Question

Explain why Hydrochloric acid is a strong acid and Acetic acid is a weak acid, how can it be confirmed?

Answer 1

By Arrhenius's theory, acids are the substances that donate ${\mathrm{H}}^{+}$ ions in an aqueous solution.

1. In this case of $\mathrm{HCl}$, when the acid is added to water, it dissociates into its ions as ${\mathrm{H}}^{+}$ and ${\mathrm{Cl}}^{-}$ completely.

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

2. On the other hand, acetic acid ${\mathrm{CH}}_3\mathrm{COOH}$, does not dissociate into its ionic forms completely.

${\mathrm{CH}}_3\mathrm{COOH}\left(\mathrm{l}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\rightleftarrows {\mathrm{CH}}_3{{\mathrm{CO}}_2}^{-}\left(\mathrm{aq}\right)+{\mathrm{H}}^{+}\left(\mathrm{aq}\right)$

3. Also, the acididic strength of any compound depends on, its ${\mathrm{H}}^{+}$ ion concentration, more is the ${\mathrm{H}}^{+}$ concentration, the more its acidic character and stronger the acid.

4. Hydrochloric acid gives more Hydrogen ion concentration than that of Acetic acid and is considered to be stronger.

Hence, Hydrochloric acid is a strong acid, and Acetic acid is a weak acid.