Science (086) — AI-generated practice question

When equal concentrations of HCl and acetic acid are tested, HCl shows a lower pH, meaning it has a higher concentration of H⁺(aq) ions in solution.

This tells us that HCl is a strong acid and acetic acid (ethanoic acid) is a weak acid.

The reason is that HCl is a mineral acid and completely ionises in water, producing a large number of H⁺ ions. Acetic acid, being a carboxylic acid, is only partially ionised, producing fewer H⁺ ions at the same concentration. Since lower pH means higher H⁺ ion concentration, HCl registers a lower pH value.

Source: Chapter 2, Section 2.3; Chapter 4, Section 4.4.2

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• Examiners expect three clear points: (1) HCl has lower pH → more H⁺ ions, (2) HCl = strong acid / acetic acid = weak acid, (3) reason = complete vs. partial ionisation.
• The textbook explicitly states: "unlike mineral acids like HCl, which are completely ionised, carboxylic acids are weak acids" — use this reasoning directly.
• Avoid vague language like "HCl is stronger" without linking it to ionisation and H⁺ ion concentration.