14 past paper MCQs on Reactivity of Carboxylic Acids, from the Carboxylic Acids unit of MDCAT Chemistry. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.
1.Which among the following has the least pH? (MDCAT 2022)
Correct answer: (c) $\mathrm{CH_3CHClCOOH}$
The chlorine on the carbon next to the carboxyl group pulls electrons away most strongly, so this acid is the strongest and its pH the lowest.
2.Acetic acid is a weaker acid than sulphuric acid because of which of the following reasons? (MDCAT 2023)
Correct answer: (b) it has less degree of ionisation
Only a small fraction of its molecules ionize in water, so the concentration of $\mathrm{H^+}$ it gives is far lower.
3.Carboxylic acid reacts with metal carbonate. The colorless gas evolved is: (NUMS MDCAT 2025)
Correct answer: (c) CO2
A carboxylic acid displaces carbon dioxide from a carbonate, as any acid does.
4.Compound X + Na2CO3 → Compound Y + CO2 + H2O. The compound X is: (NUMS MDCAT 2024)
Correct answer: (d) CH3CH2COOH
Only a carboxylic acid is strong enough to displace carbon dioxide from a carbonate.
5.Which among the following have least pH? (UHS MDCAT 2023)
Correct answer: (c) CH3CHCl2 COOH
Two chlorines pull the hardest on the carboxyl group, so that acid is the strongest and its pH the lowest.
6.Select the correct order of relative acidic strength of phenol, alcohol, water, and carboxylic acid: (SZABMU MDCAT 2023)
Correct answer: (b) Carboxylic acid ˃ phenol ˃ water ˃ alcohol
The carboxylate ion is best stabilized, then the phenoxide, and an alkoxide least of all.
7.Acetic acid is weak acid than sulphuric acid because of which of the following reasons? (UHS MDCAT 2023)
Correct answer: (b) It has less degree of ionisation
Acetic acid is only slightly ionized in water, while sulphuric acid is ionized almost completely.
8.Which of the following gas is produced during the reaction of carbonates and bicarbonates with carboxylic acid (PMC MDCAT 2022)
Correct answer: (a) CO2
A carboxylic acid displaces carbon dioxide from a carbonate or a hydrogen carbonate.
9.Salts of carboxylic acids can be converted into corresponding carboxylic acid by treating with: (PMC MDCAT 2022)
Correct answer: (d) Acid
A stronger acid displaces the weaker carboxylic acid from its salt.
10.Carboxylic acids do not give the characteristics reaction of >C=O group because of: (PMC Practice 2021)
Correct answer: (b) Resonance
The lone pair of the hydroxyl oxygen is fed into the carbonyl group, so that group is no longer a plain $\mathrm{C{=}O}$.
11.Which of the following carboxylic acids is used in medicine as a local irritant? (PMC Practice 2021)
Correct answer: (b) Acetic acid
Dilute acetic acid is used as a counter-irritant on the skin.
12.The exact reactivity order for carboxylic acid derivatives is: (PMC MDCAT 2020)
Correct answer: (d) Acylchloride > Anhydride > ester
The better the leaving group, the more reactive the derivative, and chloride leaves most readily.
13.Which of the following is the strongest acid? (PMC MDCAT 2020)
Correct answer: (c) Trichloroethanoic acid
Three chlorine atoms pull hardest on the carboxyl group, so its proton is the most readily lost.
14.Which one will act as a strong acid? (UHS MDCAT 2018)
Correct answer: (c) Trichloroethanoic acid
Three chlorine atoms pull hardest on the carboxyl group, so that acid is the strongest.