Which of the following equimolar solutions would have the highest conductivity?

Analyze the question: We're comparing the electrical conductivity of equimolar (same concentration) solutions of four nitrate salts. Conductivity depends on the concentration of ions and on the charge each ion carries.

Concept: Strong electrolytes dissociate fully in water. For equal molar concentrations, the solution that produces more ions, and ions with higher charges, conducts better.

Step-by-step solution:

Dissociation of each salt (per mole):

• A. NH₄NO₃ → NH₄⁺ + NO₃⁻ gives 2 mol ions, total charge carried 1+ and 1-
• B. NaNO₃ → Na⁺ + NO₃⁻ gives 2 mol ions, total charge carried 1+ and 1-
• C. Mg(NO₃)₂ → Mg²⁺ + 2NO₃⁻ gives 3 mol ions
• D. Al(NO₃)₃ → Al³⁺ + 3NO₃⁻ gives 4 mol ions

Al(NO₃)₃ releases the most ions (4 per formula unit), and one of them is the highly charged Al³⁺. So it has the greatest total charge-carrying capacity per mole of solute.

Note: In real solutions, highly charged ions form ion pairs, and Al³⁺ is also hydrolysed, so the actual difference is less than the simple ion count suggests. But at WASSCE level, the expected reasoning is that more ions and higher charge means higher conductivity, and Al(NO₃)₃ still comes out highest.

Answer: D, Al(NO₃)₃(aq)

Exam tip: For equimolar solutions of strong electrolytes, count the ions produced per formula unit and consider their charges. The salt with the most ions and highest charges, such as Al³⁺ with 3 NO₃⁻, gives the highest conductivity.