When ethanol is heated with concentrated sulphuric acid at 443 K, ethene is produced. When the same ethanol is warmed with glacial acetic acid in the presence of concentrated sulphuric acid, an ester is formed instead. What determines which product forms, and what role does concentrated sulphuric acid play in each case?
Generated by claude-sonnet-4-6 · 2026-06-26 01:11 · grounding rag
Model Answer
What determines the product:
The reaction conditions determine the product. At 443 K with excess concentrated H₂SO₄, dehydration of ethanol occurs giving ethene. When ethanol is warmed with glacial acetic acid and concentrated H₂SO₄, esterification occurs giving ethyl ethanoate (ester).
Role of concentrated H₂SO₄:
- In dehydration: It acts as a dehydrating agent, removing water from ethanol to form ethene.
$$\text{CH}_3\text{CH}_2\text{OH} \xrightarrow{\text{Hot conc. H}_2\text{SO}_4, 443\text{K}} \text{CH}_2{=}\text{CH}_2 + \text{H}_2\text{O}$$
- In esterification: It acts as an acid catalyst, speeding up the reaction between ethanoic acid and ethanol to form the ester.
$$\text{CH}_3\text{COOH} + \text{C}_2\text{H}_5\text{OH} \xrightarrow{\text{Acid}} \text{CH}_3\text{COOC}_2\text{H}_5 + \text{H}_2\text{O}$$
Source: Chapter 4, Sections 4.4.1 and 4.4.2
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Explanation
- Examiners want two clear points: (1) what determines the product — temperature/conditions/reactant present, and (2) the dual role of conc. H₂SO₄ (dehydrating agent vs. acid catalyst).
- Writing both equations earns full credit and shows understanding.
- Do not confuse "dehydrating agent" (removes water from a single molecule) with "acid catalyst" (speeds up a reaction between two molecules). This distinction is what the question tests.