CBSE Class 12 Chemistry Alcohols Phenols And Ethers Question Bank

Question. Which of the following is a secondary alcohol?
a) 2-methylbutan-2-ol
b) 3-methylbutan-1-ol
c) 2-methylbutan-1-ol
d) 3- methylbutan-2-ol
Answer. D

Question. Reaction between acetone and methylmagnesiumchloride followed by hydrolysis will give :
a) Isobutylalcohol
b) Isopropyl alcohol
c) sec-butyl alcohol
d) tert-butyl alcohol
Answer. D

Question. Which of the following will not be soluble in NaHCO₃
a) 2,4,6 trinitrophenol
b) Benzoic acid
c) o- Nitrophenol
d) Benzene sulphonic acid
Answer. B

Question. Which of the following reagents may be used to distinguish between phenol and benzoic acid ?
a) Neutral FeCl₃
b) Aqueous NaOH
c) Tollen’s reagent
d) Molisch reagent
Answer. A

 

SHORT ANSWER TYPE QUESTIONS

Question. How simple or symmetrical is different from mixed or unsymmetrical?
Answer. Ethers are classified as simple or symmetrical, if the alkyl or aryl groups attached to the oxygen atom are the same, and mixed or unsymmetrical, if the two groups are different. Diethyl ether, C₂H₅OC₂H₅ , is symmetrical ether whereas C₂H₅OCH₃ and C₂H₅OC₆H₅ are unsymmetrical ethers.

Question. Give a chemical test to distinguish between the following pairs of compounds: Methanol and phenol
Answer. Phenol gives a violet colouration with FeCl₃ solution while methane does not.

Question. The carbon– oxygen bond length (136 pm) in phenol is slightly less than that in methanol. Give reason?
Answer. The carbon– oxygen bond length (136 pm) in phenol is slightly less than that in methanol. This is due to (i) partial double bond character on account of the conjugation of unshared electron pair of oxygen with the aromatic ring and (ii) sp² hybridised state of carbon to which oxygen is attached.

Question. Why the bond angle in ether is slightly greater than the tetrahedral angle?
Answer. In ethers, the four electron pairs, i.e., the two bond pairs and two lone pairs of electrons on oxygen are arranged approximately in a tetrahedral arrangement. The bond angle is slightly greater than the tetrahedral angle due to the repulsive interaction between the two bulky (–R) groups.

Question. Why the boiling point of 2- Methylpropan-2-ol is less than that of butanol?
Answer. The boiling points of alcohols and phenols increase with increase in the number of carbon atoms (increase in van der Waals forces). In alcohols, the boiling points decrease with increase of branching in carbon chain (because of decrease in van der Waals forces with decrease in surface area).

Question. Arrange the following sets of compounds in order of their increasing boiling points:
Answer. (a) Pentan-1-ol, butan-1-ol, butan-2-ol, ethanol, propan-1-ol, and methanol.
(b) Pentan-1-ol, n-butane, pentanal, ethoxyethane. (a) Methanol, ethanol, propan-1-ol, butan-2-ol, butan-1-ol, pentan-1-ol.
(b) n-Butane, ethoxyethane, pentanal and pentan-1-ol.

Question. Why alcohols act as Bronsted bases?
Answer. Alcohols act as Bronsted bases. It is due to the presence of unshared electron pairs on oxygen, which makes them proton acceptors.

Question. Why p-Nitro phenol is more acidic than Cresols?
Answer. In substituted phenols, the presence of electron withdrawing groups such as nitro group enhances the acidic strength of phenol. This effect is more pronounced when such a group is present at ortho and para positions. It is due to the effective delocalization of negative charge in phenoxide ion when substituent is at ortho or para position. On the other hand, electron releasing groups, such as alkyl groups, in general, do not favour the formation of phenoxide ion resulting in decrease in acid strength.

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. 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. 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: Which of the following alcohol contains C_sp³—OH  bond?
a) Allylic alcohol
b) Vinylic alcohol
c) Phenols
d) None of these

Answer: a

Question: Among the following sets of reactants which one produces anisole?
a) CH₃CHO, RMgX
b) C₆H₅OH,NaOH, CH₃I 
c) C₆H₅OH, neutral FeCl₃
d) C₆H₅—CH₃,CH₃ COCl , AlCl₃

Answer: b

Question: Vinylic alcohol contains
a) —OH group attached to an sp³-hybridised carbon atom
b) —OH group attached to sp³-hybridised carbon atom
c) —OH group bonded to a carbon-carbon double bond
d) —OH group attached to sp³-hybridised carbon atom next to an aromatic ring

Answer: c

Question: Ethers are treated with an aqueous solution of I in order to remove peroxides from it. Identify the ‘I’ from the following options.
a) KI
b) Br₂
c) KCNS
d) Na₂S₂O₃

Answer: a

Question: In ethers, the two bond pairs and two lone pairs of electrons on oxygen are arranged in a
a) planar arrangement
b) tetrahedral arrangement
c) trigonal bipyramidal arrangement
d) linear arrangement

Answer: b

Question: The reaction of Grignard reagent with carbonyl compound is a nucleophilic addition reaction.
This reaction on hydrolysis produces
a) ester
b) alcohol
c) carboxylic acid
d) ether

Answer: b

Question: The reagent(s) used for the reduction of aldehydes and ketone into alcohols is/are
a) finely divided metals such as Pt/Pd/Ni
b) sodium borohydride
c) lithium aluminium hydride
d) All of the above

Answer: d

Question: Which of the following reagent is used to reduce carboxylic acids to primary alcohols?
a) Pd
b) R—OH
c) LiAlH₄
d) Ni

Answer: c

Question: Which of the following hydrocarbon is used for the world wide production of phenol?
a) Iso-butylbenzene
b) Iso-propylbenzene
c) Iso-pentylbenzene
d) None of these

Answer: b

Question: The IUPAC name of following structure is
a) 2-methyl hydroxy cyclopentane.
b) 2-hydroxy 2-methyl cyclopentane
c) 2-methylcyclopentanol
d) cyclopentylmethane

Answer: c

Question: Alcohols and phenols react with active metals to yield
a) alkoxides/phenoxides
b) hydrogen gas
c) nitrogen
d) Both (a) and (b)

Answer: d

Question: Phenols show the cleavage of C—O bond with
a) Na
b) K
c) Zn
d) Ca

Answer: c

Question: Identify an appropriate reagent for the conversion of alcohol to carboxylic acid.
a) PCC
b) Anhydrous CrO₃
c) Cu/573 K
d) KMnO₄/H^⊗

Answer: d

Question: Phenol on reaction with conc. HNO₃ produces
a) o-nitrophenol
b) p-nitrophenol
c) 2, 4, 6-trinitrophenol
d) m-nitrophenol

Answer: c

Question: Which of the following is also known as wood spirit?
a) Ethanol
b) Propanol
c) Methanol
d) Butanol

Answer: c

Question: A primary alcohol with molecular formula C₃H₈O   on reaction with (X ) forms C₃H₇Br   . The halide formed on reaction with (Y ) gives alkane (C₆H₁₄). Here, X and Y respectively are
a) HBr and HCN
b) HBr and Na, ether
c) Br₂ and CH₃CN 
d) Br₂ and KMnO₄/H^⊗

Answer: b

Question: The action of zymase is inhibited during fermentation if the percentage of alcohol formed exceeds
a) 5%
b) 7%
c) 10%
d) 14%

Answer: d

Question: The reagent(s) used for the reduction of aldehydes and ketone into alcohols is/are
a) finely divided metals such as Pt/Pd/Ni
b) sodium borohydride
c) lithium aluminium hydride
d) All of the above

Answer: d

Question: Williamson’s synthesis involves which of the following type of mechanism when attack of an alkoxide ion on primary alkyl halide takes place?
a) S_N¹ 
b) S_N²
c) E1
d) E2

Answer: b

Question: Select the correct increasing order of boiling point.
a) n-pentane, ethoxyethane, butan-1-ol
b) ethoxyethane, n-pentane, butan-1-ol
c) butan-1-ol, n-pentane, ethoxyethane
d) ethoxyethane, butan-1-ol, n-pentane

Answer: b

17. Phenol on reaction with Zn followed by distillation gives ‘ X ’. Which on reaction with CH₃COCl, AlCl₃ gives Y . Final product Y is
a) acetophenone
b) benzophenone
c) diphenyl
d) methyl salicylate

Answer: a

Question: The order of reactivity of hydrogen halides with ether is as follows :
a) HBr > HI > HCl
b) HCl > HBr > HI
c) HI > HBr > HCl
d) HCl > HI > HBr

Answer: c

QUESTION BANK

1. Give equations for the following: