Under ambient conditions, which among the following surfactants will form micelles in aqueous solution at lowest molar concentration ?
Show Hint
- \(\mathrm{CH_3(CH_2)_{15}\overset{\oplus}{N}(CH_3)_3\overset{\ominus}{Br}}\)
- \(\mathrm{CH_3-(CH_2)_{13}-OSO_3^-\ Na^+}\)
- \(\mathrm{CH_3-(CH_2)_8-COO^{\ominus}\ Na^+}\)
- \(\mathrm{CH_3(CH_2)_{11}\overset{\oplus}{N}(CH_3)_3Br^-}\)
The Correct Option is A
Solution and Explanation
Chain lengths: (1) 16 carbons, (2) 14 carbons, (3) 9 + 1 carboxylate = 10 carbons, (4) 12 carbons.
Option (1), cetyltrimethylammonium bromide (C16), has the longest chain and the lowest CMC (about 1 mM).
Typical CMCs: (1) about 1 mM, (2) about 2 mM, (4) about 15 mM, (3) about 100 mM.
So (1) forms micelles at the lowest concentration.
Answer: (1) \(\mathrm{CH_3(CH_2)_{15}\overset{\oplus}{N}(CH_3)_3\overset{\ominus}{Br}}\)
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