Which of the following statements correctly explains the dissociation of ethanoic acid in water?

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Let’s break down each statement in the context of the dissociation of ethanoic acid in water.
Option a: 'The equilibrium lies to the left hand side of the reaction equation.' This is the statement that the acid dissociation is not complete; ethanoic acid is a weak acid in water, so the undissociated form CH3COOH predominates and the equilibrium favors the left. This aligns with the known pKa ~4.76, meaning only a small fraction dissociates at typical conditions. Therefore, this option correctly explains the dissociation behavior as an equilibrium that lies mainly to the left.
Option b: 'The carboxylate anion is resonance stabilised.' While the acetate ion (CH3COO–) does exhibit resonance stabilization, this statement describes a property of the conjugate base rather than the directionality or extent of the dissociation itself. In terms of explaining why the equilibrium lies where it does, resonance stabilization helps explain stability of products, but on its own it does not specify the equilibrium position in water. Since the question asks for the explanation of the dissociation behavior (the equilibrium position), this statement is more about product stability than the dissociation extent, and is not the primary explanation requested.
Option c: 'Oxygen in an electropositive element.' This is a vague, incorrect criterion that does not relate to the acid–base equilibrium of ethanoic acid in water. It neither describes the reaction mechanism nor the acid–base properties involved, so this is not a valid explanation.
Option d: 'Water is acting as an electrophile.' In the acid–base dissociation of ethanoic acid, water actually acts as a base (a proton acceptor) rather than an electrophile. The proton is transferred from ethanoic acid to water, yielding H3O+ and CH3COO–, so labeling water as electrophile is inaccurate.
Option e: 'The generation of hydronium ions (H3O+) leads to an basic solution.' Formation of H3O+ makes the solution more acidic, not basic. Thus this statement contradicts the actual outcome of the dissociation and is incorrect.
In summary, option a correctly identifies the overall equilibrium behavior of ethanoic acid in water as an equilibrium that lies predominantly to the left (undissociated form), which matches the expected description for a weak acid. The remaining options describe aspects that either do not address the equilibrium position or state incorrect mechanisms or outcomes.

CHM1052 - MUM S2 2025 Week 6: Preparation quiz

Which of the following statements correctly explains the dissociation of ethanoic acid in water?

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