Free Alcohols MCQs with Answers

11. Ethylene glycol, used as antifreeze, is classified as

• A. a monohydric alcohol
• B. a dihydric alcohol
• C. a trihydric alcohol
• D. a phenol

Explanation: Ethylene glycol contains two hydroxyl groups on adjacent carbons, so it is dihydric, while glycerol with three hydroxyls is trihydric and ethanol with one is monohydric. Extra hydroxyl groups mean more hydrogen bonding, which is why glycol is viscous, high boiling and completely miscible with water. Those same properties make it effective as an antifreeze and coolant.

12. The oxidation of propan-2-ol with acidified potassium dichromate gives

• A. propanal
• B. propanoic acid
• C. propene
• D. propanone

Explanation: Propan-2-ol is a secondary alcohol, so oxidation removes the single hydrogen on the carbinol carbon and leaves a ketone, which resists further oxidation because no hydrogen remains on that carbon. A primary alcohol would give an aldehyde and then an acid. This difference in oxidation product is the standard way of identifying the class of an unknown alcohol.

13. Alcohols with short carbon chains are soluble in water, but solubility falls sharply as the chain lengthens because

• A. the hydroxyl group disappears in longer molecules
• B. long chain alcohols are gases
• C. the growing non polar hydrocarbon chain cannot form hydrogen bonds with water and dominates the molecule
• D. longer alcohols react with water

Explanation: Methanol, ethanol and propan-1-ol mix with water in all proportions because the hydroxyl group hydrogen bonds effectively, but as the chain grows the hydrophobic portion outweighs it and solubility falls until the higher alcohols are essentially insoluble. Branching increases solubility slightly by making the molecule more compact. The same principle explains why soaps need a hydrophilic head on a long tail.