(a)

Differentiate between Ideal solution and Non-ideal solution.

(b)

$\displaystyle 30$ g of urea is dissolved in $\displaystyle 846$ g of water. Calculate the vapour pressure of water for this solution if vapour pressure of pure water at $\displaystyle 298$ K is $\displaystyle 23.8$ mm Hg.

(a)

Ideal Solution	Non-ideal solution
The solution obeys Raoult's law at all concentrations.	The solution does not obey Raoult's law.
\(\displaystyle \Delta\) Vmixing \(\displaystyle =0\) and \(\displaystyle \Delta \mathrm{H}_{\text {mixing }}=0\)	\(\displaystyle \Delta \mathrm{V}_{\text {mixing }} \neq 0\) and \(\displaystyle \Delta \mathrm{H}_{\text {mixing }} \neq 0\).

(b) \(\displaystyle \frac{\mathrm{P}_{\mathrm{A}}^{\mathrm{o}}-\mathrm{P}_{\mathrm{A}}}{\mathrm{P}_{\mathrm{A}^{\mathrm{o}}}}=\frac{\dfrac{\mathrm{W}_{\mathrm{B}}}{\mathrm{M}_{\mathrm{B}}}}{\dfrac{\mathrm{W}_{\mathrm{B}}}{\mathrm{M}_{\mathrm{B}}}+\dfrac{\mathrm{W}_{\mathrm{A}}}{\mathrm{M}_{\mathrm{A}}}}\) \[\text { or } 1-\frac{\mathrm{P}_{\mathrm{A}}}{23 \cdot 8}=\frac{\dfrac{30}{60}}{\dfrac{846}{18}+\dfrac{30}{60}} \] \[\mathrm{P}_{\mathrm{A}}=\frac{46.5}{47} \times 23.8=23.5 \mathrm{~mm} \mathrm{Hg} \quad \text { or } \quad \mathrm{P}_{\mathrm{A}}=\frac{47}{47.5} \times 23.8=23.5 \mathrm{~mm} \mathrm{Hg} \]