Question

A non-volatile solute $\left(A\right)$ is dissolved in a volatile solvent $\left(B\right)$. The vapour pressure of the solution is $P_s$. The vapour pressure of the pure solvent is $P_B^0$.

If $X$ is mole fraction then which of the following is correct?

• A. $p_s=p_B^0.X_A$
• B. $p^0=p_B{X}_B$
• C. $p_s=p_B^0.X_B$
• D. $p_B^0=p_s{X}_A$

Answer 1

Answer: (C)

$p_s=p_B^0.X_B$

By Raoult's law,

$P_S=P_B^0{X}_B+P_A^0{X}_A$

But A is a non-volatile solute

So, $P_A^0=0$

$P_S=P_B^0{X}_B$

Option C is correct.