Plus Two Chemistry Chapter Wise Questions and Answers Chapter 11 Alcohols, Phenols and Ethers

Answer:
1. 95.6% ethyl alcohol is known as a rectified spirit.

2. A mixture of ethyl alcohol and gasoline can be used as a fuel in the internal combustion engine. It is known as power alcohol.

3. Commercial alcohol is made unfit for drinking by adding certain substances like pyridine, methanol etc. Spirit thus obtained is called denatured spirit.

Question 2.
Fill in the blanks:

 

Question 3.
Ethyl alcohol can be prepared by fermentation of molasses.

1. What do you mean by fermentation?
2. Explain the process.
3. What do you mean by ‘wash’?

Answer:
1. Fermentation is the process of breaking up of large molecules into small molecule in the presence of biological catalyst called enzymes.

2. Molasses is the mother liquor left behind after the crystallisation of cane sugar from sugar cane juice. It is 40% sucrose solution. First it is diluted to 10% solution. Then yeast is added. Temperature of the system is kept at 305 K. The following reactions will take place.

3. 8-10% ethyl alcohol is known as ‘wash’.

Question 4.
Raju prepared soap in the chemistry lab. A liquid remained after the preparation. He argued that it was useless.

1. Do you agree with him? Why?
2. How can you prepare glycerol from spentlye?

Answer:

1. No. It can be used to prepare glycerol.
2. Spentlye contains unreacted alkali, glycerol, water, NaCI, and soluble soap. It is first treated with acid to remove alkali, then with aluminium sulphate to remove soluble soap. It is then evaporated under reduced pressure to remove NaCI.

The resulting solution is then decolorised using animal charcoal, Then the solution is distilled under reduced pressure to remove water. In this way we get glycerol.

Question 5.
When an old sample of ether was heated, it exploded.

1. What is the reason for this phenomenon?
2. How can you detect peroxide content in ether?
3. How can we remove peroxide from old sample of ether?

Answer:

1. Due to the formation of peroxide.
2. Presence of peroxide can be tested by adding ferrous salt solution followed by addition of KCNS solution. Formation of blood red colour indicates the presence of peroxide.
3. The peroxide can be removed by washing with ferrous salt solution.

Question 6.
Alcohols are comparatively more soluble in water than hydrocarbons of comparable molecular masses. Explain this fact.
Answer:
Because of the presence of O-H group in them, alcohols are capable of forming hydrogen bonds with water molecules whereas hydrocarbons cannot form hydrogen bonds with water. As a result, alcohols are more soluble in water than the hydrocarbons of comparable molecular masses.

Question 7.
Give the structures and IUPAC names of monohydric phenols of molecular formula, C₇H₈O.
Answer:

 

Question 8.
Explain why ortho-nitrophenol is more acidic than ortho-methoxyphenol?
Answer:
ortho-Nitrophenol is more acidic than ortho- methoxyphenol because nitro group by its electron withdrawing resonance effect stabilises the phenoxide ion whereas methoxy group by its electron releasing effect destabilises the phenoxide ion. Greater the stability of the phenoxide ion, greater is the dissociation of phenol and greater is its acid strength.

Question 9.
With the help of a mixture of con. HCI and ZnCI2 how can you distinguish between 1°, 2°, 3° alcohols.
Answer:

• 1° alcohol + Lucas reagent → no reaction
• 2° alcohol + Lucas reagent → turbidity within five minutes
• 3° alcohol + Lucas reagent → turbidity occurs immediately

Lucas reagent anhydrous ZnCI₂/HCI

Plus Two Chemistry Alcohols, Phenols and Ethers Four Mark Questions and Answers

Question 1.
Match the following:

A	B
Oxidising Agent	Lucas Test.
Dehydrogenation	LiAIH4.
Anhydrous ZnCI2, HCI	Copper at 573K.
Reducing Agent	Acidified KMnO4.

Answer:

A	B
Oxidising Agent	Acidified KMnO4.
Dehydrogenation	Copper at 573K.
Anhydrous ZnCI2, HCI	Lucas Test.
Reducing Agent	LiAIH4.

Question 2.

a) Alcohols are having high boiling points than corresponding alkyl halides and ethers. Why?
b) Phenol is more acidic than ethanol. Give the reason.
c) Predict the products :

Answer:
a) Due to the presence of polar hydroxyl group alcohols can associate through intermolecular hydrogen bonding.
b) Phenoxide ion is stabilized by resonance while alkoxide ion has no resonance stabilisation.

Question 3

1. Phenol is acidic even though it has no carboxylic group, why?
2. Convert phenol to salicylic acid and name the reaction.

Answer:
1. By the removal of a proton from phenol a phenoxide ion is obtained. It is stabilised by resonance. Hence phenol acts as an acid.
2.

. 

 

Question 4.
1. Compare the solubility of diethyl ether and n- butane in water.
2. Give the product(s) from the reaction of one mole of diethyl ether with

• one mole of conc. HI and
• excess of HI.

Answer:
1. Diethyl ether being weakly polar is capable of forming intermolecular hydrogen bonding with water. Hence, diethyl ether is soluble in water while n-butane is not.

2. The product(s) from the reaction of one mole of diethyl ether.

• C₂H₅OH and C₂H₅I
• 2C₂H₅I

Question 5.
Identify X and Y.

Question 6.
1. Boiling point depends on the inter molecular hydrogen bonding.

• Ethanol and propane have comparable molecular masses but their boiling points differ widely. Why?

2. Williamson synthesis is an important method of ether synthesis. Which of the following reactions is better for ether synthesis? Justify.

Answer:
1. Ethanol molecules are associated by intermolecular hydrogen bonding.

• Ethanol molecules are associated by intermolecular hydrogen bonding. This is absent in propane. So Ethanol has higher boiling point.

2. (CH₃)₃C-ONa + CH₃-Br is better. The tertiary alkyl halide undergoes elimination in presence of base to form alkene.

Question 7.
Chloro methane reacts with aqueous sodium hydroxide to form methanol.

1. What happens when chlorobenzene reacts with aqueous sodium hydroxide? Justify.
2. Write the reaction by which chlorobenzene can be converted to phenol.

Answer:

1. No reaction. This is due to sp² state of carbon to which CI is attached, less polarity of C-X bond and resonance stabilisation.
2. Dow’s process.
   When chlorobenzene is heated with sodium hydroxide solution at 623 K under a pressure of 200 atm in the presence of copper catalyst, sodium phenoxide is obtained. This on hydrolysis gives phenol.

 

Question 8.
Phenol exhibit acidic character.

1. Why phenol exhibit acidic character?
2. Explain it with the help of resonating structure of phenoxide ion.

Answer:

1. Phenol can donate proton and phenoxide ion thus formed is stabilized by resonance.
2. The resonating structure of phenoxide ion is given below.

Question 9.
What is the action of phenol with

1. Aqueous Br₂?
2. Br₂ in CS₂?
3. Nitrating mixture?
4. dil. HNO₃?

Answer:
1. Phenol on action with aqueous Br₂ gives 2, 4, 6,- tribromophenol.

Question 10.
Write notes on
a) Kolbe’s reaction
b) Reimer-Tiemann reaction
Answer:
a) Kolbe’s reaction: When Sodium phenoxide is heated with CO₂ at 400 K and under a pressure 6-7 atm, sodium salicylate is obtained. This on hydrolysis gives ortho-hydroxy benzoic acid or salicylic acid.

Reimer – Tiemman reaction: When phenol is heated with CHCI₃ at 340 K, o-hydroxy benzaldehyde or salicylaldehyde is obtained.

Question 11.

1. Fill in the blanks:
   CH₃CH₂OH + SOCI₂ → CH₃CH₂CI+ …?… +….?….
2. This method is used to prepare extra pure alkyl halide. Do you agree? Why?

Answer:

1. CH₃CH₂OH + SOCI₂ -> CH₃CH₂CI + SO₂ + HCI
2. Yes. The by products are escapable gases. Hence, the reaction gives pure alkyl halides.

 

Question 12.
1. Arrange the compounds in the increasing order of their strength.

• 4-Nitro phenol
• Phenol
• Propan-1-ol
• 4-Methyl phenol.

2. You are given benzene, conc.H₂SO_4, and NaOH. Prepare phenol using these compounds.
Answer:
1. 4-Nitrophenol > Phenol > 4-Methylphenol > 1- Propanol. Presence of electron with darwing groups at ortho and para positions increases the acidic strength of substituted phenols.

2. By the action of benzene with conc.H₂SO₄ & NaOH, sodium benzene sulphonate is formed. This on acidification gives phenol.

Plus Two Chemistry Alcohols, Phenols and Ethers NCERT Questions and Answers

Question 1.
Explain why propanol has higher boiling point than that of the hydrocarbon, butane?
Answer:
Propanol has higher boiling point than butane because it has stronger interparticle forces. In propanol intermolecular hydrogen bonding is present whereas in butane intermolecular forces are weak van der Waals’ forces. A lot of heat is required to break intermolecular hydrogen bonding among propanol molecules.

 

Question 2.
Alcohols are comparatively more soluble in water than hydrocarbons of comparable molecular masses. Explain this fact.
Answer:
Because of the presence of O-H group in them, alcohols are capable of forming hydrogen bonds with water molecules whereas hydrocarbons cannot form hydrogen bonds with water. As a result, alcohols are more soluble in water than the hydrocarbons of comparable molecular masses.

Question 3.
Give the structures and IUPAC names of monohydric phenols of molecular formula, C₇H₈O.
Answer:

Question 4.
Explain why ortho-nitrophenol is more acidic than ortho-methoxy phenol?
Answer:
ortho-Nitrophenol is more acidic than ortho methoxy phenol because nitro group by its electron with drawing resonance effect stabilises the phenoxide ion whereas methoxy group by its electron releasing effect destabilises the phenoxide ion. Greater the stability of the phenoxide ion, greater is the dissociation of phenol and greater is its acid strength.

 

Question 5.
Give IUPAC names of the following ethers:
i) C₂H₅OCH₂-CH(CH₃)CH₃
ii) CH₃OCH₂CH₂CI
iii) O₂N-C₆H₄-OCH₃(p)
iv) CH₃CH₂CH₂OCH₃

Answer:
i) 1-Ethoxy-2-methylpropane
ii) 2-Chloro-1-methoxyethane
iii) 4-Nitroanisole
iv) 1-Methoxypropane
v) 1-Ethoxy-4, 4-dimethyl cyclohexane
vi) Ethoxybenzene

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