Free Carboxylic Acid Derivatives MCQs with Answers

1. The reaction between a carboxylic acid and an alcohol in the presence of concentrated sulphuric acid is called

• A. saponification
• B. esterification
• C. hydrolysis
• D. decarboxylation

Explanation: Esterification joins the two molecules with the elimination of water and is reversible, so the sulphuric acid serves both as catalyst and as a dehydrating agent that pulls the equilibrium towards the ester. Saponification is the reverse process carried out with alkali, which produces a soap from a fat. Decarboxylation removes carbon dioxide and shortens the chain.

2. The hydrolysis of an ester with hot sodium hydroxide solution is called saponification and gives

• A. the carboxylic acid and an alkene
• B. an aldehyde and water
• C. the sodium salt of the acid and an alcohol
• D. an amide and hydrogen

Explanation: Alkaline hydrolysis produces the carboxylate salt rather than the free acid, and because that salt cannot react back with the alcohol the reaction goes to completion, unlike acidic hydrolysis which is reversible. When the ester is a natural fat the sodium salt produced is soap, which is the origin of the name. Glycerol is the alcohol released in that case.

3. The most reactive of the carboxylic acid derivatives towards nucleophilic attack is

• A. the amide
• B. the ester
• C. the carboxylate salt
• D. the acyl chloride

Explanation: Chlorine is a good leaving group and withdraws electron density strongly, so the carbonyl carbon of an acyl chloride is highly electron deficient and it reacts violently even with cold water. Reactivity falls in the order acyl chloride, anhydride, ester, amide, since each successive group donates electron density more effectively. This is why acyl chlorides are the reagents of choice for making esters of unreactive alcohols and phenols.

4. Ethanoyl chloride reacts with ethanol to give

• A. ethyl ethanoate and hydrogen chloride
• B. ethanoic acid and chlorine
• C. ethane and water
• D. ethanal and hydrogen chloride

Explanation: The alcohol attacks the carbonyl carbon and chloride is expelled, giving the ester rapidly and irreversibly along with fumes of hydrogen chloride. This route is preferred over direct esterification when a high yield is needed, since no equilibrium limits it. The vigorous reaction with water is the reason acyl chlorides must be kept dry.

5. Soap is manufactured by the alkaline hydrolysis of

• A. ethanol
• B. benzene
• C. starch
• D. natural fats and oils, which are esters of glycerol

Explanation: Boiling a fat with sodium hydroxide splits the three ester linkages and gives sodium salts of long chain fatty acids, the soap, together with glycerol as a valuable by product. Soap cleans because the hydrocarbon tail dissolves in grease while the ionic head remains in the water. Using potassium hydroxide instead gives a softer, more soluble soap.

6. The functional group of an amide is

• A. CONH2, in which nitrogen is bonded directly to the carbonyl carbon
• B. COOH
• C. COOR
• D. COCl

Explanation: In an amide the nitrogen lone pair is delocalised into the carbonyl group, which is why amides are almost neutral rather than basic like amines, and why they are the least reactive of the acid derivatives. The peptide link joining amino acids in a protein is exactly this group. COOR is the ester group and COCl the acyl chloride.

7. Ethanoic acid reacts with phosphorus pentachloride to give

• A. ethanoyl chloride, hydrogen chloride and phosphorus oxychloride
• B. chloroethane and water
• C. ethanol and chlorine
• D. ethanal only

Explanation: The hydroxyl group of the acid is replaced by chlorine, giving the far more reactive acyl chloride, and the misty fumes of hydrogen chloride released make this a useful test for a hydroxyl or carboxyl group. Thionyl chloride achieves the same conversion with gaseous by products that are easier to remove. The acyl chloride is then used to prepare esters and amides.

8. An ester is named ethyl ethanoate. This tells us that it was formed from

• A. ethanoic acid and ethanol
• B. ethanol and methanoic acid
• C. ethanoic acid and methanol
• D. ethanal and ethanol

Explanation: The first part of an ester name comes from the alcohol and the second from the acid, so ethyl ethanoate is made from ethanol and ethanoic acid. Methyl ethanoate would come from methanol and the same acid, which is the closest distractor. Reading ester names in this order is essential when working backwards to identify the reactants.

9. Fischer esterification is which type of reaction:

• A. Condensation
• B. Substitution
• C. Elimination
• D. Dehydrogenation

Explanation: A carboxylic acid and an alcohol join with the loss of a small molecule, water, which is the definition of a condensation, and concentrated sulphuric acid catalyses it while also shifting the equilibrium by removing that water. The reaction is reversible, so the yield is never complete. Nucleophilic acyl substitution describes the mechanism, but the reaction type the question asks for is condensation.

10. Carboxylic acid reacts with ammonia to form ammonium salts which on heating produces

• A. Carbonates
• B. Alkane
• C. Ester
• D. Amide

Explanation: The ammonium carboxylate loses a molecule of water on strong heating and the nitrogen ends up bonded directly to the carbonyl carbon, giving an amide. An ester would require an alcohol rather than ammonia, which is the standard confusion here. The amide link formed in this way is the same one that joins amino acids in a protein.