Hydrochloric acid is a stronger acid than acetic acid becausee

It ionizes completely into ions in an aqueous solution.

The correct answer is option 3. It ionizes completely into ions in an aqueous solution.

Let us delve into why hydrochloric acid \((HCl)\) is considered a stronger acid compared to acetic acid \((CH_3COOH)\), focusing on their ionization behavior in aqueous solutions.

Acid Strength and Ionization:

Hydrochloric Acid \((HCl)\):

Hydrochloric acid is a strong acid. In aqueous solution, it ionizes completely according to the following reaction:

\(HCl (aq) \rightarrow H^+ (aq) + Cl^- (aq)\)

Complete Ionization: This means that virtually all molecules of \(HCl\) dissociate into hydrogen ions \((H^+)\) and chloride ions \((Cl^-)\) when dissolved in water. The equilibrium heavily favors the formation of ions, leading to a high concentration of H+ ions in solution.

Strong Acidity: The high concentration of \(H^+\) ions makes hydrochloric acid a strong acid because it readily donates protons to other substances in aqueous solutions, effectively increasing the concentration of \(H^+\) ions.

Neutralization Capability: Due to its complete ionization, hydrochloric acid can neutralize large quantities of bases (alkalis) by reacting with hydroxide ions \((OH^-)\) to form water:

\(H^+ (aq) + OH^- (aq) \rightarrow H2O (l) \)

Corrosive Properties: Hydrochloric acid is indeed highly corrosive due to its ability to donate protons effectively and react with a wide range of substances, but this property is more related to its reactivity than its acid strength per se.

Acetic Acid \((CH_3COOH)\):

Acetic acid is a weak acid. In aqueous solution, it ionizes partially according to the equilibrium:

\(CH3COOH (aq) \rightleftharpoons H^+ (aq) + CH3COO^- (aq) \)

Partial Ionization: Only a fraction of acetic acid molecules dissociate into hydrogen ions \((H^+)\) and acetate ions \((CH_3COO^-)\) in water. The equilibrium lies significantly to the left, indicating that most of the acetic acid molecules remain undissociated.

Weak Acidity: The concentration of \(H^+\) ions produced by acetic acid in solution is lower compared to hydrochloric acid. This lower concentration reflects its weaker acid strength because it does not readily donate protons to the same extent as a strong acid like \(HCl\)

Neutralization Capability: Acetic acid can neutralize bases, but its reaction with hydroxide ions \((OH^-)\) to form water is limited by its partial ionization. This results in slower neutralization compared to a strong acid.

Conclusion: The primary reason hydrochloric acid is stronger than acetic acid lies in its ability to ionize completely into ions (\(H^+\) and \(Cl^-\)) in aqueous solution. This complete ionization results in a higher concentration of \(H^+\) ions, which defines its strength as a strong acid. In contrast, acetic acid ionizes only partially, leading to a lower concentration of \(H^+\) ions and weaker acidic properties. Therefore, option (3) "It ionizes completely into ions in an aqueous solution" accurately explains why hydrochloric acid is stronger than acetic acid.