 1°
Answer: a

Question. 1-propanol and 2-propanol can be best distinguished by
(a) Oxidation with KMnO₄ followed by reaction with Fehling solution.
(b) Oxidation with acidic dichromate followed by reaction with Fehling solution.
(c) Oxidation by heating with copper followed by reaction with Fehling solution.
(d) Oxidation with concentrated H₂SO₄ followed by reaction with Fehling solution. 
Answer: c

Question. Phenols are more acidic than alcohols because
(a) Phenoxide ion is stablised by resonance
(b) Phenols are more soluble in polar solvents
(c) Phenoxide ion does not exhibit resonance
(d) Alcohols do not lose H atoms at all
Answer: a

Question. Which compound is predominantly formed when phenol is allowed to react with bromine in aqueous medium?
(a) Picric acid
(b) O-Bromophenol
(c) 2, 4, 6-Tribromophenol
(d) p-Bromophenol
Answer: c

Question. Which of the following reagents cannot be used to distinguish between phenol and benzyl alcohol?
(a) FeCl₃
(b) Litmus soln
(c) Br₂/CCl₄
(d) All of the above 
Answer: c

Question. C₂H₅OH + SOCl₂ Pyridine→ C₂H5Cl + SO₂ + HCl
(a) Williamson’s reaction.
(b) Hofmann’s synthesis.
(c) Mendis reaction.
(d) Darzen’s reaction.
Answer: d

Assertion-Reason Questions

DIRECTION: Mark the option which is most suitable:
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

Question. Assertion: Phenol is more acidic than ethanol.
Reason: Phenoxide ion is resonance stabilised.
Answer: a

Question. Assertion: tert-Butyl alcohol undergoes acid catalysed dehydration readily than propanol.
Reason: 3º Alcohols do not give Victor-Meyer’s test.
Answer: b

Question. Assertion: Boiling points of alcohols are lower than hydrocarbons.
Reason: Among isomeric alcohols, boiling point decreases in the order: 1º > 2º > 3º.
Answer: d

Question. Assertion: o-Nitrophenol is more volatile than p-nitrophenol.
Reason: Intramolecular hydrogen bonding is present in o-nitrophenol while intermolecular H-bonding is in p-nitrophenol.
Answer: a

Question. Assertion: Phenol decomposes NaHCHO₃ solution to evolve CO₂ gas.
Reason: Picric acid is 2, 4, 6-trinitrophenol.
Answer: d

Question. Assertion: Phenol is less acidic than p-nitrophenol.
Reason: Phenolate ion is more stable than p-nitrophenol ion.
Answer: c

Question. Assertion: Primary and secondary alcohols can be distinguished by Victor-Meyer’s test.
Reason: Primary alcohols form nitrolic acid which dissolves NaOH to form blood red colouration but secondary alcohols form pseudonitrots which give blue colouration with NaOH.
Answer: a

Question. Assertion: With Br₂—H₂O, phenol gives 2,4,6-tribromophenol but with Br₂—CS₂, it gives 4-bromophenol as the major product.
Reason: In water, ionisation of phenol is enhanced but in CS₂, it is greatly suppressed.
Answer: a

Question. Assertion: Solubility of alcohols decreases with increase in size of alkyl/aryl groups.
Reason: Alcohols form H-bonding with water to show soluble nature.
Answer: b

Question. Assertion: Reimer–Tiemann reaction of phenol with CHCl₃ in NaOH at 340 K gives salicylic acid as the major product.
Reason: The reaction occurs through intermediate formation of +CHCl₂.
Answer: c

Case Based Questions

1. Alcohols are derivatives of hydrocarbons in which an –OH group has replaced a hydrogen atom. Although all alcohols have one or more hydroxyl (–OH) functional groups, they do not behave like bases such as NaOH and KOH. NaOH and KOH are ionic compounds that contain OH– ions. Alcohols are covalent molecules; the –OH group in an alcohol molecule is attached to a carbon atom by a covalent bon(d) The term alcohol originally referred to the primary alcohol ethanol(ethyl alcohol), which is used as a drug and is the main alcohol present in alcoholic beverages. Alcohols are compounds find wide application in industries( preparation of dyes, drugs, solvents etc) and are of immense use in our daily life. They contain one or more –OH group (responsible for the variation in their properties). They are classified as primary, secondary and tertiary alcohol. During chemical reaction they undergoes Substitution, Dehydration , Dehydrogenation. Dehydrogenation is a chemical reaction that involves the removal of hydrogen, usually from an organic molecule. It is the reverse of hydrogenation. Dehydrogenation is important, both as a useful reaction and a serious problem. At its simplest, it is useful way of converting alkanes, which are relatively inert and thus low-valued, to olefins, which are reactive and thus more valuable. Dehydrogenation of alcohols gives aldehyde, ketone and alkene , when alcohol is heated at 573K in the presence of copper.

Question. The product of which alcohol gives positive Tollen’s test –
(a) Primary alcohol
(b) Secondary alcohol
(c) Tertiary alcohol
(d) All of the abov
Answer: a

Question. Which among primary, secondary and tertiary alcohol on oxidation gives carboxylic acid having same number of carbon atom?
(a) Primary alcohol
(b) Secondary alcohol
(c) Tertiary alcohol
(d) Isopropyl alcohol
Answer: a

Question. An organic compound ‘A’ having molecular formula C6H4O is an isomer of alcohol with excess of HI forms two alkyl halides. On hydrolysis gives two compounds B and C . Oxidation B gives an acid D and C gives a mixed ketone. The name of D and E is-
(a) Propanoic acid, Butan-2one
(b) Ethanoic acid , Butan-2-one
(c) Butanoic acid , Propan-2-one
(d) Methanoic acid, 3Methyl But-2one
Answer: b

Question. In all the following isomeric alcohols with molecular formula C₅H₁₂O , identify the isomers exhibit chirality.
(a) Pentan-3-ol
(b) 2- Methyl butan-2-ol
(c) 3Methyl butan-2-ol
(d) 2,2 Dimethylpropan-1-ol.
Answer: c

2. “Lucas’ reagent” is a solution of anhydrous zinc chloride in concentrated hydrochloric aci(d) This solution is used to classify alcohols of low molecular weight. The reaction is a substitution in which the chloride replaces a hydroxyl group. A positive test is indicated by a change from clear and colorless to turbid, signaling formation of a chloroalkane. Also, the best results for this test are observed in tertiary alcohols, as they form the respective

alkyl halides fastest due to higher stability of the intermediate tertiary carbocation. The Lucas test in alcohols is a test to differentiate between primary, secondary, and tertiary alcohols. It is based on the difference in reactivity of the three classes of alcohols with hydrogen halides via an SN1 reaction. Iodoform (also known as triiodo methane and, inaccurately, as carbon triiodide) is the organ iodine compound with the formula CHI3. A pale yellow, crystalline, volatile substance, it has a penetrating and distinctive odor (in older chemistry texts, the smell is sometimes referred to as that of hospitals, where the compound is still commonly used) and, analogous to chloroform, sweetish taste. It is occasionally used as a disinfectant.

Question. Which of the above alcohol does not give positive iodoform test?
(a) Butan-1-ol
(b) Butan-2-ol
(c) 2-Methyl propal-1-ol
(d) 2- Methyl propan-2-ol
Answer: a

Question. Which carbonyl compound is used to prepare 2-Methyl propan2-ol with methyl magnesium bromide?
(a) Methanol
(b) Ethanal
(c) 2-Propanone
(d) 2- Butanone
Answer: c

Question. An unknown alcohol gives positive Lucas test in about 5 min. When this alcohol was heated with con(c) sulphuric acid alkene was formed with the formula C₄H₈. Ozonolysis of this alkene gives a single product C₂H₄O.Identify the alcohol-
(a) Butan-2-ol
(b) 2-Methyl propan-1-ol
(c) 2- Methyl propan-2-ol
(d) Butan-1-ol
Answer: a

Question. Which isomer of the unknown alcohol forms alkene on dehydrogenation?
(a) Butan-1-ol
(b) Butan-2-ol
(c) 2-Methyl propal-1-ol
(d) 2- Methyl propan-2-ol
Answer: d

3. Both alcohols and phenols are acidic in nature, but phenols are more acidic than alcohols. Acidic strength of alcohols mainly depends upon the inductive effect. Acidic strength of phenols depends upon a combination of both inductive effect and resonance effects of the substituent and its position on the benzene ring. Electron withdrawing groups increase the acidic strength of phenols whereas electron donating groups decrease the acidic strength of phenols. Phenol is weaker acid than carboxylic acid.

Answer the following questions by choosing the most appropriate options:

Question. The compound that does not liberate CO2, on treatment with aqueous sodium bicarbonate solution is
(a) benzoic acid
(b) benzenesulphonic acid
(c) salicylic acid
(d) carbolic acid
Answer: c

Question. Phenols are highly acidic as compared to alcohols due to
(a) the higher molecular mass of phenols
(b) the stronger hydrogen bonds in phenols
(c) alkoxide ion is a strong conjugate base
(d) phenoxide ion is resonance stabilised.
Answer: d

4. An organic compound (A) having molecular formula C₆H₆O gives a characteristic colour with aqueous FeCl₃ solution. (A) on treatment with CO₂ and NaOH at 400 K under pressure gives (B), which on acidification gives a compound (C).The compound (C) reacts with acetyl chloride to give (D) which is a popular pain killer.
Answer the following questions by choosing the most appropriate options:

Question. Compound (A) on heating with compound (C) in presence of POCl3 gives a compound (D) which is used
(a) in perfumery as a flavouring agent
(b) as an antipyretic
(c) as an analgesic
(d) as an intestinal antiseptic
Answer: d

Question. Compound (C) is
(a) salicylic acid
(b) salicyladehyde
(c) benzoic acid
(d) benzaldehyde
Answer: a

Question. Number of carbon atoms in compound (D) is
(a) 7
(b) 6
(c) 8
(d) 9
Answer: d

Question. Compound (A) is
(a) 2-hexanol
(b) dimethyl ether
(c) phenol
(d) 2-methyl pentanol
Answer: c

Question.The conversion of compound (A) to (C) is known as
(a) Reimer-Tiemann reaction
(b) Kolbe’s reaction
(c) Smarts reaction
(d) Girgnard reaction
Answer: b

5. A compound (X) containing C, H and O is unreactive towards sodium. It also does not react with Schiff’s reagent. On refluxing with an excess of hydroiodic acid, (X) yields only one organic product (Y). On hydrolysis, (Y) yields a new compound (Z) which can be converted into (Y) by reaction with red phosphorus and iodine. The compound (Z) on oxidation with potassium permanganate gives a carboxylic acid. The equivalent weight of this acid is 60.

Answer the following questions by choosing the most appropriate options:

Question. The IUPAC name of the acid formed is
(a) methanoic acid
(b) ethanoic acid
(c) propanoic acid
(d) butanoic acid
Answer: b

Question. Compound (X) is
(a) ethyl iodide
(b) methyl iodide
(c) propyl iodide
(d) mixture of (a) and (b)
Answer: a

Question. Compound (X) on treatment with excess of Cl2 in the presence of light gives
(a) a-chlorodiethyl
(b) a’-dichlorodiethyl ether
(c) perchlorodiethyl ether
(d) none of above
Answer: c

Question. The compound (X) is an
(a) acid
(b) aldehyde
(c) alcohol
(d) ether
Answer: d

Question. Compound (Z) is
(a) methanol
(b) ethanol
(c) propanol
(d) butanol
Answer: b

6. Dehydration of alcohols can lead to the formation of either alkenes or ethers. This dehydration can be carried out either with protonic acids such as conc. H₂SO₄, H₃PO₄ or catalysts such as anhydrous ZnCl₂ or Al₂O₃. When primary alcohols are heated with conc. H₂SO₄ at 433-443 K, they undergo intramolecular dehydration to form alkenes. Secondary and tertiary alcohols undergo dehydration under milder conditions. The ease of dehydration of alcohols follows the order : 3º > 2º > 1º.
The dehydration of alcohols always occurs in accordance with the Saytzeff’s rule. Primary alcohols when heated with protic acid at 413 K, give dialkyl either.

Answer the following questions by choosing the most appropriate options:

Question. Which one of the following alcohols undergoes acid-cataysed dehydration to alkenes most readily?
(a) (CH₃)₂CHCH₂OH
(b) (CH₃)₃COH
(c) CH₃CHOHCH₃
(d) CH₃CH₂CH₂OH
Answer: b

Question. The alcohol which does not give a stable compound on dehydration is
(a) ethyl alcohol
(b) methyl alcohol
(c) n-propyl alcohol
(d) n-butyl alcohol
Answer: b

Read the passage given below, and answer the following questions:

Alcohol is very important organic compound widely used in industry to prepare paints, varnishes, Medicines and different types Liquor.
Ethanol is the main constituents of different types of wines. Commercial alcohols is made unfit for drinking by mixing in it copper sulphate( to give it color ) and pyridine(a Foul smelling liquid) it is known as Denaturation of alcohols. Ingestion of small quantity of Methanol can cause blindness and large quantities cause even death.
Grignard Reagent can be used to prepare different types of alcohols. Methanol when treated with Grignard Reagent followed by hydrolysis forms primary alcohols. Ethanol and other aldehydes can be used to prepare Secondary alcohols. Ketones when treated with Grignard Reagent Followed by hydrolysis leads to the formation of tertiary alcohols.

In the following questions, a statement of assertion followed by a statement of reason is given
Choose the correct answer out of the following choices.
(a) Assertion and reason both are correct statements. And reason is the correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not the correct explanation for assertion.
(c) Assertion is correct but reason is wrong statement.
(d) Assertion is wrong but reason is correct statement.

Question. Assertion: Ethanol contaminated with methanol is not feet for drinking
Reason: Methanol is highly piousness for human body.
Answer: a

Question. Assertion : Grignard reagent can be used to prepare tertiary alcohol.
Reason: Grignard reagent do not react with Ketone
Answer: c

Question.Assertion: denaturation of commercial Alcohols can be done by mining copper sulphate and Pyridine.
Reason : Denatured alcohol is unfit for drinking.
Answer: b

Question. Assertion: Isopropyl Alcohol can be prepared by using grignard reagent
Reason : Methyl magnesium bromide reacts with ethanal followed by hydrolysis form isopropyl alcohol.
Answer: a

Very Short Answer Type Questions 

Question. Give a chemical test to distinguish between 2-Pentanol and 3-Pentanol. 
Answer. 2-pentanol gives Iodoform test with yellow ppt. of Iodoform while 3-pentanol does not give this test.

Question. Of the two hydroxy organic compounds ROH and R′OH, the first one is basic and other is acidic in behaviour. How is R different from R′?
Answer. When R = alkyl, ROH behaves as a bronsted base and when R′ = aryl, R′OH behaves as a bronsted acid.

Question. The C–O bond is much shorter in phenol than in ethanol. Give reason. 
Answer. Carbon of C–O bond of phenol is Sp² hybridised, so it acquires a partial double bond character but in ethanol it is Sp³ hybridised and a single bond.Double bond is shorter than a single bond.

Question. Draw the structure of hex-1-en-3-o1 compound.
Answer. CH₂ = CH – CH(OH) – CH₂ – CH₂ – CH₃

Question. Ortho nitrophenol has lower boiling point than p-nitrophenol. Why ? 
Answer. Ortho-nitrophenol has lower boiling point due to formation of intramolecular H-bonding whereas p-nitrophenol forms intermolecular H-bonding.

Question. Give simple chemical tests to distinguish between the following pairs of compounds: Benzoic acid and Phenol 
Answer. Ferric chloride test. Add neutral FeCl₃ in both the solutions, phenol reacts with neutral FeCl₃ to form an iron-phenol complex giving violet colour but benzoic acid does not.

Short Answer Type Questions-II 

Question. Explain the following observations :
(i) The boiling point of ethanol is higher than that of methoxymethane.
(ii) Phenol is more acidic than ethanol.
(iii) o- and p-nitrophenols are more acidic than phenol. 
Answer. (i) Due to presence of intermolecular H-bonding, associated molecules are formed, hence ethanol has high boiling point while methoxymethane does not have intermolecular H-bonding.
(ii) Phenol on losing H+ ion forms phenoxide ion, and ethanol on losing H+ ion forms ethoxide ion.Phenoxide ion is more stable than ethoxide ion as phenoxide ion exists in resonance structure. Due to this phenol is more acidic than ethanol.
(iii) Both o- and p-nitrophenols contain the NO₂ group which is an electron withdrawing group. Due to –R and–I effect of the –NO₂ group, electron density in the OH bond of substituted phenol decreases and hence the loss of proton becomes easy and therefore more acidic.

 Question. Give reasons for the following :
(i) Phenol is more acidic than methanol.
(ii) The C—O—H bond angle in alcohols is slightly less than the tetrahedral angle (190°28′).
(iii) (CH₃)₃C—O—CH₃ on reaction with HI gives (CH₃)₃C—I and CH₃—OH as the main products and not (CH₃)₃C—OH and CH₃—I.
Answer. (i) Phenol is more acidic than methanol because in phenol, phenoxide ion formed is more stabilized by resonance than phenol. There is no resonance in methanol.
(ii) The C—O—H bond angle in alcohols is slightly less than tetrahedral angle due to repulsion between the lone pairs of electrons of oxygen.
(iii) (CH₃)₃C⁺ is 3° carbo-cation which is more stable than CH3 + for SN1 reaction.

Question. Why phenol is more acidic than ethanol?
Answer. Phenol on losing H+ ion forms phenoxide ion, and ethanol on losing H+ ion forms ethoxide ion. Phenoxide ion is more stable than ethoxide ion as phenoxide ion exists in resonance structure. Due to this phenol is more acidic than ethanol.

Question. (a) Illustrate the following name reactions :
(i) Reimer-Tiemann Reaction (ii) Williamson Synthesis.
(b) Give a chemical test to distinguish between 2-propanol and 2-methyl-2-propanol. 
Answer.
(b) 2-Propanol is a secondary alcohol. When it reacts with I₂ in NaOH, it forms a yellow ppt of iodoform but 2-methyl-2 propanol does not respond to this test.