Both ethanoic acid and hydrochloric acid are acids, yet they differ in strength. Explain why ethanoic acid is classified as a weak acid while hydrochloric acid is a strong acid.
Generated by claude-sonnet-4-6 · 2026-06-26 01:06 · grounding rag
Model Answer
Hydrochloric acid (HCl) is a strong acid because it completely ionises in water, producing a high concentration of H⁺ ions.
Ethanoic acid (CH₃COOH) is a weak acid because it is a carboxylic acid and does not completely ionise in water, producing fewer H⁺ ions. Hence, at the same concentration, ethanoic acid has a higher pH than HCl.
Source: Chapter 4, Section 4.4.2 — Properties of Ethanoic Acid
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Explanation
- The key distinction examiners look for is complete vs. partial/incomplete ionisation.
- Mentioning that HCl is a mineral acid and CH₃COOH is a carboxylic acid strengthens the answer.
- Referring to pH difference or the universal indicator result (from Activity 4.7) is a good supporting point.
- Avoid writing lengthy definitions — two focused sentences are sufficient for 2 marks.