A 0.10 M aqueous solution of which of the following substances will have the lowest electrical conductivity? Assume complete dissociation for strong electrolytes.
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Correct answer
C. Acetic acid (CH3COOH)
Principle or equation
Electrical conductivity of a solution depends on the concentration of ions. Strong electrolytes dissociate completely, producing more ions; weak electrolytes dissociate only partially, producing fewer ions.
Why this answer is correct
HCl, NaCl, and CaCl2 are strong electrolytes and dissociate completely, producing 2, 2, and 3 ions per formula unit, respectively. Acetic acid is a weak electrolyte and only partially dissociates, so it produces far fewer ions in solution, resulting in the lowest conductivity.
Example
Compare 0.10 M NaCl (produces 0.10 M Na+ and 0.10 M Cl-) with 0.10 M CH3COOH (produces only about 0.0013 M H+ and CH3COO-), so acetic acid has much lower conductivity.
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