States of Matter 2 Question 1
1. 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.
(2016 Adv.)
The correct assignment of the sketches is
| I | II | III |
|---|---|---|
| (a) $\mathrm{KCl}$ | $\mathrm{CH}_{3} \mathrm{OH}$ | $\mathrm{CH}{3}\left(\mathrm{CH}{2}\right){11} \mathrm{OSO}{3}^{-} \mathrm{Na}^{+}$ |
| b) $\mathrm{CH}{3}\left(\mathrm{CH}{2}\right){11} \mathrm{OSO}{3}^{-} \mathrm{Na}$ | $\mathrm{CH}_{3} \mathrm{OH}$ | $\mathrm{KCl}$ |
| ) $\mathrm{KCl}$ | $\mathrm{CH}{3}\left(\mathrm{CH}{2}\right.$ | $\mathrm{OSO}{3}^{-} \mathrm{Na}^{+} \quad \mathrm{CH}{3} \mathrm{OH}$ |
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Answer:
Correct Answer: 1. (d)
Solution:
- I $\left(\mathrm{CH}_{3} \mathrm{OH}\right)$ : Surface tension decreases as concentration increases.
II (KCl) : Surface tension increases with concentration for ionic salt.
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.
