CBSE 12th Standard Chemistry Subject Alcohols , Phenols and Ethers Chapter Case Study Questions 2021
QB365 Provides the updated CASE Study Questions for Class 12 , and also provide the detail solution for each and every case study questions . Case study questions are latest updated question pattern from NCERT, QB365 will helps to get more marks in Exams
QB365 - Question Bank Software
CBSE 12th Standard Chemistry Subject Alcohols , Phenols and Ethers Case Study Questions 2021
12th Standard CBSE
-
Reg.No. :
Chemistry
-
Read the passage given below and answer the following questions:
Reimer- Tiemann reaction introduces an aldehyde group, on aromatic ring of phenol, ortho to the hydroxyl group. This is a general method for the synthesis of substituted salicylaldehydes as depicted below.
The following questions are multiple choice questions. Choose the most appropriate answer:
(i) Reimer-Tiemann reaction is an example of(a) nucleophilic substitution reaction (b) electrophilic substitution reaction (c) nucleophilic addition reaction (d) electrophilic addition reaction (ii) Which of the following reagents is used in the given reaction in steps I?
(a) aq. NaOH + CH3CI (b) aq. NaOH + CH2Cl2 (c) aq. NaOH + CHCl3 (d) aq. NaOH + CCl4 (iii) The structure of the intermediate [A] is
(iv) When phenol reacts with chloroform in presence of KOH, the product formed is
(a) salicylic acid (b) salicylaldehyde (c) both (a) and (b) (d) none of these. -
Read the passage given below and answer the following questions:
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 cone. H2SO4, H3PO4 or catalysts such as anhydrous ZnCl2 or Al2O3. When primary alcohols are heated with cone. 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: 3° > 2° > 1°. The dehydration of alcohols always occurs in accordance with the Saytzeffs rule. Primary alcohols when heated with protic acid at 413 K, gives dialkyl ether.
The following questions are multiple choice questions. Choose the most appropriate answer:
(i) Which one of the following alcohols undergoes acid-catalysed dehydration to alkenes most readily?(a) (CH3)2CHCH2OH (b) (CH3)3COH (c) CH3CHOHCH3 (d) CH3CH2CH2OH (ii) Dehydration of alcohol is an example of which type of reaction?
(a) Substitution (b) Elimination (c) Addition (d) Rearrangement (iii) 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 (iv)
products.
The most stable product(s) is/are
(c) both (a) and (b) (d) none of these. -
Read the passage given below and answer the following questions:
Williamson's synthesis is used for the preparation of symmetrical as well as unsymmerical ether. It is SN2 reaction mechanism. In Williamson's synthesis, 1° alkyl halide are used for preparation of ethers because 2° and 3°alkyl halide give alkene: Ethers are cleaved by hydrogen halides to alcohol and alkyl halide where alkyl halide is corresponding to that alkyl which has less number of carbon atom (it is because ofless steric hindrance). In polar media unsymmetrical ether like tertiary butyl ethyl ether gives ethyl alcohol and tertiary butyl halide as reaction proceeds via carbocation.
In these questions (i-iv), 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 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.
(i) Assertion: Rate of reaction of alkyl halide in Williamson's synthesis reaction is 1°RX> 2°RX > 3°RX.
Reason: It is a type of bimolecular substitution reaction (SN2).
(ii) Assertion: t-Butyl methyl ether is not prepared by the reaction of t-butyl bromide with sodium methoxide.
Reason: Sodium methoxide is a weak nucleophile.
(iii) Assertion: When isopropyl bromide is treated with sodium isopropoxide, di-isopropyl ether is obtained as a major product. .
Reason: With secondary alkyl halides, both substitution and elimination occur.
(iv) Assertion: Both symmetrical arid unsymmetrical ethers can be prepared by Williamson's synthesis.
Reason: Williamson's synthesis is an example of nucleophilic substitution reaction. -
Read the passage given below and answer the following questions:
Due to intermolecular hydrogen bonding, the boiling points of alcohols and phenols are much higher than those of corresponding haloalkanes, haloarenes, aliphatic and aromatic hydrocarbons. Among isomeric alcohols, the boiling points follow the order : primary > secondary > tertiary. Boiling points of ethers are much lower than those of isomeric alcohols. The solubility of alcohols in water decreases as the molecular mass of alcohols increases. Amongst isomeric alcohols solubility increases with branching. The solubility of phenols in water is much lower than that of alcohols. Lower ethers such as dimethyl ether and ethyl methyl ether are soluble in water, but the solubility decreases as the molecular mass increases.
In these questions (i-iv) 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 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.
(i) Assertion: Alcohols have higher boiling points than ethers of comparable molecular masses.
Reason: Alcohols and ethers are isomeric in nature.
(ii) Assertion: The solubility of phenols in water is much lower than that of alcohols.
Reason: Phenols do not form H-bonds with water.
(iii) Assertion : Among n-butane, ethoxyethane,1-propanol and 2-propanol, the increasing order of boiling points is,1-butanol < 1-propanol < ethoxyethane < n-butane.
Reason: Boiling point increases with increase in molecular mass.
(iv) Assertion: Dimethyl ether and diethylether are soluble in water.
Reason: As the molecular mass increases, solubility of ethers in water decreases. -
Read the passage given below and answer the following questions:
Lucas test is a test to differentiate between primary, secondary and tertiary alcohols. This test consists of treating an alcohol with Lucas reagent, and turbidity, due to the formation of insoluble alkyl chloride, is observed. Lucas test is based on the difference in reacting of three classes of alcohols with hydrogen chloride via SN1 reaction. The different reactivity reflects the differing ease of formation of the corresponding carbocations.
In these questions (i-iv), 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 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.
(i) Assertion: Equimolar mixture of conc. HCI and anhydrous ZnCl2 is called Lucas' reagent.
Reason : Lucas' reagent can be used to distinguish between methanol and ethanol.
(ii) Assertion: 2-Methyl-2-butanol gives no turbidity with Lucas' reagent at room temperature.
Reason: It is a 3° alcohol
(iii) Assertion: Amongst the compounds, H2C =CHCH2OH (I), C6H5OH (II), CH3CH2CH2OH (III) and (CH3)3COH (IV), only (IV) reacts with Lucas' reagent at room temperature.
Reason : Tertiary alcohol gives turbidity immediately with Lucas' reagent.
(iv) Assertion: Lucas test can be used to distinguish between 1-propanol and 2-propanol.
Reason : Lucas test is based upon the difference in reactivity of primary, secondary and tertiary alcohols with conc. HCI and anhyd. ZnCI2.
*****************************************
CBSE 12th Standard Chemistry Subject Alcohols , Phenols and Ethers Case Study Questions 2021 Answer Keys
-
(i) (b): It is an electrophilic substitution reaction.
(ii) (c)
(iv) (b): It is known as Reimer-Tiemann reaction.
-
(i) (b): The order of dehydration of alcohols is 3° > 2° > 1°.
(ii) (b): The dehydration of alcohol is an example of elimination reaction.
(iii) (b): Dehydration of CH30H will give methylene (a carbene) which is unstable.
\(\mathrm{CH}_{3} \mathrm{OH} \stackrel{\mathrm{H}_{2} \mathrm{SO}_{4}}{\longrightarrow}: \mathrm{CH}_{2}+\mathrm{H}_{2} \mathrm{O}\)
(iv) (a):
-
(i) (a): Williamson's synthesis occurs by SN2 mechanism and primary alkyl halides are most reactive in SN2 reactions.
(ii) (c): Sodium methoxide is a strong nucleophile. In presence of a strong base, i.e., sodium methoxide, t-butyl bromide undergoes dehyrohalogenation to form isobutylene.
(iii) (d): Since secondary and tertiary alkyl halides prefer to undergo elimination rather than substitution, therefore, even symmetrical ethers containing secondary and tertiary alkyl groups cannot be prepared in good yields by Williamson synthesis.
(iv) (b): Depending upon whether the alkyl halide and the alkoxide ion carry the same or different alkyl groups, both symmetrical and unsymmetrical ethers can be prepared by Williamsons synthesis. -
(i) (b): Due to the presence of intermolecular H-bonding in alcohols, they have higher boiling points than isomeric ethers.
(ii) (c): Like alcohols, phenols also form H-bond with water. But the solubility of phenols in water is much lower than that of alcohols because of the larger non-polar hydrocarbon part (benzene ring) present in their molecules.
(iii) (d): Boiling point increases with increase in molecular mass so, 1-butanol has higher boiling point than 1-propanol. Ethers do not form hydrogen bonds thus, they have lower boiling points than the corresponding alcohols.
Due to weak dipole-dipole interactions, the boiling points of lower ethers are only slightly higher than those of the n-alkanes having comparable molecular masses. Thus, the increasing order of boiling points is n-butane < ethoxyethane <1-propanol < 1-butanol.
(iv) (b): The solubility of lower ethers in water is due to the formation of H-bonds between water and ether molecules. As the molecular mass increases, the solubility of ethers in water decreases due to corresponding increase in the hydrocarbon portion of the molecule. -
(i) (c): Both methanol and ethanol are 1° alcohols and hence, cannot be distinguished by Lucas' reagent.
(ii) (d): Tertiary alcohols immediately react with Lucas' reagent.
(iii) (d): The order of reactivity of alcohols towards Lucas' reagent is 3° alcohol > 2° alcohol > 1° alcohol. 1° alcohols do not react with Lucas' reagent at room temperature. It requires high temperature. The benzyl and allyl alcohols react as rapidly as 3° alcohols with Lucas' reagent because their cations are resonance stabilised.
(iv) (b) : When Lucas' reagent (conc. HCl + ZnCI2) is added to 2-propanol (2° alcohol) turibitity appears within five minutes whereas with 1-propanol no turbidity appears and solution remains dear at room temperature.
