Molar conductivity (Λm) of aqueous solution of sodium stearate, which behaves as a strong electrolyte, is recorded at varying concentration(c) of sodium stearate. Which one of the following plots provides the correct representation of micelle formation in the solution? (Critical micelle concentration (CMC) is marked with an arrow in the figures.)
(A)(see structure)
(B)(see structure)
(C)(see structure)✓ Correct
(D)(see structure)
Answer: (C)
Solution
Below the CMC, sodium stearate behaves as a strong electrolyte, so molar conductivity increases with dilution (decreasing concentration) following Kohlrausch's law. At the CMC, micelle formation begins, and the effective number of free ions decreases sharply because many stearate ions aggregate into micelles. This causes a break or change in slope in the Λm vs c plot. Option (C) correctly shows Λm increasing as c decreases, with a distinct change in behavior at the CMC (marked by the arrow).
JEE Advanced · 2019 · 27 May 2019 · Paper 1 · Single correct option
