CBSE 12th Standard Chemistry Subject Alcohols , Phenols and Ethers Chapter Case Study Questions 2021
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CBSE 12th Standard Chemistry Subject Alcohols , Phenols and Ethers Case Study Questions 2021
12th Standard CBSE
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Reg.No. :
Chemistry
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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. (a) -
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. (a) -
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.(a) -
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.(a) -
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.(a)