What are strong and weak acids? How does the pH scale help us distinguish between them? Give one example of each.
Generated by claude-sonnet-4-6 · 2026-06-17 12:37 · grounding rag
Model Answer
Strong acids are acids that produce a large number of H⁺ ions when dissolved in water. Weak acids produce fewer H⁺ ions in solution even at the same concentration.
pH scale (0–14) measures hydrogen ion concentration. A strong acid has a very low pH (closer to 0), while a weak acid has a pH slightly below 7. Thus, pH helps us compare the strength of acids quantitatively.
- Strong acid example: Hydrochloric acid (HCl) — completely ionised, very low pH.
- Weak acid example: Acetic acid (CH₃COOH) — partially ionised, pH closer to 7.
Source: Chapter 2, Section 2.3; Chapter 4, Section 4.4.2
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Explanation
- Examiners expect the definition of both terms linked to the number of H⁺ ions produced — this is the key phrase from the textbook.
- Mention the pH scale's role in quantitative measurement of H⁺ ion concentration, not just identification of acid/base.
- HCl (strong) and acetic/ethanoic acid (weak) are the textbook's own examples — always use these.
- 3 marks = definition of strong acid (1) + definition of weak acid and pH role (1) + one example each (1). Keep it concise.