JEE Advanced · 2008 · 13 Apr 2008 · Paper 2 · Surface Chemistry

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Among the following, the surfactant that will form micelles in aqueous solution at the lowest molar concentration at ambient conditions is

(A) $CH_{3} (CH_{2})_{15} N^{+} (CH_{3})_{3} Br^{-}$ ✓ Correct
(B) $CH_{3} (CH_{2})_{11} OSO_{3}^{-} Na^{+}$
(C) $CH_{3} (CH_{2})_{6} COO^{-} Na^{+}$
(D) $CH_{3} (CH_{2})_{11} N^{+} (CH_{3})_{3} Br^{-}$

Answer: (A)

Solution

The critical micelle concentration (CMC) decreases as the molecular weight of the hydrocarbon chain increases. This is because longer hydrocarbon chains have lower true solubility in water and a greater tendency to associate. Among the given options,

CH_{3} (CH_{2})_{15} N^{+} (CH_{3})_{3} Br^{-}

has the longest hydrocarbon chain (16 carbons), so it will form micelles at the lowest molar concentration.

JEE Advanced · 2008 · 13 Apr 2008 · Paper 2 · Single correct option

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JEE Advanced · 2008 · 13 Apr 2008 · Paper 2 · Surface Chemistry

Solution

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