NECO 2001 Chemistry · Question 24

NaCl(s) does NOT conduct electricity, but N(aq) does. This is because

Options

A.NaCl(s) is non-ionic but NaCl(aq) is ion
B.NaCl(aq) contains mobile electrons, where absent in NaCl(s).
C.NaCl(aq) contains mobile ions which Nacl,) does not contain.
D.NaCl(s) ionizes partiality while NaCl(aq) iodizes completely.
E.NaCl(s) decomposes when heated but NCl(aq) is stable to heat. –

Answer: C. NaCl(aq) contains mobile ions which Nacl,) does not contain.

Explanation written with AI and checked against the answer key

Analyze the question: Why does solid NaCl not conduct electricity, while aqueous NaCl does?

Explain the concept: Electrical conduction in electrolytes needs mobile charge carriers. In ionic compounds these carriers are ions (not electrons, which carry current in metals).

Solid NaCl: It is an ionic compound made of Na⁺ and Cl⁻ held in a rigid crystal lattice by strong electrostatic forces. The ions are present but fixed in position, so they cannot move and no current flows.
Aqueous NaCl: When NaCl dissolves, water molecules surround and separate the ions (hydration). Free, mobile Na⁺(aq) and Cl⁻(aq) can then move to the electrodes and carry current.

Check each option:

A. Wrong. NaCl(s) is ionic. It simply has ions that cannot move.
B. Wrong. Conduction in solutions is by ions, not mobile electrons.
C. Correct. NaCl(aq) contains mobile ions, which solid NaCl does not have (its ions are locked in the lattice).
D. Wrong. NaCl is a strong electrolyte, and solid NaCl does not "ionize partially". Its ions are already formed but immobile.
E. Wrong. Heating is irrelevant to this comparison.

Answer: Option C. (Option C's wording is slightly garbled in the question, but its meaning is clear: the aqueous solution has mobile ions that the solid lacks.)

Exam tip: Remember "ions must be free to move." Solid ionic compounds do not conduct, but they do when molten or dissolved. Metals conduct by mobile electrons, and electrolytes conduct by mobile ions.

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