Solutions · Chemistry · Class 12

Isotonic solutions have the same

Van't Hoff factor for $\mathrm{Na}_2 \mathrm{SO}_4 \cdot 10 \mathrm{H}_2 \mathrm{O}$ solution, assuming complete ionization is

1 mole of liquid A and 2 moles of liquid $$B$$ make a solution having a total vapour pressure 40 torr. The vapour pressure of pure $$A$$ and pure $$B$$ are 45 torr and 30 torr respectively. The above solution

If molality of a dilute solution is doubled, the value of the molal elevation constant $$\left(\mathrm{K}_{\mathrm{b}}\right)$$ will be

(a) (i) Ishan's automobile radiator is filled with 1.0 kg of water. How many grams of ethylene glycol (Molar mass $=62 \mathrm{~g} \mathrm{~mol}^{-1}$ ) must Ishan add to get the freezing point of the solution lowered to $-2.8^{\circ} \mathrm{C}$. $\mathrm{K}_{\mathrm{f}}$ for water is $1.86{\mathrm{~K} \mathrm{~kg} . \mathrm{mol}^{-1} \text {. }}$

(ii) What type of deviation from Raoult's law is shown by ethanol and acetone mixture? Give reason.

OR

(b) (i) Boiling point of water at 750 mm Hg pressure is $99.68{ }^{\circ} \mathrm{C}$. How much sucrose (Molar mass $=342 \mathrm{~g} \mathrm{~mol}^{-1}$ ) is to be added to 500 g of water such that it boils at $100{ }^{\circ} \mathrm{C}$ ? $\left(\mathrm{K}_b\right.$ for water $=$ $0.52 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}$ ).

(ii) State Henry's law and write its any one application.

(a) (i) Why is boiling point of $$1 \mathrm{~M} \mathrm{~NaCl}$$ solution more than that of $$1 \mathrm{M}$$ glucose solution?

(ii) A nonvolatile solute '$$\mathrm{X}$$' (molar mass $$=\mathbf{5 0} \mathrm{~g} \mathrm{~mol}^{-1}$$) when dissolved in $$78 \mathrm{~g}$$ of benzene reduced its vapour pressure to $$90 \%$$.

Calculate the mass of $$\mathrm{X}$$ dissolved in the solution.

(iii) Calculate the boiling point elevation for a solution prepared by adding $$10 \mathrm{~g}$$ of $$\mathrm{MgCl}_2$$ to $$200 \mathrm{~g}$$ of water assuming $$\mathrm{MgCl}_2$$ is completely dissociated.

($$\mathrm{K}_{\mathrm{b}}$$ for Water $$=0.512 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}$$, Molar mass $$\mathrm{MgCl}_2=95 \mathrm{~g} \mathrm{~mol}^{-1}$$)

OR

(b) (i) Why is the value of Van't Hoff factor for ethanoic acid in benzene close to 0.5 ?

(ii) Determine the osmotic pressure of a solution prepared by dissolving $$2.32 \times 10^{-2} \mathrm{~g}$$ of $$\mathrm{K}_2 \mathrm{SO}_4$$ in $$2 \mathrm{~L}$$ of solution at $$25^{\circ} \mathrm{C}$$, assuming that $$\mathrm{K}_2 \mathrm{SO}_4$$ is completely dissociated.

($$\mathrm{R}=0.082 \mathrm{~L} \mathrm{~atm} \mathrm{~K}^{-1} \mathrm{~mol}^{-1}$$, Molar mass $$\mathrm{K}_2 \mathrm{SO}_4 =174 \mathrm{~g} \mathrm{~mol}^{-1}$$)

(iii) When $$25.6 \mathrm{~g}$$ of sulphur was dissolved in $$1000 \mathrm{~g}$$ of benzene, the freezing point lowered by $$0.512 \mathrm{~K}$$. Calculate the formula of sulphur ($$\mathrm{S}_{\mathrm{x}}$$). ($$\mathrm{K}_{\mathrm{f}}$$ for benzene $$=5.12 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}$$, Atomic mass of Sulphur $$=32 \mathrm{~g} \mathrm{~mol}^{-1}$$ )