Weak vs. Strong Acid Dissociation

Steps:

• Hydrochloric acid (HCl) is a strong acid that fully dissociates in water, so [H+] equals its concentration.
• Ethanoic acid (CH3COOH) is a weak acid that partially dissociates, so [H+] is less than its concentration.
• At the same molar concentration, ethanoic acid has lower [H+] than HCl.
• pH = -log[H+], so lower [H+] results in higher pH for ethanoic acid.

Why C is correct:

• Weak acids like ethanoic acid produce fewer H+ ions than strong acids like HCl at equal concentrations, per the acid dissociation equilibrium (Ka < 1 for weak acids).

Why the others are wrong:

• A: [H+] is lower, not higher, for the weak acid.
• B: [H+] is lower, and higher [H+] would decrease pH, not increase it.
• D: Lower [H+] increases pH, not decreases it.

Final answer: C