Question

Why is carboxylic acid weaker than $\mathrm{HCl}$?

Answer 1

Strong and weak acids

• A strong acid is one that is completely ionized in water.
• For example, hydrogen chloride $\left(\mathrm{HCl}\right)$ ionizes completely in water to produce hydrogen ions and chloride ions.
• In an aqueous solution, a weak acid ionizes only slightly.
• Acetic acid, which may be found in vinegar, is a common weak acid.

Hydrochloric acid

• The dissociation of $\mathrm{HCl}$ is as follows:

$\mathrm{HCl}\left(\mathrm{aq}\right)\rightleftharpoons {\mathrm{Cl}}^{-}\left(\mathrm{aq}\right)+{\mathrm{H}}^{+}\left(\mathrm{aq}\right)$

• $\mathrm{HCl}$ releases their protons $\left({\mathrm{H}}^{+}\right)$ into a solution.

Carboxylic acid

• In water, carboxylic acid $\left({\mathrm{CH}}_3\mathrm{COOH}\right)$ ions do not completely dissociate.
• Since carboxylic acids only partially ionize in solution, they are considered weak acids.
• The dissociation of the carboxylic acid is as follows:

${\mathrm{CH}}_3\mathrm{COOH}\left(\mathrm{aq}\right)\rightleftharpoons {\mathrm{CH}}_3{\mathrm{COO}}^{-}\left(\mathrm{aq}\right)+{\mathrm{H}}^{+}\left(\mathrm{aq}\right)$

• The carboxylic acid will dissociate into the carboxylate $\left({\mathrm{CH}}_3{\mathrm{COO}}^{-}\right)$ anion and the Hydrogen $\left({\mathrm{H}}^{+}\right)$ ion.
• The resonance of carboxylate ion is as follows:

• The resonance structures of the carboxylate anion will grab the Hydrogen $\left({\mathrm{H}}^{+}\right)$ ion produced at the time of dissociation.
• Thus, carboxylic acid solutions do not contain hydrogen ions.
• Therefore, the carboxylic acid is weaker than $\mathrm{HCl}$.