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

(D) I : $\mathrm{CH}_{3} \mathrm{OH}$ II : KCl III : $\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{11} \mathrm{OSO}_{3}{ }^{-} \mathrm{Na}^{+}$

(A) I : KCl II : $\mathrm{CH}_{3} \mathrm{OH}$ III : $\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{11} \mathrm{OSO}_{3}^{-} \mathrm{Na}^{+}$

(B) I : $\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{11} \mathrm{OSO}_{3}{ }^{-} \mathrm{Na}^{+}$ II : $\mathrm{CH}_{3} \mathrm{OH}$ III : KCl

(C) I : KCl II : $\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{11} \mathrm{OSO}_{3}{ }^{-} \mathrm{Na}^{+}$ III : $\mathrm{CH}_{3} \mathrm{OH}$

JEE Advanced · 2016 · 22 May 2016 · Paper 2 · States of Matter

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The qualitative sketches I, II and III given below show the variation of surface tension with molar concentration of three different aqueous solutions of

KCl

CH_{3} OH

and

CH_{3} (CH_{2})_{11} OSO_{3}^{-} Na^{+}

at room temperature. The correct assignment of the sketches is

(A)I : KCl II : $CH_{3} OH$ III : $CH_{3} (CH_{2})_{11} OSO_{3}^{-} Na^{+}$
(B)I : $CH_{3} (CH_{2})_{11} OSO_{3}^{-} Na^{+}$ II : $CH_{3} OH$ III : KCl
(C)I : KCl II : $CH_{3} (CH_{2})_{11} OSO_{3}^{-} Na^{+}$ III : $CH_{3} OH$
(D)I : $CH_{3} OH$ II : KCl III : $CH_{3} (CH_{2})_{11} OSO_{3}^{-} Na^{+}$ ✓ Correct

Answer: (D)

Solution

Strong electrolytes like KCl slightly increase surface tension (sketch II shows slight increase). Low molar mass organic compounds like

CH_{3} OH

usually decrease surface tension moderately (sketch I shows moderate decrease). Surface-active organic compounds (detergents) like

CH_{3} (CH_{2})_{11} OSO_{3}^{-} Na^{+}

sharply decrease surface tension (sketch III shows sharp decrease). Therefore: I is

CH_{3} OH

, II is KCl, III is the detergent.

JEE Advanced · 2016 · 22 May 2016 · Paper 2 · Single correct option

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JEE Advanced · 2016 · 22 May 2016 · Paper 2 · States of Matter

Solution

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