Question

At $363\,K$, the vapour pressure of $A$ is $21\,kPa$ and that of $B$ is $18\,kPa$. 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

Sol. Given $P _{ A }^{0}=21 kPa \quad \Rightarrow P _{ B }^{0}=18 kPa$

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

$\rightarrow X _{ A }=\frac{1}{3} \text { and } X _{ B }=\frac{2}{3}$

$\rightarrow$ Acc to Raoult's low

$P _{ T }= X _{ A } P _{ A }^{0}+ X _{ B } P _{ B }^{0}$

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

$\Rightarrow \quad P _{ T }=7+12=19\,KPa$