Carboxylic acids Knowledge-Based Practice

Questions

1. 1.

   Which reagent is typically used in the laboratory to reduce a carboxylic acid directly to a primary alcohol?

   • A) Sodium borohydride ($\text{NaBH}_4$)
   • B) Potassium dichromate ($\text{K}_2\text{Cr}_2\text{O}_7$)
   • C) Hydrogen gas over a nickel catalyst at room temperature
   • D) Lithium aluminium hydride ($\text{LiAlH}_4$)
2. 2.

   Which reagent reacts with a carboxylic acid at room temperature to produce vigorous effervescence of carbon dioxide gas, providing a standard qualitative test to distinguish it from an alcohol?

   • A) Acidified potassium dichromate solution
   • B) Ammoniacal silver nitrate solution
   • C) Aqueous sodium hydrogen carbonate solution
   • D) Concentrated sulfuric acid
3. 3.

   Carboxylic acids exhibit notably higher boiling points than alcohols of comparable molecular mass primarily because pairs of carboxylic acid molecules associate into stable dimers through which type of interaction?

   • A) Intramolecular ionic bonding between adjacent carboxylate ions
   • B) Permanent dipole–dipole attractions restricted solely to the carbonyl bonds
   • C) Intermolecular hydrogen bonding between the hydroxyl and carbonyl groups
   • D) Reversible covalent cross-links formed directly between alkyl chains
4. 4.

   What class of organic compound is formed when a carboxylic acid is heated with an alcohol in the presence of an acid catalyst?

   • A) An ether
   • B) An ester
   • C) An acid anhydride
   • D) An aldehyde
5. 5.

   Why are carboxylic acids significantly more acidic than alcohols of comparable molecular mass?

   • A) The negative charge on the carboxylate conjugate base is delocalized over two electronegative oxygen atoms by resonance.
   • B) The hydroxyl hydrogen in a carboxylic acid is bonded directly to a carbon atom rather than an oxygen atom.
   • C) Carboxylic acids contain weaker carbon-oxygen sigma bonds that readily break heterolytically in aqueous solution.
   • D) The carbonyl oxygen donates electron density to destabilize the neutral carboxylic acid molecule relative to an alcohol.

Answers and step-by-step solutions appear after you finish the test.