Q1. [3] medium thorough-understanding
A student dips two electrodes into liquid ethanol and finds that no current flows, but when the same electrodes are placed in molten sodium chloride, current flows readily. Explain, in terms of the nature of bonding and the particles present in each substance, why this difference is observed.
Generated by claude-sonnet-4-6 · 2026-06-26 01:08 · grounding rag
Model Answer
Ethanol (liquid): Ethanol is a covalent compound. Its molecules are held together by weak intermolecular forces. When electrodes are dipped in liquid ethanol, no charged particles (ions) are present — electrons are shared between atoms, not transferred. Since there are no free ions to carry charge, no current flows.
Molten NaCl: Sodium chloride is an ionic compound made of Na⁺ and Cl⁻ ions held in a crystal lattice. On melting, these ions become free to move. These freely moving charged ions carry electric current, so current flows readily through molten NaCl.
Source: Chapter 4, Section 4.1 (Bonding in Carbon – The Covalent Bond)
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Explanation
- Key contrast examiners look for: covalent (no ions → no current) vs. ionic (free ions in molten state → conducts).
- Mention shared electrons / no charged particles for ethanol; mention free ions for NaCl — these are the scoring phrases.
- Don't write about aqueous solutions; the question specifies liquid ethanol and molten NaCl.
- 3 marks typically split as: 1 mark (ethanol covalent/no ions) + 1 mark (NaCl ionic/ions) + 1 mark (clear explanation of current flow linked to free ions).