Ethanoic acid and ethanol both contain oxygen, yet their behaviours with sodium hydrogencarbonate and with sodium metal are very different. (i) State what you would observe when each compound is separately treated with sodium hydrogencarbonate. (ii) Explain, in terms of their functional groups, why the two compounds behave differently with sodium hydrogencarbonate even though both react with sodium metal to produce hydrogen.
Generated by claude-sonnet-4-6 · 2026-06-26 01:12 · grounding rag
Model Answer
(i) Observations with NaHCO₃:
- Ethanoic acid reacts with sodium hydrogencarbonate to produce brisk effervescence (CO₂ gas), which turns lime water milky.
CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂
- Ethanol shows no reaction with sodium hydrogencarbonate; no effervescence is observed.
(ii) Explanation in terms of functional groups:
Ethanoic acid contains the carboxyl group (–COOH), which is acidic enough to react with weak bases like NaHCO₃, releasing CO₂. Ethanol contains the hydroxyl group (–OH), which is only weakly acidic — too weak to react with NaHCO₃. However, both –COOH and –OH can donate H⁺ to sodium metal (a strong reducing agent), so both produce hydrogen gas with Na.
Source: Chapter 4, Section 4.4.2 – Properties of Ethanoic Acid
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Explanation
- Examiners award marks for: (a) correct observation for each compound (1 mark), (b) functional group explanation linking –COOH to acidity and NaHCO₃ reaction, and –OH to insufficient acidity (2 marks).
- Always write the chemical equation for ethanoic acid + NaHCO₃ — it shows understanding and secures full credit.
- The key contrast: carboxylic acids are acidic enough to displace CO₂ from hydrogencarbonates; alcohols are not. Both react with Na because Na is a far stronger base/reducing agent.