Question

Molar conductivity (${\Lambda }_m$) of aqueous solution of sodium stearate, which behaves as a strong electrolyte, is recorded at varying concentrations (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.
• B.
• C.
• D.

Answer 1

Answer: (C)

Sodium stearate $\to C{H}_3(C{H}_2{)}_{16}CO{O}^{-}N{a}^{+}$
At normal or low concentration, it behaves as strong electrolyte and for strong electrolyte, molar conductance $\left({\Lambda }_m\right)$ decreases with increase in concentration.
But only above particular concentration sodium stearate forms aggregates that concentration is called as CMC. Since number of ions decreases, hence ${\Lambda }_m$ decreases.