Question

Total vapor pressure of mixture of $1 \,mol A\left(p_{A}^{\circ}=150\right.$ torr $)$ and $2\, mol B\left(p_{B}^{\circ}=240\right.$ torr $)$ is $200$ torr. In this case,

• A. there is positive deviation from Raoult's law
• B. there is negative deviation from Raoult's law
• C. there is no deviation from Raoult's law
• D. molecular masses of $A$ and $B$ are also required for calculating the deviation

Answer 1

Answer: (B)

$p_{s}=p_{A}^{\circ} x_{A}+p_{B}^{\circ} x_{B}$

$=\left(150 \times \frac{1}{3}\right)+\left(240 \times \frac{2}{3}\right)=210$

$\Delta p_{\text{mix}}=p_{\exp }-p_{\text {theo }}=- ve$