[short_answer] Ethanoic acid reacts with both sodium carbonate solution and sodium hydroxide solution to form salts. (i) Write the name and formula of the salt produced in each reaction, and write balanced chemical equations for both. (ii) A student argues that because ethanoic acid reacts with sodium carbonate — a reaction that mineral acids also undergo — ethanoic acid must be equally strong as hydrochloric acid. Evaluate this claim and describe one experimental observation that would clearly demonstrate the difference in acid strength between ethanoic acid and hydrochloric acid.
Generated by claude-sonnet-4-6 · 2026-06-26 01:11 · grounding rag
Model Answer
(i)
- With NaOH: Salt formed is Sodium ethanoate (sodium acetate), CH₃COONa
$$\text{NaOH} + \text{CH}_3\text{COOH} \rightarrow \text{CH}_3\text{COONa} + \text{H}_2\text{O}$$
- With Na₂CO₃: Salt formed is Sodium ethanoate (sodium acetate), CH₃COONa
$$2\text{CH}_3\text{COOH} + \text{Na}_2\text{CO}_3 \rightarrow 2\text{CH}_3\text{COONa} + \text{H}_2\text{O} + \text{CO}_2$$
(ii)
The student's claim is incorrect. The fact that ethanoic acid reacts with Na₂CO₃ only shows it is acidic enough to do so, not that it is equally strong as HCl. Unlike HCl, which is completely ionised, ethanoic acid is a weak acid and only partially ionises.
Experimental observation: On testing equal concentrations of both acids with universal indicator, HCl shows a much lower pH (strong acid colour) than ethanoic acid, proving ethanoic acid is weaker.
Source: Chapter 4, Section 4.4.2
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Explanation
- Part (i) is worth ~2 marks: name the salt, give the formula, write both balanced equations — examiners award marks for each correct equation.
- Part (ii) is ~1 mark: clearly state the claim is wrong, give the reason (partial vs complete ionisation), and name a specific, observable experiment (universal indicator / pH comparison). Litmus alone won't distinguish them — universal indicator/pH is the key point from Activity 4.7.