Question

At $363K$, the vapour pressure of $A$ is $21kPa$ and that of $B$ is $18kPa$. One mole of $A$ and 2 moles of $B$ are mixed. Assuming that this solution is ideal, the vapour pressure of the mixture is ______ kPa. (Round of to the Nearest Integer).

Answer 1

Answer: 19

Sol. Given $P_A^0=21kPa\Rightarrow P_B^0=18kPa$

$\to$ An Ideal solution is prepared by mixing 1 mol $A$ and 2 mol $B$.

$\to X_A=\frac{1}{3}\text{ and }{X}_B=\frac{2}{3}$

$\to$ Acc to Raoult's low

$P_T=X_A{P}_A^0+X_B{P}_B^0$

$\Rightarrow P_T=\left(\frac{1}{3}\times 21\right)+\left(\frac{2}{3}\times 18\right)$

$\Rightarrow P_T=7+12=19KPa$