Prepare for exams with solved exercises on Alcohol, Phenol, and Ether. Cover key concepts like structure, properties, reactions, and uses to strengthen your understanding and improve exam performance.
Q.4. What are alcohols? How are they classified? How will you distinguish between primary, secondary, and tertiary alcohols?
- Alcohols are organic compounds containing the hydroxyl (-OH) functional group attached to a carbon atom.
- Classification:
- Primary (1°): The -OH group is attached to a carbon atom that is connected to only one other alkyl group (e.g., ethanol).
- Secondary (2°): The -OH group is attached to a carbon atom bonded to two other alkyl groups (e.g., isopropanol).
- Tertiary (3°): The -OH group is attached to a carbon atom bonded to three alkyl groups (e.g., tert-butanol).
- Distinguishing:
- Lucas test: Tertiary alcohol reacts rapidly, secondary reacts slowly, and primary alcohol shows no immediate reaction with Lucas reagent.
Q.5. How is methyl alcohol obtained on a large scale? How can it be distinguished from ethyl alcohol?
- Methyl alcohol (methanol) is obtained on a large scale by the catalytic hydrogenation of carbon monoxide (CO) using a catalyst like zinc oxide at high temperature and pressure.
- Distinguishing: Methanol is poisonous, and when treated with iodine and sodium hydroxide, methanol forms a yellow precipitate (iodoform test), which does not happen with ethanol.
Q.6. What is fermentation? Which compound may be obtained on an industrial scale by fermentation?
- Fermentation is a biochemical process where sugars (glucose) are converted into alcohol and carbon dioxide by the action of enzymes from yeast.
- Compound obtained: Ethanol is obtained on an industrial scale by fermentation of sugars.
Q.7. Explain the following terms: Absolute alcohol, Methylated spirit, Rectified spirit, Denaturing of alcohols.
- Absolute alcohol: Pure ethanol that is 100% alcohol, free from water.
- Methylated spirit: Ethanol mixed with a small quantity of methanol or other chemicals to make it unfit for consumption.
- Rectified spirit: A mixture of ethanol and water, typically containing about 95% ethanol.
- Denaturing of alcohols: The process of adding substances (like methanol) to ethanol to make it unsuitable for drinking.
Q.8. How does ethyl alcohol react with the following reagents?
- i) Conc. H₂SO₄: Dehydration to form ethene at 170°C.
- ii) Na: Produces sodium ethoxide and hydrogen gas.
- iii) PCl₅: Produces ethyl chloride and phosphorus oxychloride (POCl₃).
- iv) CH₃COOH: Esterification to form ethyl acetate in the presence of an acid catalyst.
- v) SOCl₂: Produces ethyl chloride and sulfur dioxide (SO₂) and HCl.
Q.9. How will you obtain primary, secondary, and tertiary alcohols by reacting Grignard reagent with suitable carbonyl compounds?
- Primary alcohol: React a Grignard reagent (RMgX) with formaldehyde (HCHO) followed by hydrolysis.
- Secondary alcohol: React a Grignard reagent with an aldehyde (R-CHO) followed by hydrolysis.
- Tertiary alcohol: React a Grignard reagent with a ketone (R-CO-R) followed by hydrolysis.
Q.10. How will you distinguish between the following?
- i) An alcohol and a phenol: Phenols react with neutral FeCl₃ to give a violet color, while alcohols do not.
- ii) An alcohol and an ether: Alcohols react with sodium metal to release hydrogen, while ethers do not.
- iii) Methanol and ethanol: Methanol gives a positive iodoform test, while ethanol does not.
- iv) A tertiary alcohol and a primary alcohol: Tertiary alcohols react immediately with Lucas reagent, but primary alcohols do not.
- v) 1-propanol and 2-propanol: 2-Propanol gives a positive iodoform test, whereas 1-propanol does not.
Q.11. Give reasons for the followings:
i) Ethyl alcohol is a liquid while methyl chloride is a gas:
- Ethyl alcohol has hydrogen bonding due to the -OH group, which leads to higher intermolecular forces, making it a liquid. Methyl chloride, lacking hydrogen bonds, is a gas at room temperature.
ii) Ethanol has a higher boiling point than diethyl ether:
- Ethanol has hydrogen bonding, which increases its boiling point, whereas diethyl ether has weak Van der Waals forces leading to a lower boiling point.
iii) Absolute alcohol cannot be prepared by fermentation process:
- Fermentation always produces ethanol along with water and some impurities. It is difficult to obtain 100% pure ethanol by fermentation alone.
iv) Ethanol gives different products with conc. H₂SO₄ under different conditions:
- At 170°C, ethanol dehydrates to ethene. At 140°C, it forms diethyl ether, depending on the temperature and reaction conditions.
v) Water has a higher boiling point than ethanol:
- Water has stronger hydrogen bonding due to its two hydrogen atoms bonded to oxygen, leading to a higher boiling point compared to ethanol.
Q.12. How will you convert:
i) Methanol into ethanol:
- Treat methanol with methyl iodide (CH₃I) in the presence of NaOH to obtain ethanol.
ii) Ethanol into methanol:
- First oxidize ethanol to acetaldehyde (CH₃CHO) using K₂Cr₂O₇/H₂SO₄, then reduce it to methanol using LiAlH₄.
iii) Ethanol into isopropyl alcohol:
- First oxidize ethanol to acetone using K₂Cr₂O₇, then reduce acetone with H₂/Pd to isopropyl alcohol.
iv) Formaldehyde into ethyl alcohol:
- Treat formaldehyde with methyl magnesium bromide (CH₃MgBr) followed by hydrolysis to obtain ethanol.
v) Acetone into ethyl alcohol:
- First reduce acetone to isopropanol using NaBH₄, then dehydrogenate isopropanol to obtain ethyl alcohol.
Q.13. Explain the following terms using ethyl alcohol as an example:
i) Oxidation:
- Ethanol can be oxidized to acetaldehyde (CH₃CHO) using a mild oxidizing agent like PCC. Further oxidation leads to acetic acid.
ii) Dehydration:
- When ethanol is heated with concentrated H₂SO₄ at 170°C, it undergoes dehydration to form ethene (CH₂=CH₂).
iii) Esterification:
- Ethanol reacts with acetic acid in the presence of concentrated H₂SO₄ to form ethyl acetate (CH₃COOCH₂CH₃) and water.
iv) Ether formation:
- Ethanol, when treated with H₂SO₄ at 140°C, forms diethyl ether (CH₃CH₂OCH₂CH₃).
Q.14. Compare the reactions of phenol with those of ethanol. Discuss the difference if any.
- Phenol is more acidic than ethanol due to the resonance stabilization of the phenoxide ion. Phenol reacts with NaOH to form sodium phenoxide, while ethanol does not react with NaOH. Phenol undergoes electrophilic substitution reactions (like nitration) more easily due to the activating effect of the -OH group, while ethanol shows typical reactions of alcohols like oxidation and esterification.
Q.15. Arrange the following compounds in order of their increasing acid strength and give reasons:
H₂O, C₂H₅OH, C₆H₅OH, C₆H₅COOH
- Order: C₂H₅OH < H₂O < C₆H₅OH < C₆H₅COOH
- C₂H₅OH (ethanol) is the least acidic as it lacks resonance or strong electronegative groups.
- H₂O (water) is slightly more acidic than ethanol.
- C₆H₅OH (phenol) is more acidic due to resonance stabilization of the phenoxide ion.
- C₆H₅COOH (benzoic acid) is the most acidic due to the strong electron-withdrawing effect of the carboxyl group.
Q.16. Write down two methods for preparing phenol. What is the action of the following on phenol:
i) HNO₃: Nitration of phenol yields nitrophenol (o- and p-nitrophenol).
ii) NaOH: Phenol reacts with NaOH to form sodium phenoxide.
iii) Zn: Reduction of phenol with Zn forms benzene.
iv) Bromine water: Bromination of phenol gives 2,4,6-tribromophenol.
Q.17. Give the uses of phenols. How bakelite is prepared from it?
- Uses of phenols:
- Antiseptic (e.g., in disinfectants).
- Used in the manufacture of plastics (e.g., Bakelite).
- Used in the production of drugs and dyes.
- Bakelite preparation:
- Phenol reacts with formaldehyde under heat and pressure in the presence of a catalyst (like HCl or ZnCl₂) to form Bakelite, a hard plastic.
Q.18. (a) Write IUPAC names of the following compounds:
i) (CH₃)₃CH – OH: 2-Methylpropan-2-ol
ii) (CH₃)₂CHCH₂CH₂OH: 3-Methylbutan-1-ol
iii) CH₃ – CH – OH | CH₃: Propan-2-ol
iv) C₂H₅ – CH – OH | I: 1-Iodo-2-propanol
Q. 18.(b) Write structure formulas for the following compounds:
- Glycol (Ethylene glycol)
- Structural formula: HO-CH₂-CH₂-OH
- Glycerol
- Structural formula: HO-CH₂-CH(OH)-CH₂OH
- Carbolic Acid (Phenol)
- Structural formula: C₆H₅OH
- Acetophenone
- Structural formula: C₆H₅COCH₃
- Picric Acid
- Structural formula: C₆H₂(NO₂)₃OH
Q.19. (a) Name the following compounds:
i) CH₃ — CH₂ — CH₂ — O — CH₃
- Name: 1-Methoxypropane
ii) (CH₃)₂CH₂ — O — CH(CH₃)₂
- Name: 2-Isopropoxypropane
iii) CH₃ — CH₂ — CH₂ — O — CH₂ — CH₃
- Name: 1-Ethoxypropane
iv) C₂H₅ — O — C₆H₅
- Name: Ethoxybenzene
v) CH₃ — O — C₆H₅
- Name: Methoxybenzene (Anisole)
Q.19. (b) Write down structural formulas of the following compounds:
- Methoxyethane
- Structural formula: CH₃-O-CH₂CH₃
- Ethoxybenzene
- Structural formula: C₂H₅-O-C₆H₅
- Sodium Ethoxide
- Structural formula: CH₃CH₂ONa
- Sodium Phenoxide
- Structural formula: C₆H₅ONa
- Propoxypropane
- Structural formula: CH₃CH₂CH₂-O-CH₂CH₂CH₃
