Question

For different aqueous solutions of $0.1N$ urea, 0$.1NNaCl,0.1N$ $N{a}_{2}S{O}_4$ and $0.1NN{a}_{2}P{O}_4$ solution at ${27}^{o}C$, the correct statements are:
1. The order of osmotic pressure is, $NaCl>N{a}_{2}S{O}_4>N{a}_{3}P{O}_4>urea$.
2. $\pi =\frac{\Delta T_b}{K_b}\times ST$ for urea solution.
3. Addition of salt on ice increases its melting point.
4. Addition of salt on ice brings in melting of ice earlier.

• A. 2, 3, 4
• B. 1, 2, 4
• C. 1, 2, 3
• D. 3, 4

Answer 1

The correct option is B 1, 2, 4

Option (B) is correct.
Molar concentrations are 0.1 M urea, $0.1MNaCl$, $\frac{0.1}{2}MN{a}_{2}S{O}_4$ and $\frac{0.1}{3}MN{a}_{3}P{O}_4$

$\therefore \pi \propto C\times (1-\alpha +X\alpha +Y\alpha )\propto C(X+Y)$, if $\alpha =1$

$\therefore {\pi }_{urea}\propto 0.1\times 1;{\pi }_{NaCl}\propto 0.1\times 2;{\pi }_{N{a}_{2}S{O}_4}\propto \frac{0.1}{2}\times 3;{\pi }_{N{a}_{3}P{O}_4}\propto \frac{0.1}{3}\times 4$

Also, $\pi =C_M\times S\times T$ and $\Delta T_b=Molality\times K_b$

if $Molarity=Molality$ (for dilute solution)

$\pi =\frac{\Delta T_b}{K_b}\times S\times T$

Also, the addition of salt on ice lowers its melting point and thus, ice melts earlier.

Option A is correct.