2nd PUC Chemistry Question Bank Chapter 11 Alcohols, Phenols and Ethers

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Karnataka 2nd PUC Chemistry Question Bank Chapter 11 Alcohols, Phenols and Ethers

Question 1.
What are alcohols? Give example.
Answer:
Alcohols are the organic compounds containing hydroxyl group attached to the alkyl group.

Question 2.
What are phenols? Give example.
Answer:
Phenols are the organic compounds in which hydroxyl group (-OH) is directly attached to the aromatic ring.

Question 3.
What are primary, secondary and tertiary alcohols?
Answer:
Primary alcohols (1°) are those in which -OH is attached to primary carbon atom, i.e. one or none alkyl group attached to the carbon atom bonded to -OH group.

Secondary alcohols (2°) are those in which -OH is attached to secondary carbon atom, i.e. two alkyl group are attached to carbon atom bonded to -OH group.

Tertiary alcohols (3°) are those in which -OH group is attached to tertiary carbon atom, i.e. three alkyl groups are attached to carbon atom bonded to -OH group.

Question 4.
Give the conversion of alkenes into alcohols.
Answer:
Alkenes react with water in the pre.ence of acid as catalyst. to form alcohols.

Question 5.
Give the conversion of carbonyl compounds into alcohols.
Answer:
Catalytic hydrogenation of aldehydes and ketones gives alcohol. Aldehydes yield primary alcohols and ketones give secondary alcohols.

Question 6.
Give the conversion of carboxylic acids into alcohols.
Answer:
In presence of strong reducing agent like LiAIH₄ carboxylic acids reduced to primary alcohols.

Question 7.
Explain the preparation of phenols from cumene.
Answer:
Cumene (Isopropyl benzene) is oxidised in the presence of air to form cumene hydroperoxide. It is converted into phenol by treating with dil. acid.

Question 8.
Alcohols of lower molecular mass and phenols are soluble in water. Give reason.
Answer:
Solubility of alcohols and phenols in water is due to their ability to form hydrogen bonds with water molecules. The solubility decreases with increase in size of alkyl/aryl groups.

Question 9.
The boiling points of alcohols and phenol are high. Give reason.
Answer:
The high boiling points of alcohols and phenols are mainly due to the presence of intermolecular hydrogen bonding in them.

Question 10.
How boiling points varies when number of carbon atoms increases in linear and branched alcohols.
Answer:
As number of carbon atoms increases in linear alcohols, surface area increases, which increases the van der Waals forces and hence boiling point increases. In branched alcohols, decrease in surface area decreases the vander Waals forces, which decreases the boiling points.

Question 11.
Explain the acidic nature of alcohols.
Answer:
Alcohols react with active metals such as sodium to yield corresponding alkoxides and hydrogen, i.e. they act as bronsted acids.
2R-OH + 2Na → 2RONa + H₂
The acidic character of alcohols is due to the polar nature of O – H bond.
Number of electron releasing alkyl groups decreases the acidity of the alcohols.
Thus the acidic character decreases as

Question 12.
Explain the acidic nature of phenols.
Answer:
Phenols react with active metal like sodium to form sodium phenoxide.
2C₆H₅OH + 2Na → 2C₆H₅ONa + H₂
Phenols react with aqueous sodium hydroxide to form sodium phenoxide.
C₆H₅OH + NaOH → C₆H₅Na + H₂O
The above reactions shows that phenols are acidic in nature, i.e. phenols are Bronsted acids.

The acidic nature of phenol is due to :
The hydroxyl group in phenol is directly attached to sp² hybridised carbon of benzene ring which acts as an electron with drawing group. Due to this phenol easily donates hydrogen ion.

The phenoxide ion is more stable due to resonance stabilisation and hence it favours the ionisation of phenols.

The electron with drawing group increases the acidity of phenols.
Ex: Nitrophenols are more acidic than phenols.

The electron donating group decreases the acidity of phenols.
Ex: Cresols are less acidic than phenols.

Question 13.
Among alcohols and phenols, which is more acidic? Why?
Answer:
Phenols are more acidic than alcohols. This is because the phenoxide ion formed from the ionisation of phenol is stabilised by resonance.

Question 14.
What is the effect of
1. Electron withdrawing group on acidity of phenols.
2. Electron donating group on acidity of alcohols.
3. Boiling point of alcohols on increasing number of carbon atoms.
Answer:
1. Acidity increases.
2. Acidity decreases.
3. Boiling point increases.

Question 15.
What is the effect of the following groups on the acidity of phenols?
(a) -CH₃
(b) -NO₂
Answer:
-CH₃ group decreases the acidity of phenol.
-NO₂ group increases the acidity of phenol.

Question 16.
Explain esterification reaction with an example.
Answer:
Alcohols reacts with carboxylic acids, in the presence of Cone. H₂SO₄ to form esters. This reaction is known as esterification.

Question 17.
What is acetylation reaction? Explain the acetylation of salicylic acid.
Answer:
Introduction of acetyl (CH₃CO) group in alcohols or phenols is known as acetylation. Acetylation of salicylic acid produces aspirin (Acetyl salicyclic acid).

Question 18.
What is Lucas reagent? Give its reaction with primary (1°) and tertiary (3°) alcohols?
Answer:
Mixture of anhydrous ZnCl₂ and Conc. HCl is called Lucas reagent. Lucas reagent gives turbidity immediately with tertiary alcohols and primary alcohols gives turbidity on heating.

Question 19.
Explain the dehydration of primary, secondary and tertiary alcohols.
Answer:
Ethanol (primary) alcohol undergoes dehydration in presence of Conc. H₂SO₄or Conc. H₃PO₄ at 443K.

Question 20.
Explain the mechanism of dehydration of ethanol.
Answer:

Question 21.
What happens when 1°, 2° and 3° alcohols are passed over heated copper at 573 K.
Answer:
Primary alcohol (1°) undergoes de-hydrogenation forming an aldehyde.

Secondary alcohol (2°) undergoes de-hydrogenation forming a ketone.

Tertiary alcohol (3°) undergoes dehydration forming an alkene. (DPUE-P-2)

Question 22.
Complete the following reactions.

Answer:

Question 23.
Give two methods of conversion of primary alcohol to aldehyde.
Answer:
1. Primary alcohol (1°) oxidises to an aldehyde by CrO₃ in anhydrous medium.

2. PCC (Pyridinium chlorochromate) oxidises primary alcohol to aldehydes.

Question 24.
Identify A and B in the following reaction.

Answer:

Question 25.
Give the conversion of secondary alochol to Ketone.
Answer:
Secondary alochol are oxdisied to ketone by CrO₃

Question 26.
Explain nitration of phenol.
Answer:
1. With dilute nitric acid at low temperature (298 K) phenol yields a mixture of ortho and para nitrophenols.

2. With Conc. nitric acid phenol is converted to 2,4,6-trinitrophenol picric acid).

Question 27.
Explain bromination of phenol.
Answer:
(a) When phenol is treated with bromine in CS₂ or CHCl₃ at low temperature to form o-bromophenol and p-bromophenol.

(b) When phenol is treated with bromine water 2,4,6-tribromophenol is formed as white precipitate.

Question 28.
Explain Kolbe’s reaction.
Answer:
When -sodium phenoxide is heated with carbon dioxide and the product is acidified 2-TIydroxybenzoic acid (Salicylic acid) is obtained.

Question 29.
Explain Reimer-Tiemann reaction.
Answer:
When phenol is treated with chloroform and sodium hydroxide solution, sodium salicylaldehyde is obtained which on acidification gives salicylaldehyde.

Question 30.
What happens when phenol is heated with zinc dust? Give equation.
Answer:
Benzene is obtained

Question 31.
Complete the equation.

Answer:

Question 32.
Explain the oxidation of phenol with chromic acid.
Answer:
Oxidation of phenol with chromic acid gives benzoquinone.

Question 33.
How methanol is produced commercially?
Answer:
Catalytic hydrogenation of carbon monoxide at high temperature and pressure in presence of ZnO-Cr₂O₃ catalyst, gives methanol.

Question 34.
Name the alcohol which is called as wood spirit.
Answer:
Methyl alcohol [methanol].

Question 35.
How ethanol is manufactured from molasses?
Answer:
Sugar in the molasses (sucrose) is converted into glucose and fructose in the presence of the enzyme invertase.

Glucose and fructose undergoes fermentation iii the ¡wesence of an enzyme zymose.

Question 36.
How is diethyl ether prepared?
Answer:
Ethanol undergo dehydration in presence of Conc. H₂SO₄ at 413 K to form diethylether.

Question 37.
Explain Williamson’s ether synthesis.
Answer:
When alkyl halide reacts with sodium alkoxide ethers are obtained.

Question 38.
Complete the following equations.

Answer:

Question 39.
What is the action of bromine in ethanoic acid on anisole? Give equation.
Answer:
Anisole undergoes brornination with bromine in ethanoic acid to form ortho- bromoanisole and para-bromoanisole.

Question 40.
Explain Friedel-Crafts alkylation of anisole.
Answer:
When anisole is treated with methyl chloride in presence of anhydrous aluminium chloride 2-methoxytoluene and 4-methoxytoluene are formed.

Question 41.
How anisole reacts with acetyl chloride (CH₃COCl) in the presence of anhydrous AlCl₃? Write the chemical equation for the reaction. (Explain Friedel-C rafts acylation of anisole.)
Answer:
When anisole is Reacted with ethanoyl chloride (acetyl chloride) in presence of anhydrous AlCl₃ 2-methoyacetophenone and 4-methylacetophenone are formed.

Question 42.
Write the IUPAC name of major product formed in Friedel-Crafts acylation of anisole.
Answer:
4-methoxyacetophenone.

Question 43.
A carbonyl compound (P) with the formula C₂H₄O reacts with CH₃MgX followed by hydrolysis to form an alcohol (Q). Name the alcohol Q.
Answer:
Propan-2-ol

Question 44.
Name the major product formed when the vapours of following alcohols are passed over hot copper at 573K.

Answer:

Question 45.
Arrange water, ethanol and phenol in increasing order of acidity and give reason for your answer.
Answer:
Ethanol < Water < Phenol
Due due + I effect of -C₂H₅ group makes the ethanol less acidic than water.
Due due greater resonance stabilisation of phenoxide ion, phenol is more acidic that water.

Question 46.
A carboxylic acid is treated with an alcohol in presence of Conc. H₂SO₄. Name the reaction. Give its general equation.
Answer:
Esterification reaction
RCOOH + R¹ – OH → RCOOR¹ + H₂O

Question 47.
Name the major product formed when sodium phenoxide is heated with carbon dioxide at 400K and at 4 to 7 atmospheric pressure. What is the name of the reaction?
Answer:
Sodium salicylate, Kolbe’s reaction.

Question 48.
Mention the major product formed in the following.

Answer:
(a) Ethane
(b) Diethyl ether.

Question 49.
On treating phenol with chloroform in presence of aqueous sodium hydroxide at 340K followed by acìd hydrolysis give the product
1. Write the name of the product
2. Give the name of the reaction.
Answer:
1. Salicylaldehyde.
2. Reimer-Tiemann reaction.

Question 50.
R – COOH → R – CH₂ – OH Name the reagent used 1nhisconversion.
Answer:
LiAIH₄ in presence of THF.

Question 51.
An organic compound with moleéular formula C₆H₆O gives white ppt
with bromine water, Identify the functional group in the compound. Write the chemical equation for the reatìon.
Answer:
Functional group is phenol.