Bihar Board - Class 12 Chemistry - Chapter 11: Alcohols, Phenols, and Ethers Short Answer Question

                               Short Question Answer

Question. 1. What is absolute alcohol ? How is it obtained ?

Answer :  Absolute alcohol is 100 % alcohol. It is obtained by azeotropic distillation of mixture of alcohol and water.

Question. 2. Classify the following as primary, secondary and tertiary alcohols :

(ii) H2C =CH -CH2OH

(iii) CH3-CH2-CH2-OH

Answer: (i) Primary,
(ii) Primary,
(iii) Primary,
(iv) Secondary
(v) Secondary
(vi) Tertiary

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Question. 3. Name the following compounds according to IUPAC system :

Answer :  (i) 4-Chloro-3-ethyl-2-(1-methylethyl)-butan-1-ol
(ii) 2 , 5-Dimethyl hexane-1 , 3-diol.
(iii) 3-Bromocyclohexanol
(iv) Hex-1-en-3-ol.
(v) 2-Bromo-3-methyl but-2-en-1-ol

Question. 4. Write structures of the products of the following reactions :

Question 5. Give equation of the following reactions :

(i) Oxidation of propane-1-ol with alkaline KMnO4 solution.
(ii) Bromine in CS2 with phenol.
(iii) Dilute HNO3 with phenol.
(iv) Treating phenol with chloroform in presence of aqueous NaOH.

Answer : 

(i) CH3CH2CH2OH D CH3CH3CH2COOH
1-propanol                                     Propanoic acid

(ii) A mixture of o-bromo phenol and p-bromo is formed.

(iii) A mixture of o-nitrophenol and p-nitrophenol is formed.

(iv) Salicylaldehyde formed.

Question.5. Alcohols are comparatively more soluble in water than hydrocarbons of comparable molecular masses. Explain this fact.

Answer : Alcohols can form hydrogen bonds with water and by breaking the hydrogen bonds already existing between water molecules. Therefore, they are soluble in water.

On the other hand, hydrocarbons cannot form hydrogen bonds with water and hence are insoluble in water.

Question.6. What is meant by hydroboration-oxidation reaction? Illustrate it with an example.

Answer : The addition of diborane to alkenes to form trialkyl boranes followed by their oxidation with alkaline hydrogen peroxide to form alcohols is called hydroboration-oxidation. For example,

Hydroboration oxidation amounts to anti-Markovnikov addition of water to the unsymmetrical alkene.  

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

Answer : The three isomers are:

Question. 8. While separating a mixture of ortho and para nitrophenols by steam distillation, name the isomer which will be steam volatile. Give a reason.

Answer : O-N nitrophenol is steam volatile due to chelation (intramolecular H- bonding) and hence can be separated by steam distillation from/Nitrophenol which is hot steam volatile because of intermolecular H-bonding.

Question. 9. Write chemical reaction for the preparation of phenol from chlorobenzene.

Answer :

Question .10. You are given benzene, cone. H2SO4 and NaOH. Write the equations for the preparation of phenol using these reagents.

Answer :

Question.11.  Ortho nitrophenol has lower boiling point than p-nitrophenol. Why?
Answer: Ortho-nitrophenol has lower boiling point due to formation of intramolecular H-bonding whereas p-nitrophenol forms intermolecular H-bonding.

Question.12.  The C-O the bond is much shorter in phenol than in ethanol. Give a reason.
Answer: Carbon of C-O  bond of phenol is sp2 hybridized, So it acquires a partial double bond character but in ethanol, it is sp3  hybridized and a single bond. Double bond is shorter than a single bond.

Question 13.  Of the two hydroxy organic compounds ROH and R'OH the first one is basic and the other is acidic in behavior. How is R different from R' ? 

Answer: When R= alkyl ROH behaves as a Bronsted base and when R'- aryl, ROH behaves as a Bronsted acid.

Question.14.  Write the structures of the product when Butane 2- ol reacts with the following: 

(a) CrO3

(b) SOCl2

Answer: 

Question.15.  Draw the structure and name the product formed if the following alcohols are oxidized. Assume that an excess of the oxidizing agent is used:
(i) CH3CH2CH2CH2OH
(iii) 2-methyl-1-propanol
Answer: 

Question 16. Explain, how does the -OH a group attached to a carbon of benzene ring activates it towards electrophilic substitution ?

Answer:

The  -OH group is an electron-donating group. Thus, it increases the electron density in the benzene ring as shown in the given resonance structure of phenol. As a result, the benzene ring is activated towards electrophilic substitution.

Question.17. Name the enzymes present in yeast which can convert sucrose into glucose and fructose and then to ethyl alcohol.

Answer: Invertase can convert sucrose to glucose and fructose Zymase can convert glucose and fructose to ethanol and carbon dioxide.

Question.18. Boiling point is higher than the corresponding alkane. Why ?
Answer: Boiling point of alcohol is much higher than hydrocarbons of nearly similar molecular mass due to intermolecular hydrogen bonds. Alcohol molecules associate kilocalories mole-1 . Thus, extra energy is required for the separation of these molecules, which lead to an increase in boiling point. Hydrocarbons do not form hydrogen bonds, thus their boiling point is comparatively less.

Question.19.  Ortho-nitrophenol is more acidic than ortho methoxyphenol. Why?
Answer: NO2  the group is an electron withdrawing group while the methoxy group is electron donating in nature. The release of H+ is easier from o-nitrophenol while it is difficult from o-methoxyphenol.

Question.20.  How are the following conversions carried out?
(i) Propene to propan-2-ol
(ii) Ethylmagnesium chloride to propane-1-ol.
Answer:
(i) Propene to propan-2-ol

(ii) Ethylmagnesium chloride to propane-1-ol

Question.21. Complete the following reaction equations:

Answer:

Question.22.  Give simple chemical test to distinguish between the following pair of compounds:

Benzoic acid and Phenol

Answer:  Ferric chloride test: Add neutral FeCl3 in both the solutions, phenol reacts with neutral FeCl3 to form an iron-phenol complex giving violet color but benzoic acid does not.

Question.23.  What happens when phenol is treated with bromine water?

Answer:  2 , 4 , 6-tribromophenol is formed when phenol is treated with bromine water.

Question 24. Write an equation of the nitration of anisole.

Answer:

Question  25. 

Out of CH3OH and Which one is more acidic?

Answer:

is more acidic, as Phenoxide formed is more stabilized by Resonance.