Question 12 Marks
a. Differentiate between Ideal solution and Non-ideal solution.
b. 30 g of urea is dissolved in 846 g of water. Calculate the vapour pressure of water for this solution if vapour pressure of pure water at 298 K is 23.8 mm Hg.
b. 30 g of urea is dissolved in 846 g of water. Calculate the vapour pressure of water for this solution if vapour pressure of pure water at 298 K is 23.8 mm Hg.
Answer
View full question & answer→(a)
(b)
$
\frac{P_{A}^0-P_{A}}{P_{A^o}^o}=\frac{\frac{W_{B}}{M_{B}}}{\frac{W_{B}}{M_{B}}+\frac{W_{A}}{M_{A}}}
$$1-\frac{ P _{ A }}{23 \cdot 8}=\frac{\frac{30}{60}}{\frac{846}{18}}$ or $1-\frac{ P _{ A }}{23 \cdot 8}=\frac{\frac{30}{60}}{\frac{846}{18}+\frac{30}{60}}$
$P _{ A }=\frac{46.5}{47} \times 23.8=23.5 mm Hg$ or vapour pressure of the solution $P _{ A }=\frac{47}{47.5} \times 23.8=23.5 mm Hg$
| Ideal Solution | Non-ideal solution |
| The solution obeys Raoult's law at all concentrations. | The solution does not obey Raoult's law. |
| $\Delta V$ mixing $=0$ and $\Delta H_{\text {mixing }}=0$ | $\Delta V _{\text {mixing }} \neq 0$ and $\Delta H _{\text {mixing }} \neq 0$ |
(b)
$
\frac{P_{A}^0-P_{A}}{P_{A^o}^o}=\frac{\frac{W_{B}}{M_{B}}}{\frac{W_{B}}{M_{B}}+\frac{W_{A}}{M_{A}}}
$$1-\frac{ P _{ A }}{23 \cdot 8}=\frac{\frac{30}{60}}{\frac{846}{18}}$ or $1-\frac{ P _{ A }}{23 \cdot 8}=\frac{\frac{30}{60}}{\frac{846}{18}+\frac{30}{60}}$
$P _{ A }=\frac{46.5}{47} \times 23.8=23.5 mm Hg$ or vapour pressure of the solution $P _{ A }=\frac{47}{47.5} \times 23.8=23.5 mm Hg$