Question

The qualitative sketches I, II and III given below show the variation of surface tension with molar concentration of three different aqueous solutions of ( mathrm{KCl}, mathrm{CH}_{3} mathrm{OH} ) and ( mathrm{CH}_{3}left(mathrm{CH}_{2}right)_{11} mathrm{OSO}_{3}^{-} mathrm{Na}^{+} ) at room temperature.
The correct assignment of the sketches is
(a) ( mathrm{KCl} ) ( mathrm{CH}_{3} mathrm{OH} ) ( mathrm{CH}_{3}left(mathrm{CH}_{2}right)_{11} mathrm{OSO}_{3}^{-} mathrm{Na}^{+} )
(b) ( mathrm{CH}_{3}left(mathrm{CH}_{2}right)_{11} mathrm{OSO}_{3}^{-} mathrm{Na}^{+} mathrm{CH}_{3} mathrm{OH} quad) ( mathrm{KCl} )
(c) ( mathrm{KCl} quad) ( mathrm{CH}_{3}left(mathrm{CH}_{2}right)_{11} mathrm{OSO}_{3}^{-} mathrm{Na}^{+} quad mathrm{CH}_{3} mathrm{OH} )
(d) ( mathrm{CH}_{3} mathrm{OH} quad) ( mathrm{KCl} ) ( quadmathrm{CH}_{3}left(mathrm{CH}_{2}right)_{11} mathrm{OSO}_{3}^{-} mathrm{Na}^{+} )

JEE/Engineering Exams

Chemistry

Solution

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I ( left(mathrm{CH}_{3} mathrm{OH}right): ) Surface tension decreases as concentration increases.

II (KCI) : Surface tension increases with concentration for ionic salt.

( mathrm{III}left[mathrm{CH}_{3}left(mathrm{CH}_{2}right)_{11} mathrm{OSO}_{3}^{-} mathrm{Na}^{+}right]: ) It is an anionic detergent.
There is decrease in surface tension before micelle formation, and after CMC (Critical Micelle Concentration) is attained, no change in surface tension.